While I understand this is a basic question, I am a beginner with regard to fluid dynamics etc. To start, say you have a propulsion system capable of X Newtons and a weight of Y kg. I realize max speed occurs at the point at which the force of drag is equal to the force of acceleration, and the aircraft will neither be accelerating nor decelerating (inertial motion will be achieved). Here is where my problem occurs: Fd (Force of Drag) is partially dependent upon velocity as V^2 is part of the equation. However, the drag coefficient is non-constant as it too relies upon velocity. Can X N/Y kg be the reference velocity to find the force of drag (assuming all other quantities are known) or does max speed simply have to be tested for in another way? I can test for Fd at different velocities, but have no idea how to plot this on a graph or set it equal to Fa as Cd also depends on velocity. Any help would be appreciated.