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  #1  
Old 06-02-2019, 06:16 PM
jeff beckley jeff beckley is offline
 
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Default Glide ratio

What is the glide ratio for a 7a?
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  #2  
Old 06-02-2019, 08:17 PM
tgmillso tgmillso is offline
 
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Location: Launceston, Tasmania, Australia
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Depends on your propeller choice (CS vs Fixed), altitude, airframe cleanliness, speed you descend at (maximum range or minimum descent rate) etc.
A ballpark number is 1nm for every 1,000ft of elevation loss.
Best bet is to go out and take a few measurements and put the results in your POH.
Tom
RV-7

Last edited by tgmillso : 06-03-2019 at 06:28 AM. Reason: Removed "weight" from the parameter list. That said, weight change will affect the glide ratio if the same IAS is maintained.
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  #3  
Old 06-02-2019, 08:27 PM
Kyle Boatright Kyle Boatright is offline
 
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The CAFE foundation did a thorough test of a fixed pitch RV-6A that was published in Sport aviation in 1993. I don't remember which month.

Anyway, I seem to remember the glide ratio was approximately 10:1 at 100 mph.

A fixed pitch RV-7 should be similar.
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  #4  
Old 06-02-2019, 09:02 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by tgmillso View Post
Depends on your propeller choice (CS vs Fixed), weight,
RV-7
While the no-wind speed for maximum glide distance does depend on weight, the actual no-wind glide range, if flown at best speed, is independent of weight. You just get there sooner, if you're heavy.
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  #5  
Old 06-02-2019, 11:11 PM
Ali Ali is offline
 
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Location: Chandler, AZ
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On a related question, what is the optimal speed for best glide ratio? That should be fairly similar for most RV 7s with the same engine.
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  #6  
Old 06-03-2019, 01:50 AM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Ali View Post
On a related question, what is the optimal speed for best glide ratio? That should be fairly similar for most RV 7s with the same engine.
That depends on the weight, and, in the real world (if you’re concerned with distance covered over the ground), the wind velocity.
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  #7  
Old 06-03-2019, 02:07 AM
flyvans.com flyvans.com is offline
 
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one thing to consider in my opinion - should you get into the situation that this data may become necessary, such as in an engine failure - it may be impossible to put the prop to coarse pitch as this requires oil pressure... fine pitch
with a windmilling engine results in really poor glide performance. more like 1:8 around 85-92kts...
on the other hand, should the engine seize, the prop factor is yet a completely different animal with improved glide performance expected.
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  #8  
Old 06-03-2019, 02:55 AM
Captain Avgas Captain Avgas is offline
 
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Quote:
Originally Posted by flyvans.com View Post
one thing to consider in my opinion - should you get into the situation that this data may become necessary, such as in an engine failure - it may be impossible to put the prop to coarse pitch as this requires oil pressure... fine pitch
with a windmilling engine results in really poor glide performance. more like 1:8 around 85-92kts...
on the other hand, should the engine seize, the prop factor is yet a completely different animal with improved glide performance expected.
I’d be reasonably confident that the windmilling prop after engine failure would generate sufficient oil pressure to allow the prop governor to produce a fully coarse pitch. At least it did on my C182 after I deliberately killed the engine with mixture to ICO. And as you stated if the engine fails catastrophically and seizes then the stationary prop would probably produce an even better glide.
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  #9  
Old 06-03-2019, 03:25 AM
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DeeCee 57 DeeCee 57 is offline
 
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having had the unfortunate experience of a con rod failure on the O-320 of my Falco Series III many moons ago, I experienced a very high descent rate at best glide... no control on the prop since all the oil was dumped thru holes on the top and bottom of the crankcase.

Better plan for the worst case and also train for that attitude change between engine on initial climb and engine out a split second later...
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  #10  
Old 06-03-2019, 03:27 AM
flyvans.com flyvans.com is offline
 
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Quote:
Originally Posted by Captain Avgas View Post
I’d be reasonably confident that the windmilling prop after engine failure would generate sufficient oil pressure to allow the prop governor to produce a fully coarse pitch.
agreed. that is assuming there is still oil in the system...
but consider a gradual oil pressure loss / oil leak and a shutdown short of a seizure e.g. possibly intentional to save the engine. that will still produce windmilling but without fluid to push the prop...
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