# Lift and Drag formulas on a plane

I am going to make a R.C. airplane and need help understanding the physics behind it. I have found these formulas for lift and drag.

Lift=Cl*(r*V^2)/2*A
Cl=2*pi*AoA

Drag=Cd*(r*V^2)/2*A
Cd=Cd0+Cl^2/(pi*A*R*e)

Now I have two questions. First, are these the correct formulas for finding lift and drag on an airplane? Second, what are all of the variables? I think I know some of them, but I would like to be sure so please include them.

Gold Member
These formulas do give lift and drag, but you can't just apply them without any knowledge of their roots unless you are just going to do it on te wings, and even then it would be a pain to check your answer.

In particular, Cl and Cd (coefficients of lift and drag respectively) depend on a lot of things. They are well know for many airfoil shapes, but that's about it as far as you are concerned.

Your best shot at making a decent RC airplane is to take an existing aircraft and scale it down. Then take it out and the road with some force gauges and measure lift and drag. Once you have reasonably cambered wings it will fly. But if you're designing something new, you got a few problems on your hands.

I am going to make a R.C. airplane and need help understanding the physics behind it. I have found these formulas for lift and drag.

Lift=Cl*(r*V^2)/2*A
Cl=2*pi*AoA

Drag=Cd*(r*V^2)/2*A
Cd=Cd0+Cl^2/(pi*A*R*e)

Now I have two questions. First, are these the correct formulas for finding lift and drag on an airplane? Second, what are all of the variables? I think I know some of them, but I would like to be sure so please include them.

Here are the variables.
Cl=lift coefficient
V=velocity
r=density
A=area
Cd=drag coefficient

The equation for Cd should be pi*AR*e, not pi*A*R*e. AR is referring to the aspect ratio of the wing.

You could use the equations for lift and drag. Your equation for Cl is really just an approximation for the lift coefficient of an airfoil and should not be used for a wing. Anyways you will need a lot more than those equations to design an airplane. I would suggest finding a good aircraft design book and going from there.