Ted wrote:
Off course if it does stop, the majority of the reason for feathering now goes away. I.e drag from windmilling
I don’t quite agree. If the engine fails non mechanically (fuel exhaustion), it’s going to keep windmilling at flight speed, unless feathered. However, it may slow below 800-900 RPM while windmilling, particularly if set to coarse when the engine stopped. so now you’ve got a windmilling prop at 700RPM, which you cannot feather, which would be unhappy flying.
A stopped, non feathered propeller is still very draggy compared to a feathered one. I’ve done a fair amount of feather testing on PT6 turbines, where, with cautious engine control selection, you can feather a running engine. I’ve done this in the Caravan and Basler DC-3. Power lever to idle, wait for it to slow down, confirm engine operation by engine RPM and combustion temperature, and feather. Particularly in the Caravan, it’s like getting a big shove from behind. Then you have a luffing feathered prop, turning at only a few RPM. When you select out of feather, it’s like you touched the brakes, as the hardly turning feathered prop comes out of feather, and begins to turn first by windmiling, and then by engine power as the idling engine can overpower the feathered drag. Once the engine is driving the prop again, you have to prevent a prop overspeed, but otherwise it comes back to life normally. But you can feel the difference in drag between feathered and unfeathered with the prop hardly turning!
There certainly is a difference in drag between feathered and unfeathered prop.
However, if an engine fails in cruise and above a certain altitude you might troubleshoot before feathering by trying to restart the engine.
That entails lowering the nose, which allows the prop to turn enough in the effective wind and the engine should start on the prop. Rather like the old pushing a car and dropping the clutch when its rolling when you have a flat battery (old school). So that would suggest to me that by lowering the nose one could increase the prop speed above the 800 or 900 rpm in order to feather it. Set against this is that it could not be done if the engine or hub had seized or if you were too low to get the nose down without ploughing into the ground by the time you reach feathering rpm.
For me there is no doubt that I can get a faster, cheaper to operate, cheaper to maintain single than I can a twin.
However, generally speaking a twin like the Aztec has take of and landing performance which will compete well against the equivalent single, and that goes for most twins versus their single counterpart. Secondly the twin version will usually have a better useful load.
The twin will usually be more stable in the cruise than the single. (I know several pilots who fly a twin because their wives start throwing up at the first sign of turbulence) I’m sure Peter knows one well.
On current terms I can buy a twin for less than the price of the single version and it will usually be better equipped for IFR flying.
But for me, and I have I think written this before, is the feel of the twin along with the comforting sense that the sound of those two engines gives me on a flight from Brittany to Devon or the mainland to Corsica.
I know the Mooney will get me there 10 minutes faster and cheaper, I know that I have a parachute to save the day in a Cirrus, and I know that engines rarely fail.
So I know its psychological.
A stopped, non feathered propeller is still very draggy compared to a feathered one.
Thank you @ Pilot_DAR for pointing this out.
Most MEPs if the failure is not due to the engine seizing, the propeller will windmill at an RPM well above the feather lock, probably around 1800 RPM. If there is a problem of oil pressure to the governor the fail safe is to push the propeller to coarse, in the absence of auto feather, but even in fail safe coarse, if the engine is not seized, it should be well above feather lock.
In the event you are around feather lock RPM in the air you have a serious governor failure or the engine is seizing. Pointing the nose down to Vne is not going to help.
