Soaring – Chess in the Air

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.

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.

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.

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…

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).

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.

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:

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:

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.

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.

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.)

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.

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.

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

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.

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.

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.

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.

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.

 

On August 14, 2005, 121 people died in the crash of Helios Airways Flight 522 after the aircrew became hypoxic due to the air pressurization system being incorrectly set to manual.

On April 1, 2011 a glider flight from Boulder, CO ended in a fatal accident after the pilot had spent 14 minutes above 22,000 feet. From there the sailplane spiraled to the ground. The accident report found hypoxia of the pilot to be the most likely cause.

These accidents were on my mind when I attended yesterday’s Hypoxia Simulation Training session, provided by AirCare Facts at Independence Aviation in Centennial, CO.

After an hour of classroom training covering the causes as well as the potential signs and symptoms of Hypoxia, I had the opportunity to participate in a simulation of low pressure conditions at up to 28,000 feet.  This was accomplished by breathing through a mask feeding reduced levels of oxygen into the respiratory system.

Hypoxia is an insidious killer because it is often very difficult to recognize any symptoms before it is too late.  The potential symptoms even include feelings of wellbeing and euphoria, which may make it even less likely that a pilot would take corrective action before passing out (and eventually dying – either due to oxygen deprivation or due to the plane crashing in uncontrolled flight).

The only good news is that the symptoms of hypoxia tend to be specific to each individual and relatively constant over time.  Hence, it is possible for everyone to experience and “get to know” their early indications that something may be amiss.  Recognizing these indications early is likely one’s best (and maybe only) chance to take the necessary actions.

At the earliest onset of hypoxia symptoms at altitude it is vitally important to act immediately (while still being “usefully conscious”). Normally this means beginning a rapid descent to lower altitudes where the air pressure is higher and normal oxygen saturation levels are restored relatively quickly (normally within a few minutes).

I took the following video during my own training session so that I would be able to see my own reaction and be able to remember my specific symptoms.

I can recommend to any pilot to participate in such a simulation. Knowing your individual symptoms may one day safe your life.

I recently demonstrated that soaring is an objectively dangerous pastime.  On a per-activity-hour basis it is approx. 35 times as dangerous as driving, 70 times as dangerous as bicycling, and still about 3 times as dangerous as riding motorcycles.

One contributing factor has to do with the high number of fatalities during soaring competitions. (This article shows that during global soaring contests, the number of fatalities per number of flights has been more than 10 times higher than during flights outside of competitions.) Even though there is no (relevant) price money on the line, contests tend to tempt pilots into lowering or suspending their normal safety standards. To have a chance of winning or placing well, pilots are often inclined to take higher risks than they normally would accept – consciously or subconsciously. E.g., they will fly closer to terrain than they would on a normal cross-country day; they will fly in bigger gaggles, thermal closer to stalling speed, get closer to Vne – even in turbulent air, attempt safes lower to the ground, scrape across ridges or mountain passes, fly low over unlandable terrain, calculate their final glides with a narrower margin, etc.

It’s the same behavior I observe (and – to be honest – participate in myself) during races on the Condor competition soaring simulator.  Fortunately it’s a simulator so if you crash you still get to live another day. But I’ve found that the dynamics in human behavior are very similar to real life competitions. No one wants (or expects) to crash but at the same time, most everyone flies in ways that they would consider irresponsible outside a contest environment. Sure, taking great risks won’t guarantee a good placement, but a good placement almost inevitably means that the pilot assumed a high degree of risk.

Here’s an example: yesterday I flew a Condor race set in the foothills of the French Alps as part of a competition called Regatta Cup. It was a short 188 km Club-Class task along and across several low mountain ridges. Thermals were moderate but a steady 12-14 kt wind from west-north-west made for optimal ridge flying conditions along the steep slopes of the area. As the name Regatta Cup implies, the race was to start at a set time for everyone with all 26 gliders trying to cross the start line below 1,800m simultaneously and as close to Vne as possible. From there they would all fly along the same course, round eight tightly-spaced turn points, then dash for the finish line.

The start was set away from any of the ridges so big gaggles formed underneath one of the few cumuli west of the Romans Saint Pau airfield.  Cloud base was around 2,200 meters so everyone circled up to the base of the clouds and tried to stay there in order to maximize the potential energy when the start gate would open. 26 gliders were sharing two thermals, all flying within an altitude band of approx. 50 meters. I was not surprised when I witnessed two pairs of gliders colliding with one another. In fact, I had several close calls myself – and all of that before the race even got underway.

