Flaps zero vs reflex

[bob888]

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.

[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 need more testing.

[BobTurner]

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.

[Deweyclawson]

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?????

[BobTurner]

Originally Posted by Deweyclawson

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.

[lr172]

Originally Posted by BobTurner

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.

[1001001]

Originally Posted by Deweyclawson

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?

[scsmith]

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.

[pierre smith]

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,

[Deweyclawson]

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.