Glide planning for Bahammas Trip

[Dan OBrien]

One more and I'll give it a break. Your fine pitch glide ratio in the IV is 44% lower than your coarse pitch glide ratio. My fine pitch ratio in the ES is 38% lower than the coarse pitch ratio. It makes sense that the ES ratio would fall by less in percentage terms because we are already more draggy due to draging the fixed gear around. Lovely how basic physics works.

Anyway, the main point that folks need to understand is that if they lose oil pressure and can't stop the prop, they're not gonna glide nearly as far. For my Bahamas trip, if I think I can glide to an airport from FL175 from anywhere along the trip, I need to confirm that that's true at the lower glide ratio. I think I'll follow George's advice and rent a raft.

Some folks (e.g., Bill H suggested this to me) have conjectured that Lancair's will float, for a long time at least. When I think about the size of the ES wings and the amount of prepreg in them storing all those little air pockets, that idea sure makes sense. Unfortunately, it's not something we test for .

[George Wehrung]

Dan you’ve definitely spurred a great discussion and I know others are thinking about what they should or could do.

I always do the raft even though it’s a pain. Keep it in the back seat near the door and resist the temptation to put stuff on top of it. Well truth be told our little dogs ride on top of it…


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[Dan OBrien]

Interesting Dan. In my ES at 95 knots-ish, weight dependent I get 500 fpm.

George, you're making me wanna go test glide other airspeeds!! Is 95 better? Could differ between planes, but: A velocity of 95 kts at a 500 fpm decent is a glide ratio of

19.2 = [(95 nm/hr) x (1hr / 60 min) / (6076 ft / nm)] / 500 ft/min !!

Our airplanes may be different, but that motivates me to want to test my glide at 95 kts next chance I get. Maybe your 500 ft/min descent is a bit anectdotal? My 691 ft/min at 100 was on a pretty windy day and is an average over about 2 minutes on one of those semi-raucous turbulent days in winter moving to spring in Redmond. Speed with within 4 kts of 100, but... So I don't completely trust it. Wanna find a good calm day to test it again, maybe this time at multiple airspeeds!

[George Wehrung]

What I did was a series of different days gliding down from 10 or 12000 feet to my airport and then get positioned for the ELP and land it. I would try different airspeeds out


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[Robert Pastusek]

Dan
First of all, thanks for checking my math on descent rate versus altitude lost. I agree w your figures.
I encourage every Lancair owner to evaluate the best glide performance in their airplane—with the prop at min pitch/max RPM. and again at max pitch/min RPM. It’s a good exercise and low risk—as long as you stick with the best glide speed. Testing at lower glide speeds and trying to stop the prop from windmilling significantly increase the risk of an inadvertent stall/spin.
I did evaluate glide speed during flight testing in 2008. The best glide speed for my airplane, at gross weight (3600#) and aft CG limit, was 118-119 KIAS, decreasing to about 110 KIAS at 3000# and mid-range CG. I was new to flying it—and might do better today??- but I found it difficult to consistently fly the airplane at 110 KIAS while doing even minimal other tasks. At 120 KIAS

[Robert Pastusek]

I found it easy to trim to and maintain a glide at 120 KIAS while recording data, etc, and the difference in glide range to be insignificant. Further, it took significant time and nose lowering to recover airspeed if it dropped below 110. So I’ve elected to stick with the widely-used 120 KIAS as best glide speed for my IV-P. It glides an impressive distance in coarse pitch from the high teens where I fly these days under Basic Med. Fortunately, I’ve not needed to use it…
Bob Pastusek

[Robert Pastusek]

I found it easy to trim to and maintain a glide at 120 KIAS while recording data, etc, and the difference in glide range to be insignificant. Further, it took significant time and nose lowering to recover airspeed if it dropped below 110. So I’ve elected to stick with the widely-used 120 KIAS as best glide speed for my IV-P. It glides an impressive distance in coarse pitch from the high teens where I fly these days under Basic Med. Fortunately, I’ve not needed to use it…
Bob Pastusek