My question is about estimating drag for a rocket powered plane.
Normally for a supersonic aircraft one draws conical sections through the aircraft and compares the cross section with Sears-Haack body to calculate wave drag.
For a jet aircraft the area of the intake and exhaust can be subtracted from the cross sectional area as the air which passes through the engines can be captured in the thrust calculation.
See attached file image of a textbook method:
How is drag wave drag calculated for a rocket plane?
Presumably for an under expanded nozzle it effectively fills in the base drag though I would also expect some drag reduction or additional thrust from entraining passing air if the exhaust is going substantially faster than the vehicles velocity.
I'm ideally looking for text book methods I can apply to preliminary design hand calcs.