Trying to stay aware of everyone around me I began to dive about 20 seconds before the start of the race. Burning excess energy using the spoilers and watching the altimeter, the speedometer, the GPS, and the traffic around me all at the same time, I managed to cross the start line about 5 seconds after it opened, 20 meters below the ceiling, flying just below Vne with a ground speed of 272 kph.  I considered this a very good start even though about half of the competitors were already ahead of me and the other half only seconds (or fractions thereof) behind.  And, luckily, I was still alive.

With the wind at the tail and flying at a “conservative” air speed of 160-170 kph the altitude at the start was just sufficient to get the unballasted LS4 to TP1.  I was in the bottom third of the pack but the leaders were less than a minute ahead.  From there the ridge race began. The strongest lift tends to be near the top of the ridges and not more than one or two wingspans away from the terrain.  That means everyone will attempt to fly in that narrow zone between winning and dying, and with so many gliders packed into the same tight spot at the same time, surviving is not much more than a game of Russian roulette.

Added to this is the complexity of different climb rates based on the angle of the ridge line with respect to the wind.  You look ahead trying to anticipate where the best climbs are likely to be.  Just before you get there you pull up sharply in order to fly two or three seconds longer through the best climb zone, then you push the nose down again, even more so if you anticipate an area of sink. Everyone else tries to do the same thing: flying as close to the ridge as possible, pulling up right before the best climbs, pushing down right before any anticipated sink. In doing so the speed of the glider might vary anywhere between minimum sink speed and three times as fast. Each time the altitude fluctuates by 200-300 meters as speed gets converted into height, or height gets converted into speed.  Pulling up or pushing down too early or too late, or incorrectly judging the strength of the lift, costs precious seconds that add up and ultimately decide about your placement. Flying like this is more than risky enough if you are the only one around but doing so in the midst of a pack of more than 20 gliders is simply an enormous gamble.

After several close calls between TP1 and TP4 and being about two minutes behind the leaders at this time, I decided not to follow the gaggle in front of me on the direct route to TP 5 but to take a slightly longer route along the higher and steeper ridges further to the east, hoping not only for better climb rates along this route but for some stress relieve as well.

Soon I discovered that I faced another challenge: there was a mountain pass in front of me.  I didn’t want to waste any time turning so I hugged the mountainside and flew at minimum sink speed hoping that the lift would be strong enough to carry me over the pass before I got there.  I was aware that this was a hugely risky maneuver: if a wind gust would force the glider to stall I would not have enough altitude to recover before hitting the ground. And if a thermal would break off on the valley side and turn the glider towards the slope, I could easily get pushed into the trees. “There is no way I would fly like this in real life,” I thought.

The gamble paid off and I made it across the pass and dove for TP 5.  As I got there I noticed that I had caught up with the pack.  I could still see several gliders ahead of me but they seemed a few hundred meters lower.  With a valley to cross ahead, they would likely have to stop to climb somewhere while I could cruise along the top of the ridge at a much higher speed. I dove across the valley at over 250kph and still reached the ridge on the other side at a good altitude.  Again, I hugged the higher ridge to the east while the handful of gliders ahead of me were lower and further west.

There was another valley to cross between TP 6 and TP7.  Again I put the nose down only to realize shortly thereafter that I would arrive too low on the other side. I dialed the speed back to 140kph – my slowest cruising speed of the entire race – to conserve what altitude I had left.  As I headed straight towards TP 7 the trees on the slope ahead of me were getting closer and closer.  Would I be able to get to the turn cylinder before the trees would get me? I wasn’t sure but just as I was forced to initiate a turn right over the tree tops the GPS confirmed that I had rounded the TP.  If I had only been 20 meters lower I would have had to turn away from the slope and find a spot to climb.

Having turned TP7 I could now hug the ridge again and fly toward TP8, the final turn point.  I could only see one glider ahead of me.  My final glide calculator indicated that I would arrive a few hundred meters too low but I was confident that I could easily make that up by hugging the ridge between TP 8 and the finish line. So I decided to dive, flying a direct route towards TP8. I kept watching the other glider to my right and though that I might have a chance to beat him.  I reached the next ridge closer to the valley with only 5 kilometers to go to TP8 and 20 kilometers to the finish when … I suddenly died.

