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  #11  
Old 02-06-2018, 04:31 PM
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donaziza donaziza is offline
 
Join Date: Jun 2007
Location: Atlanta
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Quote:
Originally Posted by JohnInReno View Post
All of the Cafe Foundation reports are available here:

http://cafe.foundation/v2/research_aprs.php
Thanx Much John,

This was really helpful.
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  #12  
Old 02-07-2018, 06:11 AM
sailvi767 sailvi767 is offline
 
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Location: Charlotte NC
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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
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  #13  
Old 02-07-2018, 08:59 AM
Brent Brent is offline
 
Join Date: Jan 2013
Location: Hanover, Pa
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Default 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.
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  #14  
Old 02-07-2018, 10:52 AM
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dlloyd3 dlloyd3 is offline
 
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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.
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  #15  
Old 02-07-2018, 12:23 PM
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scottmillhouse scottmillhouse is offline
 
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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.
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  #16  
Old 02-07-2018, 12:51 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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I agree with George: wind is important. Not only does it affect glide range, it also changes optimum glide speed. Some (all?) modern efisís 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.
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  #17  
Old 02-07-2018, 02:59 PM
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tomkk tomkk is offline
 
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Location: Port Orange, Fl
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Default 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.
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  #18  
Old 02-07-2018, 05:45 PM
Brent Brent is offline
 
Join Date: Jan 2013
Location: Hanover, Pa
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Default Glide

Insightful comments by Scot, Bob and Tom. Scotís 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 wonít 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.
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  #19  
Old 02-07-2018, 06:09 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Brent View Post
Obviously we wonít have the glide range into the wind,
.
Not sure what your efis does, but the grt will show you exactly what the glide range is, given the current calculated wind, rate of descent, ground speed.
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  #20  
Old 02-07-2018, 07:59 PM
alexe alexe is offline
 
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And so does the Skyview.
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