How do aircraft fly upside down?

paddy-boy66

Can anybody tell me how aircraft fly up side down? I'm an under grad aero student and cant see how aircraft do. Can any aircraft theoretically fly up side down?

J77

You just need to adjust the angle of attack (http://en.wikipedia.org/wiki/Angle_of_attack)

LURCH

Aerodynamically, yes, any aircraft can fly upside down, but for most ut is very innefficient. Also, some have structural limitations that won't take the strain, and many have engine limitations that will stop the flow of fuel.

paddy-boy66

but doesn't the resultant lift always act in one direction relative to the "upper" surface so if its upside down wont the "lift" be downwards? Am i being stupid in saying this?

J77

Angle of attack's like sticking your hand out of the car window - if you tilt your hand, you feel the force upwards or downwards - same for a plane.

Gokul43201

No, you've fallen prey to the most pervasive fallacy in aerodynamics - the Equal Transit Time fairy tale. Google that phrase, and you'll find many places that show how it's wrong.

Danger

That having been said, aeroplanes that are designed for aerobatic manoeuvres have specialized wings, control surfaces, and engines. Stagger-wing biplanes are particularly well-suited to it.

Astronuc

Well considering that some aircraft fly upside down, it is actual rather than theoretical. Practially, it is limited to small aircaft, acrobatic and jet fighters, and the like.

Many aircraft, particularly large aircraft are not designed nor build to fly upside down, and most likely would disassemble (wings falling off or engines failing) if they tried to fly upside down.

Generally, the angle of attack is greater when the craft is inverted.

Averagesupernova

Hmmmmmmmmm. I'll have to try that with a 747 on my flight sim.

Danger

Do you also have a crash-team sim?

paddy-boy66

thats awesome thanks guys! i'd like to see a 747 flying upside down

russ_watters

Here's another way to think about it: normal wing flying upside down is just a poorly shaped wing flying right-side-up. I think, perhaps, by "any", he meant every. Though pretty much any *airfoil* is capable of producing negative lift (or positive lift while inverted), many *planes* cannot fly inverted for various other reasons (structural, fuel flow, lift/drag ratio, etc).

Hootenanny

I believe that a 747 would theoretically would be able to fly upside down, however, it's wings and tail fin would be ripped off by the forces involved in executing the role.

Cyrus

You want to fly an airliner upside down, sure here it is:

http://www.aviationpics.de/airshow/707buzz3.jpg

It is entirely possible and has been done.

Here is the corresponding video:

http://www.aviationexplorer.com/707_roll_video.htm

If done properly, the forces are not a problem, nothing would be ripped off.

It's called a chandelle and it's a 1g manuver. If your airplane is going to fall appart at 1g, you have bigger problems.

paddy-boy66

so then how do aircraft fly perpendicular to the ground, or is there a component of the thrust equal to g?

Danger

They can't do it for long. In the case of aerobatic machines, the fusilage provides lift, although not as much as the wings. With military jets, it's more a matter of pure thrust vs. gravity. Don't try it with a Cessna 150.

Cyrus

It's called a knife edge.

For one thing, you get body lift as Danger said. But that is very minor. You also get some lift from the tail fin which is now acting as a wing, but again thats only minor. And if you look carefully, you will always notice that the nose of the airplane is pointed upwards. This is for good reason, becasue the tail is pointed down. This means the thrust has a component in the upwards direction. Thrust is the name of the game here. You need to have a very high thrust/weight ratio in order to do this, or your airplane will fall out of the sky.

Here is a picture for clarity:

http://www.rcgroups.com/articles/ezo.../knifeedge.jpg

http://www.wtp.net/DBEST/webimages/lonniecaprice.jpg

http://moleski.net/rc/pix/dc3.jpg