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View Full Version : How does an aeroplane fly Upside down?

HYPNOS
17th Apr 2008, 10:25
as far as i know, the lift generated by a wing is because of the angle of attack creating a pressure difference(but i dont know how it actually works, bernoulli's principle? Newton's third law of motion?), so if a civilian aeroplane flying upside down(can they do it actually?) where does the lift come from???

is that the same reason why the fighters can fly upside down???

low n' slow
17th Apr 2008, 11:11
Any type of flat surface will fly if the proper angle of attack at a sufficient airspeed. That is, it will fly but not necesarily very well. With a semi symetrical wing profile, the AoA for inverted flight will be significantly different than for right side up flight and that will also change the performance and so on. An airliner will most likely not be able to fly inverted with this theory in mind because of the extra thrust required. It may pass the inverted state though in a roll for example (reference to the B707 famous test flight), but this is not flying inverted in the same sense as it is during a transition in a roll with positive G's.

Aircraft that are supposed to fly inverted tend to have a more symetrical type of airfoil and this will make the difference between inverted flight and right side up less apparant in regards to aerodynamics.

/LnS

Pugilistic Animus
17th Apr 2008, 16:54
you can also fly on 'knife edge' in which the wings produce zero lift...it's the fuselage entirely

portsharbourflyer
17th Apr 2008, 17:47
Aircraft flight is a bit like the creation of the universe; several theories around explaining lift but all can be disputed by someone.

However the theory taught in the PPL and ATPL studies is generally regarded as "incorrect" and you have pin pointed one of the reasons why. The theory taught at PPL and ATPL level doesn't explain why a flat plate creates lift and hence why a plane can fly upside down.

On aero degrees the Kutta Joukowsky (apologises for the spelling) explanation of lift is the accepted explanation; although I am sure someone out there will dispute this.

I would suggest you get hold of a copy of Aircraft Flight by Barnard and Philpott, one of the best non-mathematical texts concerning theory of flight; this will answer your question.

frontlefthamster
17th Apr 2008, 17:57
Carefully.

RYR-738-JOCKEY
17th Apr 2008, 19:09
I'm too stupid for any theories, so I usually stick to the fact that when you drive a car, sticking your hand out in the air you will feel the force of lift. Good enough for me.

jh5speed
18th Apr 2008, 20:03
Exactly the same way as it does the right way up - only less well - unless the aircraft was vertically symmetrical that is, and then it'd be just as good (but then nobody would know it was upside down) ...

Mark 1
18th Apr 2008, 21:47
In competition aerobatics its quite helpful to have the same flying characteristics inverted as upright.

For example the Sukhoi SU29 has symmetrical aerofoils with zero incidence and no washout. As a result level flight is 'nose up' both upright and inverted.

This makes cross country flying somewhat less efficient and the forward view not so good. The lack of wash out gives a more aggressive stall (but it flicks nicely).

jh5speed
19th Apr 2008, 18:47
As the circle tightens (radius decreasing), more centripetal force is required to maintain the circle (assume same speed (v) and mass (m) : F = mv**2/r). The centripetal force is provided by lift which is increasing as a result of increasing angle of attack (coming as a result of the pilot pulling the stick back). So if decreasing radius requires increasing lift, someone will stall first. Why this should be the FW and not the Mustang, I can't say. The vigour of stall onset may be the deciding factor.

Isn't the mist thing just condensation occurring in the lower static pressure regions, often seen at high AoA.

david1300
20th Apr 2008, 10:55
By rotating through 180 degrees.
Happy to help;)