# Lift and Drag formulas on a plane

• cjacobson22
In summary, the formulas for lift and drag on an airplane are Cl*(r*V^2)/2*A*e and Cd*(r*V^2)/2*A*e. Cl and Cd depend on a lot of variables, including the aspect ratio of the wing, and you will need a lot more information than what is provided to design an airplane.

#### cjacobson22

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.

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.

cjacobson22 said:
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.

## 1. What is the lift formula for a plane?

The lift formula for a plane is: L = 1/2 x ρ x V² x S x CL, where L is the lift force, ρ is the density of the air, V is the velocity of the plane, S is the surface area of the wings, and CL is the coefficient of lift.

## 2. How is the drag formula calculated for a plane?

The drag formula for a plane is: D = 1/2 x ρ x V² x S x CD, where D is the drag force, ρ is the density of the air, V is the velocity of the plane, S is the surface area of the wings, and CD is the coefficient of drag.

## 3. What factors influence the lift force on a plane?

The lift force on a plane is influenced by the shape and size of the wings, the air density, the velocity of the plane, and the angle of attack (the angle between the wing and the direction of the air flow). Additionally, the coefficient of lift is affected by the shape and design of the wings.

## 4. How does the angle of attack affect lift and drag on a plane?

The angle of attack plays a crucial role in determining the lift and drag forces on a plane. As the angle of attack increases, the lift force also increases, up to a certain point called the critical angle of attack. Beyond this point, the lift force decreases and the drag force increases, causing the plane to stall.

## 5. What is the significance of lift and drag formulas in aviation?

Lift and drag formulas are essential in aviation as they help engineers and pilots understand the aerodynamics of a plane. By calculating these forces, they can design and optimize planes for better performance and fuel efficiency. Pilots also use this information to adjust the angle of attack and maintain control of the plane during flight.