Low And Slow – But These Views!

August 12 was my second day flying in the Alps this year.  The forecast conditions were rather poor, which surprised me because a cold front had passed through the day before, finally putting an end to the oppressive heat wave that had lasted for more than three weeks. Post-frontal weather often offers good soaring in the Austrian Alps.

Intimidating mountains in western Austria, south of Zell am See.  Note:  I did not take any pictures during the first 2 hours of the flight: I was way too busy trying to make progress while looking for weak lift just a few hundred feet above the ridges.  Conditions improved drastically after 2PM.

The local forecast from AlpTherm predicted weak (“schwach”) climb rates around 1 meter/second (2kts) with thermals up to 3,000m (10,000 feet).  SkySight was more encouraging, indicating a potential flight distance of 400-500km (in an 18m ship) supported by a long soaring day starting as early at 10am, 1.5 – 2 m/s thermals, nice cumulus clouds, no OD, no storms, and no significant high-cloud obstruction. Light southerly winds would contribute to dense clouds stacking up on the south side of the Alps’s main spine, but were likely too weak to be usable for ridge soaring. SkySight projected even lower cloud bases than AlpTherm at the east side of my soaring area – as low as 2,400m (8,000 feet) – yet gradually rising to 3,300m (11,000 feet) further west.

Potential flight distance of 400-500km within the soaring area along the Salzach and Enns Valleys.

My drive to the airport started at the southern side of the Alps under a layer of dense clouds. As I crossed to the north at Wald am Schoberpass, the clouds gave way to deep blue skies.  The air was also much clearer than in recent days: obviously the cold front had removed the inversion layer.  A few low-hanging clouds clang to the slopes of the mountains, remnants of the moisture that the heavy rains of the passing cold front had left behind. There was no doubt that the sun would quickly dissolve them.

Dark red colors show dense cloud coverage forecast south of the Alp’s main spine. Nice cumulus clouds were projected to mark the lift within my soaring area.

By 10:30am the first new wisps started to form above the hills, indicating that lift was already starting to form.  I moved the glider out onto the grid at Runway 04 while the air on the ground was perfectly still.  I was confident that it would not take long for the valley breeze to kick in.  At 11:30am the windsock finally came alive – a clear sign that it was time to launch because the thermals above the hills were sucking in air from the valley below.

Projected thermal strength of 1.5 m/s to 2 m/s (3 to 4 kts).

I was number three on the start list and airborne by 11:44AM.  Once again I asked to be towed to the trusted release point near Karlspitz at 1,800m MSL (6,000 feet), around 1,100m (3,300 feet) above the valley floor, where I released in the first lift above the ridge seven minutes later.

Thermal height projected at 2,400 – 3,000m (8,000 – 10,000 feet) within my soaring area – gradually improving from east to west.

Unable to climb from my release point at less than 300 feet above the ridge I thought I might have released a tad too early when a thermal above the nearby hill Zachenschöberl lifted me to cloud base at 2,400m MSL (8,000 feet).  My average climb rate was 1.5m/s (3kts) – not bad considering that the day had only just started.

The local Alptherm forecast projected weak (“schwach”) climb rates of only 1 – 1.5 m/s (2-3 kts) for most of my soaring area.

I had set a tentative turn point 126km further west above Pass Thurn.  To get there, I would have to first fly along a mountain chain called the “Schladminger Tauern”, followed by the “Radstädter Tauern”, and eventually the Hohe Tauern.

The first reasonably strong climb that allowed me to take out my camera came after two hours into my flight – above the peak of Bernkogel – west of the village Dorfgastein (in the valley below). Note the steep switchbacks of the hiking trail on the face of the mountain.  Climbing is so much easier in a glider!

The peaks of the Schladminger Tauern and the Radstädter Tauern top out at about 2,850m (9,500 feet).  The ridge lines along the foothills are typically about 1,800 to 2,400m high (6,000 – 8,000 feet).  Every 5-8 km or so I would have to cross one of these ridges.

A cloud base of 2,400m did not leave a lot of wiggle room: I would have to climb to cloud base above a ridge line, glide through sink to the next ridge, hopefully arrive there with a decent safety margin, find a climb that would take me back to cloud base, fly through sink to the next ridge, and so forth.  To make progress, pretty much every ridge line had to offer a climb and I would have to be able to locate it quickly once I got there.  Should a ridge not work upon arrival, I would have to follow it towards the main valley (perpendicular to my intended route) and look for climbs along the way.  Should I find myself unable to work my way back up, I would eventually have to land at one of the few land-out fields in the main valley.

The cloud bases lifted to 3,300m (11,000 feet) by mid-afternoon – still well below some of the highest peaks of the Austrian Alps.

Eventually I would get to the “Hohe Tauern”, which were much taller with peaks around 3,600m (12,000 feet).  Low hanging clouds, tall mountains, and soaring don’t mix very well; therefore, I planned to cross the Salzach Valley around Zell am See to the north side and then continue along the lower Kitzbühler Alpen, which top out around 2,500m (8,300 feet) until I would get to my turn point.  From there I would retrace my route back towards the east, continuing on to a second turn point at Admonterhütte near the town of Admont and then return back to Karlspitz for a total task distance of 325km.  That was the plan.

As I headed out on task I observed a seemingly endless line of clouds along the south side of the Alps, just as Skysight had predicted.  On the north side, where I was flying, small but pretty cumuli started to form right above almost every ridge line.

Circling in nice lift late afternoon when conditions were great and soaring was easy. You can see the dense line of clouds in the background on the far (i.e. southern) side of the mountain range. These clouds prohibited a crossing of the Alps to the south and did not dissolve until late in the day.

My first ridge to cross would be near the peak of Gumpeneck, 2,226m tall.   I had hoped to arrive just at the level of the peak, high enough to connect with the thermal breaking off the mountain.  However, when I got there I was down at 2,080 meters, just a little too low to get into lift.  That meant plan B: follow the ridge out towards the Enns Valley.  Only one kilometer later I found weak lift above the ridge, worked my way up to to 2,300m, flew back to the Gumpeneck, and climbed back to cloud base at 2,370m.  On to the next ridge!

I arrived 130m AGL (400 feet) above the next ridge and quickly found the next climb, which took me from 2,200 to 2,570m.  Great! The cloud bases were getting higher. Onwards!

The next ridge was 2,200m high.  I arrived there 300 feet above ground, following along the ridge for about 2 kilometers but did not find a climb.  Time for plan B again: change direction, and fly above the next lower ridge line out towards the Enns Valley.  50 meters AGL I found the next climb, taking me from 2,150m back to cloud base at 2,480m. Time to push west again!

Cockpit view of the LS4. Cruising at 150 kph only became an option by mid-afternoon when the cloud bases were well above the ridges. Earlier in the day I was scratching along from one ridge to the next at 110-120 kph.

The next two ridges were good enough to maintain altitude but provided no climb. I was only 1 kilometer north of a peak that was 2,450m tall – too high.  The lift was probably above the peak but I was down at 2,350m and couldn’t get there. So I continued on.

The next ridge was slightly lower at 2,150m.  I got there 100m AGL and found a nice climb back to cloud base at 2,580m.

This is how my flight towards Zell am See continued.   I found climbs to cloud base above each of the next three ridges, then skipped a ridge and had no choice but to take the next climb back to 2,500m even though the climb rate was dismal.  A fun way of soaring but mentally very demanding. And so slow!

The mountain chain in the center is Hochkönig. On the back side is the city of Berchtesgaden in Germany.

Then came the next ridge and finally some reprieve: my first 2 m/s (4kt) climb  of the day took me to a new high: I was at almost 2,900m!   The airport of Zell am See was now within easy glide range and I could relax a bit.  But I was already 90 minutes on task and had only covered just a bit over 50km!

I continued to push on and the flying finally got faster and easier.  Climb rates continued to improve and the cloud bases increased further.  The additional altitude gave me room to increase my inter-thermal cruise speed from 120 kph to 140 kph.  Above Bernkogel I averaged 2.5 m/s and climbed to 3,050m. Oh what luxury!

Finally I had time to look ahead towards TP1.  At least in theory there were two ways to get there: 1) continue on the south side of the Salzach Valley and cross to the north side near TP1; or, 2) cross to the north side near Zell am See (as I had initially planned) and then continue along the Kitzbuühler Alpen.

The southern route looked very challenging: the mountains to my left were intimidating: the peaks towered high above my glider and were well above cloud base.  The ridge lines ahead were short and provided few options to find good climbs. There was still some wind from the south and I dreaded the prospect of flying in the lee of these monsters.  Unfortunately, the northern route did not look very promising either.  The sky in that direction was mostly blue and the cloud bases were much lower.  Crossing over to the north looked straightforward but would I be successful in crossing back south?  I didn’t know.

The town of Zell am See is below in front of the lake (Zeller See). You can spot the runway of the local airport in the foreground on the right – like Niederöblarn one of the most popular and most scenic glider ports in the Austrian Alps.  The hills on the left side are part of the Kitzbühler Alpen – the cumuli on that side were few and far between and the cloud bases lower.

For a while I contemplated my options.  The airport of Zell am See – one of the premier soaring sites in Austria – was right below and provided an easy and safe landing option in case my adventure to the north side did not work out.  However, I could not see any other gliders around, which caused some doubt in my mind regarding the conditions on the south side.  Also, it had already taken me more than two hours to get here and I didn’t know how long it would take to get back.  It was 2:15PM and Skysight had predicted thermal activity to weaken considerably as early as 4PM.  Ultimately, the doubtful voices prevailed. I decided to abandon my task and turn around.

In hindsight, my concerns were probably overblown.  Conditions continued to improve.  I averaged almost 3 m/s on my next climb and reached 3,150m.  Finally I was able to skip some ridges if the attainable climb rates did not reach my expectations.  My average speed, which had only been 56 kph on my outbound leg, improved to 78 kph on my next leg.

Another amazing look into the steep and narrow valleys of the Hohe Tauern (High Tauern) – Austria’s tallest mountain range.

Once I was back within final glide range to my start airport in Niederöblarn I reversed course again to head back west to see if I could further improve my average speed.  Indeed: on my second westbound leg that took me back to Zell am See again I averaged 82 kph.

I briefly thought about continuing to TP1 now as the Kitzbühler Alpen looked considerably improved, but it was almost 4PM and prudent caution won again.

And another look at Zell am See at the foot of the high peaks on the opposite side of the Salzach Valley.

I had not anticipated that things would get better still until thermal strength peaked around 4:30PM.  On my second eastbound leg I averaged 105kph.  I started to wonder if I could even score for the OLC Speed League despite the excruciatingly slow start.

Around 5PM, however, it quickly became obvious that the day was coming to an end.  I crossed the Enns Valley, found another climb over the Grimming and added a sightseeing flight along the Northern Limestone Range.  I had hoped for a similar late-day “radiation-lift” effect from the steep south-facing cliffs as  I had noticed on my prior flight on August 4.  However, this time the air along the shaded cliffs just produced sink.

View of the Dachstein Massif from above Planai Peak (directly below). The world cup downhill ski racers start at the top of the mountain that can be seen in the bottom left corner of the picture. This downhill track was long the fastest in the world.

Near Dachstein I crossed the valley again and found the day’s last thermal over Planai Peak, famous for world-cup ski racing.   From there I followed the ridge lines, which had become completely still, back to the airport in Niederöblarn for one of my smoothest touch-downs ever in completely calm conditions just before 6PM.

View towards the west as the clouds started to dissolve in late afternoon.

Total flight distance 392km.  Average Speed, unsurprisingly slow, at 68.5 kph. The flight track is here.

Lessons Learned

  • Flying low is (mentally) demanding.  The work load is dramatically higher when you have no choice but to fly low.  Having a plan A (where to go for lift), a plan B (where to go if lift does not materialize), and a plan C (where to escape to – if necessary to land – if plan B does not work) is critical.  And what your plan A, B, and C ought to be changes constantly.  I.e., every few minutes you may need to formulate a new plan A, B, and C. That’s a lot of work.
  • Lift above the ridges can be very narrow.  I noticed that the lift close to the ridges can sometimes be just a thin band that may be impossible to circle in.  If it is wide enough to circle a steep bank angle (40-45 degrees) is often required to stay in lift – also and especially because you can’t afford to get close to minimum speed while in close proximity to the terrain.  Two or three times I found myself circling with other gliders who ended up dropping out of the lift because their circles were just to wide.
  • Always arrive above the ridges.  Hopping  from ridge to ridge only works if you can be sure of arriving above the next ridge line, ideally above the highest peak along the ridge for that’s where you will most likely find the next climb.  If you’re not 100% certain of that, than your plan B must include a path over another (lower) ridge line that you can reach for sure above the ridge (plan B) and from where you can escape to a landable area (plan C).
  • Always watch your airspeed as you approach a ridge. When you are approaching a ridge close to terrain you might intuitively pull back on the stick and inadvertently reduce your airspeed.  Never let that happen. Flying close to terrain is dangerous and flying too slow and too close to terrain can be a fatal combination.  I kept reminding myself of this throughout the flight.
  • The combination of low cloud bases and weak lift makes you SLOW.  The obvious part of this is due to the fact that you take a long time to circle in weak lift and that you have to maintain a modest airspeed even in cruise mode. Less obvious are the other delays: i) you have to take (almost) every climb simply because it is still better than plan B. ii) And if plan A does not work you may be forced to significantly detour from your intended flight route simply to find the next climb and stay aloft – as a result you end up flying many more unintended miles along the way and this is what really slows you down.
  • Skysight has been remarkably accurate.  Always read any forecast with some skepticism and never expect it to be 100% correct in every respect.  However, once again Skysight was very close to reality:  e.g., by mid-afternoon, climb rates were a little stronger than forecast and cloud bases a little bit higher.  The most clouds were almost exactly where Skysight had predicted them to be. The start and end of the soaring day were both perhaps 30-45 minutes later than forecast.  The southern side of the Enns Valley worked a bit better than forecast and the north side a little worse.  But overall, Skysight was remarkably on target.  Having worked with it now in different geographies and widely different conditions I believe it’s the best soaring forecast out there at the moment.

Along the Spine of The Alps – Soaring from “Bone to Bone”

Europe is enduring a pro-longed heat wave with near record high temperatures from Portugal to Austria.  That means the nicest place to be is right at cloud-base where the temps are much more comfortable.

