I came across this video few days back on Edx 16.101 youtube channel.
At 7.00 min of the video, the presenter derived an equation for minimum flight power which does not depend on Cd0.$$P_\min = \frac{4}{3\pi e AR} \sqrt{\frac{2W^3CL}{\rho S}}$$
I don't have a doubt on the derivation, but this result seems to be very contradictory for me.
For example, let's take 2 identical aircrafts, one with fuselage airbrakes deployed and one without. (Identical CL, AR, $\rho$, S, CL and e but different Cd0) According to this expression the power requered cannot change. But,
- For same CL, V is going to be the same
- With airbrakes deployed, aircraft 1 drag is much higher than the aircraft 2
- Power required (D*V) should be higher for aircraft 1.
May be I am missing something simple. Why is this apparent contradiction?