IF a test bed is available the test should be preferably carried out on this, where the power given out by the engine may be more easily measured. If, however, this equipment is not available the test must be carried out in the aircraft, but for the test under these conditions a known airscrew must be available. This airscrew should not be the one normally used on the aircraft, but one that has been modified and calibrated to allow the engine to be run up to its full r.p.m. The reason for this is that the flight airscrew, for aerodynamic reasons, docs not allow the engine to reach its full r.p.m. with the aircraft stationary on the ground, and unless a test airscrew is used an engine may be sent into the air with a defect which may only make itself apparent at the higher r.p.m. Pilots should not be asked to take this risk.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: May 1, 1929