Originally Posted by
A Squared
As I said in a previous post, its really a torquemeter. The way it measures torque is the outer ringgear of the planetary gear reduction unit has helical splines around it's rim. These fit into helical splines in the nose case of the engine. the reaction to engine torque tend to shift this ring gear backward (Or is it forward?, it's been a while) opposing that axial thrust are a series of hydraulic pistons which operate off engine oil pressure from the nose case scavenge pump. there's some sort of metering mechanism so that the pistons exactly offset the axial thrust of the ring gear, and the actual measurement is of the oil pressure required in the pistons to balance that axial force, the signal from the oil pressure transducer is displayed on the BMEP gauge. As a side note, on other radial engine installations, the torque meter was calibrated in units of "Torque oil pressure" which is a more accurate description of what is actually being measured that BMEP, But again, the units are arbitrary, learn what numbers you should see for what power setting on your engine and it doesn't matter the actual units are.
Originally Posted by
MarkerInbound 
The autofeather system is armed by raising the guard and then the switch under it found at the center of the pedestal aft of the prop controls. There is one green light to the left of the switch that indicates the system is armed. When the throttles are advanced to a point that equates to ~45 inches MAP and the BMEP drops below ~70 for more than one second a solenoid pulls the feather button in and the prop feathers as if the feather button was pushed. The system also then disarms to prevent autofeathering the other prop.
And to think there are people on here who talk about the simple aircraft of the 1950s!