Another glider that I had not noticed must have been slightly above or below me.  I had not seen him at all and I must believe that he had not seen me either. It was quite a shock and a revelation.  Obviously, had this been in real life I would not be here to write about this experience.  Instead, my wife and children would stand by my graveside and wonder, with tears in their eyes, how this could have happened.

Yes, I know, Condor is just a game.  I must and do believe that I would not have taken many of the risks described, if I had been in a real glider. Also, some of the race settings described here are not realistic. For starters, contest directors are unlikely to plan a task that is as dangerous as this one.

However, there are many things that are not so different from real life. The pressure of the competition, the desire to win, the fear of embarrassment.  Also the fact that taking high risks does have the potential of giving you an advantage in the race: circling in gaggles under the cloud base to conserve energy for the start, flying close to ridges without adequate safety margin, hugging the tree tops, scraping over mountain passes, circling at minimum speed close to the ground, flying low over unlandable terrain, aggressively calculating the final glide – all these are risks that have killed many real life pilots. I believe that this is especially true in race settings when usual risk-mitigation strategies get too often ignored or even willfully suspended.

BTW – in case you’re wondering: I did analyze my flight track and those of the eventual race winners.  I believe that I would have come second or third in that race – it would have been my best result against some of the world’s best Condor pilots.  You can see the race results here. However, it was definitely not worth dying for.

 

The best soaring routes almost always correspond in one way or another to the terrain below, no matter what lift you use.

E.g., you would expect thermal lift over terrain that is most exposed to the sun (e.g. slopes that are most directly warmed by the sun based on the time of day); you would expect convergence lift where terrain features redirect the wind such that air masses collide with one another and are forced upwards; and you would expect ridge lift along long and steep slopes that are more or less perpendicular to the direction of the wind.  (It’s no surprise that pilots love to fly along the top of ridge lines where thermal, ridge, and convergence lift often come together.)

It’s no different with wave lift.  Wave lift forms when the wind pushes (relatively stable) air downward along the lee slope of a mountain, thereby warming it at the dry adiabatic lapse rate (such that it becomes warmer than the surrounding air near the ground). It will then rise again because it became lighter than the surrounding air mass, thereby starting a wave motion that oscillates on the back side of the mountain.  (You can find more details about wave lift here.)

Wave lift will form only if the wind is relatively strong.  In most locations, such strong winds usually come from the same direction.  In Boulder that is from the west – especially in the wintertime when the jet stream blows at our latitudes. What makes Boulder a particularly great wave location is the fact that a tall, nearby, mountain range – the Colorado Front Range – is conveniently laid out in north-south direction (hence the prevailing wind has to cross it at a perpendicular angle) and the Boulder airport is just to the east in the lee of the mountains.

With all that said, it should be no surprise to see that wave flights from Boulder tend to follow the same routes: parallel to the mountains on the lee side. In fact, the following chart depicts 40 wave flights from Boulder from 2010 and 2017 that were longer than 2 hours in duration and extended above 17,000 feet.

If you study the flight logs a bit, you quickly notice that the traces tend to be parallel to the curving ridge line.  The distance of each trace to the mountains depends on two things:  (1) the wave length on the particular day (it can be longer or shorter depending on the strength of the wind and the stability profile of the air); and (2) in which wave bar the pilot was flying (e.g. the primary, secondary, or tertiary wave).  The primary wave is the one closest to the mountains; it usually (though not always) provides the strongest and highest lift. As the name implies, the secondary is the second wave bar behind the mountains, the tertiary the third, and so forth.

Take a look at the red trace that extends furthest to the west – it is the only one in this set that crosses the Continental Divide.  This flight was flown by Al Ossorio on Dec 29, 2010 in the club’s DG505 and reached more than 27,000 feet within the designated wave window (Arapaho Peaks Soaring Area).  However, note that the high point was not over the Continental Divide; it was several miles further east, just where the red trace blends with all the other traces – the typical location of the primary wave.

