Elevators

Empennage tips 5

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This post covers two evening work sessions. First up – completing the vertical stabilizer tip. The tip is going to be removable, but I still wanted to fully enclose the rear. I used some foam and fiberglass. Neither are secured to the rib or skin.

I also completed the remaining sides of the rudder.

And flipped the horizontal stabilizer to do the bottoms.

Here is the completed vertical stab tip. I will clean up the edges and then use some body filler to complete the job. 

I sanded the completed areas and trimmed excess fiberglass.

Empennage Tips 3

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My buddy Mike was nice enough to give me his fiberglass 101 class tonight. We walked through working with the epoxy and fiber glass to glass in the tips of the elevators and horizontal stab. I riveted the tips in place and then we got started.

The first step was preparation. Tape off, scuff with 80 grit, and clean with acetone.

Then we mixed up some flox for the counterweights. We should have done this prior to riveting the tip in place, but we were able to get plenty of flox into the area. Flox is a mixture of ground cotton and epoxy. You can mix it to different consistencies based upon the use. Because of its high epoxy content, it’s generally pretty heavy. The cotton adds structural strength. The flox we mixed for this purpose was pretty thick. It would flow but only just.

Next we measured and cut the fiberglass cloth for placement. Here you can see the dry strips at the top and a strip that has had epoxy applied at the bottom. The secret here is to fully saturate the cloth with epoxy and remove all excess epoxy. You want the absolute minimum amount of epoxy required to saturate the cloth. The general mistake made by rookies is too much epoxy.

After setting up the left elevator we got to work on the left horizontal stab. This was a two part process. We needed to bond the intersection of the fiberglass tip and the horizontal stab, and we also needed to enclose the end of the tip. To enclose the end, I used balsa wood and flox. I recommend making your balsa or foam insert go all the way to the rib. Additionally, you should consider covering the intersection of the two with fiberglass.

For the tip to horizontal stab skin intersection we used three layers of fiberglass.

We repeated the process for the right tip. In this photo you can clearly see the 90 degree fiberglass intersection of the balsa wood and end rib.

We did the right elevator as well (one side).

Here are a few photos from the next day.

Empennage Tips 1

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Previously I began work on the fiberglass tips for the horizontal stabilizer and elevators. The tips for the elevators have very close edge distances in order to not interfere with the end ribs. Here you can see the first two reinforcement strips I made to remedy the problem for the left elevator. I expect the same thing to be required for the right side.

Picking up with the right side, I trimmed the horizontal stab’s tip by inserting it and marking the intersection.

Here is the result after the cut. This is a good point to note that I may need to trim these further after   glassing in the elevator tips to ensure I have appropriate clearance and alignment. I bought some foam at home depot to close the back portion of this tip in.

Van’s specifies that you need 1/4 inch of edge distance in the fiberglass for this tip. This can be tricky as there isn’t much room for error. My approach was to mark the 1/4 inch line, and the line at which the fiberglass intersects the horizontal stab. This allows me to measure the line for drilling on the horizontal stab that will provide 1/4 inch of edge distance. There was a little more wiggle room on the left side than there is here on the right. On the left, it was possible to get both the edge distance for the fiberglass and the aluminum. On the right, I will be slightly short of the appropriate edge distance for the aluminum but just fine for the fiberglass. Of the two, I’d rather have the fiberglass OK, and the aluminum a bit short.

Here you can see my approach a little better. 1.5″ between rivets, and I started 0.5″ from the rear.

Came out nicely.

And perfectly within the edge distance guidelines.

Again, the elevator tip needs to be trimmed to 1/2 inch to avoid interference with the end rib. This all but guarantees an edge distance issue.

I made two more backing strips from aluminum and set about drilling and epoxying them to the tips.

Here are a few different pictures. I clamped the strips in place and drilled. After drilling for the rivet holes, I removed the strips and added additional holes. These holes will fill with epoxy and create a stronger bond. I sanded the strips with 100 grit sandpaper to maximize adhesion.

Here is a good demonstration of my thought process. There strip has epoxy underneath and on top. The two are connected by multiple additional holes. In order for these strips to come apart, not only will the aluminum need to separate from the epoxy but the epoxy will need to crack at these points. 

Here is the strip in place for curing overnight.