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Actually, it was much less sophisticated an analysis than that….the full feathering system was more expensive, and I probably (? Never did decide) needed an accumulator to get it out of full feather…therefore more complex. So upon the recommendation of friends, I went with the counterweighted MT and “took my chances.” I’ve been more than pleased; as I noted at the bottom, today I wouldn’t do the full feather if they were the same cost… The engine out descent of my airplane is very manageable, allowing good perspective for planning a touchdown at a chosen location. A couple more miles of glide might be nice in some conditions, but flying around the east coast, I am pretty hard pressed to be outside gliding range of a suitable airport. The ability to manipulate the descent rate with the prop was a very nice “added benefit.” It’s far more effective than those “puny” speedbrakes!
Bob
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of John Hafen
Sent: Monday, June 20, 2011 8:00 AM
To: lml@lancaironline.net
Subject: [LML] Re: And how about a full feathering prop? Bob: Did you reject the fully feathering prop idea so you could manipulate the prop to adjust drag on the way down, versus just go full feather for a longer glide? On Jun 18, 2011, at 5:32 PM, Robert R Pastusek wrote:
For what I have gathered so far the lancair 4p has a glide ratio similar like a piano LOL In other words if the engine quits then open the door, throw out your keys because there is where you land LOL Well, this might not be true, or is it? So how about the full feathering prop ? Does anyone have experience with the before and after installation? How much they cost and data? And I needed to respond to this… My IV-P has a glide ratio (at 120 KIAS) of between 5:1 and 20:1, depending on configuration. The difference is truly amazing/impressive/sobering… depending on your situation and mind set. With the gear and flaps down and the RPM at max (prop all the way in), the glide ratio approximates that of a brick…not really, but you’re coming down so fast relative to forward progress that it’s difficult to plan and execute a planned touchdown (at least for me). With the gear and flaps up, AND THE PROP CONTROL ALL THE WAY OUT, my glide ratio at gross weight is approximately 18:1, increasing to a bit better than 20:1 at 800# under gross. At this glide ratio, the performance and “sight picture” approximates that of some gliders. It’s easy to plan and execute an approach and landing to a pre-planned spot…ideally a runway. I have practiced this many times from various altitudes/distances from the airport to a full stop on the runway, using the gear to increase my descent rate, and then the flaps and/or the prop control to adjust the touchdown point. Using the prop control is ideal because the drag effect/descent rate increase almost immediately reversible by pushing it back in. Not so with the flaps. One feature of my Chelton EFIS is a wind-adjusted glide range predictor. I have tested this many times starting at altitudes up to 17,500’ and (set at 18:1) gives me a very accurate and immediate sight picture of airfields within glide range. If it’s within the green circle, I can turn toward an airfield and execute a safe landing there. My MT 4-blade is not full feathering, but allows the engine to run at approximately 700 RPM when at idle and the RPM set to min. I believe this is pretty close to 0 thrust, as the engine idles at approximately 600 RPM on the ground. So, in summary, the throw out the keys and follow them down scenario can be executed if you really want to go down, but a planned glide at 120 KIAS (very close to best glide for my airplane) in clean configuration yields approximately the performance of a 2-place sail plane—and you have the ability to transition easily between these limits as needed. Try it; you’ll be impressed. PS: I considered and rejected a full feathering prop for what I have. Wouldn’t trade for any amount of money… |
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