Also quite interesting are the two greenish traces that extend furthest to the north. Both were flown much more recently by Bob Faris on two subsequent days in December 2017 (Dec 1 and and Dec 2) in his DG800.  Both flights reached altitudes of just under 18,000 feet. During the more yellowish of the two, Bob got above 17,000 feet only on the outbound leg (following a fairly straight line parallel to the mountains).  He then lost the wave near the Wyoming border and had to fly the return leg at much lower altitudes between 9,000 and 12,000 feet mostly in thermal lift (a very warm day in December!). During the more greenish of the two traces, Bob stayed in wave above 16,000 feet almost the entire time and actually flew back and forth along the mountains three times, covering 617 kilometers at the remarkable average speed of 174 kph (108 mph).

Preface: I wrote the article below in January of 2018 and I have since done more detailed research about the same question.  My most recent effort uses slightly different (and probably more reliable data) but the overall conclusion remains valid.   If you’re interested in seeing the results of my most recent research that also considers the relative risks of other air sports such as General Aviation, Hang Gliding, Paragliding, and Skydiving, you can find it here.

The tragic death of Tomas Reich during the last day of the most recent Sailplane Grand Prix final in Santiago de Chile and the ensuing debate about the safety in soaring competitions brought – once again – a key question to the forefront of my mind: How Dangerous is Soaring Really?

When I started soaring in 1983 at the age of 16, I often heard people say that “the most dangerous aspect of gliding is the drive to the airport”. Intuitively this never felt right to me and several people have since pointed out that it is indeed far from the truth. (See, e.g., the speech Safety Comes First, delivered by Bruno Gantenbrink).

But just how dangerous is it? To get a better sense we need a reference point. I believe the best way to think about the dangers of soaring is to compare it to the dangers of other relatively dangerous activities we might indulge in: e.g. we could go on a road trip, ride a bike, or ride a motorcycle.  And I think the best way to make such a comparison is on the basis of participation hours (rather than on the basis of miles traveled for example). E.g., when we have an afternoon to spend we may want to know: is it more dangerous to spend that time riding our bike or to go fly our glider? We have all seen the white-painted “ghost bikes” on the side of the road marking the spots where a cyclist was killed but we haven’t seen any “ghost gliders”.  However, we would be kidding ourselves if we thought that gliding was somehow less dangerous. (Spoiler Alert: the comparison is not even close.)

Unfortunately, good, global statistics about the dangers of soaring are hard to come by. In most countries, a comprehensive and reliable database of gliding accidents does not exist. Nor is there a reliable global record of the number of flights or hours flown that would provide a good reference point.

However, while the available data is not globally comprehensive, there is enough out there to draw these comparisons – at least directionally.

My analysis of gliding accidents is based on data from Germany: the German government keeps meticulous track of all flights and even separates out glider flights and flights in motor gliders. It also maintains a database of all flight accidents and reports on an annual basis the the number of fatalities, and the number of persons injured.  Now, one might think that using German data is rather limiting.  But that is not quite true because gliding is much more popular in Germany than elsewhere.  In fact, according to a report presented to the International Gliding Commission in 2010, Germany accounts for approx. one third of all glider flights worldwide.  If there is a limitation to using German data, it might be that it actually underestimates the dangers of soaring elsewhere simply because Germany has such a particularly well developed soaring and safety culture. But, since I can’t prove that, let’s assume the German stats do a fair job of representing the dangers of soaring in general.

So here is what I found.  The result is – unfortunately – rather sobering.

On average, soaring pilots have an accident every 10,000 flights (this is based on all flights in Germany from 2002 through 2016 – the exact number is 10,070). Fortunately some of these accidents only damage the glider or some other property. But once every 60,000 flights someone (usually the pilot and/or passenger) is seriously injured, and once in 83,000 flights the pilot and/or passenger dies.

If you consider that the average glider flight takes about 38 minutes (arguably my least generalizable assumptions since it is simply based on the flightlog of all club flights of members at the Soaring Club in Boulder between 2002 and 2017) this means that soaring pilots can expect to get seriously injured every 40,000 hours and die every 50,000 hours.

Wow! Fortunately we do also other things in life because these stats mean that we would die every 6 years if we did nothing else but fly gliders!

So how does this compare to other activities? Well, not favorably to say the least.  On a “per hour” basis, gliding is about 35x more dangerous than driving; 70x more dangerous than riding a bike, and still 3x more dangerous than riding a motorcycle.

Another way to look at this is to say that 1 hour of gliding is about as dangerous as going on a 35 hour road trip in a car, e.g. from Denver to San Francisco and back again. Or as dangerous as riding a bicycle from Denver all the way to Minneapolis (70 hours). Or as dangerous as riding a motorcycle from Boulder to Salida (3 hours).

