What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Flaps -3 degree reflex

Gahannaflyer

Active Member
I finished my transition training in the factory 14A. (N214VA). There is a -3 degree setting on the flaps. I don't recall this setting in the rigging instructions. I have to assume that a digital angle gauge is the best way to achieve this setting. Has anyone else rigged their flaps this way? This setting is used in normal cruise. Did I miss something somewhere? I think I heard of a couple others making this adjustment.
 
Assuming the 14's flaps are the same or similar to the 10's, full up is the -3 deg reflex setting.
 
When an RV-14 (and RV-10) is built and rigged per plans, the ailerons and flaps (when fully retracted) are in a neg. 3 degree reflex position.

To obtain a zero setting you just lower the flaps 3 degrees from the fully retracted position and then label that as the zero setting.

We use that position for no flap take-offs and climb mode, and only fully retract the flaps to neg. 3 for level cruise flight on the RV-14 and RV-10.
 
Steve,

When you get home, I can show you how things are rigged on my RV-10.

So when does it get out of the paint shop?

bob
 
Hello,

What's the effect of the Reflex position on stall speed and/or landing distance?

I'm wondering how you backup the flap actuator in case of failure while in Reflex mode.

Thanks.
 
Hello,

What's the effect of the Reflex position on stall speed and/or landing distance?

I'm wondering how you backup the flap actuator in case of failure while in Reflex mode.

Thanks.

I can't give you detailed specifics but I have made landings in an RV-10 and RV-14 with flaps in reflex and the influence is no more than occurs with all of the other RV's with the flaps fully retracted, so no special procedure/workaround is required.

With no flaps deployed the stall angle of attack is higher. Because of that you wont like rotate to anywhere near stall angle of attack during the flair and with the higher stall speed of not using any flaps, the landing will be longer but not so much that it should be an issue (RV's only require a small portion of the runway that is available at most airports).
 
I can't give you detailed specifics but I have made landings in an RV-10 and RV-14 with flaps in reflex and the influence is no more than occurs with all of the other RV's with the flaps fully retracted, so no special procedure/workaround is required.

With no flaps deployed the stall angle of attack is higher. Because of that you wont like rotate to anywhere near stall angle of attack during the flair and with the higher stall speed of not using any flaps, the landing will be longer but not so much that it should be an issue (RV's only require a small portion of the runway that is available at most airports).

I know it is an old threat, but I repeatedly stumble over it when searching datas to the Flaps rigging. And as always I highly appreciate Scott‘s inputs. I completely understand and of course I don‘t doubt it, but is there any official Van‘s source for that?
 
Reflex Flaps

The negative flap setting was used by Steve Wittman before the first RV was built. My limited understanding is that the reflex can be used to reduce trim drag.
I think the high performance gliders use it also. Been around a long time.
 
The negative flap setting was used by Steve Wittman before the first RV was built. My limited understanding is that the reflex can be used to reduce trim drag.
I think the high performance gliders use it also. Been around a long time.

The benefit of the reflex flap during cruise comes from keeping the airfoil in the middle of its "drag bucket". The RV-10 and -14 airfoil does achieve some laminar flow, so keeping it at the best angle of attack pays off. I could have designed the airfoil to have the reflex built in, and call that zero flap, and then recommend a +3 flap setting for TO and climb. Same difference.

And yes, all but "Standard Class" gliders routinely use camber-controlling full-span flaps that go negative, by as much as -10 degrees or so. Over the wide speed range that gliders operate at, keeping the camber optimum for each speed is extremely beneficial, because of the laminar-flow airfoil.

It is true that the reflex would ALSO reduce the section pitching moment a little, so it would reduce the tail download at cruise, with a small additional benefit from that. But the airfoil already has a pretty small section pitching moment - not quite zero like the RV3,4,6,7,8 airfoil, but close.
 
Sooooo...... I'll admit that I just chalked up -3 to best position and have been doing all my takeoffs that way; the performance is awesome didn't know I was missing anything. Something to check out now. But with the Garmin flap controller will it operate the flaps from 0 to -3 if the speed is above the flap switch cutout speed?
 
I tested power-off stalls in my RV-14 with flaps in -3, 0, and full positions. There was no discernable difference in the stall speed or behavior between -3 and 0 flaps.
 
Will leaving flaps in the 0 position for the entire climb to cruise altitude result in a faster climb?
 
Will leaving flaps in the 0 position for the entire climb to cruise altitude result in a faster climb?

Yes, but perhaps not measurably so. Good mixture management will probably have more measurable affect on total time to climb than the small change in airfoil drag.
 
Flaps

Anyone have any data in cruise for -3 and 0 flap position? I called my -3, zero, and take-off with one notch which is about 15 degrees.
 
Anyone have any data in cruise for -3 and 0 flap position? I called my -3, zero, and take-off with one notch which is about 15 degrees.

