Uncontrolled Roll on Full Flaps

[TY2068]

http://kitfoxaircraft.com/images/ser...etins/SB-3.pdf

[av8rps]

If it doesn' t have them, I wouldn't fly that Kitfox unless it had counterbalance weights put on it. Continuing to do so could cause catastrophic in flight airframe failure. Most of the time the flutter just tears the flaperon off the trailing edge of the wing. But what happens if its bad enough to tear off part of the wing with it I commend you for tightening up all of the control mixer points, but that will not stop flutter. Balanced flaperons along with a nice tight control system is the best way to avoid flaperon flutter.

As far as rolling one direction when full flaps put in: it isn't at all uncommon to see the ailerons move a little with flap actuation, especially on Model 1 through 3 Kitfoxes. But typically all you have to do keep a reasonable grip on the stick to control that from being an issue. If your Kitfox is worse than that, until you are able to figure out the fix, stop using full flaps. The Kitfox slips so well that most wonder why they ever put flaps on it to start with? The flaps really didn't start working on a Kitfox until the Model 4 was designed. And even then they still aren't great for descent control. But all model Kitfoxes benefit from the flaperons for additional takeoff lift. So if you feel the need to use flaps for takeoff, limit that to no more than 1/2 flap. If you don't find anything wrong with the control system, I would take a hard look at how the flaperons are set in relationship to one another as well as when neutral. You can get flaperon reversal issues if they are set wrong, so take the effort to go through the flaperon setup carefully using the manual used to build the Kitfox.

Aside from the issues mentioned, I'm glad to hear you enjoying that early Kitfox. For pure flying fun the early and super light models were some of the most fun. But they were a bit quirkier than the current models, and manuals and tech info wasn't quite as refined as what we have today, so there can be a little more experimentation required to get them operating properly.

[Osprey220]

Again, the offending Kitfox does indeed have one mass balance per flaperon.

I eliminated/reduced linkage slop and tightened the shoulder bearing and so far no flutter.

I have not found clearly offending causes of the uncommanded left roll. Flaperon attachments and associated ribs are all firm with no unexpected movement when stressed. The flaperons appear to be at same angle (left compared to right) before and upon full flap deployment - and travel appears to be the same.

Owen

[TY2068]

Does the plane have a slight tendency at all to roll left in straight and level flight with no flaperon set ?

[avidflyer]

When setting the flaperons, it is helpful to clamp a stick on each flaperon bottom the same distance out from the fuselage. Have the end of each stick project back the same distance from the flaperons. 18" - 24" is fine. With the aircraft level side to side, and the joy stick centered, ends of both sticks should be at the same height. You should also have the same amount of travel up and down at the ends of each stick when the joy stick is all the way to the right, and all the way to the left. The nice thing about using the sticks is it magnifies the differences between the two sides, and gives you something to measure to. JImChuk

[ppilotmike]

On flutter, have you removed the flaperons and verified that the "mass balance" weights truly balance the flaperons. I would suspect the uncontrolled roll is due to a rigging problem, Jims post is a good way to check that.

[kitfoxjim]

As I recall many years ago, when I did the rigging on my Model 2 (90-91) there was a possibility that one of the aileron push rods could go over centre if the flap handle was not limited in travel. Went back to look at the manual rigging instructions but that section is now missing.
I would suggest looking at the aileron mixer assembly while deploying full flaps as there may be this over centre condition.
The aileron push rod could be too short but the best cure would be to limit flap handle travel.
Jim