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Best glide range speed & best min rate of descent speeds for an 8

donaziza

Well Known Member
I know all RV 8's are different, but can you guys give me pretty good ideas of best "glide range speeds", for making that good landing spot when your engine quits, and the "minimum sink rate speeds" if I'm lucky enough to make "that" spot. Constant speed Whirlwind prop, ECI IO 180 Hp engine? Say about 1500 Lbs. total. Of course winds play a factor. Yeah, I can match my GPS ground speed against my TAS, but that probably will be quite different close to the ground when its too late to change it.:( I know, I know, look for the direction the smoke is blowing. I hardly ever see smoke on the ground.:eek: Look for the direction the trees are blowing. Who can see that from altitude, and by the time you "are" low enough to see it, well its too late "then".:eek:

I "do" have a "best glide range ring" on my Garmin Pilot which helps, but still, I'd really like to know those 2 speeds for an 8 if you guys can.

And Oh yeah, I'm familiar with one's "intended" landing spot going up or down in the front of your canopy, to try to decide if you can make a spot or not---but best glide speed would sure help---with that
 
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Don, when I ran the numbers for my -8 I got a Vy of 97kts IAS at MTOW. Min weight had about 96kts - very little difference. The curve is very flat between 90 and 110 so I use 100kts to keep it simple in my lizard brain when the time comes that I need this info. In order to further burn it in, I trim for 100 on most descents to the pattern. Again, to create a habit.

I've set my glide ratio in the ipad to 8:1 to give myself a little margin, since I don't know what the impact of a windmilling prop on a dead engine will be. I guess reality is probably closer to 9:1.

Nigel Speedy has an excellent Kitplanes article on this topic here:

https://www.kitplanes.com/sawtooth-climb-performance/

His numbers are slightly different from mine, but still in the ballpark.
 
My non-scientific personal experience practicing engine out procedures with feathered prop, is the glide path in the standard POH and Foreflight is optimistic. Maintaining non-stalled AoA is not get greedy on glide path and I approach it like a helicopter engine out procedure - Autorotation and descend straight down. Obviously depending on your altitude, for me, anything under 5000' AGL is finding the best spot directly below in a gradual spiral descent.

I like rv8ch's trim for 100kts. With engine out that's a pretty fast vertical speed drop.
 
Clearly there are lots of variables: prop fine pitch, prop coarse pitch (if the governor works at that rpm and there’s oil pressure), prop stopped; weight; wind.
Don’t disregard the wind. Best glide speed over the ground will be higher into the wind. Easy to verify on a day when you’ve got a 20 kt headwind on final.
 
Fast..

I lost the engine in my 8 a few years back at 6,500 feet, about 6,000 agl. I stopped the prop and was on yhe ground in slightly over 5 minutes. Hartzell ACS wide bladed prop. I used 90ish KIAS and the best I could doo was about 1,100 fpm.
No harm, no foul, no damage. A truck ride home for me and the plane.

Just a reminder. Never, never, NEVER!,! try to stretch a glide. Of course, we all know that, but think about it if it ever happens to you.
 
Just a reminder. Never, never, NEVER!,! try to stretch a glide. Of course, we all know that, but think about it if it ever happens to you.

This is great advice! You don’t happen to have a brief to share with us? Oh S#*t to getting out of the plane. Great learning opportunity for everyone.
 
Below is some data that Nigel Speedy published awhile ago for his RV-8. Note that the plot is in terms of TAS, the throttle is at idle (not shut down), and the prop is at low RPM. Some may be familiar with Nigel's work.

As others have said, your airplane/engine/prop/power configuration may lead to different results.

i-Gbrv3xR.png
 
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