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# Lift?

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I''ve been messing around with an aeroplane idea, i;ve got the rest of the forces, but lift is causing a problem, I don''t need anything overly complicated and i''m guessing it should be something like Lift = v*a*k where a is angle of attack, k is a lift constant thingy and v being velocity of plane

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I think it''s proportional to the square of the velocity. When I was modelling it I just had a constant ''coefficient of lift'', much like the coefficient of drag, so it became

k * A * v^2

where A is the area. This was for a car though which doesn''t usually have adjustable flaps, but I imagine you could simulate them by varying k accordingly.

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Yeah, as with drag, lift is approximately proportional to the square of velocity for an airplane wing operating away from a stall condition. The more formal representation is:

Lift = 0.5*rho*CLV2S

where rho is the fluid/air density (kg/m3 for example)

The 0.5*rho*V2 part is often called the "dynamic pressure"

V is the fluid/air velocity relative to the airplane

S is a reference area, typically wing area

CL is the lift coefficient, which, when the wing is not near stall, is linearly proportional to angle of attack. A reasonable approximation to the value of CL for subsonic airfoils running a Reynold's number above, say, a quarter-million (250000) or so, is:

CL = 0.1*alpha

The 0.1 is the slope of the lift curve, called dCL/dalpha in engineering/calculus terms. (That 0.1 is more accurate for long wings with high aspect ratio and no sweep. The value reduces for stubbier wings and wings with sweep, and there is a formula to calculate the lift curve slope based on aspect ratio, sweep, etc.)

alpha is angle of attack, in degrees, measured relative to the angle-of-attack where lift is zero.

Drag and pitching moment are also critical things to be calculated for airplane flight simulation. Not to mention side force, yawing moment and rolling moment if you're going to do any turning.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

[edited by - grhodes_at_work on November 23, 2002 1:27:57 AM]

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thanks for your help i''ll give it a try

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