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Glide at idle power vs prop stopped

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Sep 24, 2009 11:06 am Post subject: Glide at idle power vs prop stopped

I don't want to beat the corpse any more but I did say that on my next flight I would do some glide testing, which is what I did earlier today.



Glide with engine at idle power, NO FLAPS.

65 mph IAS - Descent rate approx 900 fpm

55 mph IAS - Descent rate approx 800 fpm

45 mph IAS - Descent rate approx 700 fpm



Glide with engine at idle power, 1/2 FLAPS (my normal landing config)

65 mph IAS - Descent rate approx 1,500 fpm (See why I don't need full flaps?)



Glide with prop stopped, NO FLAPS i.e. engine not running and no wind milling.

65 mph IAS - Descent rate approx 1,200 fpm



Your results may differ, but that is what my airplane does.

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Thom Riddle
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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Fri Sep 25, 2009 6:24 pm Post subject: Re: Glide at idle power vs prop stopped

Thanks for the report Thom, I'm glad to see that my MK III Xtra is not the only Kolb in the world that comes down faster with the engine off than at minimum allowed idle.   This is a good subject, it will help people to be more prepared for engine failures.



Mike

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Mon Sep 28, 2009 10:12 am Post subject: Re: Glide at idle power vs prop stopped

I have found this thread to be quite interesting, and most of it different from my experiences. I had wanted to wait until I had actually done some testing to be sure of my results before posting them.



I managed to get in a flight to the Alvord a couple of days ago, and while I was approaching my landing spot I cut back on the throttle to idle and set up 50 mph, which is my usual landing speed. I was showing somewhere between 390 and 450 FPM descent. Apparently my direction of travel was such that it was blocking my view of enough of the satellites  that I wasn't getting a steady enough reading that I didn't want to cut the engine to do the other check. After I got back, John H and the wife and I were looking at pictures that we had on our cameras. I came across a video that I did coming off the top of the Steen's a month or so back. I had cut the engine at 8000 feet and was talking about the amount of descent that the plane was making. At 50 MPH I was showing better than 700 FPM. I finally had to restart the engine so that I could make the desert. I have always known that mine will extend the glide dramatically with the engine at idle. After all, it will push the plane on asphalt with the engine at idle, it stands to reason that it will also influence the distance that the plane will advance through the air as well. If your prop will free wheel or spin in the air  as it does in an E Box for instance, then things may be different. 



I also once did a test on the Alvord concerning distance flown at 50 MPH and 40 MPH, and with my totally unscientific methods could find no appreciable difference in distance traveled. I suspected however that 50 mph was a bit better than 40.



Things may be different for you, but my Firestar II will not descend faster with a stopped prop than with the engine at idle. 

Larry

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Mon Sep 28, 2009 10:45 am Post subject: Glide at idle power vs prop stopped

I guess I hit send too soon. What I intended to say is  that my descent with a stopped prop is a lot faster than with the engine at  idle.

 Sorry!

 Larry

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