Page 26 - November 2022

“I prefer to always have a propeller wind- milling at takeoff RPM while conducting a windmilling airstart, since it leads to very comfortable starting ITTs.”
two things of interest involving the propeller. First, the windmilling blast will keep the propeller turning. In fact, hard to believe at first, but at any airspeed above about 140 KIAS, the propeller can windmill as fast as takeoff RPM even with no fuel flow! Second, the cowling design provides ram air to the compressor inlet and the rotating power turbine (the one connected to the propeller) helps suck air through the engine from the compressor out through the exhaust stacks. This combination of push (from the ram air in the cowling) and pull (from the power turbine) keeps the compressor from ever stopping ... yielding an N1 or Ng speed of 12% or more, depending upon altitude and airspeed.
So not only does the oil pump inside the propeller governor keep turning at high speed and hence providing normal propeller oil pressure, but also this pump keeps getting fed new oil supplied by the oil pressure pump in the accessory gearbox. Granted engine oil pressure will have dropped well out of the normal range since the pump is only turning at 12% speed or so, but that is still enough speed to get the oil from the tank to the propeller governor and also to scavenge the oil from the nose case back to the tank.
Unless we manually feather the propeller (dumping propeller oil into the nose case through the primary propeller governor) or have autofeather activate (dumping oil through the overspeed governor) the propeller will continue to windmill indefinitely following a fuel shut-off in flight.
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24 • KING AIR MAGAZINE
NOVEMBER 2022