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  #11  
Old 05-31-2017, 07:01 AM
BillL BillL is offline
 
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Quote:
Originally Posted by Robert Anglin View Post
. . . Also try to get your numbers with the aircraft as close to gross as you can. This will give you a little extra bonus distance if you have to glide at a lower weight. . . . Yours, R.E.A. III 80888
Hi Bob, I was curious about this a found this:

"Variations in aircraft weight do not affect the glide angle provided that the correct airspeed is flown. Since it is the lift over drag (L/D) ratio that determines the gliding range, weight will not affect it. The glide ratio is based only on the relationship of the aerodynamic forces acting on the aircraft. The only effect weight has is to vary the time the aircraft will glide for. The heavier the aircraft is, the higher the airspeed must be to obtain the same glide ratio. If two aircraft have the same L/D ratio but different weights and start a glide from the same altitude, the heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time. Both aircraft will cover the same distance but the lighter one will take a longer time to do so."
Reference: http://www.skybrary.aero/index.php/Glide_Performance

As a practical matter, it would appear either AoA or known glide speeds vs weight should be documented for ones serial number - right?
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  #12  
Old 05-31-2017, 08:14 AM
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N804RV N804RV is offline
 
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In "Engine Out Survival Tactics", Nate Jaros quotes a glide ratio of 8:1 for an RV-8. That makes that 1.3 (k)mi per 1,000' a pretty good rule of thumb.

He also reaffirms that glide ratio is not affected by weight. Good book!
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  #13  
Old 05-31-2017, 08:18 AM
pvalovich pvalovich is offline
 
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Location: Ridgecrest, CA
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Default -8A Glide Ratio

I've done several semi-accurate glide tests (didn't shut the motor down) but had prop full low rpm, throttle at idle, 90 kts. Wind will have a significant effect.

I came up with an optimistic 1.5 miles per 1000 ft.

Procedures:
1) Get over the "What the **** just happened?" factor as soon as possible.
2) Turn toward intended landing spot while slowing.
3) Prop full decrease.
4) Trim for 90 kts.
5) Figure out the winds and recalculate / reevaluate decision.
6) Troubleshoot.
7) Recalculate/Reevaluate
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  #14  
Old 05-31-2017, 09:18 AM
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nigelspeedy nigelspeedy is offline
 
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Default Here is what mine does

Here is the glide performance for my RV-8: Flaps up, Throttle idle, Prop low RPM.
Nice thing is that the top of the curve is pretty flat from 90 - 110 KTAS so if you are a little fast or slow you don't get penalized that much. I tell ForeFlight that I glide at 100 knots with a 1000 fpm descent rate and this is a little on the conservative side. When practicing I prefer to fly a little faster than min sink, this way if I slow down my situation gets better.
One thing to remember if you are trying to calculate a glide ratio is that the forward speed has to be in units of True airspeed and you have to correct the vertical speed to tapeline (i.e. take into account the change in pressure altitude caused by non standard temperature).
[IMG][/IMG]

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  #15  
Old 05-31-2017, 09:37 AM
brad walton brad walton is offline
 
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When sailplanes race, they often carry water so that they go down their glide slope faster. They can jettison the water if the lift gets weak or cool off the crowd at the finish line.
If you calculate your glide speed with the engine running, even at idle, you will get a false glide ratio and sink rate. A windmilling prop causes significant drag that a prop at idle power will not simulate. So if you get 11:1 glide ratio at idle, you are likely to get no better than 8 or 9:1 in a true engine out windmilling situation.
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  #16  
Old 05-31-2017, 10:26 AM
flyinga flyinga is offline
 
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Don't forget bank angle. If you have to do that 180 to get to a good landing spot and have to use a significant bank angle, best glide speed will increase and rate of decent will increase.
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  #17  
Old 05-31-2017, 10:34 AM
dcurrier dcurrier is offline
 
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Question

Quote:
Originally Posted by brad walton View Post
When sailplanes race, they often carry water so that they go down their glide slope faster. They can jettison the water if the lift gets weak or cool off the crowd at the finish line.
If you calculate your glide speed with the engine running, even at idle, you will get a false glide ratio and sink rate. A windmilling prop causes significant drag that a prop at idle power will not simulate. So if you get 11:1 glide ratio at idle, you are likely to get no better than 8 or 9:1 in a true engine out windmilling situation.
So - novice pilot/early builder here. Taking a stab at your logic... For me, I would want to measure the actual performance in the specific airplane I am documenting since no two RV's are the same. However, I don't know anyone crazy enough to actually turn the engine off in flight just to measure true power out glide performance.

So, my current plan when I finally make it to Phase 1 is to take my RV8 up fairly high (4,000' - 5,000') and cut to idle / low RPM and measure the distance and time to descend 1,000'. I would do this several times, in several different directions (noting the wind speed and direction each time). Then when back on the ground, I will average the figures together and subtract 10%-15% to account for actual engine out with windmilling prop. That's the number I would use for the POH.

Does that sound like a solid plan?

Thanks,
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  #18  
Old 05-31-2017, 11:08 AM
flyinga flyinga is offline
 
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Damien,

I'd have the prop in high rpm for the tests; more conservative. If you have an engine failure with low oil pressure the prop will go to low pitch (high rpm).
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  #19  
Old 05-31-2017, 11:17 AM
spatsch spatsch is offline
 
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Mine is 1:10 with an IO-360 fixed pitch Sensenich prop with the engine off at 90mph. Prop doesn't stop windmilling unless I get into a stall (and loose a lot of altitude doing so) so I wouldn't try to get my prop to stop if the engine quit on me and just take the 1:10 and be happy with it.

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  #20  
Old 05-31-2017, 12:19 PM
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AX-O AX-O is offline
 
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Quote:
Originally Posted by BobTurner View Post
The GRT EFIS units look at your real, current rate of descent and your actual ground speed (so wind is taken care of) and show how far you can go in your current direction. Tells you right away if you can make an airport or other landing site, or not.
What function is that? Where do you turn it on and off?
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