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 OrangeR620 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.