Spacing for rudder and vertical stabilizer

[scottr]

Hi everyone,

I have a question I'm sure someone can answer. I have a Kitfox 5 with the speedster tail. When I follow the manual directions for spacing between the rudder and vertical stabilizer I end up with a slight interference between the two pieces of fiberglass and they rub each other when rotating the rudder.
The manual calls out 1-1/2 inch gap at the top and 2-5/16 gap at the bottom. Should I remove material from the rudder ribs that the fiberglass fits around to give more spacing between or can I adjust the rod ends out for more clearance?

From reading the manual I believe that I need to overlap fabric around the rudder which will make it even worse. Please let me know what you have done and I appreciate the help.

[Dave S]

Rick,

When you say "Speedster tail" I am assuming that is the same as what is referred to in later manuals as the "Airfoiled tail" (as opposed to the slab sided tail)

1) You do have to get rid of the interference and have enough clearance for the covering/paint.
2) Doing so by adjusting the rod ends out has some limitations - you need enough threads in the vert stab And, the rod end adjustment controls the rudder swing which you want to pay attention to. I'd keep the upper and lower rod end spacing pretty close to spec. A little maybe, but not a lot - maybe a thread or two but check against the rudder swing as spacing affects the rudder swing (on the bottom rod end).

3) I worked with being sure the fiberglas on the vert stab was up tight against the square tube when it was bonded. Sanded the little bumps off the backside of the fairing so it was level and flat and fit tightly against the square tube as well as over the vert stab ribs.(this should be assured first)

4) Also worked back the rudder ribs so the fiberglas faring would fit back against the rudder far enough.

Be aware how much space the covering and paint will take up.

Sincerely,

Dave S
KF 7 Trigear

[scottr]

Hi Dave,

I do have the Airfoiled tail. I haven't bonded the fiberglass pieces in yet, I'm just dry fitting them in place to check clearance. Any idea of how much space is required for clearance? I haven't started any fabric work yet so I don't know for sure how much room I need to clear that thickness either. I appreciate all help.

Thanks, Rick

[Dave S]

Rick,

I took some time and went back to my manual and construction log. What I did not find is any notation of the actual clearance I accounted for between the rudder and the vetr stab.

What I do have is notations of the order of construction and what was done to get the gap right. Here goes:

1) The gap of 1 1/2" and 2 5/16" was set before the fairings were attached and before the ribs were installed.

2) Ribs for the vert stab were fit and the fiberglass fairing was fit and bonded to the vert stab. Kinda Like I indicated in my first e-mail - being sure the fiberglass was sanded flat and bonded tightly to the square tube to minimize interference.

3) Ribs installed on rudder and bonded

4) My construction notes say that I did the fitting between the vert stab and rudder by sanding down the front edges of the rudder ribs till the clearance was adequate - however I have no record of what the pre-covering clearance was.

5) A person has to take into account how thick their covering and paint will be; and, I am pretty sure the tech writers of the manual would not care to venture a guess as to what that might be since everyone's covering will be a different thicknesses and different degrees of smoothness. What I can tell you is the covering over the front of the rudder will be thinner than the covering over the back of the vetr stab if a person layers over tapes as they should on the vert stab. This will also depend on how well a person irons down the fabric on the vert stab - because it is somewhat concave - it takes a bit to iron that area down. I am not at the airport today, so I don't have a chance to measure what my final gap was with the covering and paint - however, I believe I ended up with somewhere around 1/8" so the pre covering must have been with a gap closer to 3/16" but certainly no more than that.

I think the manual pretty well tells a person to take the gap out of the front edge of the rudder ribs.

Again - I am very reluctant to mess with rod ends once they are set because the will mess up the rudder swing too.

There are a lot of the airfoiled tails out there so I have to assume people get this figured out.

Hope that helps some.

Sincerely,

Dave S
KF 7 Trigear

[scottr]

Thanks Dave, I'll follow your advice.

[jtpitkin06]

I found the fairing on the vertical stab required a minor amount of fitting and trimming. This included relief around the rod end bolt holes, straightening the edges with a belt sander, smoothing bumps and notching the ribs.



Notching the ribs allowed the fairing to fit flat and snug against the rear spar of the vertical stab. I bonded it to the spar with Hysol and clamped it firm while the epoxy cured.


The leading edge fairing of the rudder required the same notching around the ribs.



The rod end dimensions from the rear vert stab spar will position the rudder with about 1/4 inch gap between the rudder leading edge and the vertical stab fairing. The 1/4 inch gap is adequate clearance for fabric covering and cover plates over the rod end access holes. There are plenty threads in the rod ends for additional clearance if you need it.


It was easiest to remove the center rod end during the fitting process. Once the top and bottom rod ends were positioned, I put the center rod end in the stab and used a 3/16 inch steel rod for alignment to get things close. It got the rod end within 1/2 turn on the first try.
One additional area I found needing modification was the rudder stop tangs. On my aircraft they were sized for the slab tail. When adding the speed kit the rudder is further aft and the stop tangs are too short. This allows the rudder to swing too far and it will hit the elevator. By adding two AN3-4A bolts to the tangs I created adjustable rudder stops. Adding or removing washers adjusts the rudder limits.


JP

[scottr]

Thanks JP,

I'm going to look at it again today. I bought the kit from another owner, it's a Kitfox V, about 1994 vintage. It doesn't look like anything has changed in the design as far as this goes, but I really don't have the clearance like you have. I already removed some material from the ribs and still have a slight drag on something when I rotate the rudder. I can fit a sheet of paper between the rudder fairing and the vertical stabilizer fairing but that's about all.

I'll look at it again today and let you know what I find, if anything.

[jtpitkin06]

If you don't have room between the rudder leading edge and the vert stab spar and fairing; and,

If you don't have enough adjustment with the rod ends to provide clearance; then,

recut or radius the leading edge on the ribs to the rudder. There is plenty of material on the ribs to shave them back if necessary. It sounds like you are within a 1/4 inch or so. Based on that, I'd shave the leading edge of the ribs to move the curved rudder fiberglass leading edge aft.

This operation is about as easy as you will get to make things fit and it won't affect aerodynamics one iota.

If you hear or feel some scraping, check the area around the rudder stops. Mine was dragging on the inside and it required a small bit of filing. It now quiet and smooth.

Let me know if you need pictures as I have not covered this area, yet.

John Pitkin
Greenville, TX

[scottr]

I got it figured out today. The ribs on the vertical stabilizer were not completely symmetrical and one side was rubbing the rudder fairing. Also the "V" shape in those ribs let the center section of the fairing sit against the square tube but the outer part of the "V" didn't fit well into the fairing. I'm surprised I didn't see it before but somehow I missed it.

I was able to reshape the ribs slightly to obtain a symmetric shape on them and modified the "V" to fit better in the fairing without removing a lot of material. I also trimmed the sides a little more for the outside of the fairing to fit flush on the sides. Everything works well, in fact I have about .15 clearance between the fairings, which should be enough for clearance after putting the fabric on.

I should be able to finish installing the fairings tomorrow and then move on to the next part.

Thanks for all of the help, I really appreciate it.

Rick

[MotReklaw]

This is a great forum.....
Faced this same problem and just put it on hold while I worked on other stuff. Now I see my way out of the conundrum
Thanks guys!