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Countersunk washers on tail intersection fairing

sblack

Well Known Member
On my ultra slow build -4, the front vertical fin spar missed the pickup tab on the horizontal stab front spar by half an inch. I understand this is fairly typical. The airplane was designed with pencil and paper and the various tolerances can add up. The upshot is that the fit of the supplied intersection fairing was laughable so I made a fairing by laying up 4 layers of carbon cloth over clay. It is thin, light and very stiff. Came out great but took a lot of time.

Should I use countersunk washers on the fasteners that hold it in place? Or will the composite hold up to an unsupported #8 screw head? I guess this fairing comes off at annual? Any comments appreciated, especially those based on long experience with older airplanes.
 
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Since we can now post pics here is the fairing for fun. In the last pic you can see that I remolded most if the other glass parts too. The fit of these pre 1990 parts was not up to my standards. I think the glass parts on newer kits are much better. I used the supplied parts as plugs, modified them to fit and molded in a joggle to accommodate the skin thickness. If you want to finish your project in a timely fashion I don’t recommend this. Months of work to save a few oz. i seem to like to complicate things. Plus I like molding.

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I used #6 screws and a fairing molded like yours. It hasn't caused any problems over 19 1/2 years.

You mentioned the fairing's stiffness. Before you paint the airplane, fit the fairing with the elevators attached. Think about how you're gonna get that fairing on and off without beating up your paint. It isn't necessarily easy, and is made more difficult the stiffer the fairing is.

I wish I had barely wrapped the fairing around the LE of the horizontal stab. On mine, I have to pull the whole fairing forward a couple of inches to get it to unhook. The challenge is that the back portion of the fairing hits the elevator weldments if you just slide it straight forward. So I have to flex the vertical portions at the aft end of the fairings a LOT to get the fairing off. This can be helped by a more generous (and draggy) cutout aft of the elevator weldments.
 
Wow this is exactly the kind of wisdom I was looking for. I did trim back the underlap on the stab leading edge because it was very tough to install and remove. I think I will try some teflon tape on the inside of the fairing so as not to chew up the paint. Also I have not tried it with the elevators installed. I will do that for sure. Thank you so much Kyle.
 
Should I use countersunk washers on the fasteners that hold it in place? Or will the composite hold up to an unsupported #8 screw head? I guess this fairing comes off at annual? Any comments appreciated, especially those based on long experience with older airplanes.

Yes I would recommend using the washers. I used #8 screws and some reduced diameter washers that look nice, not sure where I got them or maybe I just used #6 for a #8 screw? Don't really remember. There doesn't seem to be a lot of movement so the washers are more to protect the fiberglass during removal / installation, which in itself can wear that fiberglass pretty quickly.

I have seen installations with just one at the front and one at the back, and IMHO that's not enough as the fiberglass tends to warp a bit over time unless it's stiffer than the normal stuff. I've also seen planes with them spaced as close as 1.5" which seems like overkill. I'd recommend just evenly spacing 3-5 screws along the length of it. I'll try to post pics of mine later today.

I wish I had barely wrapped the fairing around the LE of the horizontal stab. [...]
I second that!
 
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