For the aeronautical engineers

[sluggish]

How much of Bernoulli's principle is fact and how much is theory?  Some say it's what makes flight possible but it seems to me that angle of attack is much more important and you could probably make a sheet of plywood fly if the angles and control surfaces were right... .  The one thing that shoots down Bernoulli's principle is sustained inverted flight.


Please don't flame me for asking a stupid question.

[Halo]

Not a stupid question at all.  Flight is made possible simply by how fast you flap your arms.

[Airscrew]

Just something I found when i asked my friend Mr. Google

http://www.av8n.com/how/htm/airfoils.html

Lots of stuff just this one page

Inverted Flight, Cambered vs. Symmetric Airfoils
You’ve probably been told that an airfoil produces lift because it is curved on top and flat on the bottom. But you shouldn’t believe it, not even for an instant.

Presumably you are aware that airshow pilots routinely fly for extended periods of time upside down. Doesn’t that make you suspicious that there might be something wrong with the story about curved on top and flat on the bottom?

Here is a list of things you need in an airplane intended for upside-down flight:
You need super-duper seatbelts to keep the pilot from flopping around.
You need to make sure the airframe is strong enough to withstand extra stress, including stress in new directions.
You need to make sure that the fuel, engine oil, and battery acid stay where they are supposed to be.
You will notice that changing the cross-sectional shape of the wing is not on this list. Any ordinary wing flies just fine inverted. Even a wing that is flat on one side and curved on the other flies just fine inverted, as shown in figure 3.11. It may look a bit peculiar, but it works.

On some airplanes, the airfoils have no camber at all, and on most of the rest the camber is barely perceptible (maybe 1 or 2 percent). One reason wings are not more cambered is that any increase would require the bottom surface to be concave --- which would be a pain to manufacture. A more profound reason is that large camber is only really beneficial near the stall, and it suffices to create lots of camber by extending the flaps when needed, i.e. for takeoff and landing.

Reverse camber is clearly a bad idea (since it causes earlier stall) so aircraft that are expected to perform well upside down (e.g. Pitts or Decathlon) have symmetric (zero-camber) airfoils.

We have seen that under ordinary conditions, the amount of lift produced by a wing depends on the angle of attack, but hardly depends at all on the amount of camber. This makes sense. In fact, the airplane would be unflyable if the coefficient of lift were determined solely by the shape of the wing. Since the amount of camber doesn’t often change in flight, there would be no way to change the coefficient of lift. The airplane could only support its weight at one special airspeed, and would be unstable and uncontrollable. In reality, the pilot (and the trim system) continually regulate the amount of lift by regulating the all-important angle of attack; see chapter 2 and chapter 6.

[loser]

Originally posted by sluggish
How much of Bernoulli's principle is fact and how much is theory?  Some say it's what makes flight possible but it seems to me that angle of attack is much more important and you could probably make a sheet of plywood fly if the angles and control surfaces were right...

True.

[Airscrew]

also some explainations here,  several links

http://www.allstar.fiu.edu/AERO/airflylvl3.htm

http://quest.arc.nasa.gov/aero/question/aerotheory/Lift_and_inverted_flight__.txt

http://www.aeronautics.ws/blunder1.html

[Airscrew]

Loser, that sure is a purdy piece of plywood