Some thoughts on props. While building my 360 I considered going with a feathering prop. At the time I could not come up with a strong advantage for it, and went with the flow.

1… My question was and is, what are the most common failure modes with a featherable prop and governor combination, and what are the probabilities of each of those failure modes?

My uneducated guess is that the most common failure would be a sheared driveshaft leading to loss of oil pressure to the prop and feathering of the prop, requiring a dead stick landing with a perfectly good engine.

If so, the next question is, does the advantage of improved glide ratio more than offset the disadvantage of a slight increased frequency of power [thrust] failure? If not so, why don’t all single engine planes have feathering props?

2…During flight testing I discovered that with the prop on the flat pitch stops I could barely keep the plane in the air at 2700 rpm. In a real emergency the engine temps would rapidly move past red line.

To test this at altitude, set the prop for max rpm. Then slow down gradually until you see the rpm begin to decrease, indicating the prop is on the stop. Can you maintain that speed without overheating?

I adjusted the pitch stop [ screw on centerline, front of dome] to maintain 120 mph at 2650 rpm. I do not see 2700 rpm until deep into the takeoff roll, but it still accelerates like a dragster, so I do not see it as a big sacrifice. I would not detect a governor failure till late in the takeoff, but I can stop on a long runway or fly it safely around the patch on a short one.

3… My normal cross country power setting is 1,800/18 inches which gives 200 mph tas on 6 gph above 10,000’. This has the prop very close to the high pitch stop. Running into the stop would be a bit like trying to turn your power steering past full lock. I check this occasionally by turning the rpm down briefly and looking for a drop. If no drop you must increase the rpm setting until you get an increase. I try to keep it at least 20 rpm above the stop in cruise.

On descent I would like to hold the rpm down and keep the mp up to keep the engine warm without making much power, but I must increase the rpm to keep it off the stop, increasing fuel flow and power when I don’t want it. The feathering prop would solve this problem.

From: farnsworth <farnsworth@charter.net>
Subject: [LML] Re: Legacy Crash Watsonville?
To: lml@lancaironline.net
Date: Tuesday, December 15, 2009, 2:33 PM

It is my understanding that the crash occurred close to the airport. I think
I read it was about 1 mile. If that is true I think that the glide range
difference between a standard constant speed prop and a feathering prop
would have made the difference between making the airport and not.

I believe it was reported that the pilot said he was at 7,000' when the
problem occurred. The fact that he made it to within 1 mile of a safe
landing with a standard prop (I don't know if he pulled his prop control
back of not. I think the engine was not turning at the time of ground
contact.)is evidence that the higher glide ratio of the feathering prop
would have extended his range enough to land at the airport. With loss of
oil pressure the feathering prop I have in my plane feathers automatically.
It does not require me to pull the prop control back.

Three years ago, at the Reno Air Races, Lee Behel was flying his Legacy in
the valley to the West of Stead when he had an engine failure. It was touch
and go on whether he would have an off airport landing or not. The
difference was the feathering prop on his plane. If he had had a standard
prop he would not have made the airport for an uneventful landing. 

I just think a feathering prop is cheap insurance.

>
> Lynn Farnsworth
> Super Legacy #235
> TSIO-550 Powered
> Race #44
> Mmo .6 Mach
> Feathering Prop


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