Archive for the ‘Elevators’ Category

Extended elevator stop

Saturday, April 14th, 2007

I wrote to Van's to ask their opinion of my elevator travel situation, and their reply was:

Matt,

You can either make a new elevator up stop or add a piece to the existing stop. The horns hitting the aft bulkhead is not a bad thing, but that will not happen when you fix the up stop.

Bruce Reynolds

Okay, I can do that. Since the existing elevator stop is already drilled for the bolts that attach the vertical stabilizer, I decided to leave it alone to avoid causing further problems. Instead, I created this little elevator stop extension out of some 1/8" angle:

It's riveted to the underside of the existing stop, using the existing three rivet holes through the stop and aft deck. It effectively moves the face of the stop forward about 3/32".

I also added three flush rivets to attach the other leg of the stop extension to the aft bulkhead. Probably overkill, but it makes me feel good.

Now to test the new elevator travel. Here's neutral:

Here's the new up position:

I now have 29.4 degrees of up elevator travel, which puts me in the allowable range of 25-30 degrees. I probably could have made my stop extension even a little bit longer, but as long as the elevator travel is within the okay zone I'm happy.

Empennage fairings part VI

Sunday, March 4th, 2007

I was either in class or studying for half the weekend, but I got a little bit done on the empennage fairings. I ground down the elevator tip fairings until I got the shape pretty much how I wanted it – they turned out not bad at all. I sanded them down to 320 grit once I got the shape right.

This is why I hate working with fiberglass – dust everywhere.

I removed the horizontal stabilizer from the airplane and laid it out on the bench to receive its fairings.

Trimmed the stabilizer tip fairings to fit and drilled and clecoed them in place:

The plans call for a minimum gap of 1/8" between the elevator counterweight and the fairing – mine is more like 3/16" in the neutral position, or slightly less when the elevator moves through its range of travel. Good enough. I did open up the other side a bit so the gap would be even on both sides of the stabilizer.

You can also see where I'll need to build up the outboard part of the stabilizer fairing to match the contour of the elevator.

I made some ribs for the stabilizer tips out of 3/16" balsa sheet. This reminded me a lot of how I used to build model airplanes as a kid. Actually balsa is really nice to work with. Maybe I'll take up model building again someday… nah.

I epoxied the ribs into the fairings and left them to dry overnight.

Since it was fairly nice outside, I decided to mask off the elevator tips and shoot a coat of primer. This will help me find the low spots and imperfections.

Not too bad. I got the look I was going for, and they turned out pretty nice. I will probably come back and do some more filling and sanding in order to work out a few minor imperfections, but overall I'm pleased.

Before I turned in, I managed to get the tail fairing nutplates riveted to the stabilizer.

All this work on fiberglass fairings, and this guy made his out of aluminum. I can't even comprehend the amount of skill that takes.

Empennage fairings part V

Saturday, February 24th, 2007

I decided on a new plan of attack for the elevator caps – I'll attach them permanently, but I'll make them look like they can come off. Then at least all the fairings on the tail of the airplane will have a consistent look, which is important if you're obsessive like me. First I rounded off the forward edges of the lead counterweight with a file, then I match drilled the untouched elevator cap and installed nutplates and reinforcement strips:

The two nutplates at the aft end are very close together. If I hadn't been forced to use the prepunched holes I would have staggered these a bit to avoid interference, as I did with the aftmost rivets holding the aluminum strips to the fairing. As it is I had to cut down some screws to keep one screw from trying to push the other one out.

Here's another thing that I'll do differently on my next airplane – when you dimple the attachment holes for the elevator caps, the rib flange gets between the dimple die and the skin and all your dimples end up with this little crease on the inboard side. You won't be able to see this once it's all painted, but if I'd known this I would have at least match drilled the fairings and dimpled these holes before riveting the elevators together.

Here's a test fit to make sure all the nutplates and holes are lined up:

I riveted a #10 nutplate to the outboard side of the counterbalance arm, using the 3/16" tooling hole that was already there. The reason for putting a nutplate here is that I can use it to bolt on a wide-area washer or two if it turns out that my elevator needs a little bit more weight up front… call it balancing insurance. Also, this photo is proof that I checked the torque on the outboard counterweight bolt on the right elevator – it will be inaccessable once the fairing is on for good.

Okay, I wasn't able to take pictures of how I performed the next series of steps, but I'll describe it and show the result. I mixed up a slurry of epoxy and flox, and applied a thick layer between the lead counterweight and the inside face of the tip fairing. This should glue the fairing to the lead and also fill in the gaps between them. Then I put in all the screws, and covered the edge of the skin with a layer of electrical tape. Next I mixed up a big batch of epoxy and micro, and used it to fill the gap between the skin and fairing on both sides of the elevator. I also applied a generous helping of filler to cover over the forward face of the counterweight, and the corners with the fairing and the counterweight come together. Most of it will get sanded off later, but this should hopefully provide the basis for a nice looking fairing closeout.

After all of the above was finished, I figured the right elevator would be out of commission for the rest of the day before the goo was cured, so I started thinking about the left elevator. It turns out that a replacement elevator cap is thirty bucks from Van's, so instead of throwing away the one I'd previously tried to put glass on, I spend some time sanding off my mistakes and restoring it to nearly-new condition.

Then I performed the same series of steps – match drilling, installing nutplates, and so forth. This photo is proof that I installed the spare nutplate and checked the torque on the inaccessable bolt on the left elevator

After all that (a couple hours of work) the left elevator cap got the same filler treatment:

Once both elevators are dry I'll start sanding them down. For now, though, I'm sick of composites.

Empennage fairings part IV

Wednesday, February 21st, 2007

One more application of filler to the rudder cap – hopefully the last one, save for the inevitable pinhole filling. I'm really happy with the way the rudder cap has turned out.

I'm much less happy with the elevator tip I did the other day. I will probably throw this away and start over with a new one from Van's. The stupid counterweight is totally in the way, and it's looking less likely with every try that I'll be able to have removable tips on the elevators. Darn.

Here's the other, mostly untouched tip fairing, just to illustrate the situation.

Once again, I'm really glad the whole airplane isn't made of this crap.

Empennage fairings part III

Monday, February 19th, 2007

Okay, so the first try at closing up the elevator tip fairing didn't turn out so well. I forgot to take a picture, but basically the fiberglass had nothing to adhere to (the lead was coated with tape to prevent sticking) so it was very wavy and uneven. Also, since I only used three plies of 1 oz cloth it was very flimsy.

One of the nice things about fiberglass is that if you screw up you can usually grind off your mistake and try again. This time I'm going to try using a piece of aluminum to provide the structural strength, and the fiberglass will just be there to hold it all together. I made a forward bulkhead out of some scrap alclad (0.040" I think), scuffed it up so the epoxy would stick, and temporarily attached it to the counterweight with double-sided tape.

Then I laid up three layers of 5 oz cloth, with a single layer of 1 oz cloth over the top to help fill in the weave. We'll see how this turns out.

I must say, the new style of elevator counterweight is a real pain. The old arrangement seems like it would allow you to spend a lot less time messing around with fiberglass to get the tip fairing to come out just right. But what do I know…

Back to the rudder, I mixed up another batch of micro and applied it here and there. This photo is kind of hard to interpret, but what you're looking at is a glob of micro applied to the front face of the rudder cap, with a piece of scrap alclad (covered with duct tape to make it non-stick) taped in place to make it cure with a nice smooth, even surface.

My cat wanted to help write this entry: