Vertical stab tip - advice sought

[Sonex1517]

So...reading all the builder sites and Yahoo posts makes me realize I ain't alone in this challenge.

The vertical stabilizer fiberglas tip is kicking my butt.

I am asking for suggestions - so far my thinking is one or combinations of:

- put the fairing on last after I redo the top rib and cleco the skin in everywhere else. Advice I read was to force the tip in between the skin and the stabilizer frame.

- change the way it mounts

- leave it off and go back to complete it later

This one is a real challenge and I ruined some parts last weekend doing it. Thankfully not expensive parts! :-)

anyone have suggestions?

Thanks
Robbie

[Andy Walker]

Where are you in the process, Robbie? Any pics would help.

I did the entire stab, then tried to do the tip (the factory way, fiberglass sandwiched between the VS skin and frame). I was able to make it all fit and line up, but there was a lot of cursing and elbow grease involved. In retrospect, this is not the right way to do it. Ideally before you drill the skin to the frame you would put the tip on, line it up, and then drill all the parts together.

If you have the skins/frame already drilled, you can do what Robert Frost (I think) and some others have done: Make a strip of 0.025" aluminum that goes all the way around under the skin, then where you'd normally notch the tip to clear the rudder, just cut it straight across the entire tip. Then you can slide the tip over the 0.025" strip makin sure it fits tight against the top of the skin, drill, and rivet.

However you do it, make sure you align the tip to be both straight /symmetrical to the stabilizer, and also "twisted" correctly so the rear of the tip is aligned with the rudder when the rudder is in the neutral position. If the rudder alignment is off a bit it's not functionally a problem, but you want to get it as close as possible so that it looks good. This took me a couple of tries, and I had to re-drill the holes in the base of the tip (filling in the old holes with bondo before re-drilling).

[Sonex1517]

Hi Andy

Thanks - I have to shoot some to post. We are to the point where the entire vertical stabilizer is drilled and cleco'd with the skin on. I have the fairing on and everything drilled, but as I went back and checked it out the alignment of the fairing and top rib are AFU.

My wife and I agreed that at a minimum I have to replace the top rib on the stabilizer frame and the nose rib due to holes that are too close to the edges. Those parts are on order.

I plan on filling any extra fairing holes and redrilling but at this point am about ready to cleco the new top rib in place and proceed to the horizontal stabs before I get too discouraged. Several others said that they encountered this and then in the end just basically forced the fairing between the skin and the frame....that makes me cringe. But I can see where it may be the only way to succeed.

The issue has its roots in my failing to confirm the fairing was aligned as I began to drill - I had checked it and it was good but it must have moved as I began....the rest of the vertical stab came out square and fine.

I will post a few shots so if nothing else, the next person knows what the battle is all about....and I will look over your suggestion to see what I can do from here.....

Bring on any and all suggestions, criticism, opinions, whatever!

thanks

[Andy Walker]

Hmm...if I'm understanding you correctly, you are going to replace two ribs because of holes too far (up or down) on the rib flange. Here's the problem with that:

If you put the new ribs in, what keeps the new holes from also being too close to the edge? After all, the geometry is fixed by the other skin/rib hole relationships. The only way this will work is if you drill new holes in the spar channels to change the position of the ribs, or change where on the end flanges the holes are positioned (which risks those holes being too close to an edge unless you make longer flanges than what is on the plans).

Just something to think about.

I had to kind of "force" mine as you say, but it's not that big a deal. I sent e-mails back and forth with Sonex about a lot of it, and Kerry said that even if there are some aspects of your build that you don't like so much, it's probably fine because the forces acting on the vertical stab are pretty low, the horizontal stab gets far higher forces on it.

Also, I found the tail to be one of the harder parts of my build so far, mainly because almost all of the parts are builder fabricated, so every little millimeter error adds up and leads to things not quite lining up. I threw away about 25-35% of the parts I made for the tail, because they just weren't close enough to use or didn't fit right. Don't get discouraged, I'm working on the fuselage now and my error rate has gone down a LOT and things just seem to work out better on that part of the build. :)

[Sonex1517]

Believe me - I agree about replacing the ribs. In this case it is required and while it will be a formidable challenge I bascially have to.

Thanks for the encouragement as I need it....more to followas you know what my weekend plans are now!

I should add I am working from the tail kit so luckily I did not make all these parts...

Basically for the nose rib I mde it too close to the frame and the flange did not line up right. One laser hole from the skin is right over a flange flute. Ain't gonna cut it. So I can easily reposition the rib.....but getting the old one off and the new one aligned.....ugh

[Sonex1517]

Attached is a shot I took today. I am not afraid to admit it - I screwed this one up bad.

Apparently the nose rib does not go perfectly flush against the spar as I thought it does, at least not with my vertical stabilizer skin. This is looking up from the bottom and as you can see, the one edge where I drilled through the laser cut holes definitely did not line up. In this shot there is no real tension on the skin so it is away from the rib intentionally for the purposes of taking this photo.

I believe I actually need to space the rib a teeny bit off the spar in order for the pre-drilled holes in the skin to line up. If you look closely at the top center where there is a small area between the two flutes the hole almost completely missed.

So I am replacing this part.

[Andy Walker]

Robbie, that's not a big deal. If you drill out the four rivets holding the nose rib, you can slide it forward to get it to a place where all the rivets through the skin hit close to the right spots. Then just draw a line on the nose rib where the clip is in the new position, clamp and drill. You probably don't need a new nose rib; if the holes in the rib end up too close together with the "bad" holes, you can put a piece of 0.025" scrap inside and drill through that. This will give a strong grip surface for the rivet and "sandwich" the rib. I had to do stuff like that in a couple of spots, and Sonex recommended it so it's definitely okay to do as long as it's not a high stress area.

All the nose rib does is provide some additional strength to the leading edge so it will resist impacts better, and hold the skin tight to the rest of the frame. Even if your tip rib ends up looking pretty hacked up, nobody will ever see it and it will still do its job. Just deburr and clean it up as best you can before final assembly.

[radfordc]

I didn't build my plane, so take this for what it's worth. Fitting the fiberglass tip between the skin and the rib seems somewhat diffcult. On my plane the rudder tip rib is made of two identical pieces. These two ribs are riveted together back to back (mirror image fashion) so that the tip rib has a flange on both sides. The rudder skin rivets to one flange and the tip rivets to the other.

[vicdelgado9]

I didn't build my plane, so take this for what it's worth. Fitting the fiberglass tip between the skin and the rib seems somewhat diffcult. On my plane the rudder tip rib is made of two identical pieces. These two ribs are riveted together back to back (mirror image fashion) so that the tip rib has a flange on both sides. The rudder skin rivets to one flange and the tip rivets to the other.

I did the same thing for my stabilizer tips, and it worked out well. Here is a photo of mine: