Is this description of lift and drag coefficients correct?

In my course (Principles of Flight) written:

The effect of CLift is not linear. This means that Lift doubles for double the lift coefficient.

And

The effect of CDrag is linear. This means that for double the drag coefficient the drag force doubles.

If it's correct? And if yes, why effect of CL is not linear? Seems the same for me: coefficient doubles - force doubles.

1 Answer

The quoted text is in error. Lift (for a given airspeed) is directly (linearly) proportional to the lift coefficient. Lift (for a given lift coefficient) is proportional to airspeed squared. Likewise, Drag (for a given airspeed) is directly (linearly) proportional to the drag coefficient. Drag (for a given drag coefficient) is proportional to airspeed squared.

• Thank you for explaining Feb 9 at 21:21