At cloud base above the Central Alps in the middle of Austria. The Tappenkarsee is below. The peak to the left is called Faulkogel, 2,654m (8,700 feet) MSL. Where else would you rather be?

This past Saturday promised nice soaring conditions in Central Austria:

Moderate thermal strength of 2 m/s (4 kts)…
… cloud bases around 3,000 meters (10,000 feet) …
… high probability of cumulus clouds marking the lift …
… only modest risk of overdevelopment …
… a moderate risk of thunderstorms mainly confined to the area north of the northern limestone range …
… hardly any wind within the boundary layer …
… convergence lift of 1-2 kts along the spine of the mountains (as a result of the valley breeze that lifts air along the slopes of the mountains, converging and rising off the tops of the ridge lines) …
… no high clouds shielding the sun …
… culminating in a projected attainable flight distance of 500-600 km in an 18 meter glider.  (I was flying a club class ship with a projected attainable flight distance of approx. 400-500km).

Skysight’s predictions were also confirmed by the local soaring forecast from Austrocontrol, which projected:

“Good” thermal conditions in line with Skysight’s prediction of a thermal strength of 2 m/s (4 kts), …
… a trigger temperature of 24 degrees C, expected to be reached as early as 7 am (!), and a maximum thermal height of approx. 3,300m (11,000 feet) MSL.

Considering the consistency of both forecasts, I thought it appropriate to plan my first pre-declared 300km triangle in the Alps:

  • Start above Karlspitz, approx. 7 km south of my launch point at LOGO (Niederöblarn airport).  This is the location of one of the “house-thermals” and a frequent release point for gliders flying from LOGO.  From there I would head 85 km westward towards …
  • … TP1 near the village of Wörth in the province of Salzburg at the foot of Austria’s tallest mountain, the Grossglockner.  The peak of Grossglockner (3,798 m or 12,461 ft) was well above the projected thermal height and likely unattainable.  A second eastbound leg of 156 km would take me to …
  • … TP2 above the village of Vordernberg, in the province of Styria near the town of Leoben. And from there it would be 69 km to the …
  • … finish line, once again above Karlspitz.  Total task distance: 311 km.
Task as shown on Google maps.

I had reserved the LS4b of the fleet of Niederöblarn.  It’s a very comfortable club class ship with a performance slightly worse than that of the Discus that I’m usually flying from Boulder.  Since I had not flown in Austria in more than 12 months I had to take two brief check-rides in the DG 1000 with a local instructor.  This was a nice opportunity to refresh my spin training (a lot of fun!) but it meant that I wouldn’t be able to launch on my own before noon.  Given my relatively late start, the 300km task distance seemed appropriate.

I released near Karlspitz a few minutes past noon and rounded the start sector above the peak four minutes later at an altitude of 2,200m MSL.  I followed the ridge line to the SSW to further gain altitude.  One of the great phenomena of flying in the Alps is the amazing predictability of thermal lift directly above the ridge lines, especially in low-wind conditions and in the middle of the day when the sun heats both slopes equally: warm air rises up along either side of the ridge and when it reaches the top of the ridge line, both streams converge and the air has no place to go but up.

The lift is not necessarily consistent, but it often averages 1-3 kts, which is usually sufficient to maintain or even slightly gain altitude as long as one flies directly above the top of a ridge.  Thermals will then break off the ridge line as well, usually above distinctive peaks.

The flight track off tow shows how I’m following the ridge line. It’s often easy to maintain altitude when flying along the top of the ridge (up to about one or two thousand feet above the ridge) and it’s a great strategy to identify the best thermals – especially in blue conditions – as they tend to break off from spots directly along the ridge.
View from Mausgarkopf (below) to the north across the Salzach Valley towards Hochkönig in the distance (above the wing tip) – near TP1. The line of clouds in the background is approx. over the border between Austria and Germany and confirmed the higher Cape index forecast for that area. The ridge line below the wing is a good example of where to find lift: the sun heats the slopes on either side of the ridge. That means air ascends on both sides and then lifts off the ridge top. The best thermals tend to be above the peaks.

The main spine of the Alps resembles a giant fishbone.  The spine itself is the ridge line in the center, which is in the direction from west to east.  On either side of this main ridge are individual ridges (i.e. individual “bones”) protruding north and south with steep and narrow valleys in-between.   Soaring usually involves a series of valley crossings as you’re flying from one of these bones to the next.  More often than not, the valley crossings involve significant sink, while the lift is concentrated above the bones.

The fishbone structure of the Alps is easily visible in the Google Maps image.

Cloud-bases tend to be much lower than in the western United States and are often not far above the ridge line.  Arriving below a ridge line can mean trouble (because usable lift is sometimes only available above the ridge-tops), so the safest strategy is to ensure that you’re high enough before leaving a ridge and heading through the sink to the next.  Depending on the height of the cloud base and the performance of the glider it is often possible to skip one, two or several ridges before taking and centering another climb.

The village of Bad Hofgastein is below. In the distance is Austria’s tallest mountain, the Grossglockner.

In the western US my cross-country flight path is predominantly determined by the location of the clouds (and the terrain is often secondary – especially if it is many thousand feet below), whereas in the Alps, the terrain plays a much more prominent role in determining the optimal flight route.  Obviously, that doesn’t diminish the  importance of clouds as a marker of thermals. However, I have found that clouds that have formed directly above the ridges but have drifted away with the wind are often no longer marking usable lift. The ridge itself, on the other hand, is often still producing lift even if no cloud has yet formed to mark it.

Cloud shadows above another ridge. Compared to the Western US, the thermals in the Alps tend to be narrower and closer together.

Just before TP1 I found myself circling with three raptors – possibly small eagles – at an altitude close to 3,000m (10,000 ft).  One of the raptors must not have attended flight school as it changed the direction of turn and started to circle in the opposite direction. I saw the bird coming straight at me and remember watching it to see how it would react to my presence.  Fractions of a second later, just when I was surprised that it would dare come so close, I felt a bang as it collided directly with my left wing.  My Oudie flight computer, which was only attached to the canopy via suction cup, fell off on impact and landed in my lap.  My adrenaline rushed and my first reaction was a mix of empathy for the bird, which must have lost its life, and concern for the integrity of the glider and my own safety.  I looked out at the wing and saw to my relief that it was still in one piece and that there was no obvious damage.  I tested the controls and confirmed that the glider reacted just as I expected it to. Where the bird had struck, approx. 3m (10 feet) from the root of the wing, I saw a shiny spot on top of the leading edge of the wing. But there did not appear to be any dent or some other form of damage. Not knowing what else to do, I kept circling for another few turns, while I tried to decide whether to cut my flight short.  After inspecting the wing as best I could and confirming again that everything was working just fine, I ultimately decided that there was no reason to change my flight plan, and thus I continued on route.

Flight path to and from the first TP.  Flight from “bone to bone”: all climbs are directly above the ridge lines. I did not skip any of the “bones” to stay high and keep the airport in Zell am See within easy glide range as there are no viable land-out fields in this area.

I reached TP1 70 minutes after leaving the start line 85km earlier.  The average speed of 72 kph was not particularly high but – except for the bird strike – my flight had been stress-free despite the relative lack of land out opportunities.

View of the “Glocknermassif” at the intersection of the provinces Salzburg, Carinthia, and Tyrol. Cloud bases were higher in this direction but the tallest mountains were obscured and the peak of the Grossglockner appeared to be out of reach.

TP1 was only 25km northeast of Austria’s tallest peak, Grossglockner, 3,798 m (12,460 ft) high.  Cloud-bases at my location were around 10,000 feet. Even though the bottom of the cumuli was someone higher to the southwest, Grossglockner was obscured by clouds and appeared to be unattainable.  There was a chance that the cloud base would lift later in the day but I decided to turn around and continue on task.

The posh skiing village of Badgastein is below. To the left are the high peaks of the Ankogelgruppe. The mountains in the distance on the far right are in Northern Italy.

Looking at the sky ahead of me I had to make a decision: should I continue on the north side of the central spine of the Alps (essentially retracing my flight path), or should I follow an almost continuous line of clouds that were perhaps 15-20 km further to the south.  The southern route looked much faster and easier but I had not researched the land-out fields to the south (except for the airport of Mauterndorf where I obtained my winch training back in 1984).  There was also a military air space around Zeltweg that I suspected to be inactive on the weekend, but I did not know the proper radio frequency to verify this.  Looking at the clouds I could not tell for sure if I would be able to follow this line without encroaching on the military airspace. Thus I decided to fly on the north side.  The main challenge was that the cloud coverage in this area had become very scattered with large blue holes on course.  Well aware that my average speed would suffer, I decided to maintain my strategy of staying high and keeping known airfields and land out spots within glide range at all times.


En route to TP2 looking NW. Big sections of the sky were blue along this stretch. The town of Trieben is below in the Palten Valley at the foot of the Reichenstein. The mountain to the right is the Hochtor.  I crossed the valley approx. 15 km further southeast.

The execution of the plan worked as expected.  I found practically all the climbs directly above one of the ridges, usually above one of the mountain peaks. There was a major variability in climb rates.  Sometimes I would average 3-4 m/s (6-8 kts), sometimes as little as 1 m/s (2 kts) or even less. With mainly blue skies ahead of me there was no way of knowing how strong the next climb would turn out to be.  My conservative strategy worked but my progress was predictably slow.

Just after crossing the Palten-Liesing Valley, looking north. The two parallel mountain chains in the background are traversed by the river Enns in a deep and narrow gorge – the “Gesäuse”, one of Austria’s National Parks.

Another obstacle on course was the crossing of the Liesing-Palten Valley.  As I approached the valley I noticed a nice cloud right at the top of the divide at Wald am Schoberpass.  However, as I got closer, the cloud was dissolving and I decided to stay on the west side, gain additional altitude, and cross further to the south.

Stadelstein, Hochstein, and Schwarzenstein are below. The open iron ore mine called Erzberg (“ore-mountain”) is visible center right. In the background are the Wildalpen (“wild alps”).

The crossing was uneventful. I ended up loosing less altitude than I had expected.  But there was a lot of traffic in this area.  I encountered seven or eight other gliders as well as hang gliders and paragliders.  Most gliders in Europe are equipped with Flarm systems but  hang gliders and paragliders are not.  Traffic density in the Alps is orders of magnitude higher than in the American Rockies.  Paying close attention is paramount at all times.

The free-standing mountain in the center is called Gößeck. The Liesing Valley that I crossed earlier is right behind it.

TP2 turned out to be well-picked as the sky further east was significantly overdeveloped with some emerging storms. I rounded it just before 3PM in the afternoon.

The road over the Präbichl mountain pass is below. This is were I learned to ski at the age of three. In the background is the Hochschwabmassif. TP2, the village of Vordernberg is in the valley just to the right edge of the picture. I considered pushing further east to extend the flight but this area seemed to be rapidly overdeveloping and so I decided to stay on route after rounding my turnpoint (indeed there were heavy rains in this area less than one hour later).

Cloud bases on the east side of the Liesing valley were significantly lower and now I had to transition back to the west side.  Concerned about arriving too low I ended up wasting more time in weak lift before crossing the valley again.  Again, my hesitation turned out to be overly conservative.  After the crossing I quickly regained my altitude and was back at cloud base.  I was also on final glide even though I had almost 50km in front of me.

I got another good look at the open iron ore mine of Erzberg as I circled above the Eisenerzer Reichenstein to gain height in advance of my second crossing of the Palten-Liesing Valley.

With my goal already made, I finally started to fly less conservatively.  I flew 170 instead of 140 kph in-between thermals, skipped several ridges, and only took the strongest climbs.  This strategy would likely have worked for much of the entire flight and would have resulted in a significantly higher average speed.

I finally reached the finish line after 4 hours and 40 minutes with an average task speed of 67 kph.  Slow, but stress free, and happy to have completed my third pre-declared 300km goal flight and my first in the Alps.  🙂

After crossing the finish line I traversed the Enns Valley and continued to fly west above the tops of the Northern Limestone Range (Nördliche Kalkalpen). The Dachstein Massif is right in front.

After completing the task I took another climb and decided to add some sight seeing on the northern side of the Enns Valley.

The small remnants of the Hallstädter Glacier are on the right edge of the picture. When I was a little kid, the glacier was much thicker and wider flowing down into the valley below. Directly behind the peak in front I got a glimpse of the Hallstädter See (Lake Hallstatt), one of the most picturesque lakes in the entire Alps and a UNESCO world heritage site. Many of my American friends know it from their Sound of Music tours. 😉

I crossed to the Kammspitze, climbed again and headed west over the Scheichenspitze, the Hohe Dachstein (the highest peak of the day at 3,004m or 10,000 feet), and the picturesque Bischofsmütze.  From there I retraced my flight path below the level of the peaks.

The prominent Bischofsmütze (Bishop’s Mitre) is in the center. The valley behind it leads to the city of Salzburg.

This final section turned out to be the most scenic and enjoyable part of the flight.  I was flying along the steep south-facing cliffs of the Northern Limestone Range (Nördliche Kalkalpen).

The south face of the Dachsteinmassif was aglow in the early evening sun. The cliffs were still emitting heat and producing great upslope lift close to 6pm in the evening.

These cliffs had been exposed to the sun for the entire day and were radiating heat that caused the air to ascend along the slopes at 1-2 m/s allowing me to fly along the entire range at about 130-140 kph without loosing altitude.  I even ended up climbing above the top of the Grimming, all in straight flight for about 50 km.

Nice view across the back side of the Dachsteinmassif. This high plateau sits about 6,000 feet above the floor of the valleys. You do not want to get caught low above it in a glider as there is no way out.  The mountain hut below is the Guttenberghaus – you can see the very demanding hiking trail hewn into the cliffs at the bottom left of the picture.

Unfortunately, this last section did not count for the OLC Speed League because I omitted climbing back another 300-400 feet at the end (which had been my low point earlier).  There’s no doubt that the final 2 1/2 hours were easily the fastest of the entire flight (probably averaging more than 100 kph).

The upslope lift along the cliffs took me above the top of the Grimming, the beautiful and prominent mountain next to the airport of Niederöblarn.

Overall, I had a very nice and relaxed flight in good conditions.  I’m happy with the result especially considering my conservative tactics and the fact that my speed was right in line with that of others flying in this area on the same day.  My flight track is here.

