Tomas J

Tomas J

Active Member
I've made some test of gliding the RV-4. You can see the result here...
https://dl.dropbox.com/u/3745995/WAF/gliding RV-4.kml
Open the file in Google Earth. Click on the track with right button and choose "view elevation profile"...
You see three downhills. First is flown at idle and speed 85 kt, second at idle and 80 kt.
The third is with stopped engine by full leaning. Prop windmilling (fixed pitch metall, IO320-160). No flaps in any of the examples.
As you can see the third curve is steeper. That was what I have expected, but it's intresting to see how much.
If you look between 5000 and 3000 feet, where the test is done, you find that the distance is 4,9 - 5,2 -3,6 nm. Not big difference between 80 and 85 kt at idle. But with the engine stoped it's a lot shorter. That is something to think about if the engine really stop.
I would like to make a test with the prop stoped, but maybe someone else has done that and know the difference between windmilling and stoped prop? At what speed will the prop usually stop? At the end of the gliding I got some increase in vibration. I guess that was indicating that the prop was close to stop?
 
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A wood prop will stop much quicker than a metal prop, I've heard that the metal prop RV's need a very high deck angle and low speed to get the prop stationary. You'll get a longer glide with it stopped, but you'll lose some altitude doing it. The crossover point where it makes sense depends on a lot of things, and could vary between 3000 and as much as 6000' AGL.

Be confident in your starter before you try it... Getting the blades to start windmilling with aerodynamic pressure takes speed, and a steep dive.
 
Personal experience: RV4 with fixed pitch wood prop. I lost power and the engine stopped on a high base. The prop stopped turning at exactly 100 mph. At that point I was turning final on a 5000 foot runway and felt that I was way too high and that I would likely end up off the far end of the runway. As it turned out I landed on the numbers on the correct end of the runway. I was use to the engine turning the prop on final and with a fixed pitch prop it is still pulling the airplane even at idle. The difference in stopping distance was between 4 and 5000 feet shorter then I thought it would be.
 
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What Tom said:
I always train for deadstick landings a good ways down the "landing site" knowing that if the engine had truely quit, the glide would be Much shorter.
Jim Triggs, a member of EAA326 gives a good presentation on fight safety, with special emphasis on deadstick landings.
 
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