Archive for the ‘Empennage’ Category

Misc stuff

Sunday, March 25th, 2007

I spent the whole day in the garage but didn't take many pictures. I guess I didn't actually get all that much accomplished – mostly I puttered and cleaned up the garage. It was great to be outside in the nice weather though.

One of the pre-tail-mounting chores I've been meaning to do is drilling the holes for the strobe and nav light wires that will go through the vertical stabilizer spar into the rudder. I picked the same location as Dan for much the same reasons – with the taildragger there aren't many other good choices for where to run these wires. I drilled a 5/16" hole for the strobe cable and a 3/16" hole for the nav light wires. Both holes are a little oversized so I can use a few layers of shrink tubing and some RTV to protect the wires from chafing.

Another day, another round of filling and sanding empennage fairings. I'm just doing a little bit every work session, fitting the glass work in between other tasks that are more fun.

I rearranged the garage a bit, and made a little table out of a sheet of plywood and a couple sawhorses. This is where the canopy is going to sit while I work on it. Yes, I've decided to work on the canopy some more before I put the airplane on the gear and mount the engine. Matthew convinced me that it'll be easier to get to it while it's down low and not high up on the wheels. Plus it seems to be warm enough these days to start thinking about working with plexiglass again.

I got out the canopy frame to make sure it still fits – yep:


Installed empennage gap fairings and horizontal stabilizer

Saturday, March 24th, 2007

The plans call for you to install nutplates along the F-709 bulkhead where the fiberglass empennage fairing and the forward end of the aluminum empennage gap fairings will attach, and then drill and tap holes in the longeron underneath the stabilizer to attach the gap fairings along the rest of their length. I decided to install nutplates everywhere instead of tapping the longeron – a tapped hole has no ability retain a screw and I remembered how one or two of these screws were always backing out on my old airplane.

Installing nutplates here took only a few extra minutes and was no big deal to accomplish. I did check with Van's before I did this, since I was wondering if the extra rivet holes would do anything structurally back there. Here's what they said:

Date: Tue, 12 Dec 2006 07:38:14 -0800
From: Van's
To: Matt
Subject: Re: Nutplates for empennage fairing

It's OK, but why would you want the extra expense and work?

Vans

I think they must have an automated process that sends that reply anytime they receive an email that starts with "Is it okay if I…"

After double checking my todo list to make sure I wasn't forgetting anything, I vacuumed out the tailcone one last time and bolted the horizontal stabilizer on for good.

Here is one of the empennage gap fairings installed. The topmost hole is left open because it's shared with the fiberglass empennage fairing. I used the hand seamer to get the forward edges of these fairings to lay down nicely on the fuselage skin. I'm not sure what to do about the forward end of the rubber channel – maybe I'll trim it at an angle to try and help keep the wind from peeling it up.

Before turning in I reattached one of the horizontal stabilizer tips and put on another coat of filler to help smooth out the forward edge where the fiberglass and alunimum come together.


Finished rudder cable fairings

Tuesday, March 20th, 2007

I installed the other rudder cable fairing, same as the first. Ignore the black lines, those are sharpie marks I was using to help tweak the part to lay down properly against the fuselage skin.

Same type of nut ring too. Matthew says my airplane will have ten pounds of nutplates in it. Oh well, I won't be carrying an angle valve engine around under the cowl, so I have a few pounds in the weight budget to play with. And hey, check out the dead moth that lives inside my fuselage.

It's nice to be able to check something off my to-do list. Also, I got a perfect score on the commercial written exam, which was nice.

Rudder cable fairings

Sunday, March 18th, 2007

On Saturday I tripped going down the stairs with a big basket of laundry and wrenched my ankle rather smartly, so between icing down my swollen ankle and studying for the commercial written exam I didn't get a lot accomplished on the airplane this weekend.

I did however manage to get one little task mostly done, which was fabricating and installing the rudder cable exit fairings. The plans just have you punch the rudder cable fairings straight through the fuselage side, and there's probably nothing wrong with that, but it does seem like a small set of fairings would help to aerodynamically clean up that area. You can get pre-made fairings, but I wanted to do it the hard way and make them myself. So, first I drew a whole bunch of lines on a piece of 0.020" alclad scrap, using the dimensions given by Sam Buchanan as a starting point.

Then the two pieces were cut out:

A little work with the hand seamer, and I had a nice looking pair of fairings. All for the low low price of free.

I laid out holes along the flanges and drilled the fairings to the fuselage. They are aligned with the main longerons, which are level in cruise flight. Notice there are three holes on top and only two on the bottom – that's because the lower fuselage stiffener is in the way of where I would have put the third lower hole. Actually I did drill a hole in that location, which you can see in one of the other photos below, but it's too close to the stiffener to dimple so I just covered it up with the undrilled fairing.

I had several choices for how to attach the fairings to the fuselage. In order of increasing difficulty, they were: A) round-head pop rivets; B) flush pop rivets; C) flush screws and nutplates. If you've been reading this site for long you've already guessed that I picked option C. However, it wasn't just as simple as riveting nutplates to the fuselage skin, because it was too tight inside the already-riveted tailcone to have any kind of decent bucking access. So, after some head scratching and trial and error, I made a nut ring to support the nutplates on the back side of the skin. The odd shape lets it clear the cable slot and the various other structural elements back there.

The same screw that attaches the adel clamp to the fuselage side also holds the nut ring in position. The fairing and fuselage skin are dimpled, and the nut ring is countersunk to accept the skin dimples.

On the exterior side, flush stainless 4-40 screws hold the fairing to the skin. Since it's removable I was able to iteratively shape the edges with my hand seamer until the whole thing laid down tight against the skin with no gaps anywhere. Now I have custom, scratch-built rudder cable fairings that continue the cool attached-with-screws motif that I have going on with the other empennage parts. Hopefully at least one person at a fly-in somewhere will look under the stabilizer and go "woah, how'd he do that?". Plus if I ever need to replace the rudder cables I won't have to drill out any rivets and mess up my paint.

I still need to finish installing the other fairing, but now that I have a template to make the nut ring it should be no sweat.

Empennage fairings part VII

Sunday, March 11th, 2007

Still not too much time to work on the project lately. I did have a chance to reinforce the balsa ribs on the horizontal stabilizer tip fairings with a mixture of epoxy and flox, and to fit and install the 4-40 nutplates that will hold the fairings on.

I mixed up the usual batch of micro filler and smoothed out the transition between the tip fairings and the stabilizer, with an extra blob at the nose to allow a perfect fit after it's all sanded down later. I also put a big glob of filler on the outboard corners – a lot of this will get sanded off, but what remains will be the the first step of building up the tip fairings to match the contour of the elevator tips.