How do aircraft fly upside down?

  1. 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?:smile:
  2. jcsd
  3. You just need to adjust the angle of attack (
  4. LURCH

    LURCH 2,507
    Science Advisor

    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.
  5. 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?:confused:
  6. 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.
  7. Gokul43201

    Gokul43201 11,044
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
  8. Danger

    Danger 9,663
    Gold Member

    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.
  9. Astronuc

    Staff: Mentor

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

    Danger 9,663
    Gold Member

    Do you also have a crash-team sim? :biggrin:
  12. thats awesome thanks guys! i'd like to see a 747 flying upside down :biggrin:
  13. russ_watters

    Staff: Mentor

    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).
  14. Hootenanny

    Hootenanny 9,676
    Staff Emeritus
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    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.
  15. Last edited: Sep 3, 2006
  16. so then how do aircraft fly perpendicular to the ground, or is there a component of the thrust equal to g?
  17. Danger

    Danger 9,663
    Gold Member

    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.
  18. 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:
    Last edited: Sep 4, 2006
  19. russ_watters

    Staff: Mentor

    I don't want to get too much into semantecs, but since it was a 1g, transient maneuver, I don't know that I'd call that "flying upside-down".

    I suspect an airliner could structurally handle flying inverted, but that its wings would not be efficient enough to keep it in the air (high angle of attack required = too much drag).
  20. It's because Santa Clause is your Parents:


    Ah, xkcd -- has an answer for everything! Thank you Randall.

    But, for the record, I agree with thrust and momentum being the critical components; though it doesn't mean the Bernoulli principle isn't real.
  21. I ended up over here by way of the XKCD forums. This seems like a neat place, I look forward to looking around and maybe learning some new physics.

    Regarding how airplanes can fly upside down:

    Regarding how airplanes can fly knife-edge: It is NOT the vertical component of the thrust. Most high-performance airplanes have a thrust-to-weight ratio of just over 1, so they'd have to point almost straight up before the vertical component of the thrust can offset the weight. Airshow airplanes do knife-edge flight by getting lift off the fuselage, i.e. by flying like a lifting body and using the fuselage as a wing. Anything will produce SOME lift if you get it going fast enough and orient it at the right angle ;]
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