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  #1  
Old 11-24-2020, 09:01 AM
bob888 bob888 is offline
 
Join Date: Jul 2012
Location: Fresno, CA
Posts: 293
Default Flaps zero vs reflex

Does anyone have data on performance differences between flaps zero and -3 degrees...esp takeoff performance? I can't subjectively appreciate any difference and it would be simpler to use just 3 flap settings...-3 deg, 15 deg, 30 deg and forget about 0 deg.
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  #2  
Old 11-24-2020, 11:58 AM
rdrcrmatt rdrcrmatt is offline
 
Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 312
Default

I get airborne earlier with flaps 0°.

Also, noticed even at low DA I lose 1-2 kts when I go flaps -3°

I need more testing.
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  #3  
Old 11-24-2020, 02:27 PM
BobTurner BobTurner is online now
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,286
Default

I get a slightly shorter ground roll at flaps zero (in trail). And, at sufficiently high density altitude, slightly faster cruise at flaps zero. I wouldn’t remove the option.
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  #4  
Old 11-25-2020, 09:10 AM
Deweyclawson Deweyclawson is offline
 
Join Date: Jun 2014
Location: Enon Valley
Posts: 201
Default flaps 0

With 150 hrs in my RV10, I still don't understand the flaps.
1-2 kts faster with flaps 0
shorter ground roll flaps 0
What good is the -3 position?????
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F100, A7D, A10, F16,
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  #5  
Old 11-25-2020, 12:26 PM
BobTurner BobTurner is online now
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,286
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Quote:
Originally Posted by Deweyclawson View Post
With 150 hrs in my RV10, I still don't understand the flaps.
1-2 kts faster with flaps 0
....
What good is the -3 position?????
Are you certain about this? I see a speed gain at flaps zero only with DA above 16000'. Lower, flaps -3 is faster.
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  #6  
Old 11-25-2020, 01:26 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,865
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Quote:
Originally Posted by BobTurner View Post
Are you certain about this? I see a speed gain at flaps zero only with DA above 16000'. Lower, flaps -3 is faster.
I believe most of us see the same.
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  #7  
Old 11-25-2020, 06:07 PM
1001001's Avatar
1001001 1001001 is offline
 
Join Date: Dec 2014
Location: Just Minutes from KBVI!
Posts: 1,128
Default

Quote:
Originally Posted by Deweyclawson View Post
With 150 hrs in my RV10, I still don't understand the flaps.
1-2 kts faster with flaps 0
shorter ground roll flaps 0
What good is the -3 position?????
Hey Dewey, maybe we should check your flap angles and see what they actually are; could the rigging be off?
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  #8  
Old 11-25-2020, 08:28 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,801
Default

It is interesting to read that there is some variation in builder experience with the cruise performance at different flap settings.


The RV-10 airfoil was designed to achieve a modest amount of laminar flow, and part of the expected benefit of the -3 flap setting at high IAS is that it increases the angle of attack a little to keep the airfoil well positioned in its modest laminar drag bucket.

If you have paint stripes along your leading edge, or less-smooth-than-average rivets on the wing forward of the spar - especially on the spanwise skin stiffeners, or anything else that might cause early transition, like just not washing the bugs off, then you may have early boundary layer transition and are not getting as much laminar flow - so you would not see the benefit of the reflexed flap setting (-3).

At very high altitudes, the IAS is low enough that zero flap is probably better. Also when flying very heavy, the altitude where the performance crosses over will be lower.
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Last edited by scsmith : 11-25-2020 at 08:32 PM.
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  #9  
Old 11-26-2020, 12:45 AM
pierre smith's Avatar
pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,892
Default Thanks...

Thanks, Steve, for the clear explanation of the ‘reflex’ system. I’ve had my -10 for ten years and never run at zero degrees. Heavily loaded, on the way to the Bahamas, 4 aboard, baggage and full fuel, we still got 190 MPH, Plus, at 7500”.

Regards,
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  #10  
Old 11-26-2020, 05:32 AM
Deweyclawson Deweyclawson is offline
 
Join Date: Jun 2014
Location: Enon Valley
Posts: 201
Default confused

Sorry. I did not mean to cause some confusion. I said this:

"With 150 hrs in my RV10, I still don't understand the flaps.
1-2 kts faster with flaps 0
shorter ground roll flaps 0
What good is the -3 position?????"

based on this:

BobTurner "... slightly faster cruise at flaps zero."
rdrcrmatt "... I get airborne earlier with flaps 0°. Also, noticed even at low DA I lose 1-2 kts when I go flaps -3°"

I have not done any flt testing to to verify any of this. While my plane is very well built, the POH is somewhat lacking in performance data. It is on my lilst.
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Super Sabre Society
2012 RV10; 1947 Cessna 140, in progress
2021 dues exempt but paid anyhow
F100, A7D, A10, F16,
Fokker, Boeing, McDonnell-Douglas
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