The GeeBee Sportster X gets flaperons!

by alibopo | April 24, 2014 | (7) Posted in Projects

The GeeBee Sportster X  gets flaperons!

Following on from my success fitting flaps to my Morphocoupe, I decided to try flaperons on my GeeBee.

I’ve never really managed to get the GeeBee to land without it nosing over, which, ignoring the issue of long grass, is mostly due to the high landing speed. I felt it was worth trying to get the landing speed down and flaperons seemed the best way to achieve this.

(If you watch the video you’ll think I wasted my time, but the grass on my flying field hasn’t been cut for a while and just now  I can’t land anything without it nosing over!)

Deploying flaps or flaperons makes two things happen; the wing produces more lift (which can allow you to fly slower) and there’s more drag (which will slow the plane). I was after the first effect of producing more lift.

I read that on an RC plane up to 30 degrees of flap deployment produces a steady increase in lift, but beyond that angle only the drag increases.

I also read this cautionary note about flaperons. If too great a flaperon deflection is dialled-in at the start, when additional aileron deflection is applied to bank the plane, it can create so much drag it can slow the 'down-aileron' side of the wing so much, it actually produces an opposite turning effect to the one you expect!

I already had seperate servos for each aileron, but they ran through a Y lead to the single aileron output on my receiver. Fortunately I was using an OrangeRx R620 DSM2 receiver which has 6 channels, so I was able to run the leads separately and plug the second aileron servo into the AUX port. My Spectrum DX6i has a preset programming function for adding flaperons, so, after a visit to youtube to get it all explained, setting things up was fairly easy and painless.

The GeeBee has full-width ailerons so I decided to keep the flaperon angle pretty conservative....

                                                         ...only about fifteen degrees.

This gives me a good undercamber wing profile without adding a great deal of drag. You’ll spot my assistant, Chester the cat, helpfully pointing to the important bits.

                                                Here's Chester again, inspecting the undercarriage.

From the flight testing I’ve done so far I can fly the GeeBee significantly slower with the flaperons deployed than without, and at a lower throttle setting. In fact if I ‘retract’ the flaperons at these slower flight speeds there’s not enough lift produced to keep the plane flying level and it immediately starts to lose altitude.

Another small issue I never thought about is prop torque. I must have a few 'blips' of right aileron dialled-in for level flight at speed, but when I deploy the flaperons and reduce revs the prop torque reduces as well, resulting in a very slight left roll tendancy. For complete easy-peasy control, I need to find a youtube video that can tell me how to link a few less 'blips' of right aileron adjustment to the flaperon deployment. Any suggestions?

Here's some flight footage...

I need the nice men from the Parks Department to come and cut the grass before I get a real landing test, but it’s looking promising at this stage.

Cheers, alibopo.


AG Pro on April 25, 2014
Flaperon is a simple thing, yet effective. I do also implement that mixing for take-off, level-flight and landing.
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alibopo on April 27, 2014
Hi AG Pro, I think it is possible for the DX6i to produce 3 position flaps, though I'm not sure about 3 position flaperons. 3 position flaps would definitely add to the versatility of my Morphocoupe, but to be honest I was just happy getting 2 positions working! :) Still... I might just give it a go :) On the GeeBee, even if I could work out a way to get 3 position flaperons I doubt I'd want any more deflection than I have at present. Flying with the flaperons deployed requires a bit of extra concentration to keep the bank angle low during turns. I've 'overdone' the banking on turns a few times and the plane has instantly snapped-over onto its side - requiring a quick catch to stop it diving into the ground. A mid position might make for an easier transition from fast to slow flight, but fiddling with different switches on the DX6i to get the 3 positions would probably get the better of me. Cheers.
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AG Pro on April 28, 2014
By referring to replies by FinalGlideAus in my article (Flaperon Mixing and 3-Pos Flap Switch) , your aircraft might experienced wing tip stall as explained by FinalGlideAus. I highly recommend to read his explanation. Cheers.
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OrangutangSurfer on April 24, 2014
Pretty cool! I need to figure out how to do this on my radio, there's no preset so I have to do it manually through a mix or two. as far as your "blips" are concerned, when you enable the flaps do you have the option of setting a percentage of how far to move each channel? Try setting one to say 13 degrees and the other to 15 degrees when the flap switch is flipped. I haven't actually done this on my radio but i know the mix ties the two channels together and I have to manually set the percentage for each servo, and supposedly I can use one of the pots on the radio to adjust the amount of flaps. Hope that helps!
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alibopo on April 25, 2014
Hi, thanks for that - it sounds really obvious when you explain it like that. I did manage to create a mix to do the job, but I'll need to look at your suggestion to see if that would work on my DX6i. Cheers.
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The GeeBee Sportster X gets flaperons!