Lift and Drag formulas on a plane

[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.

 

[boneh3ad]

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.

 

[viscousflow]

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.

 

[RandomGuy88]

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.

 

[alphy]

First of all, congratulations on taking on the challenge of building an R.C. airplane! Understanding the physics behind it is a crucial step in ensuring its successful flight.

To answer your first question, yes, these are the correct formulas for finding lift and drag on an airplane. The first formula is known as the lift equation and the second formula is known as the drag equation. Both of these equations are fundamental in understanding the aerodynamics of an airplane.

Now, let's break down the variables in each equation:

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

- Cl = Coefficient of lift, which is a dimensionless number that represents the lift generated by an airfoil (such as a wing) at a certain angle of attack (AoA). This value is dependent on the shape of the airfoil and the AoA.
- r = Density of the air, which can vary depending on altitude and temperature.
- V = Velocity of the airplane through the air.
- A = Wing area, which is the total surface area of the wings.

Drag = Cd * (r * V^2) / 2 * A

- Cd = Coefficient of drag, which is a dimensionless number that represents the drag force generated by an airfoil at a certain AoA. This value is also dependent on the shape of the airfoil and the AoA.
- Cd0 = Parasite drag coefficient, which represents the drag caused by the shape of the airplane's body and other non-lifting surfaces.
- Cl = Coefficient of lift, as mentioned above.
- A = Wing area, as mentioned above.
- R = Wing aspect ratio, which is the ratio of the wing's span to its chord length.
- e = Oswald efficiency factor, which takes into account the effects of wingtip vortices and other factors that can impact the overall efficiency of the wing.

It's important to note that these equations are simplified and do not take into account all the complexities of real-world flight. However, they provide a good starting point for understanding the basic principles of lift and drag on an airplane.

I hope this helps clarify the formulas and variables for you. Best of luck with your R.C. airplane project!