Incorrect Theories of "Lift"

[Bevan]

Yes, the mass of air being forced down results in an equal and opposite reaction... the force pushing the plane up. The airfoil is configured to do this with minimum drag so that the engine can keep up with the adding the required energy into into the "system". No? The Jato bottle mounted on the old car comes to mind.

Bevan

[Yen]

My other aeroplane is a Corby Starlet, which has fabric covering on the wings aft of the spar. If Bernoulli was correct the fabric should tend to bulge upwards when flying. It doesn't, it is definitely depressed, so how can it be a low pressure area.
I don't know who first thought of Bernoulli theorem for aircraft, but I still believe it is just the pushing down of air that does the job.

[strahler13]

Finally NASA has come around to my way of thinking. I've always said, "Who says that two molecules hanging around near each other have to end up next to each other once they have gone different directions from a passing wing?" NASA's second bullet point agrees with me.

[49clipper]

Originally Posted by Yen

My other aeroplane is a Corby Starlet, which has fabric covering on the wings aft of the spar. If Bernoulli was correct the fabric should tend to bulge upwards when flying. It doesn't, it is definitely depressed, so how can it be a low pressure area.
I don't know who first thought of Bernoulli theorem for aircraft, but I still believe it is just the pushing down of air that does the job.

Contrary to your thoughts. My Pa-16 clipper inflight photo clearly shows bulging in between the ribs in flight on top of the wing and from underneath concave fabric between rigs. Obviously low pressure on top and high pressure above. Have seen that on many aircraft. the distance between the ribs on the cub wing are far enough apart to make it obvious.

[BobTurner]

Originally Posted by Yen

I don't know who first thought of Bernoulli theorem for aircraft, but I still believe it is just the pushing down of air that does the job.

The authors don't say Bernoulli's theorem is wrong, but rather the calculation of air velocity that is being used is incorrect.
Saying that physics 'explains' lift is fundamentally incorrect. Nature is what it is. Physics tells you how to calculate the observation. It is only an explanation to the extent that one can relate to something similar in his common experience. In this case, Bernoulli's theorem (using the correct velocities) or Newton's law (every action has an equal and opposite reaction) applied to the down wash will give the same answer.

[Bevan]

Originally Posted by BobTurner

In this case, Bernoulli's theorem (using the correct velocities) or Newton's law (every action has an equal and opposite reaction) applied to the down wash will give the same answer.

Or "trump's law" which says money makes everything work.

Bevan

[PerfTech]

Originally Posted by 49clipper

Contrary to your thoughts. My Pa-16 clipper inflight photo clearly shows bulging in between the ribs in flight on top of the wing and from underneath concave fabric between rigs. Obviously low pressure on top and high pressure above. Have seen that on many aircraft. the distance between the ribs on the cub wing are far enough apart to make it obvious.

... I also have two fabric covered aircraft that exhibit this same behavior and have witnessed in many times in others. Thanks, Allan..

[Av8torTom]

A friend of mine works for Boeing, and helped design the wing on the 787. He made me promise never to tell anyone that:"We have no idea what really makes a wing fly". Take a look at this photo of a wing that struck a turkey vulture in flight.

http://www.vansairforce.com/communit...Turkey+vulture

It's hard to imagine there could be an undisturbed flow of faster air traveling over the top of that wing, and therefore hard to believe Bernoulli's principal contributes to a significant portion of lift. Despite the damage, the OP stated that the airplane flew quite well after the strike.

I think it's Keebler Elves....

[sblack]

the first thing wrong with that picture is that it shows the top and bottom flows dividing at 0% chord. That's not what happens. That point, called the stagnation point, moves well down on the airfoil as AOA increases. That's why those little tab switches work on cessnas to give you the stall warning horn. The distance traveled on the upper surface is much longer, even on a flat plate, because of this movement of stagnation.

If you put lots of pressure ports on the top and bottom of an airfoil in a wind tunnel and measure all the pressures and add them up and multiply by the areas that they represent you will get something pretty close to the lift being measured by the wind tunnel balance. I have done it often. When we test scale models of biz jets and passenger jets we put pressure taps on the wings to check the pressures vs our computer models. The pressures from either the computer model or the wind tunnel pressure ports can be added up to calculate lift. We usually find we are very close in our estimates of lift when we fly the airplane. The computations tend to fall down right around stall, because the prediction of flow separation is more art than science and once the flow separates in one place it influences everything around it. This can also be difficult to get right even in a wind tunnel, due to scaling effects. But in the linear range, before stall, lift calculated by adding up (or integrating) pressures is pretty accurate.

And if you were to measure the change in momentum of the air being pushed down by the wing you would also get the same number if you could measure it accurately. The advantage of using pressures is that you can calculate the forces on any part of the airplane and thus work out the moments as well as the over all force. Measureing the momentum just gives you the overall lift. Not useful for predicting the loads on different parts of the airframe.

The relationship of velocity vs pressure, as predicted by Bernoulli, who did this long before man had built wings, is correct.

[dsteinfeld]

This podcast (when you get to the good stuff at the end) begins to hint at the complexity of lift.

Note that this is perhaps not the best of Marcus' podcasts. You can find others on flight (interviews with SR71 and U2 pilots, for example) on http://omegataupodcast.net.