Ken Kochanski (KK) wrote:

OK, what is the better explanation to give fledgling students. Should
you say the wing deflects/pushes/thrusts the air down to hold the
aircraft up ... or should you say the wing/airflow creates a low
pressure area that sucks the wing/aircraft upwards.

I suggest you tell them to hold their hand out a car window like a wing,
and experiment with the angle of attack. Anything more complicated than
that isn't going to help them fly a glider better. You don't have to
understand the physics to fly well, as ras demonstrates repeatedly, and
I don't see how explaining it with Bernoulli's theorem, or f=ma, or
pressure differentials is an aid to flying. It's hard enough to get
across the idea of angle of attack for stalling, much less Bernoulli or
Newton.

Like many people, Bernoulli was the initial and only explanation I was
aware of ... but I now think it is easier and more accurate to explain
that a wing/airfolil pushes the air downward. Yes, you do have
pressure differences, but that is just an artifact of the process.

And this illustrates part of the problem. Ken, whom I believe to be a
good instructor, wants to explain it to the student, but he doesn't
understand it either (I'm not suggesting I do, either). Nonetheless, his
students can fly well, because you have to know what to do at the right
time, and (fortunately) you don't have to figure it out from an
explanation of the physics involved.

Pragmatically, telling the student whatever explanation makes them happy
is probably good enough, but maybe referring the really interested to
good book like "Fundamentals of Sailplane Design" would be a good idea.

--
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Eric Greenwell
Washington State
USA