Hi,
In my reply (post #24), On RR Tyne with 4 bladed variable pitch props, we had to have both Prop RPM and torque within limits before we called power was set. The engine and gearbox were bolted together so it was not possible to measure their individual torques separately.
Hence the torque sensor (which was bolted between an engine mount and the airframe) simply measured the reaction to the propeller torque - so it indicated actual Prop Torque.
In order to keep passenger comfort during stepped climbs, we kept the prop RPM constant, but varied the fuel flow by "trimming" the (guarded) HP fuel levers. Power changes were called for ("50% trim" etc) and measured by observing the torque.
Since we measured both torque (force) and prop RPM (velocity) one could calculate the propeller horse power being generated (with a known p.e.) - even when stationary on the runway
Since there is no torque meter fitted on a bypass jet engine, the most useful parameters are N1 / EPR which only give an indication of thrust, not power.
Edit for Capt Pit Bull's comments below.
Rolls-Royce Tyne - Wikipedia, the free encyclopedia
"RTy.1 Mk 506
3,259 kW or 4,985 e.s.h.p"