Lessons Learned

  • Follow the ridge lines whenever possible.  When the sun heats the slopes on both sides of a ridge, warm air will ascend and converge right at the top.  The best thermals will also almost always break away from the top of the ridges, usually above prominent peaks rising above the ridge line.
  • Lower may actually be faster.  You may be able to fly directly along the top of a ridge line without losing altitude.  This type of lift works best in relative proximity to the terrain, i.e. a few hundred feet above the ridge, but not several thousand feet above.  This means you are likely to fly faster if you fly lower. This is at first counterintuitive because you can’t take advantage of the fact that the delta between IAS and True Airspeed increases the higher you fly.  (This is a big contributing factor to the high average speeds in the American West.) Obviously, flying low above the ridges is mentally demanding and implies a reduced glide range requiring great situational awareness with respect to land-out fields and any terrain obstacles that may get in the way.
  • Arrive well above the ridge top when flying from “bone to bone”.  The fishbone structure of the Alps makes constant crossings of narrow valleys inevitable if you want to get anywhere.  Thermals almost always break away from the ridge tops and it may be difficult to find lift if you drop below ridge-line. So don’t, especially if the wind is insufficient to produce usable ridge lift helping you work your way back up.
  • Terrain is at least as important as clouds. Sunny ridge lines are constantly generating lift and new thermals will periodically break off from the ridge tops.  These thermals can drift away with the wind and I have found that they often are no longer working once they have moved away from the ridge that spawned them.  You are more likely to find lift in the blue above a ridge line than under an aging cloud drifting away from a ridge.
  • Rocks store heat extremely well. The south facing cliffs along the northern limestone range stored a ton of heat energy throughout the day.  Flying in constant lift along the face of the cliffs at the end of the day was an amazing experience.  However, remember that whenever you get close to terrain it is paramount to fly at a safe speed and to know the locations of cable cars and similar obstructions as they are very difficult to see from the air.
  • Birds can be stupid.  I have always admired birds for their maneuverability and I never thought that a bird would be so stupid as to directly collide with a glider. But apparently that can happen. It’s a good thing that gliders are pretty sturdy.  However, I hate to imagine what would have happened if the bird had collided straight with the canopy or the horizontal stabilizer.
  • Traffic!  The air along the spine of the Alps is very busy – especially compared to the empty skies above the Rockies.  During my flight I encountered at least two or three dozen other gliders in addition to para gliders and hang gliders. Especially the latter are not equipped with Flarm systems and it’s critical to keep your eyes outside the cockpit at all times and pay close attention to other traffic.
  • Mind the altitude rule for the OLC Speed League.  The last 100 km of my flight were by far the fastest of my entire flight but they did not count for the OLC Speed League because I didn’t climb back to my previous low point during the flight.  I would have scored considerably better had I climbed back another few hundred feet towards the end before coming back down to land.  It is actually beneficial to have more altitude variability throughout the flight as this allows for more opportunities to calculate the fastest 2 1/2 hour segment of the flight. Something to remember.



Into the Mosquito Range – Three Tries Is The Charm…

The forecast had last Thursday pegged as another great soaring day in Colorado.  High cloud bases (around 19-20k feet), strong thermals (up to 10+ kts), no significant risk of over-development, and nice CU clouds to mark the lift.  What else could you want?  Well, maybe less wind aloft.  The forecast showed winds of > 20 kts from WNW – stronger to the north, a bit weaker to the south.

High cloud bases…
… strong thermals – especially along the lower foothills …
… no significant risk of overdevelopment …


… but windy, especially to the north (and along the Continental Divide).

Since it was a weekday there was no reason to go fast to earn OLC points for the Speed-League (only flights on weekends count). Conditions were projected to be best along the lower foothills on the east side of the Divide but fairly strong across most of Colorado.  With the winds being somewhat weaker to the south I felt it would be a good day to see of I could bag one or more 14ers in the Mosquito Range – a chain of mountains flanking the western edge of South Park, separating Fairplay from Leadville.

There are five 14ers in the Mosquito Range: Mt. Lincoln, Mt. Cameron, Mt. Bross, Mt. Democrat, and Mt. Sherman. I decided to pick Mt. Sherman, the one located furthest to the south and therefore farthest away from Boulder, as my targeted turn-point.  I thought that if I could round Mt. Sherman I might be able to also pick off one or more of the others further to the north.

I also decided that it would be fun to follow up my previous pre-declared 300+ kilometer triangle with another one, and so I picked Lookout Mountain to the west of Ft. Collins as my second turn-point.  Start and Finish would be at Bighorn Mountain, just east of the old mining village of Gold Hill. Bighorn Mountain is a great start location when towing to the NW from Boulder. It often produces good thermals early in the day coming off its charred south-east facing slope and it lies just within the 15km start cylinder for the Speed League. Total task distance: 325 kilometers.

My forecast had the day start around 10:30AM.  However, the westerly wind had produced a thin lenticular cloud on the east side of the divide and so I decided to wait until after noon to get going even though two other Boulder pilots took off (and stayed up) considerably earlier.

The tow into the foothills was very choppy and characterized by significant rotor turbulence.  I got a lot of slack line recovery practice. 🙂  I released at just under 10k feet MSL, higher than I had intended.  Even then it was hard work to get the first decent climb.  There was a lot of rotor mixed in with the thermals: my first two climbs were very rough and uneven with strong lift and strong sink mixed on every turn, requiring constant corrections.

My first good climb that allowed me to gain 4,000 feet in 7 minutes came after I had struggled in middling lift for about 20 minutes following my release from tow.  Funny enough it came directly off the south side of Bighorn Mountain just after I had passed through the Start Line.

From my new vantage point above 16,000 feet I could now see past Mount Evans into South Park.  The cumulus clouds were still few, thin and sparse but it seemed that they were developing quickly and so I felt good about getting underway towards my first turn-point.

Climbs near Rollinsville and Idaho Springs – there always seems be be a thermal right over Idaho Springs – brought me close to 18,000 feet, allowing me to fly past Mount Evans into South Park.  Thanks to decent climbs every 10-15 miles I continued to make good progress along the course and reached Fairplay less than an hour after leaving Bighorn Mountain.   Up until this point my average speed was around 100 kph despite a cross-wind of almost 20 kts.

The Mosquito Range looking south. Mt. Sherman is in the upper middle of the picture, straight above the winglet of the Discus.

Mount Sherman, my targeted turn-point was about twelve miles straight ahead.  But the question was: how do I get there.  Just before Fairplay I started to feel the effects of the lee-side sink from the mountains in front of me. I flew directly under the last remaining cloud near Alma Junction.  If I could climb back up to just under 18,000 feet I would likely be high enough to glide the last seven miles directly to the top of Mt. Sherman even if it meant pushing into sink.  However, there was no lift to be had under this cloud.  Despite trying to climb for about seven minutes I was only able to maintain my altitude of 15,400 feet – definitely too low to fly straight to Mt. Sherman and back.

As I circled in vain I was debating between two options: 1) there was a nice looking cloud eight miles to the SE over Reinecker Ridge but that would take me much further away from my target and my distance would further increase with the wind drift.  I might get back to 18,000 feet but then what?  2) there was a promising looking ridge on the NNW side of Silverheels Mountain, about five miles north.  The wind seemed to be blowing right onto the ridge and the entire mountain was in the sun.  If I could get a climb off that ridge I would have a much shorter distance to transition onto the top of the Mosquito Range, albeit several miles north of my target.

From the perspective of reaching my target the ridge was clearly the better option.  But what if it didn’t work?  There were other mountains further upwind so there was a considerable risk that the ridge would be in their lee and instead of lift I might only find turbulence and sink. What would I do then?

I glanced at my flight computer and confirmed what I knew anyway: my nearest decent land-out field was on the east side of Elkhorn Road, just east of Como.  If the Silverheels ridge didn’t work I would escape in that direction along Little Baldy Mountain with the wind in my back.  There was another cloud between Silverheels and Como. Chances were good that I would be able to find a climb there. And if not, Elkhorn Road was definitely within glide range.  If it became necessary I would be able to land parallel to the road and almost directly into the wind.  I estimated the risk of having to land out at less than 20% and I had a plan B and a plan C.  With those thoughts in mind I decided to go for the ridge.

The road between Leadville and Copper Mountain is below. The next valley behind connects Leadville with Minturn. Mount of the Holy Cross is in the distance.

As expected I had to cross more sink as I pushed into the wind to get to the northern ridge of Silverheels, and when I got there my altitude had dropped to 13,600 feet – right on the ridge and just below the level of the summit.  And voila, the ridge worked!  Not very well, but it did.  Phew! I flew a few turns in figure eight loops until I was well above the ridge line.  Given that I was fairly close to terrain I also made a conscious effort to maintain extra airspeed for added safety.  I was able to gain some altitude back but unfortunately the lift did not extend more than about 600 feet above the summit.

Just as I was contemplating my options again I noticed a new cloud forming two miles southeast next to the summit of Little Baldy Mountain.  It was in the opposite direction of where I wanted to go but it was clearly the best choice.  I headed straight to the cloud, losing all the altitude I had just gained on the ridge in the process and finally I found decent lift.  Eight minutes later I was back up at 17,500 feet and the world looked a lot friendlier.

To my delight there were two additional new clouds between my position and the Mosquito Range so it was time for a second attempt.  I pushed back into the wind and managed to get onto the Mosquito Range without losing much altitude. The route south towards Mt. Sherman did not look great but Quandary Peak, another 14er – though technically part of the Ten Mile Range and not the Mosquito Range, was just two miles to the north.  It was a peak I was definitely able to reach without taking any risks so I went for it.

One down. After rounding Quandary Peak I started to head back south along the ridge, glancing at my flight computer to locate the exact positions of the other 14ers between Quandary Peak and Mt. Sherman.  Unfortunately I hit a lot of sink and quickly dropped back down to 15,500 feet.  I wasn’t too keen on ridge soaring again so I made a quick decision to head back east under the cloud over Silverheels.

After “refueling” back to almost 18,000 feet, I decided to make my third and final attempt for the day to get to Mt. Sherman.  I headed straight back to the Mosquito Range and was able to pass directly over Mt. Lincoln, Mt. Cameron, and Mt. Democrat – three additional 14ers directly along the same ridge line.  (Unfortunately I missed Mt. Bross by less than a mile.)

The Mosquito Range and the Ten Mile Range behind looking north. Mt. Lincoln, Mt. Cameron, Mt. Democrat, and Mt. Bross are topping the two ridge lines in the upper middle right of in this picture. The road over Hoosier Pass between Fairplay and Breckenridge is visible in the upper right. Three tailings ponds from the mining industry north of Leadville are visible in the top left. Mt. Quandary is just to the right of these ponds.

From Mt. Democrat I still had 8 miles to go to get to Mt Sherman.  I followed the ridge line, hoping that the combination of northwesterly wind and sunshine hitting the western slope would carry me along.  Unfortunately that wasn’t the case and my altitude kept dropping again.  There was a nice looking cloud two miles west of the ridge (directly east of the town of Leadville) so I decided to seek another climb under that cloud before going to Mt. Sherman. That was plan A.

There’s always a risk that a cloud won’t work so having a plan B was important because I was now on the west side of the Mosquito Range and potentially unable to cross back to the east side.  Fortunately, coming up with plan B was simple.  With the wind from the northwest I would fly on the upwind side of the ridges to the south and eventually land at the airport in Buena Vista should I be unable to find a climb before then.  I considered this a very remote possibility but felt good about knowing exactly what to do if plan A did not work.

The town of Leadville is clearly visible as I circle on the west side of the Mosquito Range.

There was indeed no need for plan B.  The cloud east of Leadville offered a quick and easy climb to 17,800 feet.  The top of Mt. Sherman was now only three miles to the southeast and more than 3,500 feet below.   Rounding it felt almost anticlimactic after all the work that it took to get there:  the final seven miles to get from Alma Junction to Mt. Sherman had taken me more than one hour and ten minutes!

With the wind at my back and no mountain to climb in front I was back at Alma Junction in less than five minutes and on route towards Lookout Mountain, my second turn point, 100 miles NNE.

There were two reasonably looking ways to get there.  1) A more direct route following the spine of the Continental Divide; and 2) A longer and more easterly route along the lower foothills via Conifer, Golden, Jamestown and Estes Park.

The longer route looked a lot easier:  there were several nice looking clouds between Como and Conifer and then a continuous line of – likely convergence induced – clouds all along the lower foothills to the north.  I had already flown this route in similar conditions and have seen it work extremely well.

The direct route had fewer compelling clouds but I thought it would benefit from the afternoon sun hitting the westerly slopes of the mountains and the northwesterly winds blowing up along the divide.  And it was shorter.

I opted to go for the direct route.  Initially I made reasonable progress via Boreas Mountain, Geneva Peak, and Grays and Torreys Peak. But from there this choice of route turned out to be a big mistake.  The further north I got the stronger the wind became.  And as the wind got stronger the thermals became weaker, more turbulent, and less organized.  Weak climbs meant I had to spend a long time working my way up, and while I did that, I was subjected to major wind drift.  What I thought would be a shorter route, actually ended up being a longer one if you add up all the miles that I had to push back into the cross wind.

The worst section was north of Longs Peak when my turn-point  was no more than 20 miles away.  I was just one good climb away from making my final turn point and the good climb just never came.  I spent way too much time in weak wind-blown lift, hanging on to my poor route choice for no apparent reason.  In retrospect, I would have been much faster had I simply departed from the divide and flown along the convergence at the base of the foothills.   The last 20 miles to TP2 took me 45 minutes – a ridiculous amount of time given that I did not have a major peak to climb.

After I finally rounded TP2 it took me a while to understand how easy the line along the foothills would have been.  My brain was so conditioned to the poor conditions along the divide that I instinctively took the first climb I could find along the foothills, spending another 10 minutes in weak lift to work my way up to final glide altitude of 13,000 feet.

Only then did I realize how easy this line could have been.  I flew the next 20 miles to the Finish Line without another circle and without losing any altitude, finally reaching Bighorn Mountain five hours and three minutes after I had started my 325km task from there.

Since flying was now so easy I continued for another 20 miles straight to Golden before turning around to come back to Boulder where I landed after having been in the air for six hours total.

This was a difficult flight (which I made a lot more difficult than it should have been) but with some nice accomplishments: I bagged five additional Fouteeners (Quandary Peak, Mt Lincoln, Mt. Cameron, Mt. Democrat, and Mt. Sherman) and I completed my second pre-declared 300+ kilometer triangle flight (i.e. Diamond Goal).  My flight track is here.

