Zzz wrote:mtv wrote:who knows how to shut down a 985 with a 2D-30 prop.
How did you pick up on that? I had to Google the procedure and found it (I think) on some T-6 forum that says "run up throttle to 1450 rpm then pull prop back to full coarse for 1 minute, then shut down with mixture."
Is that right? What's the mechanics behind this? When he shows the control levers after the pilot hops out, the prop is full fine.
And how easy is that to do on the water?
The Hamilton Standard 2D-30 prop should be shut down in full coarse pitch, at least when it'll be parked for a while. I picked up on that because when the climbed into the cockpit after the plane had been parked, the prop lever was in full coarse pitch. It's no big deal to do so, just pull the prop lever to full coarse, run the power up a tad to get it to cycle, then go to the dock.
The reason for that is that the blades on that prop are controlled by a large piston, which slides in and out of the hub of the prop with oil pressure. In full fine pitch, most of that piston is outside the hub. When the prop is in full coarse pitch, that piston is almost fully housed within the hub. Since this piston is bare (and VERY smooth) steel, it can and does corrode. So, if that piston is outside the hub when the plane is parked at the dock or outside, the piston is going to corrode.
Why is THAT important, other than corrosion in general is bad? Because what seals that piston to the hub is a very thin but large diameter O-ring. That O-Ring prevents engine oil, which circulates within that hub, from exiting the prop. Get too much corrosion, and every time you cycle that prop, you're grinding away on that O-Ring.
Which brings up another mandatory procedure with those props: After every significant maintenance, during the maintenance test flight, the pilot should verify that, with the prop in full coarse pitch, the airplane can be flown so as to maintain level flight.....this generally requires use of some flaps, reduced power, etc. But, the pilot needs to verify that the blades are set at an angle that permits maintaining altitude IF that O-Ring breaks. Because when that happens, if the pilot does nothing, all the engine oil will be discharged out the hub of the propeller. The answer is to pull the prop to full coarse pitch, which houses the piston in the hub, and seals the prop from leaking as long as the prop is in full coarse pitch.
That gets messy, at the very least. At the worst, it means an engine shut down and look for a place to park.
Only place I ever had that happen was near the Barren Islands, halfway between Shuyak Island and the Kenai Peninsula.....lots of open water, and VERY big waves.
Pulled the prop lever to full coarse pitch, pumped down some flaps, adjusted power, verified I had plenty of fuel to get to Kodiak and motored on.
MTV