# Airplane lift

1. May 10, 2006

### Poposhka

the force of lift excerted on an airplane is defined as
F = Lc * D * v^2 * A
where Lc is the lift coefficient, D is the air density, v velocity, and A the lift area of the wing structure. If i use SI units, the Force is expressed in Newtons.

What i'm trying to grasp here, is how does this apply in practicality?
If i use the numbers Lc = 1.0, D = 1.225, v = 100, A = 21, (not random values) the result is 257,250 N ... now ... what does that MEAN? that the wings on that airplane produces enough lift to accelerate a 2000 kg airframe upwards at 128.6 m/s^2 ? Or, am i not calculating in gravitation? should the correct formula be 257250 / (2000 * 9.8) = 13.1 m/s^2 ? That just seems like an awfully high number... Or is it impossible to determine accurate lift unless you account for drag?

Thanks for any help
-- Pops

2. May 10, 2006

### Hootenanny

Staff Emeritus
Remember that lift is not the only force acting, don't forget gravity. The resultant force would be something like;

$$F_{total} = F_{lift} - mg$$

~H

3. May 10, 2006

### Astronuc

Staff Emeritus
The thrust pushes the plain forward and drag pushes/pulls against the aircraft.

In level flight, the lift balances the weight of the aircraft.

The forward velocity of the aircraft cause the lift as the air passes above and below the wing. The pressure over the wing is slightly less than the air pressure under the wing. In fact, the average differential pressure across the wing of a Boeing 747 is about 1 psi, and there is about 1 in2 of surface area for each lbm (weight of 1 lbf) of plane + load.