Spring trim on a Kitfox IV?

[jonbakerok]

Has anybody tried a spring trim system on a Kitfox IV? Sonex sells a really slick spring trim system that looks like it might be easy to install.


I've been scratching my head about this trim problem ever since I bought this kit. The drawings for the trim tab and cutout aren't available and I'm not comfortable designing my own modification. A new elevator would cost more to ship than the parts are worth.

Merle Williams sells a trim tab kit, but he said there's no welding. I don't know how you would make a cutout in the elevator without welding -- glue a bunch of wood parts in? That doesn't seem safe. Anybody know more about it?

[DesertFox4]

Jon
Murle had a trim system for the early Kitfoxs' that involved no cutting or welding of the metal structure but did involve cutting the fabric for the servo. I looked at installing one on my model 3 years ago. It was a hinged tab that rivitted to the trailing edge of the elevator and had an electric servo that actuated it. He sold several over the years and they worked well. Simple and safe. Not the sexiest looking but effective. Personally I like the "cut-out" version. Good luck.

[jonbakerok]

Maybe that was what he was talking about. But the picture on his web site shows a trim tab installed in a cutout in the elevator. I guess I need to call him back.

I considered making an external trim tab like that, after I saw one on an older Sonex. But when I scaled the size of my RV's elevator to my Kitfox's, I would have needed a full-span tab on one side two inches wide. And since the Kitfox is much slower, I would think it would need to be even bigger. (Wish I knew a better way to calculate the size)

[DesertFox4]

Jon the tab I built for my model 4 is about half of what everyone else installs and it works great. If I think of it , the next time I get to the airport I'll snap a photo and measure the size.

[airlina]

John, I recently added a servo controlled rudder trim to my Series 5 and it works great. I do not know if the setup i have would have enough "umph" for elevator trim but it might give you some ideas on a trim system. I used a high torque model airplane servo, cockpit adjusted by a servo controller that I found on the internet. I posted the specifics on the forum a while back so you should be able to search it out . If you have any questions give me a holler. Bruce Lina N199CL

[catz631]

Jon,
Check out highwingllc.com. Lowell has a very nice retro elevator trim kit. I have it on my aircraft and it works great ! The trim knob is a "witches hat" on the stick. Can almost trim hands off on final now !
Dick

[jonbakerok]

That looks great! How did you make the cutout in the elevator?

[catz631]

I removed the elevator and sent it to Lowell. He did the work and sent it back to me. He had to recover the elevator and make the trim tab,install servo ,make cover piece,etc. I had to repaint the elevator (no big deal) and reinstall it. The turnaround was fast and believe me it makes a huge difference to be able to trim the elevator forces out on approach as well as triming for cruise flight. He also made my oil and radiator shutters and my bush gear. I now have all the things fixed on my aircraft that were bugging me. It is a totally different aircraft and a real pleasure to fly !

[jonbakerok]

Well, I decided to try the spring trim from Sonex ("Aerotrim"). It wasn't too hard to adapt it, but I ran into one problem. For some reason, Sonex runs the cable all the way around the back side to the spring that's connected to the rear side of the control stick -- instead of simply attaching it to the front spring as I did. The result is that the labels are now backwards. When I turn it toward "UP", it moves the stick forward instead of back.

It's a shame because the control knob is a real thing of beauty. But if this works out, at some point, I'll have to grind off the pretty engraved labels and paint on my own. I think I'll wait until after I get a chance to flight test it, though, so I can resell it if it turns out that it won't work in a Kitfox for some reason.

Anyway, if anyone else is interested, I thought I'd post a picture. As you can see, I'm hoping the throttle cable will fit on the left, but we'll see how that works out when it arrives. Standard disclaimer: This is all completely experimental and I'm not recommending it.