Is this an acceptable risk to take? I think that is a question we all have to answer for ourselves. But the important thing is that we should all ask that question and think hard about what we can do to minimize the risk in our own flying decisions.  And no one should kid themselves into believing that those stats don’t apply to them because they are simply a better pilot.  (Instead, they should remind themselves that it’s often the best pilots, like Tomas Reich, who make up the sad statistic.)

With sincere condolences to the family and friends of Tomas Reich.

Unseasonal warmth greeted me this morning as I stepped out onto our porch to film the clouds in the rising sun. Wearing only shorts and a t-shirt I felt as comfortable as I would on a mild summer’s day. A gentle breeze whisked around the corner as I mounted my camera onto the tripod, pointing it east towards the horizon.

The clouds told a story of winds aloft, but where I stood, in the lower foothills, 400 vertical feet above the valley, and 5,800 feet above sea level, the movement of the air was gentle and kind.

The night before, the outlook had already looked promising for my first soaring flight in the New Year: TopMeteo projected westerly winds of 30 kts at 12,000 feet, increasing to 40 kts at 18,000 feet.  Meteoblue projected a stable layer between 11,000 and 15,000 feet – right around the tops of the mountains. Dr. Jack’s cross-section chart for Boulder indicated multiple wave bars with modest climb rates even though it projected the wind to have a pronounced southerly component. Based on past experience, I decided to – once again – dismiss the Soaring Forecast from the National Weather Service, which predicted good thermals (very unlikely in the flat January sun despite the unusually high temperatures) and poor wave conditions.

But the best indicator for good soaring conditions was right in front of me: beautifully turning rotor clouds – as always an unmistakable indicator of mountain wave.

On my way to the airport I reflected upon my most recent wave flight, which was characterized by extreme turbulence below 13,000 feet. I braced myself for the possibility of earning another set of bruised shins even though I was hopeful that the comparatively modest wind speed might be a mitigating factor.

One decision was made for me already: I had learned at my club’s monthly meeting that a recent attempt to open the Arapahoe Wave Soaring Area (which allows flights above 18,000 feet within a pre-defined area) had failed because Air Traffic Control was completely unaware of its existence. This would be clarified in an upcoming meeting with ATC but until then it would be better not to put in further requests. This meant that I would have to stay below 18,000 feet and not have a chance to earn Diamond Altitude (which requires a 5,000 meter (16,400 feet) altitude gain in soaring flight after release from tow).  It also meant that I would not need to bring the more sophisticated oxygen equipment required for flights further aloft; and there was one more benefit: the risk of freezing my toes off would be much reduced 😉

At 11:00am local time I was the first pilot of our club ready to launch.  There were two beautiful lines of rotor clouds in the sky, indicating the positions of the primary and the secondary wave. There were also some isolated rotor clouds from the tertiary just to the north of the airfield.  I asked the tow pilot to take me to the upwind side of the secondary, which seemed to promise the opportunity for a longer flight along the wave bar.

After two initial turns near the airfield to gain altitude I followed the towplane toward the northwest. Soon after we had passed underneath a small rotor cloud from the tertiary we encountered the first pockets of strong lift.

When the third pocket of lift had lasted more than a few seconds I felt comfortable to release from the tow. I would try to climb in the tertiary and then attempt to push forward into the secondary without the help of a tow plane.

After releasing my first focus was to stay in the area of lift to reach a more comfortable altitude. (2,600 ft AGL may sound unproblematic but where there is strong lift there is also strong sink, and 2,600 feet may only equate to two minutes of remaining flying time if I were to encounter a major downdraft.)

I looked at my GPS (mounted to my right and not visible in the pictures) and quickly worked out the the crab angle necessary not to drift further away from the mountains. The wind speed was considerably weaker than during my previous wave flight. There was some turbulence but nowhere near as pronounced as during my prior wave flights in Colorado.

The area of lift in the tertiary was not very large. However, it was surprisingly calm even though I never reached a truly laminar air flow. The lift was moderately strong, varying from 5 to 10kts. Within 20 minutes after takeoff I climbed through 17,000 feet.

