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Glide ratio

Does anyone know the glide ratio for our planes?

A while back I watched a EweTube video (they're a bunch of sheep, but that's another story) where someone on this forum did a long, dead-stick, prop-stopped glide to landing. The claim was made that a -12 can do 12:1. That seems optimistic, but may be true.

Jerre
 
RV9A Cafe

The Cafe report for the RV9A shows 12 to 1 at 1738lbs and 95mph.

Edit: Idle power coarse pitch
 
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Other airplanes for reference

12:1 sounds reasonable to me with the prop stopped; probably closer 10:1 if the prop is still spinning (due to the extra drag).

For reference, my Baron B58 with feathered props is 10.5:1 and the B747-200 is 15:1.
 
I recently had an engine fuel delivery problem. I shut down and stopped the prop and got over 3 minutes of glider time. I held 60 kts, and averaged 582 fpm descent by Dynon. Solo with full fuel. Do the math and it is 10.43 for my plane for those conditions. Only a final turn from a 45 for final. The Dynon pretty much had the glide distance nailed.
 
Do the test cards for YOUR plane then make a POH for YOUR airplane. You will learn a bunch. I?m surprised this isn?t required to finalize the Phase 1 period.

Bevan.
 
One thing to consider that I rarely see mentioned is that winds are critical to actual glide performance. This is especially true in a aircraft with a low best glide speed like a RV. A modern EFIS is a great tool since you have a wind readout. Depending on winds the airport 15 miles downwind may be a much better choice than the airport 10 miles upwind when you hit the nearest button after the motor decides to take a break.
G
 
Glide distance

In a different life, I had experience in engine out operations both in military jets and civilian prop aircraft. Those CAFE results are very interesting, but rather than discuss glide ratios, it might be easier in the heat of the moment to visualize it all as miles/1000ft. The only time that this knowledge is particularly useful of course, is when the engine quits. This is when the adrenalin may be a little higher than usual, so it is best to have an easy number to aim at. What we are looking for then, is the best lift over drag speed, theoretically for a specific weight, but from a practical standpoint figure out a good glide speed which will be about VY or a touch less, and STOP the prop. The CAFE charts mention TAS but what we are interested in is IAS. It is always better to err on the plus side of speed rather than being slow, because induced drag builds up very quickly. Many folks have got themselves in a pickle by trying to STRETCH the glide. This cannot work!

As a matter of interest since someone mentioned it, all of the conventional swept wing jets that I tested have a glide ratio of a touch under 3 miles/1000 ft. At about 230kts. Strange but true....ish. That held true from the 707 and others, to single seat fighters.
 
Brent is correct. In the heat of the moment, an engine failure, you need to be able to calculate in a few seconds: how far am I above the ground, how far am I from and airport. Close enough, go there. Not close enough, pick a spot. Been there, done that. Stretching a glide will not work.
 
As others have mentioned it is good to do some testing on your plane and not use the CAFE report numbers as representative. For me I now know that on the 12 with the prop stopped my glide ratio is about 10.43:1 or about 2 miles per 1000' at 60 knots.

On my old RV-9A built with the exact same configuration as Vans with the 0-320 and CS prop, I got greatly different figures than the 12:1 glide they showed, although all other performance was identical. My 9 with throttle to full idle could not hold any prop pitch change so the prop went flat. With CS pulled back to coarse I actually got a worse glide (assumed because the governor was trying to keep the pitch coarse and modulating it caused more drag.) Actual testing showed the best speed to be 80 mph giving only 1.35 miles per 1000' or a 7.2: 1 glide ratio. Perhaps with higher engine RPMs the governor could hold a pitch but then you would be getting some engine thrust. My real world testing vastly altered my airport pattern entry. I always flew a very tight pattern. Actual pattern testing found if all power was pulled mid-field and you turned immediately you could just make the runway and land. Absolutely no time or height for a stabilized approach and you had to use much steeper than normal turns. That testing kept me at about a 1/2 mile airport pattern.
 
I agree with George: wind is important. Not only does it affect glide range, it also changes optimum glide speed. Some (all?) modern efis?s will do the calculation for you: e.g., on my GRT Hx, if I head for an airport, dial in its altitude, a green arc appears showing my glide range. I can try a faster (or slower) airspeed and see if the arc moves further away or not. Or head for a different airport and repeat. Or find a field within range.
 
EFIS glide performance

The Dynon Glide Ring can help with info at a glance once properly set up. I assume Garmin has something similar. I don't use it myself but I think I read ForeFlight has a similar function that might be more sophisticated.
 
Glide

Insightful comments by Scot, Bob and Tom. Scot?s experience illustrates the importance of stopping the prop. It was always claimed that we should go for the minimum sink rate downwind and best glide speed any other time. I always had doubts about the logic of this, but now we have the EFIS and its glide range ring to play with. Obviously we won?t have the glide range into the wind, but with the glide range ring we can actually check it in the same conditions at various speeds ...... interesting times! There is a fascinating App... CloudAhoy ...which might also be an interesting addition to the EFIS for playing around with such questions.
 
And don't forget, that at least on the Skyview, the size of the glide arc is influenced by the aircraft's GPS-determined height above the ground directly under the aircraft. This is important to know if you are flying over terrain with varying heights.
 
I don't have a wind vector arrow showing wind direction, (I'm using Garmin Pilot), BUT, the other day, I noticed the glide ring compressed on one side, and very oblong on the other end. Not hard to figure which direction the winds were coming from. (I was dealing with about 22 Kt winds, so the glide ring was really compressed from the northwest----and elongated to the southeast.)

Poor mans wind direction arrow.:cool:
 
Glide

Hi Carl, Quite aside from the subject of glide capability as shown considering the terrain, that is a most impressive display. I will be using GRT HXr EFIS and Skydemon. I hope that I can get as much information displayed from Skydemon as you have there. I hope to have my RV 8 flying this year.....(if I can ever finished installing the baffles!). I may have to check Foreflight. Skydemon is good because it is world wide, and my poor old brain only has to cope with one system, but what a beautiful system you have!
 
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