If you take three attempts to round a TP and pick a poor line between two TPs something has to give: task speed only 35kts – almost twice as slow than during my first Diamond Goal flight.

However, it is truly humbling when I put these accomplishments next to the flight of another Boulder pilot, Pedja Bogdanovich, on the same day: Pedja covered 1,163 kilometers including a 916km FAI triangle.  His average speed: 131 kph!  Pedja’s flight track is here. So much to learn!

Lessons Learned

  • Don’t pick a high mountain top as a turn-point unless you really, really want it.  Rounding Mt. Sherman took me 1 hour and 10 minutes.  That is fine (and perhaps even necessary) if the primary objective of the flight is to reach that specific TP.  (Would I have tried so hard to get a Fourteener had I picked Fairplay as my TP?).  But if the primary goal is to complete a pre-set task, pick an easier TP and try to achieve a secondary goal (such as a nearby 14er) along the way.
  • Don’t expect to find good thermals on the upwind side of slopes if the wind is strong.  Strong wind wreaks havoc with thermals: a) the air cannot cling to the ground long enough to warm up sufficiently (hence the thermals are weaker); and b) rising thermals can be so wind-blown that it’s almost impossible to fly a full circle in lift.  On very windy days the best thermals may be further downwind of mountain ranges where they are protected from the wind; – especially if the wind is forced to slow down by another airmass and a convergence line forms (like on Thursday along the foothills).
  • If you pick a poor line, correct it (if you can).  Don’t stick to a decision if it can be easily corrected.  I had plenty of evidence that the line along the divide did not work and the amazing-looking cloud street along the foothills was in plain view and at all times easily reachable.  I should have course-corrected when I found out that my line was clearly sub-optimal.
  • Always have a plan B (and plan C if appropriate).  I felt I was appropriately disciplined on Thursday whenever there was a risk of getting low.  I did not decide to approach the Silverheels Ridge without a clear escape plan and a viable land-out spot picked. I did not cross into the Leadville Valley without having a clear plan of where to land and how to get there if needed.
  • Don’t base your expectations on your last experience if you transition to a different area.  On Thursday, I intuitively felt that the thermals along the Continental Divide would be as good as those that I had used on my outbound leg to TP1.  That was a mistake.  I should have anticipated that the strong wind would weaken and blow out those thermals.  Likewise, my experience with the poor lift along the divide clouded my judgement with respect to the conditions when I returned to the base of the foothills at the end of the day.  Different areas will likely mean different conditions – different thermal strength, different wind characteristics, etc.  I have to get better taking this into account when transitioning from one area to another.

Diamond Goal in 2 Hours 34 min

The soaring forecast for this past Saturday suggested strong thermals along the lower foothills but strong westerly winds – and therefore much more difficult conditions – on the west side of the Continental Divide.

Here are some of the key weather charts that I looked at the night before my flight:

Strong thermals of 3-4 m/s (6-8 kt) along the foothills from Colorado Springs in the south to the Colorado/Wyoming border in the north.
Thermal height at 2PM – quite high – to be expected for the mountains but higher than usual for the plains along the foothills. Cloud bases near the legal limit of 18,000 or even higher mean that much of the flight can be high above the terrain and therefore stress-free, with a wide glide radius and therefore a wide range of landing options as long as one can stay in contact with the clouds.
30+ knot winds to the west of the Continental Divide (at the top of the boundary layer)
Modest risk of overdevelopment north of Boulder but no risk of thunderstorms.
The net result presented in the PFD chart: strong thermals, a high base, and not much risk of over-development = strong attainable flight distances, especially along the lower foothills.

Plus, very important to look at, especially in Boulder, is the convergence forecast.

Projected convergence (and divergence) lines at 2:30PM.  The chart shows several convergence zones along the lower foothills. These are super helpful especially when they are marked by curtain clouds and/or different cloud bases. In blue conditions a situation like this can be confusing for the pilot as it is not possible to see why there is lift in some areas (where air masses are coming together, i.e. converging) and sink in others (where air masses are drifting apart, i.e. diverging).
Convergence forecast for 4PM. This shows a very pronounced line along the lower foothills. It is particularly useful to look at the projected development of convergence lines over the entire soaring day. (Just as it is important to look at the development of thermal height, depth, and strength). Skysight makes this easy to do by pressing on the triangle icon to the right of the time slider.  Note, however, that there are so many variables at play that it is impossible to predict precisely where the convergence zones will be at any given point in time.  Especially this part of the forecast can only be directional at best.  However, I have found it to be extremely useful in forming a mental picture of the potential movements of air masses throughout the day. By reading the clouds it is then much easier to understand what is going on and to adjust accordingly.

Given these conditions I decided I would stay on the east side of the divide and plan a pre-declared 300km triangle route that would take advantage of the strong thermal conditions along the lower foothills as well as the convergence lines.  If the convergence forecast would hold and if I did my planning right, I might even be able to fly relatively fast and get some points for the OLC speed league as well.

With these objectives in mind, I declared the following triangle that would meet the requirements for a Diamond Goal Flight according to the FAI.

Start at Gross Reservoir Dam.  I wanted the start to be within a 15 km radius around the Boulder airport since you have to fly through this cylinder after getting off tow to qualify for OLC speed league points.  Gross Reservoir is just within the 15 km mark.  It is also on the west side of the Flatirons, where thermals tend to start much sooner than on the east side where the inversion can be very persistent. Another advantage is the fact that the south-tow route from Boulder runs along Eldorado Canyon, just a little south-east of the reservoir.  (When towing north, a good alternative start point within the 15 km cylinder would be Bighorn Mountain.)

First TP at Halligan Reservoir, 103 km to the north of Gross Reservoir.  According to my forecast, the convergence line would likely be a few miles east of Halligan.  There were two reasons I wanted to stay on the west side: 1) the lift tends to be much weaker once you get into the more humid air mass that typically lies east of the convergence; and 2) the cloud bases on the east side are often much lower.  The last thing I wanted was to be forced to descend down low just to round a turn point and then have to work my way back up.  I also considered moving the TP further north but the mountains get lower the closer you get to the Wyoming border and this often means that the prevailing westerly winds tend to be stronger and therefore the thermals weaker and less organized.

Second TP at Conifer, 151 km to the south of Halligan Reservoir.  The projected location of the convergence was, once again, among my top reasons to pick Conifer.  It also has the advantage of being less than 60 km away from Boulder, which means that given the forecasted height of the cloud base around 18,000 feet, it would be well within final glide range of the Boulder airport. I therefore considered it a stress-free turn point even if the conditions would be less than ideal.

Finish back at Gross Reservoir Dam, 48 km to the north of Conifer, for a total triangle distance of 302 km (164 nautical miles).

Task as shown on Google Maps

I knew, of course, that reality never exactly matches the forecast.  To prove this point, as I drove to the airport in the morning, a long and wide lenticular cloud shielded the sun from reaching the ground along the foothills over a stretch of at least 100 miles.  The temperature at the airfield was pleasantly cool but this only meant that without direct sunshine, thermal activity would start much later than 10:30AM as projected in the forecast.

However, given that it was June 22 – just one day beyond the summer solstice – there was a lot of daytime left for the lennie to disappear and for the day to develop.

Around 11:30AM the cirrus shield had become noticeably smaller and thinner and the temperature on the ground started to rise quickly.  The more impatient pilots decided to launch, unfortunately only to return to the airfield 20-30 minutes later.  Clearly, it was still too early.   I kept telling myself that there was no reason to rush.  Sunset was at 8:34PM and thermal activity would likely last until well past 6PM.   And my task should not require more than 4 hours,  maybe even considerably less.

I decided to remain on the ground until the first pilot would stay air born.  That was the case around 12:30PM.  I waited for one more pilot to launch and finally took off just before 1PM.

A beautiful cumulus cloud had formed right above the Flatirons – ideal for a south tow towards my start point.  I stayed on tow probably a little longer than necessary and released in the second good lift at just under 10k feet MSL.  My climb rate immediately improved once I was off tow – funny how that works – and within minutes I was up at 15k feet and ready to get on task.

There were some nice looking cumuli right along the task line interspersed with some blue gaps in between.  The first gap was perhaps the biggest at about 15 miles but I wasn’t bothered by it.   I had enough altitude and the cloud ahead looked very promising.  I was also within glide range of Boulder and knew that in the worst case I could try again.  I also saw some developing wisps along my path and slightly adjusted my route by a few degrees here and there to take advantage of any rising air, always staying slightly on the upwind side.

Beautiful skies on my first leg. The town of Estes Park is below. Longs Peak is on the left side of the picture just below the wing. I just left a very strong climb and am heading north towards Halligan Reservoir.

A very powerful climb near Estes Park (up to 15 kts average!) took me to 17,000 feet and another over Signal Mountain to 17,500.  The path forward to my first TP was along the convergence zone:  generally the air was just rising up by 1-2 kts and I was able to fly in a straight line while maintaining altitude as long as I wasn’t pushing for speed.

As I got closer to Halligan Reservoir the cloud base dropped a little so I flew a bit faster to come down as well, rounding the turn point at an altitude of 16,000 feet.

Rounding the first TP over Halligan Reservoir

Looking back to the south after my 180 turn, I noticed the convergence had continued to develop and the line was now better marked.

A few miles after rounding TP1, heading south. The convergence line is clearly visible and the cloud bases ahead are rising. Horsetooth Reservoir is visible 20 miles ahead in the distance, approx. 20 degrees left of the nose. There’s a long paved private airstrip (“Christman Field”) just east of the northern tip of the lake, probably the best land-out option in this area because you could just get a tow plane instead of having to trailer back. However, with skies like this in front I was not at all worried about having to land out.

West of Ft. Collins I stopped to get back to over 17,000 feet before continuing my convergence surfing:  the line wasn’t completely straight so I curved gently along its west side, flying faster in sink and slowing down in lift, for the most part able to avoid any thermaling.

Well-marked convergence line on my second leg, heading south. The low hanging curtain clouds mark the boundary between the different air masses. The air on the drier side (where the cloud base is significantly higher) is rising. When you see clouds like this just fly along the curtain clouds and stay on the side with the higher cloud bases. It works!

West of Golden, the convergence line made an obvious turn toward the west so I decided to make a little detour as well:

You can see my detour to the west on my second and third leg as I followed the convergence. The straight line between Gross Reservoir and Conifer is the task direction. My flight path curved west via Squaw Mountain as I flew along the west side of the curtain clouds that marked the convergence. If you look closely at the slight change in color of the flight trace, you can see that I gained altitude between Gross Reservoir and Squaw Mt. on the southbound leg. At Squaw Mt. I had to leave the convergence line to reach Conifer 20+ km further SE. You can also see my altitude drop (the trace line changes color from blue to turquoise) as I tug underneath the lower cloud base near Conifer. After rounding the turn point I first headed WNW instead of flying straight towards Gross Reservoir in order to follow the best available energy line. Although this meant a longer flight track it was likely still faster than going straight and stopping in (likely weaker) thermals along the way.

Conifer lay about 10 miles east of the convergence requiring me to temporarily leave the air mass that had carried me so well.  Once again I had to drop down to about 16,000 feet to make the turnpoint and stay clear of the clouds.

After rounding Conifer, I headed right back toward the convergence line, following along a ridge towards Mt Evans where the air was slightly ascending which meant I was also to get back to the convergence without losing much altitude.  Near Squaw Mountain I stopped in a thermal to top up to 17,700 ft and from there it was a straight glide to the finish line over Gross Reservoir.

Steep celebratory turn over Gross Reservoir just after crossing the finish line :-). You can see the dam straight below.

A glance at the flight computer told me I had completed my 302 km task in just 2 hours and 34 minutes.  That equated to a respectable average task speed of 118 km per hour.  I’m sure an experienced XC pilot could have shaved off another 20-30 minutes but I’m definitely happy with this result for my fist 300 km goal flight. (I even arrived 1000 feet higher than I had started out!)

My flight computer happily announced that the task was indeed finished. Average task speed 64 kts (118.5 kph)
The red line shows my route on task. The blue line is my flight trace before and after the task portion.

With my task completed, I wondered what I could add-on to enhance my OLC score.  I thought it would be great if I could turn my overall flight track into into a big FAI triangle.  To do that I would have to cross the Continental Divide and fly west to a point roughly perpendicular to the line between Halligan Reservoir and Conifer, and approx. in the middle of it.  Kremmling, I thought, would be an ideal turnpoint to shoot for.  If this worked I might be able to post a 400 km FAI triangle.

The first practical question was how to get to the Divide.  The straight line west from Gross Reservoir did not look promising as it meant pushing into a big blue hole against a 15-20kt headwind.  There were no clouds for 20 miles and I expected a lot of sink in the lee of the mountains.  Quick decision: I would return towards Mt. Evans where the convergence line had already proven to work – then I would fly north along the divide and look for a cloud street that could take me west.

In trying to execute this add-on plan, the first part worked well.  Within 20 minutes I was on the divide near Silver Plume Mountain.

Above the Continental Divide near James Peak, looking SW towards Vail. This cloud street looked very good but it wasn’t exactly in the direction I was most interested in taking. Also, the clouds were now developing very rapidly with the first virga are already visible on the horizon. Lastly, I am still not sufficiently familiar with the land-out options in this direction so I did not seriously consider taking this route.

As I continued to head north along the ridge I hit significant sink.  I stopped at Mt. Flora to get back to 17,500 before a blue gap to the next cloud near Mt. Jasper.  There I only found a very weak climb in turbulent conditions.

Unfortunately the clouds to the west of the divide were now rapidly over-developing.  As I circled around Mt. Jasper I could see more and more virga and rain showers developing in the direction I wanted to fly in and so I decided to shelf my FAI triangle plan for another day.

Continuing along the divide also seemed pointless as the thermals on the ridge were weak and extremely wind-blown. The convergence over the foothills still looked promising, however, and so I headed back towards Gold Lake.  With the wind from behind this was a quick transition but I still lost quite a bit of altitude flying through the lee side sink.  I had been right not pushing into the wind earlier.

Leaving the Continental Divide heading east. The wing points north along the Divide. Niwot Ridge, Left Hand Reservoir, and Brainard Lake are visible below. Longs Peak and Mount Meeker are clearly visible in the distance. The blue skies above are indicative of the lee side sink on this side of the mountains.