After some time in the tertiary I decided to try to move forward into the secondary. I looked for a gap in the clouds along the secondary rotor line and pushed forward into the wind. Vividly remembering my prior wave flight where I lost more than 6,000 feet during a wave bar transition I prepared for the potential of a similar loss in altitude.

This time however, the transition turned out to be easy and smooth.  There was some modest sink along the way but the entire push into the wind did not take more than three minutes during which I only lost 1,500 feet.

Having arrived in the secondary, the lift was clearly stronger, and within two minutes I was back at just under 18,000 feet. Although the line of clouds was interspersed with blue skies it was fairly easy to locate the area of lift. I increased the airspeed of the Schweitzer 1-34 to 80mph and flew south where I could see the next clouds to the west of the Flatirons. I looked at the shape of the Continental Divide to my right and sought to maintain a more or less constant distance to the mountains, accounting for the direction of the wind, blowing from WSW.

West of the city of Golden I turned around and retraced my route to the north, again following the line of lift. Without a single turn I continued to fly straight for over 40 miles until I was just west of Carter Reservoir. The lift in this area (north of Lyons) was the strongest of my entire flight: I had to fly at 90 mph with the air brakes fully extended in order to neutralize the lift and keep the plane below 18,000 feet. Next to me was an imposing rotor/lenticular cloud, its western side almost vertical, extending many thousand feet above and below my flight level. Based on my location and the direction of the wind, I assumed that the airflow forming this massive cloud was likely triggered by the steep downslopes of Mount Meeker and Longs Peak.  (I noticed that this area lies outside the boundaries of the Arapahoe Wave Soaring Area so I could not have used this location to climb above 18,000 feet even if the wave window had been active.)

From there I flew back towards the south. I briefly contemplated a push forward into the primary but at this point my feet had become quite cold and I decided to call it a day and return to the airport.

The frozen lakes surrounding the Boulder airport reminded me that it was the middle of winter.  Obviously, they were of no help detecting the wind direction on the ground.  However, the windsock, once in sight, was easy to read, showing a stiff breeze straight from the west.

I entered the landing pattern at 1,500 feet AGL and turned onto final at the end of the runway, still almost 1,000 feet above ground.  I pushed into the wind, flying the final approach at an airspeed of 80mph.  Seconds later, I touched down gently at a very low ground speed, just fast enough to roll the remaining 100 feet right up to the parking position.

Here is a link to the flight track.

For those interested, I have also compiled a lot of information about wave flying that you can find here.

Lessons Learned

• A high tow may not be necessary to reach wave lift. I released at 7,900 feet and had no problem at all to climb into the tertiary. Today, the first good climb on tow was at 7,300 feet. It would have probably been sufficient. To practice, I need to be willing to release early and risk having to take a second tow. This is especially important with respect to reaching Diamond altitude. With today’s release altitude I would have had to climb to 24,400 feet to accomplish a gain of 5,000m (16,404 feet).  If I could release even earlier, I would not have to fly all that high.
• Rotor turbulence can be gentle. Today’s rotors were very different from those I encountered during my most recent wave flight. I attribute today’s conditions to the much lower wind speed at altitude (about 25 kts versus 50 kts). On Nov 16 the winds were so strong that I struggled to make progress along the wave bar because most of my air speed was needed to push into the wind, whereas today the necessary crab angles were fairly modest. The flight on Nov 16 offered a bigger challenge. Today’s offered more pleasure.
• Laminar air flow may only start above 18,000 feet. During today’s flight I never encountered a fully laminar air flow. That tells me that the rotors extended well above 18,000 feet. There was only little moisture at altitude; however, I did see a few lenticular clouds high above the rotors  (my guess is above 30,000 feet). Today would have likely been a great day to reach Diamond altitude.
• Good climb rates are possible even when wind speeds are moderate. It does not take a howler to produce good climb rates in wave conditions. Today’s climb rates were between 5-10kts in the tertiary and reached well above 10kts in the secondary. At one point the average netto climb rate was 14kts at an altitude of just under 18,000 feet (demonstrating the great potential of today’s lift.)
• Wave transitions don’t have to cost a fortune (in altitude). Rotor clouds can be super helpful in identifying the best locations for a (forward) transition from one wave bar to another. Today I deliberately picked a spot “in the blue” to push forward into the wind. This did not only reduce the risk of getting sucked into a cloud, it also dramatically reduced the sink rates encountered and therefore the amount of altitude lost during the transition.
• New rotor clouds develop within seconds.  While I experienced no close encounters with developing clouds I observed numerous times how new clouds can form within seconds. It is critical to always be aware of your location relative to the line where new clouds could possibly form. Especially when a strong crab angle is required it may be difficult to spot that you are about to be engulfed in (newly developing) clouds from behind.

