Remember my previous theory about the coefficient of drag? Now, I have a new theory on the coefficient of drag. My theory is for the coefficients that affect the coefficient of drag. First, let's start off with the coefficients themselves. The equation for Cd in terms of other coefficients is: Cd=Cf+Cw+Cs+Cl2/eπAR First, lets start with Cl2/eπAR, where e is the efficiency factor and AR is the value of the span squared over the area, s2/A. That is the equation for induced drag. Cl is the lift coefficient, and my theory does not cover that. A new theory I am still developing does, but I need to finish a separate theory in order to have an equation for that. Now, lets go on to the parasitic drag. Let's start with the form drag coefficient. The form drag coefficient is: Cf=Dcosθavg Where D is the drag coefficient it would have if it was a flat 2D plate and is a function of Reynold's Number. θavg is the average of the angles that each surface makes. The angles are relative to the axis perpendicular to the velocity. The reason that I think this is the equation is because the form drag goes around the object. Let's say you had two 2D plates joined together at one side and they were both tilted at an average angle of θavg. Then they would now have a form drag coefficient of Dcosθavg. This can be applied to all shapes. The form drag is moving around the object. But we do not count angles that are greater then 90 degrees in the average. The drag from that is covered in the interference drag. The skin friction drag coefficient Cs already has an equation for it that I did not come up with. The equation is:
Cs=2dΘ/dx
where Θ is the momentum thickness.
Finally, let's talk about the wave drag. The wave drag is the drag from shock waves and only has an affect for supersonic or transonic velocities. The equation for that is: Cw=Av/vs Where A is the area of the shock wave, v is the velocity, and vs is the speed of sound. v/vs is a ratio called the Mach number. It is the ratio of the velocity to the speed of sound. I think this because the more area the shock wave covers, then the more dag it would make, and A=0 when v<vs, and this means there is no drag from the shock waves when there is none, which is correct. I put the Mach number into the equation because when you have a bigger Mach number, you have stronger shock waves, and so more drag. This makes the equation for drag coefficient:
Cd=Dcosθavg+Av/vs+2dΘ/dx+Cl2/eπAR
What do you think?