Got it. From a helicopter point of view we use the expression (vector) of Total Rotor Thrust. We can map out the various forces on a vector diagram, and vertical component of TRT will equal the mass/weight in a stable hover. But the TRT will never be equal to zero unless you sitting on the ground with no pitch applied. But I see where you are coming from.
The helicopter example was probably out of place or just confused the discussion.
The other reason that the helicopter example fails is, what is your point of reference? If you are using the ground then the aircraft has not moved, so you are correct. But the ground is irrelevant.
Use a random parcel of air adjacent to the aircraft in hover as your reference point. This parcel of air is being induced to flow down past the rotor blades by the pitch applied. The parcel of air is travelling at somewhere near 300 feet per second (we call it downwash). The force applied to the air is what keeps the helicopter in a stable hover, so the THP is huge.
Now apply that same reference point to an aircraft sitting on the ground at idle. The aircraft has not moved reference the ground (irrelevant) but measure the THP against the speed (dist/time) of the parcel of air being driven across the prop.
Or is thrust only measured against the distance that the aircraft moves ref the earth?
Last edited by CYHeli; 30th Mar 2012 at 02:54.