Pitch stability in a Kitfox 4

[avidflyer]

Hi all, looking for some suggestions here. I've been flying my Kitfox 4 since the complete rebuild I did on it for a bit more than a year ago. Got about 60 hrs on it so far. I really do like the plane, and performance is pretty good even with just 80 HP in the 912. Here is my one concern or issue. I have an electric trim set up, uses the Ray Allen switch and servo, but I just can't get it to hold altitude very well with the trim. Seems like it's balancing on a pin point. And with the same trim setting, it may choose to go up or down. With my Avid Flyer, I could set the trim tab (cable operated) and fly for miles with out touching it. One real calm evening I flew about 25 miles and only had to give a bit of rudder control. The Avid is about 9" shorter then the Kitfox, so I would think that should help the Kitfox track better. Been playing with the single axis autopilot some lately, and not holding altitude is kind of a bummer. Any thoughts? Thanks, JImChuk

[Eric Page]

Is the M4 tail setup the same as the S5-S7 (trim via changing the horizontal stab angle)? If so, is there any play/backlash in the trim mechanism that might account for the random up/down wandering?

[avidflyer]

The trim on the Kitfox 4 isn't like the Kitfox 5-7 at all. It actually was an option to put a trim tab in the elevator. When I rebuilt mine, I put a trim tab in. It's not sloppy or anything either. For just hand flying, it's not really that bad, but with no elevator input, it has a mind of it's own. (might be part woman, cause it changes that mind frequently for no apparent reason) :-) With no flaps at all, it will wonder some in roll as well. Paul Seehaufer suggested I pull in just a little bit of flaps, and that made the roll axis much more stable. JImChuk

[rv9ralph]

The issue may be the relation of the incidence of the HS and the wing. In Type Certified aircraft (I believe the HS is slightly negative) which requires some trim almost all the time, giving the trim more authority.

Ralph

[avidflyer]

Thanks, Ralph. I can move the front of the HS pretty easy. I'll try it. JImChuk

[Jerrytex]

Another thought....double check the flaperon rigging. Mainly making sure they are neutral when in straight and level flight.

[jrthomas]

It sounds like we both have similar Model 4's. Mine is the longwing with all the speedster features including the Ray Allen trim that's built into the elevator. Mine works very well. Mine will never be a "hands off" airplane but the trim sure helps. I had a couple of ideas. The first thing I thought about is flaperon rigging. If they're not absolutely neutral when all up, that will effect pitch. I had to make some fine adjustments to mine when I was in my test phase. Also, I set my horizonal in the middle position. Mine has 3. That might be a possibility if yours is set different. I assume your CG is good. That shouldn't be an issue with the 912. Mine worked out fine without any problems. I'd check the flaperon rigging 1st. That would be my most likely suspect. Just some ideas. Good luck with model 4. I hope you love yours like I do mine. James Thomas

[t j]

The kitfox was designed to trim pitch with the flaperons. When I had my model 4, when level and trimed in flight I could fly without touching the stick and even do 360 degree turns with just rudder and still stay level.

[Slyfox]

I have a model 4 1200. Mine flys perfect. I have the electric trim in the elevator. love it. My suggestion would be to do a complete weight and balance and use aircraft scales. My thought is you have too much nose heavy, just a guess. yesterday I was flying with the wife and messing with something with no hands on my stick and maintaining perfect altitude 1000ft agl. my wife did freak cus I had no hands on the stick. that's my wife though. Oh and it was a little turbulent as well.

[avidflyer]

Thanks for the comments to this point. As far as CG goes, I don't have the W&B sheet in front of me, but it's not nose heavy. I actually had the 12 lb battery about 24" behind the seat to start with, and had to move it to just behind the seat to stay in the envelope if I filled the baggage sack to maximum allowed amount. Someone else mentioned that if there is to much friction on the elevator movement, it may do what I describe. If the elevator moves a bit and resists going back, then it will head off in that direction. One time it may go up, another time it may go down. I'll look at that as well. Thanks again guys. JImChuk