A mediocre climb near Jamestown (I wondered: would I have taken this had I been trying to get somewhere?) took me back to 17,000 and a vicious rotor over the Twin Sisters (i.e. in the lee of Longs Peak) brought me to 17,500 feet.  From there I tried to connect with the clouds on top of Trail Ridge Road to maybe push a little further west from there.  However, by now I should have known better than to approach the Divide from the lee side on such a windy day.  After hitting heavy sink I scrapped that plan as well and headed back to the tried and true convergence line north of Estes Park. By now overdevelopment set in almost everywhere around me and although the lift was still strong, the lack of sunshine in the cockpit meant I was getting cold.

Estes Park viewed from Triangle Mountain around 6PM. There’s still a nice cloud street to the west of Estes Park but it is too late for new adventures on the other side of the divide. Also, the amount of virga and rain showers is rapidly increasing at this time.

With 6pm approaching the next decision was simple: enough for the day.  I started my final glide north of Estes Park, flew straight to Golden and from there back to Boulder where I arrived with plenty of altitude to spare.

Flight stats.

My total flight distance ended up being 523km.  So in addition to Diamond Goal I also completed Diamond Distance.  And my bonus goal of earning OLC Speed League points for our club worked out too.  With 118 points I scored second for SSB this past weekend and first among those flying from Boulder. The flight track is here.

Evening scenery at the Boulder airfield after a great day of flying.


Lessons Learned

  • Careful task planning can pay off.  Usually a pre-declared route should mean a lower average speed than simply following the best visible lines.  However, by carefully planning my task in accordance with the thermal and convergence forecast I was able to pre-plan the flight in a way that took advantage of the best projected energy lines.  And since the reality was not very far off from the forecast, requiring only a deviation of about 20 miles or so, I was able to complete the task as quickly as I did.
  • Flying with a specific goal in mind greatly focuses in-flight decision making. On previous flights when I took off without a specific objective in mind, the choices were endless.  This meant I often took a while to make up my mind and I also found myself reversing decisions I had made simply because small changes in the sky momentarily made some other direction look more promising.  This Saturday I had a clear goal and all my decision were made to safely get to the goal as fast as possible.  The difference this makes to the thought process is amazing. At any given point there are much fewer choices available and I’ve found myself homing in on those choices much faster.
  • Flying with a specific goal makes soaring even more fun.  Sure, even without a goal it is fun to take advantage of the wind and the sun and enjoy the amazing sight-seeing that can be had high above the Rocky Mountains with all of Colorado spread-out below.  However, I’ve found that on days when staying up is super easy the level of fun increases to another level by adding some additional challenge and being able to measure progress against that challenge.  Try it out!
  • Convergence lines can be the key to flying fast – especially in this area where they are a very frequent phenomenon.  Even if the lift along the convergence is only 1-2 kts it basically means you can fly in a straight line (maybe with slight route deviations here and there) without having to stop to thermal.  You are much faster overall when floating along at 60 kts IAS at 17,000 feet than to push 80 – 90kts between thermals, then stopping to climb before putting the nose down again.
  • Always remember the power of lee side sink.   I made the right call when I decided to transition to the divide from Gross Reservoir via an established convergence line towards Mount Evans.  Flying there directly into the wind would have likely been impossible.  I should have remembered this lesson when I tried it again a bit later over Estes Park.  Although the distance to bridge was much shorter flying in heavy lee-side sink against the wind requires a lot of excess altitude.

First 500km Flight, Pikes Peak Bagged

This past Thursday was likely going to be the best soaring day of the week.  Still, I wasn’t sure whether it would be a great day or merely a good day.

SkySight predicted a strong thermal flying day with attainable flight distances from Boulder between 500-600k for 18m ships (which have a somewhat better performance than our club’s Standard Class 15m Discus). Note that going east from Boulder into the dark red colored area is not practical since most of that area is part of restricted Denver Class B airspace.
Topmeteo was a lot more bullish and predecited outstanding soaring conditions for almost all of Colorado with potential flight distances of up to 1000 km.

Thermal height was going to increase throughout the day to approx. 20,000 feet MSL over the mountains with the highest cloud bases to the southwest.  Thermals were projected to be strong with climb rates of up to 10kts or even more.  There were going to be winds of 10-20kts aloft, mostly from the southwest.  These winds could complicate thermal flying:  increasing winds with altitude tend to distort thermals breaking off from the ground and the strongest lift is often limited to upper-level convection, i.e. close to cloud-base.  In addition, it is important to be careful on the lee side of taller mountains where such winds tend to cause significant sink and rotor turbulence. There was a good chance for cumulus clouds and a low risk for overdevelopment.

From the soundings it looked like the day might start as early as 10AM over the foothills and significantly later in Boulder – a common scenario due to the morning inversion down in the valley.

As I did the pre-flight checks on the Discus there was a slight easterly breeze on the ground – also a very common phenomenon – and an indication that there was likely a convergence line somewhere over the foothills where the easterly wind from the plains meets the westerly airflow aloft.

SkySight illustrates the convergence line running along the foothills (shown in dark red): this is where the eastern airmass from the plains meets the dryer western air mass spilling over the Continental Divide. Note that this forecast is for 1:30 PM MDT. The position of the convergence line tends to shift throughout the day – often it moves further west as the day progresses. I speculated about the reasons for this in my previous post.

Whenever conditions conform to this fairly typical pattern I have learned that it is important to get to the west side of the convergence line as quickly as possible:  thermals on the east side tend to be fairly weak and often top out at less than 1000 feet AGL – especially in the morning when they are trapped by the inversion layer.  Unfortunately this often means a long (and expensive) tow over the foothills is necessary to connect with the lift on the west side of the convergence.  (Note that usually you don’t have to tow all the way back to the convergence but you have to tow high enough to be able to glide west until you’re able to connect with rising air on the west side.  If you don’t steer decisively west and linger on the east side you might quickly find yourself too low to get far enough west.  This is especially true early in the day when the thermals on the east side are still non-existent or extremely weak. )

When I launched at 10:42AM MDT the air above Boulder was still as calm as it could possibly be – a sign that the inversion still suppressed any thermal activity over the plains. The first time the air started to stir just a little was after the towplane had turned west over the foothills (west of Altona).  However, the climb rate on tow remained constant until we had climbed to 10,800 feet over Jamestown and I decided that I was now high enough to push further west on my own as we still had not reached a thermal.

Flight path on tow shown in dark gray. Flight path off tow shown in light blue. Release point over Jamestown. My first attempt to climb off tow was on the east side of the convergence line. Lift was weak and uneven. A few miles further west everything changed and climbing from 10,000 to 16,000 feet was almost effortless.

I headed straight toward a cloud a few miles further west.  East of Hidden Lake I reached the east side of the cloud and found some weak lift.  I tried to climb in it but the air was rough and the lift weak and inconsistent.  The wind drift was from the SE towards the NW.  These were all indicators that I had reached the convergence line but that I was still on the east side.  After several turns (probably too many) I decided to push to the western edge of the cloud.  And voila, just as I had hoped, I had reached the west side of the convergence line and within 10 minutes I climbed from 10,000 feet to just under 16,000 feet.

As I started to head south I could easily see the position of the convergence line by looking at the curtain clouds underneath the next cloud in front of me.

The curtain clouds in this picture are a perfect indicator for the position of the convergence line. Good climbs can be found on the west (dry) side.  The nice clouds further south (on the right hand side of the picture) suggest a quick and easy flight route ahead.  My position in this picture is a few miles north of Ward above the Peak-to-Peak Highway, looking SSE.  The city of Boulder is on the left edge of the picture.

Two quick climbs above Nederland and south of Idaho Springs took me up to 17,000 feet – high enough to push through the potential sink on the lee side of Mount Evans.  The air above Evans was rough but I found two reasonable climbs southwest of Mount Bierstadt that gave me the altitude needed to fly further southwest into Southpark where I saw some promising clouds north of Como.  At this point my goal was Buena Vista and – if all went well – perhaps Salida.

I climbed in ok-ish lift near Fairplay and headed for some nice looking clouds near Antero Junction.  However, none of the clouds along the western rim of South Park worked well at all.  I could not make out a good reason for this but when the fourth or fifth cloud provided only mediocre lift I decided to change course and save Salida as a goal for another day.  A few miles to the north I saw several nice clouds right through the middle of South Park, spread about 10 miles apart.

These worked and within 20 minutes or so I had reached the east rim of South Park.  This area worked particularly well: it was now early afternoon and the combination of wind and sunshine from SSW provided for great lift above the SW facing slopes on the east side of South Park.

At this point I had my eye on Pikes Peak. There was a blue hole right around the mountain but it was not nearly as big as during my prior attempt.

Pikes Peak approx. 10 miles away and – somewhat surprisingly – free of any clouds. At the point of this picture I was above 17,500 feet and the summit at 14,114 feet seemed within easy reach. However, it wasn’t going to be that easy.

The wind was blowing at 18 kts from SSW so I decided not to fly straight toward the mountain but instead to pass it on the west side and then approach it from the SW.  If I wouldn’t find any lift along the slope, I would have an escape route to the south towards Fremont County Airport near Cañon City, which I figured was easily reachable even flying against the wind.  There were also some nice looking thermals in that direction giving me extra confidence.

As I approached Pikes Peak the air turned very rough with strong sink.  A few miles SW of the summit I reached a low point of around 14,500 feet – just a few hundred feet higher than the mountain itself – too low for comfort to fly over the peak.  Fortunately I found a turbulent thermal breaking off from the ridge line below me.  Although it was extremely disorganized and caused erratic movements of my vario from +10kts to -10 kts I was able to climb to 16,700 feet – high enough not only to fly over the summit but also to reach the next cloud, which was approx. 10-15 miles further north.

I was surprised to find strong sink on my approach to Pikes Peak. The climb above the ridge SW of the summit was quite rough.  Also note the sudden (and non-obvious) change in wind drift from SW to WNW after I crossed the little lake below the summit.  The air near big mountains can be very fickle.

Having “bagged” Pikes Peak, I decided to head back towards Boulder while remaining on the lookout for worthwhile excursions.

View of Pikes Peak from the West just as I was getting into strong unexpected sink during the approach. The climb that took me back up over the top was just above the ridge line near the little lake on the right edge of this picture.

The clouds in front of me looked solid.  However, when I got to the nearest one, north of Woodland Park, the climb rate was disappointing.  I wondered if I was too far east – perhaps the air from the prairie had penetrated over the foothills, suppressing thermal activity?

I decided to turn west again towards the east rim of South Park where I had experienced much stronger climb rates some 40 minutes ago.  However, my next three thermals were equally poor and each time I decided to push on without gaining much altitude.  Lee-side sink north of Buffalo Peak caused me to loose another 1,500 feet.  I was now below 13,000 and worried that I might lose my connection to the clouds.

Just as my mind was working on fall-back options: Perry Park airfield was still within reach (though barely) and an off-landing field near Roxborough Park (which I recently checked out on the ground) was more easily accessible, I found a modest climb southeast of Bailey.  When you’re down to 12,700 feet over unforgiving terrain and with another 50 miles to go to Boulder you can’t be picky.  I carefully centered the thermal and happily spent the next 12 minutes climbing back up to 17,500 feet.

A succession of frustratingly weak climbs led me to a low point of 12,700 feet SE of Bailey. Perry Park Airfield was 30 miles away (requiring a 35:1 glide ratio). The nearest comfortable out-landing field was just over 20 miles away, NE of Roxborough Park.

It only takes one climb for the world to look totally different again. I steered to the SW side of Mount Logan (just SE of Mt Evans), climbed again to just under 18,000 and decided to fly north.  Maybe I would find lift above the Continental Divide so I could extend the flight to the north towards the Wyoming Border?

However, when I got to the Divide near Mt. Eva the route to the north along the Divide did not look promising.  Rain showers and virga obscured the sight and the area appeared over-developed.  To my left however, there was a nice-looking cloud street towards the SW.  I followed this line until Berthoud Falls when the route ahead also seemed be over-developing.

I made a 180 degree turn.  Looking north from my new vantage point I could suddenly see what was going on:  the convergence line that had sat over the foothills in the morning had crossed over the Continental Divide.  What had looked like rain showers and virga when viewed from the East side were in fact curtain clouds marking the position of the convergence line.  Further to the west the sky was completely blue.

Beautiful view of the convergence line on the west side of the Continental Divide. I took this picture after my northern turn-around point. The curtain clouds marking the convergence are clearly visible.

I decided to follow this line to the north, always staying to the west of the curtain clouds. It worked amazingly well.  I followed the line of curtain clouds that paralleled the divide.  Flying between 80 and 100 kts IAS I was able to maintain my altitude of around 17,500 feet over a distance of 38 miles in just 16 minutes.

The power of a convergence line: 38 miles in 16 minutes, that’s an average ground speed of 142 mph. Without losing altitude.

North of Longs Peak the line became less clearly defined and the cloud base dropped so I decided to turn around.  I followed the line south past Apache Peak and then decided to return towards Boulder.

Grand Lake and Lake Granby viewed from the west side of the Continental Divide near Longs Peak.

My final glide took me past Gross Reservoir towards Golden where I checked out the model plane airfield near Arvada from the air.  I recently visited this field on the ground and determined for myself that its perfectly paved 700 foot runway is a viable out-landing option (land on the N side of the runway to minimize the risk of hitting a fence and watch out for the power lines on final).

From there I followed the ridge line of the Flatirons on my way back to Boulder.  The winds at Boulder airport were 3 kts from the NE.  I briefly considered landing on G26 but ultimately opted for Runway G8.  I’m glad I did: as soon as I climbed out of the cockpit to get the dolly a freakish 27mph gust hit the airfield straight from the east. The gust lasted for about 2-3 minutes, then total calmness returned.  I have absolutely no explanation for this gust.  I just know that landing with a 27 mph tailwind would have been quite troublesome.

It was an interesting end to a challenging and rewarding first 500km flight. The full flight track is here.

