[Rhouse9044]

I read an article in Sport Aviation about RV10's that mentions a speed benefit from the flaps being reflexed 3 degrees in the cruise position. A thread search turned up discussion of this in relation to both the 10 and the short wing RV's, but nothing relating to the RV9. Has anyone tried this on a 9, or would any of the more aerodynamically enlightened speculate on the effects? A couple of knots for a minor adjustment and a little sheet metal work sounds attractive, even if it would mean giving up the same amount of flaps down extension. Thanks for any replies.
Bob House RV9A N462BD

 

[rvbuilder2002]

I read an article in Sport Aviation about RV10's that mentions a speed benefit from the flaps being reflexed 3 degrees in the cruise position. A thread search turned up discussion of this in relation to both the 10 and the short wing RV's, but nothing relating to the RV9. Has anyone tried this on a 9, or would any of the more aerodynamically enlightened speculate on the effects? A couple of knots for a minor adjustment and a little sheet metal work sounds attractive, even if it would mean giving up the same amount of flaps down extension. Thanks for any replies.

The RV-10 airfoil was specifically designed for a slight drag reduction when flying with reflexed flaps and ailerons at high speed.
The Ailerons are fixed in the reflexed position, the flaps can be raised beyond the neutral position (used for climb, etc), to the reflexed position.
The RV-9 airfoil was not designed for any benefit to be gained by reflexing the flaps.
This is not something that works on all airfoils. On some it might even be a bad thing to do.

 

[Vlad]

I tried a touch of flaps on my long trip to TN @10.5 for an hour speed 130Kts. Thought if modern bombers could do it after the raid why not RV9? Didn't notice any difference.

 

[pierre smith]

Try it

The -10 has an exceptionally thick wing in order to have the strength for the 33' wing to be cantilevered, according to Van. That said, it has an overabundance of lift at 200 MPH, so the reflexing helps with a better in-flight attitude.

Try it on the -9 if it doesn't take too much effort. Remember that the -10's ailerons are also reflexed, always. The -10's rigging says to put the flaps in the 3 deg up position and then align the ailerons with them....vice versa on the other models.

Best,

 

[JSOliveira]

RV9 Roncz (sp) Airfoil

The airfoil on the 9 is also thick. The Airfoil also has considerable reflex in it for the upper surface. The RV10 does also, but it does not seem to be proportionally as great. That may be one reason reflexing the flaps may not have much effect.

 

[scsmith]

It may help

HI all,

I designed the RV-10 airfoil specifically to use the -3 degree flap setting at cruise. The two main benefits are that you keep the fuselage a bit more level, less nose down, and you create a pressure distribution that is a bit more favorable to laminar flow on the lower surface.

We don't get much laminar flow on our riveted aluminum wings with skin seams at the spar, but we do get some.

The more-level fuselage attitude also reduces the trim drag slightly, as well as a slight reduction in fuselage drag.

Evaluating the Roncz airfoil on the RV-9, it would achieve a lot of laminar flow on the bottom if the wing were smooth enough, and I think it has enough reflex designed into it that it already essentially has the effect of slight negative flap built right into it. But that doesn't mean that its incidence on the fuselage is also correct to capture that benefit -- I don't know.

So, I would suggest giving it a try. See if you can rig both the flaps and ailerons to about -2 or -3. Report back what you find. The difference may be very small, so try to use some consistent test procedure if you can -- lots of threads here on the forum about that.

You may want to do the take-off with a small amount of positive flap, although I doubt you would notice any adverse affect of the slight negative flap -- just a slightly longer ground roll and slightly more nose high in climb.

 

[terrye]

RV-10 Custom Airfoil

I knew the RV-9(A) airfoil was a Roncz custom design, and I knew the RV-10 was a custom design but I didn't know Steve Smith designed it. Steve, I am fascinated by this topic and wonder if you could tell us how the opportunity to design this airfoil came about and the process you went through to optimize the airfoil to the aircraft.

 

[Steve]

A guy would have to modify the the lower flap skin to raise it into a reflex position because said skin lays on the bottom of the fuselage when the flaps are retracted to 0 degrees.

 

[bruceh]

I think you would have to modify the hinges and upper wing skin if you were to retract the flaps on a -9 above 0 degrees. When mine are all the way up, they are in perfect alignment with the ailerons in the neutral position (using the positioning tool and bellcrank aligning tool).

 

[rocketbob]

Not sure if this is relevant but in the past I've dropped my flaps slightly in my -6 to see if there was any loss in speed while in cruise, and found no change.