Italia:
For the sake of clarity I agree that THP will not equal BHP because of prop efficiency (I should have been more careful to specify SHP in front of a pedant) and frictional losses in the intermediate gearing. But that is just semantics, beside the principle morrissman was getting at, which was I believe:
At constant RPM the power required at the prop shaft = power provided by the crankshaft.
The torque, were it to be measured on each shaft, would be different however. Really quite simple. He wasn’t talking about the inertia tangent you went off on.
Now, about this stopped aircraft knocking out 200 BHP but no THP because it doesn’t have any velocity nonsense. What about a helicopter in a hover? Any thrust there (and you can include frictional losses and rotor efficiency in your answer if it will make you happy)? The answer is pretty self-evident. The aircraft doesn’t have to move to produce thrust. Do you, as a flight instructor, agree with that or not?
Because when you say “Today’s lesson is…” you quote an extract from a credible text on aerodynamics. But you have taken the text completely out of context. Of course we can work out power required by taking drag and multiplying by airspeed! But that does not mean a stationary aircraft can do no work and therefore produce no THP!!! The work is done by moving the mass of air one way and the mass of the Earth a tiny imperceptible amount the other way.
