This is a question that has bothered me on and off ever since I learnt
about the physics of the aerofoil many years ago, when I was at
school.  (I am now 48.)

If I understand correctly, the air that passes over the normally upper
surface of an airplane?s wing has to travel further and therefore
faster than the air that travels under the normally lower surface of
the wing.  As stipulated by Bernouli?s principle, the faster moving
air has a lower pressure and hence, the aerofoil of the wing generates
lift - because its curved upper surface is longer than its flat under
surface.

What I would like to know is this: 

How is it that an aeroplane that is being used for aerobatics can fly
straight and level when it (and of course its wings) are upside down
(I have seen them do this) because I would have thought that the force
generated by the plane?s aerofoils would then act downwards towards
the ground rather than up into the sky?

Yours sincerely,

Yaffle, England.

I am hoping that one of GA's pilots will answer this one. In the
meantime, here's a very brief but informative article:

http://www.straightdope.com/classics/a3_141.html

The answer is that it's a bit of a myth that Bernoulli's principle
supplies most of the lift. This principle is true, but the difference
between the over & under wing paths isn't sufficient to generate the
lift which is displayed by aircraft at their actual airspeeds.

   The real workhorse in generating lift is the wing's angle of
attact. It's like if you ride in your car with the window down and
your hand out in the wind. If you hold your hand flat and horizontal
(parallel to the flow of air), there's not much force either up or
down. But change the angle of your hand away from horizontal, and
you'll feel a definite force deflecting the hand.

Thanks ever so much, pinkfreud, I think that what you have said,
together with that article, does in fact almost count as an answer. 
Now I see it: that Bernoulli's effect is not the main contributor to
the lift - that is the angle of attack.  Bernoulli's effect mainly
reduces drag, therefore enabling the plane to fly without stalling and
crashing.

It seems that what I was taught (here in England) years ago was very
misleading - wrong even.


Yaffle, England.

(PS sorry I spelt Bernoulli wrong)

Thank you ever so much, too, ged100 for your responsethat bears out the other one.

Yaffle

"It seems that what I was taught (here in England) years ago was very
misleading - wrong even."

Don't feel too embarassed by it. Everyone, everywhere has been taught
it that way for decades. I remember being taught the same thing when I
was a kid in the U.S. 40 years ago.

Yaffle,

It's good to know that the link I posted was useful! I had expected
that someone who is an experienced pilot (and GA has several) might
pop in and post an answer, but since that hasn't happened, I'd be glad
to gather more material from the Web on this subject, if that would
provide a satisfactory answer. Please let me know if you'd like me to
do this.

~Pink

Hello again qed100,

Thank you for telling me that you had been taught the same rubbish
years ago in your country as what I was also taught years ago in mine.
 I was beginning to wonder if I had remembered it wrong and that I was
imagining that the functioning of airplane wings was ever taught as
being entirely down to Bernoulli?s principle.  I am glad that you
remember being taught that too.

It is very odd how myths like that develop.

Thanks.  Yours sincerely,

Yaffle, England.

Hello again pinkfreud,

I do not really think that I need any more information about this
because that article that you directed me to has completely answered
my question in fact, thanks.

Yours sincerely,

Yaffle, England.

Yaffle,

If you are no longer seeking an official answer to the question, you
may want to cancel it so that all you'll pay is the fifty-cent listing
fee.

~Pink

Dear pinkfreud,

I shall indeed cancel it and save myself $20 - so thanks and goodbye.

Yours sincerely,

Yaffle, England

over and out.