Lessons Learned:

  • If there is a convergence over the foothills get to the west side before you are too low. This is especially true in mornings with strong ground inversions when there are still no viable thermals on the east side.
  • Always have a viable landing field in mind.  I caught myself a bit by surprise when I was down at 12,700 feet and noticed that getting to Perry Park would have been doable but already a bit of a stretch.
  • Approach big mountains with respect.  They can make their own weather and it’s not always what you might expect.  E.g., Pikes Peak surprised me with sink on the west side, which had direct sun exposure and was facing the wind. (It reminded me of a video from Bruno Vassel confidently approaching the Tetons from the west only to find unexpected sink.)
  • Keep in touch with the clouds when you can.  Throughout the flight I noticed that the climb rates improved the closer I got to the clouds.  This phenomenon seems to get more pronounced throughout the day.  Thermals down low were quite poor and wind-blown.  But close to the clouds the upper-level convection was quite strong, often with climb rates of close to 10kts or even more.  Staying high isn’t only safer, it might actually also make you faster (even though you have to center more climbs.)
  • Never get caught in lee-side sink.  I should have been more mindful of the terrain when I was flying just below 14,000 feet N of Buffalo Peak.  I turned northeast in direct pursuit of the next cloud and got into sink on the back side of Windy Peak. This could have been easily avoided had I followed the ridge line before turning towards the cloud. (It probably would have saved about 1,000 feet, which could make all the difference when it comes to reaching a land-out field.)
  • When it comes to wind, always expect the unexpected, especially in the pattern.  The freakish gust after landing was completely and literally out of the blue. (I had monitored the conditions in Boulder on the radio off and on for the past 20 minutes and conditions had always been calm.)

Venturing South

One of the advantages of soaring in the American West is that frequent cloud bases of 18,000 feet or more allow for significant flight distances without ever leaving the glide radius of the home airport – especially if you’re lucky to have a high performance plane.

20 miles from Pikes Peak

E.g., let’s say you’re flying a ship with a glide ratio of 40:1 from Boulder, CO.  The airport elevation is 5,300 feet.  Pattern altitude is 6,300.   That means on good thermal days you often fly 11,000 feet or more above pattern altitude.  And 11,000 feet of altitude at 40:1 equates to a glide distance of more than 80 miles!  This means, at least in theory, you can start a final glide at 18,000 feet MSL above Pikes Peak to the west of Colorado Springs and reach the Boulder airport 700 ft above pattern altitude – provided that you’re flying at optimum glide speed and absent any sink or headwind.  Reality isn’t usually so kind, i.e., you’re not able to maintain optimum glide speed, there is at least some cross wind component to deal with, and you’re spending more time in sink than in lift. Therefore it’s prudent not to rely on a glide ratio that’s better than half the theoretical maximum.  But even that gets you home from 17,300 ft MSL above Mt. Evans, or from 17,300 feet above the northern-most corners of Rocky Mountains National Park.  In other words, on days with high-reaching thermals (not uncommon) you can fly more than a 200 km FAI triangle without ever leaving the glide radius around Boulder.


Above Mount Evans

In my first 9 months of soaring from Boulder I have largely stayed within this “glidable” area.  Having acquainted myself with the area I feel it’s time to start venturing beyond these confines.

One of the motivating factors are the remarkable differences in soaring conditions in Boulder’s vicinity based on the overall weather situation.  This past Wednesday provided a great example.

Boulder lies directly at the foot of the Front Range of the Rocky Mountains.  Usually a dry air mass dominates to the west of the mountains, whereas a more humid air mass lies above the flat prairie to the east.  These two air masses tend to have different characteristics in terms of moisture content, temperature, wind direction, atmospheric pressure, etc.  The western airmass is typically pushed eastwards by the prevailing westerly airflow whereas the low level winds over the plains tend to come from easterly directions.  As the morning sun heats up the east facing slopes over the foothills, this easterly flow is augmented by convective activity, pulling in yet more air from the plains.  Where these two air masses meet and mix – usually somewhere over the hills in the vicinity of Boulder – the soaring conditions can get very complex.

On Wednesday, a south-westerly mid- to upper-level flow pushed dry air up and across the Continental Divide.  The air above Boulder was more moist and the temperature gradient was very stable.  A typical morning inversion lay over the plains.  The skies were blue and the sunshine intense but at 11:30 AM any lift over the city of Boulder still topped out at less than 1,000 ft AGL, trapped by the inversion layer.  Some wisps had formed over the foothills but they seemed to be short-lived.  The only nice cus could be seen some 30-40 miles to the north, inaccessible by glider from  Boulder.

As so often, Skysight had projected the convergence between the western and eastern air masses to follow a line over the foothills, parallel to the Continental Divide.  In the morning this line was supposed to be approx. 10-15 miles east of the Divide and over the course of the day, it was projected to gradually shift westwards – I assume due to the fact that increasing thermal activity over the hills would strengthen the easterly airflow and push the convergence further back towards the mountains.

Thermals to the east of the convergence were projected to be weak, especially between Golden and Fort Collins.  By contrast, much stronger conditions were forecast to the south of Mount Evans with particularly strong thermals along the foothills between Denver and Colorado Springs, and along the southern end of South Park towards Salida.  I tend to think that this difference has to do with the fact that the Front Range is much higher to the north or Mt. Evans than to the south:  where the mountains are high they slow down the westerly flow and the air from the east can penetrate further westwards.  Where the Front Range is lower (to the south of Evans), the westerly flow is stronger and prevents the easterly air mass from penetrating westwards.

The following sketch illustrates what I think the situation looked like in the morning on April 16.  My limited experience suggests this situation is pretty common in Boulder so I think it’s worth capturing it for my own learning.

Approximate situation in the morning of April 16, 2018. This seems to be a relatively frequent scenario in Boulder.

– a strong morning inversion at first prevented, then capped early thermal developments above the eastern plains (shown in blue)

– first thermals could be expected to pop up over the foothills where the morning sun warms the east-facing slopes.  A prime spot for first thermals would be over the Flatirons thanks to their steep eastern face which get the most direct sun exposure in the morning.  However, before noon these thermals would still top off at a few thousand feet above the terrain. (shown in green)

– better (but not great) thermals could be expected to the west of the convergence line. However, because this area is in the lee of the Rocky Mountains, these thermals would likely be turbulent and there could also be significant sink in-between them as air would spill down the mountains (shown in orange).

– much better lift could be expected south of Mount Evans (in the red shaded area) because the south westerly airflow could bring the dry westerly airmass into this area.  Note how the convergence line shifts further east.  Due to the wind direction from the SW this area would also not be subject to lee-side turbulence and sink. The best lift would likely be along the lower, west-facing slopes on the east side of South Park, especially after noon when the sun would warm these slopes most directly, and the wind would help to break the thermals off from the slopes below.

Given these projections my plan was to try to get towards the south.  If I could make it past Mount Evans, I expected to find much better conditions there.  If all went well, I might even make it all the way to Pikes Peak, and maybe from there into South Park towards Salida.  Knowing that this plan could take me well beyond conservative glide ratio calculations, I had researched the airfields to the south of Denver as well as a few potential off-field landing spots between there and Boulder, as well as in the area around South Park.

If the intent was to go south, the question was how to get there. It was around 12:45PM when I took a tow.   I released near Crescent Mountain (just south of the Flatirons) where I only found a very weak climb that topped off at 11,000 ft.  But it was high enough to push to a promising-looking cloud SE of Thorodin mountain where I climbed in 3-4 kt thermal lift to 13,000 ft.  This lift was still on the east side of the convergence line: the wind drift in this thermal is clearly from east to west.

The additional altitude allowed me to move a few miles further to the SW where I noticed a cloud with a higher cloud base.  This time I aimed straight to its western edge.  And indeed: I had made it to the west side of the convergence line where I could expect higher thermals and better climb rates!  The direction of the wind drift was a sure sign that I had made it to the “right” side of the convergence.  The climb rate was also significantly better at approx. 8 kt.  In only 5 minutes I had gained another 4,000 feet and was now at cloud base around 17,000 feet, ready to push further south.

Notice the yellow arrows depicting the opposite wind drift when circling southeast of Thorodin Mountain and northwest of Ely Hill: The climb near Thorodin mountain is in thermals on the east side of the convergence line: the wind drift is from the east. The climb near Ely Hill, just a few miles further southwest is on the west side of the convergence line: the wind drift is from the west.  So the convergence line must have roughly followed a line from Thorodin Mountain to Ely Hill.

I passed Mount Evans, following a row of clouds along the eastern rim of South Park, headed towards Pikes Peak.   Unfortunately the clouds ended and the sky turned blue when Pikes Peak was still 30 miles away.   This was clearly too much for my comfort zone and so I decided to turn and backtrack towards the NW.  20 minutes later I was back on the south side of Mt Evans.  Now the clouds looked better towards Pikes Peak and I decided to make another attempt.  This time I got within about 20 miles when, once again, the clouds came to an end.  Once again I decided not to take the risk.

Circling southwest of Cheeseman Lake, above pretty but quite inhospitable-looking terrain.

From there I headed north intent on seeing if I could fly the convergence line past Boulder to the north towards Wyoming, despite the much poorer thermal forecast for this area.  This turned out to be impossible.  Once I was north of Mt Evans, the conditions deteriorated quickly.  For a while I could still make out the position of the convergence line by looking at the positions of some interspersed clouds with different cloud bases but once I got to Ward thermals were few and far between, climb rates had deteriorated, and there was no viable way forward in sight.

Instead, I decided to head west towards an emerging cloud that was just west of the Continental Divide.  I pushed through heavy sink in the lee of the mountains and crossed the Divide at just below 15,000 feet MSL.  There was some ridge lift from the westerly winds along the divide, but 2,000-3,000 feet above the ridge it was just sufficient to maintain altitude.  The cloud was another few miles further west.

Exploring ridge lift over the top of the Continental Divide.

I had to decide between heading back towards Boulder, i.e. flying back through the lee-side sink with very poor prospects of connecting back up to cloud-base, or taking the risk of pushing for the cloud, firmly on the west side of the divide.  Given that Granby Airport was clearly within reach I decided to take the plunge and continued towards the west.  I got to the cloud – the only one around at that time – but found only very weak lift.  It took me 25 minutes to gain 2,000 feet back.  Had this been a race, here is where I would have lost it.

In the meantime, new convection had formed several miles further south, still on the western side of the divide.  Gingerly I continued my way south trying to stay at altitudes that would have allowed me to cross back to the eastern side.  A few poor climbs later I was able to fly directly over Grays Peak and Torreys Peak, two Colorado 14ers that I had not passed over before.

Circling in weak lift on the west side of the Continental Divide. Keystone ski resort is below.

Southwest of Mt. Evans I spotted what looked like a powerful new convergence line that stretched all across South Park.  It was already late in the day but the line looked extremely compelling so I decided to go for it.  I was not disappointed.  In 14kt (!) lift I quickly climbed back up to just under 18,000 feet and from there I had to shift my main focus to staying at legal altitudes.  The lift was so strong along this line that I had to open the spoilers at 100 kts IAS to avoid climbing above 18,000 ft.  Within 13 minutes I covered 30 miles without losing any altitude – that’s an average ground speed of 220 km per hour.  I don’t think I’ve ever flown a glider this fast!

View of South Park from the east rim, much earlier in the day. I have no pics of the flight under the convergence line as I had my hands full keeping the ship below 18k feet while flying at 100 kt IAS.

Given the late hour in the day I didn’t go further south than Jefferson before returning back toward the north.   I crossed the Divide NW of Mount Evans and continued in the weakening convergence line along the east side of the divide.  I flew all the way past Mount Audubon without a single circle (50 miles in just over 30 minutes), took a brief climb to fly over the top of Longs Peak, from where I started my final glide via the east side of Estes Park and Longmont to the Valmont Reservoir and finally back to the Boulder Airport.

Final climb of the day before flying over Longs Peak, straight ahead, just below the yaw string.

It was a long (five hours) and satisfying flight in very varied conditions where I experienced everything from weak thermals, and weak ridge lift to the strongest convergence zone lift I have ever encountered.  It was definitely my greatest triangle flight with a triangle distance of 276 km, and possibly my greatest distance flight overall with 472 km.

A link to the flight track is here.

Lessons Learned

  • If there is a convergence line parallel to the Front Range, getting to the west-side of it is key to climbing high enough to push to the south, past Mt. Evans.
  • Increasing thermal activity through the day may cause the convergence line along the Front Range to move further west as more air is pulled in from the plains, thereby strengthening the lower level easterly airflow.
  • Timing can be an important factor when it comes to reaching the convergence line.  Launch too early and the first thermals may be too weak and too low.  Launch too late and the convergence line may have moved so far west that you can’t reach it.  (Several pilots who launched after me struggled all day in middling lift around Boulder and were never able to make it to the higher cloud bases on the west of the convergence.)
  • The wind drift when thermaling can be a sure sign whether you are on the east or the west side of the convergence line.  This is particularly helpful when there are no clear indicators (e.g. in blue conditions, no different cloud bases, no curtain clouds).
  • Lift along a convergence line can be incredibly powerful.  I never before experienced lift as strong as 14 kts average.
  • A glide ratio of half the ship’s maximum seems to be a good rule of thumb when it comes to estimating a safe final glide distance.  (Note that this will not hold up in extreme conditions such as heavy lee-side sink, wave / rotor flying, thunderstorm activity, strong headwinds, etc.).
  • There are several things that I did not understand on this flight:  Why was the lift to the west of the Northern Front Range so weak?  What caused the late-day development of the convergence line parallel to the mountains on the NW-side of South Park and why was the lift there so strong?  Are conditions south of Mt. Evans typically stronger when the wind is from the SW?  Why did the convergence line to the north of Mt. Evans support climbs to 18,000 until Ward but not beyond?

The Smoking Tire – A Relict for the Wall of Shame

I have put off telling this story for several weeks.  It’s a lot more fun to talk about cool flights than to write about my own stupid mistakes. And this is definitely about a stupid mistake.

This is what happens to a tire when pulling on a break-lever too hard and too soon after landing. “Flat-spotted” is too nice a way to put it. This tire is destroyed.

So here’s the precursor to what happened.  On April 28 I had taken our club’s Discus to the west side of a north-south convergence line.  Cloud bases on the west side were close to 17,000 feet whereas to the east of the convergence conditions were much more difficult.  A persistent inversion lay over the plains supporting only weak thermals topping out at less than 8,000 feet.  With the help of a deep tow I was able to push into the western airmass and get all the way to 17,000 feet.  There were plenty of snow showers and virga above the mountains and my cautious self told me to stay within glide range of the Boulder airport.  Still, I had a good flight, scoring over 300 points on OLC-plus by covering more than 270 km including a 177 km triangle in just under 4 hours.   The flight track is here.

