Turnbuckles & rudder fixtures

[Dave S]

This new thread is a reflection off Rosslr's comments about DesertFox4's photos under "oz build"

The turnbuckles in this location at the rudder can certainly be used to centralize the rudder/rudder pedals and, to take up some cable length to keep the rudder pedals from contacting the firewall if a little interference developes there.....they are not cable tensioners.

The neat thing about the Kitfox controls, rudder controls in this case, is that it is a "zero slop" system because of the Open System at the rudder pedals (rather than looping the pedals together as is most commonly done in certified aircraft in a "closed system") so the return springs at the pedals tension the cables always and prevent any of the cable slop we see in things like Cessnas. It's a neat engineering feature that gives us that refined control feel.

When I did a couple tests flights in a KF before I bought one, I recall that the excellent control feel, total lack of slop and minimal friction in all the control systems was one thing that caught my attention right away.....so unlike the somewhat clunky, sloppy and draggy control feel of the rental airplanes I had been using.

In the construction without turnbuckles, a person can make the same adjustments in a somewhat more tedious manner.......by changing the length of the rudder links to compensate for pedal alignment or minor cable lenght.

Here is what I have a question about for DF4.......In the photos, I see that you have the airfoiled tail on your IV; and, there is an extension bolted to the rudder arm. Question is....did you fabricate the extension or was there one that could be purchased to install in this location to accomodate the thickness of the rudder with the airfoiled design? How much did the extension change the rudder pedal swing?

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

St Paul, MN

[DesertFox4]

Forwarded from another thread:


Desertfox4 - thanks for the pics on the turnbuckles. The ones you have used look really tidy - I like the closed body on them. What is the material? Bronze? - they dont look like SS?

As Jim says, given the springs tension the cables they would be only partially useful in tensioning the cable but more useful in ensuring 'centre'. do you use them much - in other words, do you find them a useful addition?

cheers

r I chose not to add the little adjustable metal tabs on the rudder pedals so I had to have some adjustment somewhere. The turnbuckles gave me that at the rear where it was easier to get to anyway. Once I initially set up the pedal/rudder relationship I've never had the need to touch them again. Besides the locking pins are so dang hard to remove that I think I'd damage them and have to buy new ones.
You may or may not have noticed that my rudder cables come out of the fuselage sides much further back than most model 4's. This is because I've installed a set of aircraft pulleys in the tail that allows the cable to exit the fuselage much closer to the rudder. It is cleaner looking and I get no cable rubbing through the fuselage fabric.

I did have to add an extension to the rudder bar to keep the cables from rubbing on the rudder fabric. I still have the same rudder travel as any other model 4. The extension piece is made out of chromoly steel. Very strong. I'd have no problem running a tail wheel if I ever decide to convert.

[rosslr]

Thanks for starting the thread Dave - At this stage I can only see advantages in fitting the turnbuckles but will need to look more carefully at how they will fit once the covering complete and tail installed. However, it will be interesting to see if others have fitted them and find them useful also.

cheers

r

[jiott]

Since the only benefit of the turnbuckles is to 'center' the rudder, a comment on this may help. The rudder is in reality 'centered' by the slipstream, not by your feet, so no fine tuning of rudder trim is possible with cable adjustment. If any rudder trim is required it must be done with a trim tab added to the rudder trailing edge. The turnbuckles would only be useful to center the pedals when the rudder centers itself. It is fairly easy to adequately center the pedals with the rudder when you swage the cables. I doubt that small fractions of an inch error matter much or could be felt by your feet. Nothing wrong with turnbuckles but I adhere to the KISS principle.

Jim

[jrevens]

I may be wrong, but actually since the rudder system is spring-tensioned, by shortening one of the cables (with a turnbuckle or whatever) you will apply a little more tension on that cable's spring when the rudder is centered, which should create a trimming effect, just like light foot pressure on that pedal would.

[HighWing]

Since the only benefit of the turnbuckles is to 'center' the rudder, a comment on this may help. The rudder is in reality 'centered' by the slipstream, not by your feet, so no fine tuning of rudder trim is possible with cable adjustment. If any rudder trim is required it must be done with a trim tab added to the rudder trailing edge. The turnbuckles would only be useful to center the pedals when the rudder centers itself. It is fairly easy to adequately center the pedals with the rudder when you swage the cables. I doubt that small fractions of an inch error matter much or could be felt by your feet. Nothing wrong with turnbuckles but I adhere to the KISS principle.

Jim

I totally agree with Jim. I have seen the turnbuckles on several Kitfoxes over the years and always wondered the reason. From my sailing days, I can see the advantage of turnbuckles in a closed system like the stays and shrouds supporting the mast, but in our open rudder cable system, to me it is just more wieght. With my Kitfox, my feet react to what my eyes see and I don't think they have much of a clue as to exactly how far they are from the firewall.

[SkyPirate]

I've got to adjust mine, with my pedals even my rudder is kicked to the right, it drives me nuts that my feet arent centered when flying straight, it screws with my muscle memory especially switching to another plane, im not going to use a turn buckle, i will just adjust one of the pedals to match the other for straight rudder/pedal alignment

[cubtractor]

Hey Chase
Do your rudder cables have alternate holes in the attach points to the rudder?
Mine does to offset the rudder pedal alignment issue. I'll try to get a pic so you understand what I'm talking about.

[jiott]

Regarding Jrevens comment; technically he is correct-cable adjustment will affect spring tension and rudder trim. But I don't think you want to do this because it will probably take more than a little adjustment to have much effect on spring tension which then moves your pedals off center. Rudder trim is much better handled by a trim device on the rudder itself.

Jim

[SkyPirate]

I dont think it does Mike, its a looped end with a swedge, i think that is because of the adjustable pedal option , which i dont have

My model 2 had that set up on it

[jrevens]

Thanks for confirming what I was trying to say, Jim. Whether the rudder is forced to "offset" with a tab, or spring tension, the result is the same. With spring-tensioned rudder cables on some airplanes, I've been able to adjust cable length a small amount, with turnbuckles, to allow the ball to stay centered with my feet off the pedals in cruise, without having to add a trim tab. Of course, it depends on the strength of the springs, & you can substitute a stronger spring on one side also. You can't do that with an RV-6 (no springs).
I agree, Lowell, that a trim tab is best, especially if you need a lot of rudder offset. My choice would be to add a tab, and adjust cable length to synch pedal position if you're sensitive to that. I guess if you just need a little adjustment the turnbuckles could be more convenient/accessible than the multi-hole links at the cable/pedal attach points, but I see your point.