Originally Posted by
Mach E Avelli
....The centred rudder in the video taken from outside the aircraft still suggests close to symmetric power - whether a lot or a little at the time is not so easy to deduce simply from estimating prop RPM. You'd need to know the manifold pressure and TAS to get a better idea.
Any analysis should benefit from the comparison between the performance of the failing engine's prop and that of the good engine which, to state the obvious, is operating at the same TAS. So that leaves the question of the manifold pressure. Your statement implies that the prop pitch could modulate - i.e., become finer - to maintain take-off RPM in the event of failing manifold pressure? In other words, being controlled by the constant-speed function of the CSU.
My only experience of big radials was the Twin Wasp, half a century ago. But my recollection is that, when the pitch levers are set to full-fine for take-off, the propellor pitch is fixed at full-fine and the RPM becomes a function of the manifold pressure as the throttles are advanced to obtain the rated manifold pressure for take-off. (As you suggest, the RPM rises slightly as the TAS increases.) If that's the case, the engine/prop RPMs are directly related to the power available, and in turn the thrust produced by the prop.
It's not until the first power reduction after take-off that the constant-speed function of the CSU comes into play. The throttle is retarded slightly to the desired manifold pressure, followed by the pitch lever. Once the desired RPM is obtained with the pitch lever, the CSU maintains it for a wide range of manifold pressures by varying the pitch of the prop.