However, this story is not about the flight but about my landing.  And, as so often in aviation, stupid mistakes begin with chain reactions.

In this case the beginning was when I noticed on prior flights that the wheel break on the Discus was basically ineffective.  However hard I would pull on the break lever, there was no noticeable deceleration at all.  This is not an issue on the long runway in Boulder but it could be an issue when landing in a short farmer’s field. So I worked with others in the club to adjust the break and thought I would test it again on my next flight.

While I was flying another unrelated thing occurred: after about two hours the battery supplying the main electric system including the 2-way radio ran out of power.  This had not happened to me before. Unfortunately I didn’t remember that flipping a small switch on the instrument panel would have shifted the power supply to the ship’s second battery.  I made a mental note to get the battery replaced after the flight, but otherwise, having no power didn’t bother me too much at first:  the plane’s transponder, which broadcast my position to air traffic control was powered by a separate battery and still working fine. The airspeed indicator and the altimeter don’t require battery power and the ship is equipped with a second mechanical variometer that was also still working.  In addition, I had my own flight computer as well, which also has its own independent power supply. So the only thing I didn’t have was the radio, the optional Flarm system, the acoustic vario, and the ship’s built-in flight computer, which I didn’t need anyway.

As I came back to land, however, the lack of a working radio was back on my mind. There didn’t seem to be much traffic around the airport but without a radio I wasn’t able to announce my position and intentions and I also could not receive other pilots’ announcements.  So I concentrated on watching for traffic and on making my own position and intentions as clearly visible and predictable as possible.  I watched another plane land on runway 8 despite a slight westerly wind on the ground.  I remember thinking that I would land on Runway 26 (against the wind) if I could announce my intentions but with other traffic using runway 8 (which is the default runway in Boulder for calm conditions), I decided that I would also land on runway 8 despite the slight tailwind.

Somewhat preoccupied by these considerations I did not think at all about the break and the adjustments we had made to it.  So after touching down, somewhat faster than usual given the tailwind, I instinctively pulled on the break lever just like I had done on prior flights.  I noticed some deceleration and I remember thinking, “oh, the break is working now”.  I did not notice, or even consider, that I might have pulled the break lever too hard.

Just before the plane came to a stop the back pressure on the stick was no longer sufficient to keep the tail wheel on the ground, and the plane veered slightly off the tarmac.  Reactively, I must have pulled on the break again and thus the plane briefly dipped forward with the nose touching the gravel just before it came to a halt.

Other pilots watching my landing had noticed a smoke trail from my tire and came to tell me that I had been breaking way too hard.  Still, I had no appreciation for what “breaking too hard” could mean for the tire.  I basically destroyed it – there is no better way to say it. (See the picture of the actual tire above).

Dipping the nose into the gravel also caused some scratches in the gel coat on the underside of the fuselage.  Fortunately these are minor and only cosmetic in nature, and apparently relatively easy to repair.  Had the plane dipped forward on the tarmac and/or at a higher speed, the damage could have been much greater.

I’m obviously not proud of this incident.  With 1000s of feet of remaining runway in front there was no reason at all to break hard, or to use the break at all.  Drum brakes are not the most effective brakes and they are best used sparingly and only when really needed.  I decided to share this story because I hope other pilots may learn from it before “gaining” a similar experience themselves.  (Since my incident I have witnessed two other pilots damaging their tires as well).

I will also say that I learned a lot from the process of replacing the tire.  It is not a quick and easy thing to do and definitely a lot more involved than pushing the plane an extra 100 yards to its parking position. 😉

Lessons Learned

  1. Remember that battery switch, stupid!  If the plane you’re flying has more than one main battery it stands to reason that there is also a switch to toggle between these power sources.  If a battery runs of power, find that switch and use the good battery!
  2. Land against the wind whenever possible.  Even a slight tailwind can cause or exacerbate issues.  In this case it resulted in a higher ground speed at touch down, a longer ground roll, and it contributed to the plane veering off the runway at the end of the ground roll (because the back-pressure on the stick was no longer sufficient to keep the tail on the ground, and the rudder was no longer effective in steering while the plane was still moving). (However, I still think that my decision to land on runway 8 was acceptable considering other traffic, the fact that the wind was only light, and my inability to announce an approach to runway 26.)
  3. Breaking at speed kills the tire. Do not engage the wheel break at all when the plane is still moving fast unless you absolutely have to (i.e. there is a danger of hitting an obstacle on the ground).  The faster the plane moves, the more lift the wings still produce; therefore: the less weight is on the wheel and the easier the wheel locks up.
  4. You may not notice when the wheel locks up. If you use the break, use it gently and only when the plane has already slowed down.  You probably will not notice the wheel locking up when you engage the break, especially when the plane is still moving fast.   (The deceleration of a locked-up wheel is only small.)
  5. Only use the break when you must.  Safe the brakes in a glider for situations when you have to use them (e.g. a short off-field landing).  Don’t use them for the convenience of not having to push the plane back for a few hundred feet.   I believe for some planes with drum brakes this is even explicitly mentioned in the manual (e.g. for the LS4).
  6. Glider tires are soft. Tires of gliders are much more prone to flat spotting than car tires or bicycle tires.  Gliders also don’t have ABS systems 🙂
  7. Replacing tires on a glider is a complex and error-prone process.  Make sure to lubricate all moving parts (except the inside of the break itself!) and do not over-tighten the nuts on the axle for this may lock up the gear-retract mechanism.  After working on the wheel or tire make sure to cycle the gear retraction mechanism several times to ensure that it works smoothly and without requiring excess force.

My Skills Getting Tested – Challenging Start of the OLC Season

Beautiful view of the Continental Divide near Ward. The Peak to Peak Highway is directly under the wing.

This past weekend marked the start of the 2018 OLC season for the Northern Hemisphere.  For those who don’t know, OLC stands for Online Contest and is an informal worldwide soaring competition. Pilots anywhere can upload their flight tracks to a website hosted by a group of soaring aficionados in Germany. The tracks are automatically analyzed and classified according to the rules of various leagues.

My club, the Soaring Society of Boulder (SSB), is very active in the “OLC Speed League”.  The Speed League runs on 19 consecutive weekends starting on the third weekend in April.  Club rankings are determined based on the three fastest flights per club on any particular weekend during a 2 1/2 hour soaring window.  You can read the full rules here.  In 2017, SSB pilots won first place in the US Gold League and came in eight place worldwide (out of 1,162 participating soaring clubs).

Participating in this friendly competition seems to be a good way to track the progression of my own skill level over time when measured relative to the skills of much more experienced pilots.  At the same time, I am acutely aware of the potential risks that participating in any kind of soaring competition could entail.  I have written before about the risks of soaring, especially in a competitive setting, and ultimately it is up to the pilot to stay disciplined and put his or her safety firmly ahead of any competitive ambitions. This is the only way to stay safe.

Both Topmeteo and Skysight predicted weak to moderate thermals up to about 10-11k feet.  A snowstorm had just dumped a few inches over the foothills the day before and – unsurprisingly – the forecast looked best for thermals over the plains that were sure to be free of snow cover.

A strong inversion lay over Boulder as I drove to the airport and the air was still on the ground. Speculating that conditions would likely improve later in the day I delayed my launch until 1 pm and watched other pilots take to the skies before me.  The fact that most seemed to be able to stay up was encouraging.

Just before 1 PM I took off into the glider box just south of the airfield thinking that I would try to stay over the plains as the forecast suggested.  However, as the tow plane climbed through 6000, 7000, and 8000 feet the air did not stir one bit.  That’s when I got on the radio and asked the tow pilot to take me over the foothills where I saw that some white wisps had already started to form.

View from the foothills towards the east. You can clearly see the thick inversion layer above the plains.

I kept my hand on the release ready to let go when I would notice a tangible updraft but the air remained still for a long time.  We had climbed to almost 11,000 feet above Big Horn Mountain when I decided it was time to set myself free even though we had still not crossed a single patch of rising air.

I pointed the nose straight towards a tiny cloud that was forming above Gold Lake.   Just as I hoped, I found the air stirring just enough to slowly gain some altitude back.  I could also see a convergence line with a much higher cloud base several miles further west but getting there seemed very difficult or even impossible to me given the lack of usable landing spots over the foothills.  With no other reliable options for lift in sight I decided to hold my ground for a while and wait for conditions to further improve.

After flying holding circles for almost 45 minutes a few additional small clouds had popped up here and there and I decided it was now or never if I wanted to get some cruising miles in.

The OLC rules require that the start of any flight has to be within 15 kilometers of the take-off airport.  Gold Lake is 20 km away from Boulder and I could not remember whether I had released from tow before or after leaving the 15 km radius around the Boulder airport.  So I decided to first head back and fly through the start cylinder near Lee Hill.

From there I returned to the area of lift near Gold Lake.  Now I had to decide whether to go north or south.  I remember flying several circles unable to decide.  There was a promising looking cloud with a slightly higher base about 6 to 8 miles to the south but it was uncomfortably far away.  If it did not work when I got there I would have no option but to bail towards the airport.  There were a few smaller clouds to the north.  Although they looked less compelling and had somewhat lower cloud bases they seemed to offer a more promising path forward overall.   My indecision with respect to my course direction clearly was not a good tactical move: I had already crossed the start line, the clock was already ticking, and I was just staying in place…

I have found once again that the best thermals are often near bodies of water. The temperature contrast between the cool air above the lake and the much warmer air above the surrounding forest and grassland can serve as trigger. The additional humidity that gets sucked into the thermal from the surface of the lake enhances the thermal.

If took me almost 15 minutes to make up my mind but eventually I decided to take the route to the north.  Once made, the decision felt liberating for now I had a direction and a plan I was going to pursue.  Why could I not decide quicker?

As I headed north towards the Twin Sisters I spotted some newly forming wisps that were about 2,000 feet higher than the cloud I had just left behind.  It seemed like a long shot but I wanted to give it a try.  I thought that if I could gain another 2,000 feet I might be able to get under the convergence line.

However, as I crossed the area below these wisps there was nothing but sink. There went my hope for reaching the convergence.  Fortunately I had already worked out a plan B and a plan C.  Plan B was sufficient.  A small cloud above some rocky outcroppings north of Cabin Creek allowed me to get back to cloud base at 10,800 feet and to continue my track to the north.

I headed toward another small cloud just across US36 between Lyons and Estes Park.  My Oudie indicated that my altitude was now barely enough to make it back to Boulder.  The cloud worked again and provided the strongest lift of the day with an average of almost 4kt.

This allowed me to keep going a little further north until I reached a point between Estes Park and the north side of Carter Lake where my Oudie indicated an arrival altitude above Boulder just below pattern altitude.  Considering the generally weak conditions it felt the right time to turn and head back south.

I followed a similar route on my return leg tracing along the most promising little clouds.  I made sure to maintain a reasonably comfortable altitude above the undulating terrain, rarely dropping below 1,500 feet AGL and never below 1,000 feet AGL.  I also always kept an escape path towards the plains and generally was within glide range of the Boulder airport (albeit sometimes with little margin).

View of the Convergence line along the Continental Divide. My glider in the foreground is to the east of the convergence line. The yellow arrows point at the relatively low hanging curtain clouds that separate the two air masses along the convergence. The cloud base east of the convergence was around 11,000 feet. The dotted red lines mark the much higher cloud bases to the west of the convergence line. Cloud bases there were around 14,000 feet and thermals there were likely considerably stronger.

Little by little, cloud by cloud, I made it to the town of Nederland, 30 miles from my turnaround point.  It was already 4PM MDT and the clouds began to dissolve around me.  So I decided that it was a good time to for a scenic cruise back to Boulder.I took advantage of the Discus’ 42:1 glide ratio and detoured via Gross Reservoir to Eldorado Canyon.  From there I followed the ridge line of the Flatirons  where I provided some entertainment for the hikers atop of Bear Peak.  The easterly flow was unfortunately insufficient to maintain altitude when soaring along the ridge.  (The windward side of the Flatirons was already in the sun shadow so I suspect any lift from the wind might have been negated by cool air descending the face of the mountains.)

Overall, this was a challenging but satisfying start to the 2018 OLC season.  Looking at the score board of the OLC Speed League, my flight was just fast enough to qualify to be scored for the Speed League as the third of the three Boulder flights that count this weekend.   (The Boulder pilot who flew the greatest distance yesterday did not fly through the start cylinder and consequently his flight doesn’t count for the speed league.)

A link to my flight track is here.

Lessons Learnt

  • Safety First, Always.  Not a new lesson but worth keeping in mind, especially when flying with a competitive streak.  There is nothing to be gained in soaring competitions; however, many lives have been lost when competitors didn’t always put safety first.  Only fools risk life and limb for no gain.  So don’t be one.
  • Always Keep a (Safe) Escape Path.  The terrain over the foothills is tricky.  Your computer may tell you that you are within glide range of the airport but it might not account for terrain that’s in the way.  Be especially careful south of Nederland where there is higher terrain to clear to the east if you want (or need) to get back to the plains.
  • You Cannot Fly In the Foothills, You Have to Fly Above Them.  When flying in the Alps you often fly very close to terrain and most of the time the steep valleys provide escape routes into wider valleys with land-out options.  There are no land-out options in the foothills and the canyons don’t provide safe escape routes into the plain.
  • 1,500 Foot Ground Clearance Above the Foothills Feels Ok.  1,000 Foot Feels Low.  That’s for a high performance ship such as the Discus.  For lower performance ships, maintain more ground clearance.  If the thermals don’t support it, get out of there while you can.
  • Don’t (Blindly) Trust the Weather Forecast. Again.  Both Topmeteo and Skysight had predicted the best thermals over the plains.  In reality the plains – where the inversion was very persistent – provided only very weak lift up to 8,500 to 9,000 foot while the better lift was clearly over the foothills and mountains. (Much of the snow over the foothills was gone by early afternoon and the south facing rocks heated up nicely.)  Skysight missed the convergence line along the divide.  (Topmeteo does not predict convergence.)  I will keep reading the forecast but always consider that reality is likely to be different.
  • Good lift can often be found next to lakes.  Today the first lift I found was next to Gold Lake.  Two of my other thermals were next to lakes too.  Most textbooks tell you to stay away from lakes but my (limited) empirical evidence suggests that the best thermals are often next to bodies of water.  There’s also a great German soaring textbook called Meteorologie für Segelflieger by Henry Blum (Meteorology for Soaring Pilots) that convincingly argues that humidity enhances thermals and the best ones are often found next to lakes, rivers, or next to moist forests, mainly because moist air is lighter than dry air.
  • Indecision Costs a Lot of Time.  If I want to improve my performance for the speed league, I need to get better at making decisions based on the information available at the time instead of flying holding circles until I have made up my mind.