 

 

Soaring is not exactly a contact sport.  I always thought the only time you could get hurt is when making contact with the ground (or, very rarely, another object in the sky). Well, today I learned there is also another way.

But first things first: my last flight on Monday taught me not to trust the wave forecast but instead to rely on observing the sky.  When I woke up this morning, this is what I saw: a whole sky full of wave.

There was even this little, frazzled-looking, rotor cloud right above our house in the foothills:

This made it easy for me to ignore the National Weather Service, which, once again predicted “poor wave”, and “good thermal” conditions.  A glance at the sky at 6:15am, and I already knew better than that. (Of course that’s not quite true: as always, I did look at a sounding, the winds aloft, the thermal projections from topmeteo.com and meteoblue.com, and the distance of the next front that was projected for Friday.)

So off to the airport I went. And I wasn’t the only one. Other pilots had put their own reading of the sky ahead of the forecast as well.

Once again, I got the Tin Can ready. As I filled the oxygen tank I talked to the tow pilot who had just come back from his third tow of the day. He gave me a taste of what to expect: rotor turbulence “bordering on violent”. He said this with a big grin on his face, so apparently it was also going to be fun. He advised on where he suggested to tow, and explained that he would speed up to dive through an area of heavy sink. He would slow down before we would hit the heaviest turbulence.  Or, rather, he said he would try: for neither of us could be sure that it would still be at the same place as before.

I climbed into the cockpit, secured all loose items, fastened the straps as tight as they would go, looked through the checklist again, and off we went. (You can see the flight track here.) Takeoff was relatively smooth although we didn’t climb much until the end of the runway. Then came the first bump. Suddenly it went up at 8-10kts but it was still surprisingly smooth.  At about 1,000 feet above ground we entered the wind shear zone. The wind at the ground had been 5-8 kts from the northeast but now the wind shifted to the strong westerly flow above.

The towplane in front of me started to jolt around: sometimes it would drop all of a sudden, sometimes it would bank to one side or the other, sometimes it would rise straight up.  Any of these erratic motions were also an indication as to what would happen to my glider about two seconds later, for that’s about how long it took for the glider to reach the air that the tow plane had just passed through. “Compared to the tow pilot I’m really lucky”, I thought, “Unlike him, I know exactly what to expect.”

The tow pilot turned west and dove through the sink just as per our briefing.  I followed right behind, mentally preparing for the heaviest jolts that were yet to come when we would hit the next rotor. Glancing back at the airport I felt reassured by our altitude: if the tow-rope would snap or if I was forced to release, I felt certain that I could make it back on my own. Just after I had finished that thought, my glider was tossed down in a sudden down-draft.  The tight straps kept me in my seat but my legs were out of control: inertia wanted them to be 20 feet higher but they only had a few inches to move up until they hit the instrument panel. Bang! Then, a split second later, I was firmly pushed down into my seat as the plane was lifted up again and my feet regained contact with the rudder pedals.

This up and down, left and right, had lasted for maybe 20-30 seconds when the vario indicated strong lift. Just as I moved my hands towards the release knob, the tow pilot came on the radio to say that this is where the other pilots had released as well. A quick pull and off I was.

From there I worked the front side of the rotor to about 13,000 feet when I pushed into the laminar flow of the secondary wave. The wind was so strong, blowing at about 50-60 mph, all I really had to do was point the nose into the wind and rise, stationary above the ground.

The strength of the wind made it difficult to fly sideways along the wave bar.  To maintain the same velocity into the westerly wind while also moving north or south, I had to speed up, which resulted in a greater sink rate.  Also, I noticed that the lift was less consistent than during my flight this past Monday. Several times I returned to an area where there had been strong lift only to find myself in sink.

I was just a few miles northwest of the airport when I decided to attempt a push into the primary. I started at well above 17,000 feet knowing that I would have to fly very fast and loose a lot of altitude while penetrating through an area of heavy sink. Determined to keep the airport within reach at all times, I resolved to turn around if I would not get to the primary at an altitude of at least 12,000 feet.

