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Kaze

How does a aircraft work?

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I am having a bit of trouble making a aircraft fly right, Im using ode so have gravity and thrust working fine and added aerodynamic drag that seems to be working ok. The two force I'm having trouble with are lift that should oppose gravity and be relative to speed and some sort of lift coefficient and whatever force makes it so that if you tilt the airframe up it will change it direction to match but still enforce conservation of energy so going up will cost momentum. I also want it to have a different lift and drag values for each of its three axis's but I think I know how to do that. I tried reading some resources on this but had trouble understanding a lot of it, especially how to apply the more general purpose physics equations. I'm not aiming for perfectly accurate simulation but a reasonable representation of real flight mechanics.

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I dunno if you're taking this into account, but Lift doesn't always directly oppose gravity. For example, if you roll over 180º then lift will actually be pulling you down with gravity ;)
Lift should be applied using the aircraft's "up" vector - this will have the side-effect where when you are tilted upwards you won't receive as much 'upwards lift' - a portion of the lift vector will actually be going backwards, slowing you down.

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If I understand correctly lift should work just fine upside down with the right angle of attack but I am a bit confused about the physics since lift can oppose gravity with more efficiency that strait conversion of horizontal momentum to vertical momentum but does do that to some extend depending on the angle.

EDIT:
I could be totally wrong here but the way I see it lift can be broken down into two forces. One is like a super version of drag the resists movement perpendicular to the wing surface and gets stronger with more fluid moving parallel to it. The other can convert velocity in one vector into velocity in another, so if you pitch up you can convert forward movement for upward movement.

[Edited by - Kaze on August 14, 2008 11:22:44 PM]

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Never programmed a flight simulator but I can tell the wings in an aircraft present a slanted position against the air thus causing the force of the air which comes in an horizontal direction to decompose in a horizontal and vertical components.
To simplify the things, just use a decomposition factor on the tip of each wing, like:
rwingfactor = 0.1;
lwingfactor = 0.1;
verticalthrust = windfriction * rwingfactor;
verticalthrust = windfriction * lwingfactor;

Now, the controls in the cockpit may vary the factor, like if you turn the stick forward, backward, left or right, you change the orientation of the wing (the mobile section of the wing) and the factor will be affected. Say you move the stick backward (pull it to you) and the wingfactors will increase, say it will become 0.3. Then the friction will decompose in a greater vertical force thus pulling you up. Of course you must compute the new forces in the new direction.

If you push the stick your factors will decrease or even turn negative. this will make you turn forward but may be completely dangerous.

If you move the stick left or right, the wingfactors may vary. Say you turn the stick right then you are basically increasing the left factor while decreasing the right factor. The force in the left wing increases while the force in the right wing decreasses. What you get is your plane spinning to the right.

I guess thats all. The rear flap may also help in guidance but the idea is similar.

Latest generation reactor jets use this same ideas but also allow the escape from the thrusters to be directed allowing for sharper turns.

Luck!
Guimo

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