Surprise: Fastest Flight of the Day

Wednesday, April 4.  I didn’t try but my two-plus-hour-easy-cruising soaring flight ended up being the fastest flight in a glider on that day.  Fastest as in: highest average speed. Worldwide. That came as a big surprise to me because I hadn’t even thought about it.  I had just been flying along – as it turns out at an average speed of almost 152 kilometers per hour (82 kts).  Equally surprising is the fact that the 325 kilometer flight was also the 10th longest flight that day. Here are the stats from the Online Contest:

List of soaring flights on April 4, 2018 sorted by average speed in kilometers per hour.
List of the longest soaring flights on April 4 sorted by flight distance in kilometers.

So how did that happen?  The answer is easy: strong winds from the west, increasing with altitude, blowing across the Front Range of the Colorado Rocky Mountains. In other words: mountain wave.

Looking at the sky in the morning it wasn’t all that obvious that a strong wave day was afoot.  Here’s a short time lapse of the sunrise from our home in the foothills looking east.  The wind seems to be coming more from the left, i.e. from the north.  The fuzzy edge of the cloud does not look like a lenticularis and you have to look very carefully to spot any indications of rotor activity.

The forecast from Skysight on the other hand looked very confident:

Forecast of vertical velocity at 13,000 feet for 13:00 MST (Skysight). The dark orange band indicates wave lift of approx. 5 m/s (10 kts) over the Colorado foothills along the lee side of the Rocky Mountains. Winds are westerly with a slight northerly component. 

Around noon, however, the wind on the ground was blowing firmly from the east.  The sky was overcast due to a layer of high clouds and seemed deceptively calm.  The only real indication of wave aloft came from pilots flying into Jefferson County Airport a few miles south of Boulder, who reported moderate to severe turbulence a few thousand feet above ground:  just because you can’t see any rotors doesn’t mean that there aren’t any.

Just before 1pm I was ready to launch.  The air became turbulent at about 1,000 feet above ground and when I hit the first strong climb at 1,600 AGL I released without hesitation. That turned out to be a mistake. After climbing in very choppy lift to 2,300 AGL I bumped up against a strong wind shear layer that I was unable to get through.  After a few attempts in different locations I returned to the airport and decided to take another tow.

This time I asked the tow pilot to take me above the wind shear layer and over the foothills.  After a very bumpy ride on tow where I involuntarily practiced several slack line maneuvers I released at 10,400 MSL directly in rotor lift. I had no difficulty to climb to 12,500 MSL where I first encountered laminar airflow and the climb rate improved. Within a few minutes I had ascended above 16,000 feet and from there everything became very easy.

The lift was strong and consistent, the wave bar wide and forgiving.  The wind was blowing at about 40 kts but the Discus flies fast and so I could easily cope with the necessary crab angle and make rapid progress relative to the ground.  As the air got thinner and thinner the difference between Indicated Airspeed and True Air Speed (and therefore ground speed) increased.  The lift was so strong that I had to trim all the way forward and fly at 100-110 kt IAS to avoid climbing above 18,000 feet.  At several occasions the lift was so strong I even had to open the spoilers to stay below Class A airspace.

View of the Front Range from 17,500 feet MSL. The cap cloud above the mountains was poorly defined. You can see the Föhn Gap at the top of the picture with a thin cirrus layer high above.

The clouds were only moderately useful to gauge the location of the wave.  There was a fuzzy cap cloud along the front range with a Föhn gap between it and the next layer of clouds to the east.  However, a high cirrus shield often obscured the position of any lenticular clouds.  For most of my flight I navigated by looking at the position of the mountain ranges relative to the direction of the wind, which blew from northwesterly directions.

Cockpit view. The town of Estes Park is directly in front of the nose and about 10 miles ahead. Note the fuzzy cap cloud indicating air streaming down the mountains on the left. There is one very clearly defined lenticular cloud far in the distance to the right of the picture (the brightest cloud in this shot). The high cirrus shield on top obscured the location of other lenticular clouds.

The position of the primary wave was a few miles further west than Skysight had predicted, and the northerly component of the wind was a bit more pronounced, but other than that the forecast turned out to be pretty accurate.

Unlike prior wave flights, I had no difficulty passing Longs Peak and continuing beyond Estes Park to the north.  To the south I crossed I-70 until I had a great view of South Park behind Mount Evans to my right.  I briefly considered an attempt to fly past Mount Evans but decided to err on the side of caution not knowing where I would land in South Park if things didn’t work as well as I thought they might. (I later learned that Bob Faris, another Boulder pilot flying that day, ventured into the South Park area.  He reported that the wave turned violent around Mount Evans and that conditions were much more difficult further south.  He dropped below the laminar layer and worked rotor lift and thermals all the way to Fairplay and back.  Otherwise his average speed would have been much faster than mine.  His flight track is here.)

Nice view of Mount Meeker and Longs Peak partially shrouded by the cap cloud.

So I kept cruising back and forth along the Front Range.  There was very little effort involved and not much decision making.  I enjoyed the scenery and was happy that my transponder was broadcasting my location and altitude so that air traffic control could make sure that no jets would suddenly emerge out of the cap cloud and into my flight path. After about two hours I felt quite cold and decided to return to the airport.  There is no doubt that I could have kept yo-yoing along the mountains for several more hours. It was one of my easiest wave flights to date.

The return from laminar airflow into the rotor zone brought me back to the harsher realities of wave flying. I encountered severe turbulence as high as 16,000 feet in the secondary wave and cautiously descended with open dive brakes at a save speed of around 70 kts through some of the most violent wind shear turbulence I had so far experienced. Fortunately I had remembered my lessons from earlier flights and tightened my straps and removed all loose items before starting the descent.

As I got close to the airfield I was surprised that the wind on the ground was still blowing hard from the east.  I checked three times to make sure that my mind wasn’t playing tricks on me.  There was no turbulence in the pattern and the landing was smooth and easy.

Here’s a link to my flight track.

Post flight: the level of moisture increased later in the day and the position of the wave became much more visible.  Here’s a short time lapse of the wave at sunset:

Lessons Learned:

  • Wave may be hard to see even if there are clouds in the sky. For most of my flight, the moisture level was too low at the height of most of the wave activity so no clouds formed except for the fuzzy cap cloud over the Front Range and the high cirrus shield above (that probably had little to do with the wave itself.)
  • Being fast can be really easy if the conditions are right. I made no attempt to fly fast.  My high average speed was simply a function of flying straight in consistently strong lift, even requiring high speeds to avoid climbing above 18,000 feet into Class A airspace, coupled with flying at high altitudes where true air speed is 36% higher than indicated airspeed.  So my cruising speed of 100 kts IAS was really 136 kts TAS at 18,000 feet.  My average ground speed was “only” 82 kts.  A big factor explaining that difference is the crab angle necessary to compensate for the wind drift when flying along a wave bar (when the wind must logically always come from the side).
  • Ground speed varies dramatically in strong wind conditions depending on your heading relative to the wind.  This is rather obvious and not a “new” lesson.  But the stats make it very clear: my flight trace shows that my maximum ground speed was more than 160 kts (considerably faster than the maximum airspeed of the glider) even though I never flew above 110 kts IAS, while my minimum ground speed was below 20 kts (much slower than the minimum air speed of the plane).
  • Remember that flutter, and therefore Vne, is a function of TAS, not IAS.  Don’t trust the red line on the airspeed indicator to determine how fast you can fly safely at altitude.  Fortunately the Discus is built to go fast, even high. According to the flight manual,  Vne is 135 kts all the way to 13,000 feet and only then begins to drop off.  At 16,400 feet it is still 131 kts and at 19,600 feet it is 124 kts.

It Doesn’t Take Much Sun

Thermal flying under overcast skies

Yesterday was supposed to be a really good day for my first thermal flight of the year.  I now use several soaring forecasts to see which ones are most reliable in Colorado. However, this tends to be more pain than boon and can be quite confusing because these forecasts rarely agree with one another.

To my amazement, yesterday they all pretty much lined up, forecasting moderately strong thermals between 11:30AM and 5PM MDT, attractive attainable flight distances, no risk of overdevelopment, and an amazing 100+ mile convergence line all along the foothills.

Thermal height around 14,000 feet over the foothills.
Possible flight distance in a standard class glider (like the Discus) around 400-500 km.
Virtually no risk of overdevelopment.
Amazing convergence line all along the foothills of the front range – from south of Denver, CO all the way to north of Cheyenne, WI.

The thin cirrus shield above the plains soon dissolved after sunrise and the day started out under cloudless blue skies.

The thin cirrus clouds visible at sunrise soon disappeared and the day started out blue.

I planned on a takeoff around 12:30PM MDT.  When I arrived at the airport around 11 AM the sky looked just like the forecast.  A long line of cumulus clouds had already formed to the west of the Boulder airport, stretching from Golden, CO to the north as far as the eye could see.

I hadn’t rigged a plane in more than four months and things went slower than I had expected.  There was also a lot of activity at the airfield as many pilots had turned out for their spring checks and by the time I was ready to get in the air it was already past 1PM.

In the meantime the clouds had developed much faster than projected and when I finally took off around 1:20PM, the sky had become completely overcast.

The cumulus clouds during the second half of my flight were fairly easy to read and provided good indications of lift. During the first hour of the flight however (sorry no pictures), the sky was an amorphous grey.

There wasn’t much lift as I followed the towplane into the foothills where I hoped to find rising air from the convergence.  The clouds were dense and grey and I could not discern where the best lift was likely to be.  With my hand on the release I followed the tuck for a long time and finally set myself free in weak lift over the mountain hamlet of Ward at an altitude of 11,000 feet.

I looked all over the sky around me and still detected very little movement in the clouds.  I was able to hold my altitude in the narrow, broken lift and was basically just buying time to see if the conditions would change.  I was also at the bottom of a wind shear layer and had to pay attention not to stall each time when I turned into the direction of the wind.

Some streeting along the conversion line over the foothills.

After more than 10 minutes of parking in the sky I saw than the sun had broken through the clouds  a few miles further to the east, directly warming a south facing slope.  I held my position for another five minutes to give the slope some time to warm the air before making my move.

By the time I got there the slope was already in the shade again and I was doubtful that five minutes of sunshine could have made much of a difference.  However, to my surprise the slope actually worked.  The lift wasn’t strong but I managed to climb about 1,000 feet in six minutes before the energy was exhausted.  In the absence of clear indications in the clouds, the same strategy helped me locate my next lift as well.

Pretty view of the Continental Divide from a position along the Peak-to-Peak Highway south of Ward. The Eldora ski resort is just atop the wing and James Peak is in the background.

Then the weather changed.  The clouds over the plains started to dissolve and once again I headed for the area that was in the sun.  I followed the first row of foothills where the canyons open up towards the plains.  There are several bowls into which an easterly wind from the plains gets funneled. Yesterday there was a light wind from the southeast at the lower levels.  Combined with the afternoon sun (shining from the southwest) I was hoping to find lift above one of these bowls.

Lift along the bottom of the foothills with winds from the southeast: the wind is funneled into the canyons and up along the south-east facing slopes that are warmed by the sun. When the air reaches the top of the slope it can no longer cling to the ground and instead rises above.

I crossed over these bowls flying from north to south (from right to left on the map above) and found my best climb of the day in the Seven Hills area (the second such indicated bowl from the left) allowing me to climb from 7,500 to 10,500 feet in about 12 minutes.

As I was climbing, dark clouds began to rapidly form once again.  Unlike earlier in the day they were much better organized and provided much clearer indications of the areas of lift.  I followed a cloud street a few miles north where I effortlessly climbed to cloud-base.  Then I pushed south-west under another row of dark clouds where I finally topped out at 12,000 feet, my highest altitude on this flight.

Once again, the sky had completely overdeveloped. Heavy snow showers had engulfed the peaks around Rocky Mountains National Park, about 25 miles north of my position.  With the sun completely shielded off, the thermals rapidly weakened once again.  Even under the completely closed ceiling there was still enough lift to stay in the air.  However, climbing was slow and after a while I lost interest in flying holding circles and decided to return to the airfield.

Here’s a link to the flight track.

Lessons Learned

  • Five minutes of sunshine can be enough for thermals to form.  If the temperature profile is right (i.e. the air is sufficiently unstable), it doesn’t take long for the sun to heat the ground for thermals to develop. The sun at the end of March is already quite powerful.
  • When the clouds don’t tell you much, the ground can. For the first 90 minutes of today’s flight I was unable to read the clouds for indications of lift. Observing areas where the sun broke through the clouds to warm the slopes, and overlaying my understanding of the direction of the wind helped me identify areas of lift.
  • Weak thermals can even persist in a completely overcast sky.  Thermals definitely weakened when the sky was completely grey and overcast but there was still enough lift to stay airborne.
  • Parking in weak lift can pay off. When the sky over-develops and the thermals dramatically weaken it may pay off to hold on to a spot with weak lift where you can hold your position and wait for conditions to change.  Had I not done this, I would have landed within 40 minutes of releasing. I just waited long enough for the sun to break through the clouds and warm certain areas long enough for new thermals to form.
  • Stalls can happen very quickly when thermaling in wind-shear conditions. Finding the best speed to fly when circling in narrow, broken lift can be quite tricky. At my first climb of the day staying in lift required steep circles flown just above minimum speed.  I was coming up to a wind shear layer and once in three circles or so I was hit by a gust from behind that was sufficiently strong for my flying speed to drop below stall.  Small, hard-fought altitude gains can quickly be lost in a stall and then the slow and steep thermaling technique becomes quite inefficient. At one point my inside wing dropped and I had to quickly correct with opposite rudder. Flying so slow is definitely a no-no when close to the ground (I was at least 2,000 feet AGL and there were no other gliders around so safety was not an issue.)
  • The weather forecast can be wrong even when all forecasts agree. I learned that I cannot rely on the forecast even when all forecasting tools say the same thing.  None of the forecasts for yesterday predicted any over-development. Forecasts are still far from perfect even when based on data collected just a few hours before the flight.