How can an aircraft fly upside down. The wing lift should be in the wrong direction?

Answer 1

The shape of an airplane's wings (ie: aerofoil) the "right way up" forces the air passing under them to flow at higher pressure than the air passing over them. This produces the upwards force called lift that, well, lifts the airplane up and make flight possible.

The control surfaces at the trailing edge of the wings modify the overall shape of the wings. This is done by angling the flaps downwards or upwards. When they are angled downwards, the wing's effective curvature is increased, the pressure of the air under the wing is increased and lift is increased. When the opposite is done, the wing's effective curvature is inverted (ie: instead of looking like the shape of an eyebrow, it looks like a smile), the pressure of the air flowing over the wing becomes greater than the pressure of the air flowing under it.

A typical fixed wing aircraft would have 2 sets of wings: 1 at the front and 1 at the rear. The control surfaces of the wings at the front, called ailerons typically control the roll of the aircraft while those at the rear, called elevators control the pitch (whether the nose points up or down). This is done by modifying the amount and direction of lift acting on each of these wings.

For an aircraft the right way up to gain altitude, the ailerons would be angled upwards (creating higher pressure above the wings than below them) to push the tail of the aircraft down, angling the thrust and direction of travel of the aircraft upwards. The reverse applies for when the aircraft is to dive - the ailerons would be angled downwards to push the tail upwards.

Because an inverted aircraft would have the lift generated by the wings working in the direction of gravity (downwards), a counteracting force would have to be applied to keep the aircraft airborne. The ailerons would help do this by modifying the pitch of the aircraft so that the aircraft travels angles upwards (downwards in relation to the upside down pilot) just enough to counteract gravity and negative lift.

Answer 2

The simple answer is the angle of attack (the angle the wing chord is hitting the air). If you take an imaginary line and draw a line from the front of the wing to the back of the wing (called a Chord) and point it into the wind assuming you have a high lift (asymmetrical) wing, it will produce lift. If you have an aerobatic (symmetrical) wing you have no lift. but if you point the Symmetrical wing a few degrees up, you get high pressure on the bottom side of the wing and low pressure on the top of the wing. This is lift. now if you flip the plane upside down, and point the leading edge of the wing a few degrees to the sky, you still have lift, just upside down lift.

Answer 3

"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,

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.
airfoil-terms


To help us discuss airfoil shapes,

1. The chord line is the straight line drawn from the leading edge to the trailing edge.
2. 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.

This figure could be considered the side view of a symmetric wing, or the top view of a rudder. Rudders are airfoils, too, and work by the same principles.

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. . 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 4

Good question and you are correct; with commercial airplanes small and large, the wing lift would be in the wrong direction. The wings are designed to lift upwards only, while moving forwards at moderate speeds, to carry cargo and/or people with reasonable fuel efficiency.

With aerobatic and military aircraft, the wing is specially designed to be able to fly upside down for short periods. It requires the airplane to be much lighter and have much more powerful engines than regular commercial aircraft. The resulting airplane will be spectacular to fly fast, in aerobatics and upside down but will be twitchy to fly straight and level right-way up, will use a lot of fuel and be able to carry little cargo beyond the pilot, fuel, weapons, etc.

This is a fine example of how most engineering is a compromise of designing enhancements in one requirement at the expense of other parameters.

Answer 5

Commercial aircraft have a large asymmetric camber wing which produces lift only in the normal up direction. Airplanes designed to roll or fly upside down have a thinner wing with less camber and it is more symmetric. Lift is produce by adjusting angle of attack. Flying upside down can be achieved by rolling the aircraft to the inverted position and pushing the stick forward as required to hold the nose "up" and maintain the required angle of attack.

Answer 6

Are you thick?
The aircraft flies because of the lift produced by the wind under the wing.So if the aircraft is flipped, the wind is on the upper surface of the wing which is now the downside.So anyway, It can fly upside down.How it does this,you ask?
Each wing has two flaps.Turn the joystick to the right,the flaps on the left go up,and the flaps on the right go down.So it turns right.And vice-versa for the left.If it continuously is turned it'll flip in the air.Here,the controls get mushy and get reversed,rather like when reversing a car.

Answer 7

whether the wing is inverted or not ther is still an area of low pressure on one side and high pressuer on the other. As long as there are wings and a tailplane present then you can fly right way up, inverted, on your side, straight up or down. If they are missing then your troubles are only jus beginning. The flaps, elevators, leading edges etc all contribute to the amount of air and pressure of the air moving over the surface of the "wings". They are the only part of an aircraft that "truly" flies. The rest (fuselage, engines etc) are just along for the ride, and are referred to as parasite drag. Hence why everybody wants to make a commercial flying wing eg. the B-2 bomber or Stealth fighter, but on a bigger scale.

Answer 8

That's a very good question. I used to be an Aircraft fitter and that never crossed my mind. All I can imagine is that it must be a great strain on the planes elevators (the flaps on the wings at the back of the plane)
It must make the plane quite unstable and an unpractical way to fly to say the least.

It's clear that JD and sQricky don't understand how wings actually work.

Answer 9

Brian H is correct - the lift a wing produces is a function of its angle of attack, so inverted, the nose of the airplane is pointed up producing a positive angle of attack, and lift. However, most wings are very inefficient flying up-side down, so more power is required to maintain level flight when the aircraft is up-side down.

Some aircraft, designed for acrobatics and up-side down flight, have symmetrical airfoils so they fly equally inefficiently whether right-side-up or up-side down.

See also:


airfoils.com/why.htm

Answer 10

Not all aircraft can do this. Only those that have a symmetrical wing cross section can accomplish it. A normal airfoil would just produce a force downwards