How can some aircraft fly upside down?

Question

I understand it is the wing shape which gives 'lift'.

Answer 1

No, it's not necessarily the wing shape. You can make a 4x8 sheet of plywood "fly", it just won't do it efficiently or aerodynamically, nor with a lot of stability.
That said, the reason an airplane can fly upside down is that the air hits the wing on the underside, no matter if it's right side up, or upside down. The pilot has to do more work to stabilize the aircraft in upside-down mode, but as long as the air hits the wing "underneath", and he's got the "angle of attack" ( VERY important concept, look it up on the Internet ) correct, it will fly upside down. It would be difficult to start an airplane from a dead stop on a runway and try to take off upside down, as you said because of the wing shape, but an aircraft can fly either way, just not as easily. Again, search on Angle of Attack, this is a very important aspect of flying theory that people do not understand, and you need to understand it before truly understanding how things "fly".
A side point, a "flying squirrel" can't truly fly, but it glides...and all it has is skin stretched out between it's legs and body, which is not wing-shaped, nor curved like a wing. So how does it "fly" ? By using the Angle of Attack to stabilize it's flight. A parachute isn't wing-shaped, but it can be made to glide ( at least the square ones ). Same principle, Angle of Attack, to achieve a stable gliding position to the ground.
- The Gremlin Guy -

Answer 2

Actually, you're right to a certain degree. Airplanes like commercial jets, private jets, and propeller planes you see flying around can only fly upside down for a few seconds because of their wing shape that gives them lift will force them to start moving down towards the ground, and eventually flip back up or crash. The pilot will have to be very skilled to keep it under control while flying upside down.
But military jets and fighter jet's wings don't have the wing shape, as their wings are completely flat. The reason is to improve aerodynamics, so if they have a target on lock they don't start drifting upwards and lose it, and when they upside-down they don't start dropping and can fly a straight line. Hope this helps.

Answer 3

the biggest problem is really the fuel system. If it has a gravity fed fuel system it can't fly upside down, the engine will stall. If it has a pressurized fuel system it can.

However some aircraft simply can't fly upside down, they just aren't built for it. Larger aircraft usually have highly optimized wings that are not easy to use upside down.

Answer 4

Wing shape is a secondary factor to inverted flying. The primary factors are the provision of:-

1) Lubrication oil which will not starve the engine and consequently seize it.

2) The fuel system which continues to function despite the attitude of the aircraft.

The wing shape is the last factor, since when even inverted, the pilot can feed in enough angleof attack (when inverted) to generate sufficient lift to keep thje aircraft flying.

Answer 5

Most performance aerobatic airplanes, like the Pitts Special, have symmetrical airfoils. In other words, the top surface of the wing is shaped exactly like the bottom surface. Both curved or cambered unlike most wings which only have a top surface camber. A symmetrical airfoil could care less whether it's right side up or upside down. There is one modified airshow Pitts that has upper and lower landing gear. It easily takes off and lands upside down.

Answer 6

You’ve probably been told that an airfoil produces lift because it is curved on top and flat on the bottom. This is “common knowledge” ... but alas it’s not true. 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, It may look a bit peculiar, but it works. The misconception that wings must be curved on top and flat on the bottom is commonly associated with the previously-discussed misconception that the air is required to pass above and below the wing in equal amounts of time. In fact, an upside-down wing produces lift by exactly the same principle as a rightside-up wing. To help us discuss airfoil shapes, some useful terminology. The chord line is the straight line drawn from the leading edge to the trailing edge. The term camber in general means “bend”. If you want to quantify the amount of camber, draw a curved line from the leading edge to the trailing edge, staying always halfway between the upper surface and the lower surface; this is called the mean camber line. The maximum difference between this and the chord line is the amount of camber. It can be expressed as a distance or (more commonly) as a percentage of the chord length. A symmetric airfoil, where the top surface is a mirror image of the bottom surface, has zero camber. At small angles of attack, a symmetric airfoil works better than a highly cambered airfoil. Conversely, at high angles of attack, a cambered airfoil works better than the corresponding symmetric airfoil. . The airfoil designated “631-012” is symmetric, while the airfoil designated “631-412” airfoil is cambered; otherwise the two are pretty much the same. At any normal angle of attack (up to about 12 degrees), the two airfoils produce virtually identical amounts of lift. Beyond that point the cambered airfoil has a big advantage because it does not stall until a much higher relative angle of attack. As a consequence, its maximum coefficient of lift is much greater. At high angles of attack, the leading edge of a cambered wing will slice into the wind at less of an angle compared to the corresponding symmetric wing. This doesn’t prove anything, but it provides an intuitive feeling for why the cambered wing has more resistance to stalling. 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

Answer 7

You really need to define what you mean by "upside down". Just about any airplane can go upside down for a limited period of time (like doing a roll, immelmen, loop, figure 8) given enough horsepower and airspeed regardless of the wing shape. Wing shape is a factor in efficiency but horsepower and airspeed are more important. However, to keep "upside down" for a more sustained period of time, you not only need a pump for inverted fuel, as the previous answerer said, but you also need an inverted oil system. This is true for piston driven, propeller airplanes. I don't know the answer with regard to jet engines.

Answer 8

an airfoil that is made to fly with a greater
curvature on the top can fly - though not as efficiently - inverted as
long as the angle of attack is established in the upward (opposite of
gravity) direction. Some airfoils are made symmetrical to allow them to
fly equally well right-side-up and up-side-down. Airliners are unlike
candidates for symmetrical airfoils, but nimble aerobatic aircraft often
feature these.

The short answer... angle of attack controls lift.

Also oil and fuel pumps that can transfer to the engines are most important as most fuel and oil systems are gravity fed.

Answer 9

Wing shape isn't the only way to achieve lift. Angle of attack will do it too. You just need to keep the wings angled up into the airflow.

If you stick your hand out the window of a moving car, you can quite easily make it generate lift even though it does not have a wing shape.

Answer 10

Ah, have you knicked my question he typed jokinly.
Yup wings are designed to give lift, so one would think that in in inverted flight they would produce a downwards force.
No so, as "float" comes into the equation. Any planar object going fast enough with enough height will roughly stay there, regardless of attitude. Ballistics, until in the case of a bullet or cannon-ball, gravity takes over, as it has no more forward input. Planes do, so you can angle the thing upwards a tad to compensate.

There we go,

Bob