I put the nose down, increased my indicated airspeed to 110 mph, and flew straight into the wind. As expected, the needle of the altimeter began to spin backwards and the surface got visibly closer. When I got down to 13,000 feet I began to wonder it it would work. Just as I prepared to turn and make a quick escape towards the airport, I entered the rotor zone behind the primary.  I quickly reduced my air speed to 80mph (the maximum for rough air in this glider) and continued to push into the wind.  The sink rate slowed but I wasn’t out of the woods just yet.

As before, the plane got tossed around by heavy turbulence. My legs were loose sticks again, and I couldn’t keep my feet on the rudder pedals even though I tried. A few more bangs against the instrument panel and finally: I started to climb again.  At the low point I was down to 11,500 feet, a bit lower than I wanted to be, although still high enough to make it back to the airport. (I lost almost 6,000 feet during the transition into a 50-60 mph headwind. I estimate that a backward transition with the wind at my tail would have cost at most 2,000 feet in altitude, probably less. That would have put me at 9,500 feet into the rotor zone of the secondary – roughly at the same spot where I released from the tow plane and definitely within reach of the airport.)

After a short climb in the rotor I was back in laminar flow: I had made it into the primary! I climbed back up to 17,000 feet and began to explore along the wave bar flying between Longs Peak and just west-southwest of Boulder.  Just as I had experienced in the secondary, the strength and location of the lift was inconsistent.  Within 20 minutes, regions with strong lift turned into regions with modest sink.  E.g., in an area to the west of Lee Hill I had found strong lift on my first leg to the south.  On my second leg, I only found moderate sink at the same spot.  I explored back and forth along a few streamlines but wasn’t able to find any lift that would carry me back up.

From there I retreated closer to the airport, all the while expecting to get into massive rotor turbulence again. However, the air stayed surprisingly smooth as I gradually drifted back towards town.  Whenever I noticed some lift, I would turn into the wind and remain stationary over the ground, trying to climb. But in all cases the lift evaporated after a minute or two, and I finally decided to return to the airport to land.

Then, just as I arrived directly south of the airport, I found strong and unexpectedly smooth lift right next to the runway.  I pointed the nose into the wind and, without doing anything, climbed back up from 8,000 feet to over 13,000 feet within about 13 minutes.

Observing the curls of water on the surface of the nearby lakes, I noticed the wind on the ground now also blowing straight from the west, and it appeared to be getting stronger.  So after leveling off at 13,200 feet, I took advantage of the Tin Can’s terminal velocity dive breaks to begin a rapid descent to 7,500 feet.  Now, just 2,200 feet above ground, the wind was still blowing at almost 50mph.

I crossed the runway at 2,000 feet above ground and flew a close pattern to Runway G26 with a very steep and fast descent against the strong headwind.  Once in ground effect, calmness enveloped the plane and I touched down smoothly at a very low ground speed.

Lessons Learned

• You can get bruised while in flight.  Even very tightly worn straps cannot prevent your legs and feet from flying around the cockpit and hitting the instrument panel. (It’s not as bad as it sounds, though. The fun factor was definitely greater than the pain from the small bruises. Playing soccer is definitely more hazardous for your shins.)
• Slack-line training is not for naught. It’s impossible to prevent slack-line while towing through rotor turbulence, all you can do is correct it when it happens.
• Forward wave transitions cost a lot of altitude. 6,000 feet in my case today.  Always keep a safe escape route – ideally to the airport.
• Wave lift is not always stationary to the ground. During my flight on Monday it stayed reliably in place.  Today, I frequently encountered situations where strong lift was replaced by moderate sink within minutes.
• Wave lift can be where you don’t expect it. The smooth climb right next to the Boulder airfield today is a good example.  (I’m not sure if it was from the secondary or the tertiary.)
• Rotor turbulence can happen at very high altitudes. As I flew in the secondary today above 17,500 feet I ran into rotor turbulence that I had not expected at that height.  This is a safety consideration as one might be flying well above rough-air speed at this level.
• Progress along a wave bar can get really difficult in very strong winds. Today, most of the plane’s forward motion was needed to not drift backwards. To fly along the wave bar required high air speeds corresponding to sink rates that at times consumed more than the available lift.
• More moderate wind speeds are preferable to very high wind speeds: they are better for XC flying (smaller crab angle required), and the rotor turbulence will be less severe.