At about 17,000’ density altitude, mid weight (2+bags), my -10 seemed maybe a knot or two faster with flaps 0 (in trail) than flaps full up (-3). The air was just a bit bumpy for good data, but in trail was definitely not slower. Steve confirmed that high and/or heavy enough this was expected behavior.
Again following Steve’s advice - coupled with Vans removing speed restrictions on flaps 0 (in trail) - I now routinely take off and climb with flaps in trail.
 
At about 17,000’ density altitude, mid weight (2+bags), my -10 seemed maybe a knot or two faster with flaps 0 (in trail) than flaps full up (-3). The air was just a bit bumpy for good data, but in trail was definitely not slower. Steve confirmed that high and/or heavy enough this was expected behavior.
Again following Steve’s advice - coupled with Vans removing speed restrictions on flaps 0 (in trail) - I now routinely take off and climb with flaps in trail.

I have tried altitudes from 3 - 15k and various loading and cg conditions from light to max gross and I gain 1-3 knots in trail every time. I have NEVER seen it fly faster in reflex. Does anyone else have experience with reflex providing a speed gain in cruise?
 
I'm shocked people find the reflex position slower than 0 degree flaps.

I've gotten to cruise and left the flap at 0 degrees and let the airspeed stabilize. When bringing the flap up to reflex, the acceleration from removing the drag is unmistakable.

I'll post some data after my next flight rather than quote numbers from memory.

If rigged correctly, your flaps are always in reflex in level cruise. Are people suggesting that slows you down?
 
If rigged correctly, your flaps are always in reflex in level cruise. Are people suggesting that slows you down?

As I said, Steve, the airfoil designer, mentioned here on VAF that high enough (high teens?) and/or heavy enough the -10 wing is smaller than ideal, and you may see a small increase in airspeed with flaps in trail. For similar reasons he thinks best rate of climb may be slightly higher with flaps in trail.
 
...and

This is the case with my -10. Reflex gives very little performance gain, if any, on my -10. I have tested it at gross weight and 12,500', and see no significant difference.

I tend to fly with flaps in trail...
 
I'm shocked people find the reflex position slower than 0 degree flaps.

I've gotten to cruise and left the flap at 0 degrees and let the airspeed stabilize. When bringing the flap up to reflex, the acceleration from removing the drag is unmistakable.

I'll post some data after my next flight rather than quote numbers from memory.

If rigged correctly, your flaps are always in reflex in level cruise. Are people suggesting that slows you down?

A couple of times, I have left the flaps in trail after climb. On each occassion, I picked up a couple of knots or more after noticing it and going to reflex. I have not yet flown higher than 14.5K.

Steve has mentioned that this wing gets some laminar flow, but many different factors, like paint lines, can spoil some of that. Not surprising that different folks get different results. I suspect that rigging variances can also create differences in noted performance.

Larry
 
Last edited:
This is the case with my -10. Reflex gives very little performance gain, if any, on my -10. I have tested it at gross weight and 12,500', and see no significant difference.

I tend to fly with flaps in trail...

There is a crossover point that I assume is tied to IAS, aircraft weight, and CG. If you’re blazing along at 170 knots indicated, reflex is your friend. If you’re showing 125 knots, flaps in trail is better. Somewhere in between is a crossover point.
 
3 degrees doesn't seem like much reflex. In the Lancair community, 7 degrees reflex is the typical negative flap setting in cruise. I can say negative 7 degrees in my lancair definitely is faster than 0 degrees flaps. Has anyone experimented with more than 3 degrees in a RV? I presume it has been tried and 3 degrees was found to be optimal.
 
3 degrees doesn't seem like much reflex. In the Lancair community, 7 degrees reflex is the typical negative flap setting in cruise. I can say negative 7 degrees in my lancair definitely is faster than 0 degrees flaps. Has anyone experimented with more than 3 degrees in a RV? I presume it has been tried and 3 degrees was found to be optimal.

I am pretty sure a reflex position is specific to the airfoil design.
Just because one wing is best with -7deg, does not mean it would be on another.

Just like some airfoils do not benefit from any reflex at all.
 
3 degrees doesn't seem like much reflex. In the Lancair community, 7 degrees reflex is the typical negative flap setting in cruise. I can say negative 7 degrees in my lancair definitely is faster than 0 degrees flaps. Has anyone experimented with more than 3 degrees in a RV? I presume it has been tried and 3 degrees was found to be optimal.

Just a caution that such experimenting may push components, like the flap actuating rod, beyond their design limits. As a practical matter, such testing would involve a lot of work - in the RV10, the flaps are in physical contact with the aft spar at -3 deg. To go higher you’d need to move them further aft, which makes them more Fowler-like at zero (in trail), etc.
 
There is a crossover point that I assume is tied to IAS, aircraft weight, and CG.

I'm sure this could be true. I'm a flatlander so I pretty much fly at 7 to 10k feet in cruise, rarely higher. I also built the 14 to go fast, so 172kt TAS at max gross is normal on a trip.

I could see lower and much slower, it might not make much difference. I've never been above 12000, so no experience there.
 
Back
Top