Flying Faster

In February 2019, AeroClub Albatross hosted a seminar series called “Soaring with the Champions”.  Below is the YouTube link to a talk by John Good entitled “Flying Faster” and a summary of the key takeaways.

Flying Faster – John Good

“If you run through the woods, the fastest way is to follow the path.”

If you take the direct route and crash through the undergrowth you will waste a lot of energy and be slower. The same thing is true for a glider between thermals: you must find and follow the best path!

The limitations of McCready Theory

  • McCready Theory has some important assumptions that don’t always hold true:
    • You can predict lift strength in the next thermal
    • Air is still between thermals
    • You won’t land out before you get to the next thermal
    • Finding the right line between thermals that is better than still air is hugely important
    • Read John Cochrane Article: “McCready theory with uncertain lift and limited altitude”

How Are Better Pilots Flying Faster?

    • Overall: they make a lot of choices a little better; this accumulates over the course of a long flight and provides a big advantage overall
    • They may climb better in any given thermal by making better adjustments and staying closer to the core, e.g.:
      • Better bank angle – in many cases the optimum bank angle is a bit steeper than 40 degrees
      • They can better sense where the air is rising
      • But: in most cases the differences of climb performance of different pilots flying with the same type of glider with the same wing loading in the same thermal are quite small.
    • They may be better able to fly at the right speed between thermals
      • But: usually there is not a lot of penalty for flying too fast or too slow – the curve is pretty flat; i.e. you have to be pretty far off the correct speed before you pay a significant penalty;  this means: flight computers that are barking at you when the speed is off are putting a lot of emphasis on something that is not all that important, while other things matter a lot more.
      • One exception: they may not make the mistake of flying too slow in sink.  This is one situation where flying the wrong speed (too slow) matters a lot: this is where the optimum curve isn’t flat and there is a big penalty for flying too slow (My editorial comment: the same must also be true for flying into a strong headwind)
    • The biggest factor by far: they fly a better line between thermals; this one is hugely important
      • They lose less altitude between thermals
      • Therefore, they need fewer thermals to climb in
      • And they get to sample more potential thermals to find the best ones to climb in
      • By climbing more in straight flight and flying fewer circles they also don’t get penalized as much by the minimum sink increase when flying circles (i.e. the load factor penalty)
      • By flying in better air between thermals the best pilots are usually able to keep the thermalling time as a percentage of total flight time quite low – on a decent day often as low as 20-25%. (McCready theory would predict a much higher percentage of circling time – up to 37%).

Strategic choices that can help you complete a task faster

    • Round Turnpoints Strategically
      • Turn upwind TPs low, and turn downwind TPs high (obvious: you want to minimize time spent circling when drifting backwards and take advantage of wind drift when you circle forwards toward your goal
    • Ballast Decision
      • Mass at the same height gives you more energy; but: you need more energy to climb
      • Note: wings of older gliders can get somewhat distorted by putting water in the wings, making them less effective; take this into account
      • Also remember that turn radius increases directly proportional with mass (because you have to fly faster in a heavier glider) – so ballast significantly impacts thermalling performance because you have to fly bigger circles (i.e. further away from the core of the thermal) at any given bank angle
      • Rule of thumb: use full ballast when you expect at least 4kt+ thermals
        • But: how narrow/wide thermals are also plays a big role
      • In contest: having full ballast at least for the first glide is an advantage even in relatively poor conditions; however, this makes only sense if:
        • You can reach the max start altitude
        • And you can do so at the best time to begin the task (not so good if you have to delay the start just so you can reach the optimum start altitude and then conditions deteriorate)
      • Ballast is an advantage when pulling up in lift
      • If you expect to do a lot of cruising and not so much circling, having ballast will be much better.
      • Ballast is a big advantage if you still have it for your final glide, even more so if the final glide is into a headwind.
    • Should you pull up in surges?
      • At least in theory, yes: you reduce the amount of energy in the air and the energy comes into the glider (I don’t understand this concept?); conversely, if you’re pushed down in down going air and push negative Gs – the energy goes into the glider in the form of speed; but: gliders (and pilots) aren’t constructed well to take advantage of this.  Also keep in mind the increase in drag when you pull up.
      • Pulling up in surges makes sense unless the surges are so short lived that you find yourself in sink and have to accelerate in sink again.  If you get fooled by surges on a particular day, don’t keep doing it.
    • Final Glide Strategy
      • Start final glide aggressively and try to fly in good air picking up extra energy.  (But be more conservative if the day is already dying and you might not find any extra energy)
      • Do not fly straight – continue to follow energy lines on final glide!  Especially don’t follow a sink line on the way home! On days when you see good energy lines: it’s very likely that the air in-between is a bad energy line; so don’t just fly straight!
      • If things go well on final glide and you add extra height, increase MC setting and fly home faster (pretty obvious).
      • If you lose on final glide, admit it the sooner the better, and take climb before you are too low; climbs from down low tend to be harder to find and weaker.
    • When to Make Last Turn on an Assigned Area Task with a minimum time?
      • Finishing right on time is usually best because you can amortize your final glide over a shorter flight duration!
      • Be careful: glide computers will often underestimate how well you do on the final task.  So if you turn when the glide computer tells you to turn, you may come in under time.  Especially if the final glide is along favorable lines, many people will come in too early (under time!).
    • Speed to Fly Along Ridges
      • Best air is always found at the ridge top.  So try to fly at ridge top.
      • That means, you will find yourself flying faster in lift and slower in sink and this will still give you the fastest speed!
      • There is yypically a large penalty if you drop below ridge top.  Shift to thermal approach on weak day when you need to climb.
      • Ridge transitions are basically final glides. Good to have points in database that you want to fly to, so you know how high you need to be to make it.
      • If you’re way above a ridge (eg after wave climb) and want to get back down to ridge: how fast to fly? Answer: at least 1.5x ridge speed.  Penalty of flying too fast is very low.