Control Surface Repair Tip

This article is about a repair that I did on my Parkfun Fusion.

A while ago I tore off my elevator due to an overly aggressive stabilizer (it didn’t let me correct on my final approach in high grass during the testingfase).

First I taped it on with some tape, which functioned quite well in the beginning. But after a while the tape became loose and there was movement in all kinds of ways that you don’t want on an airplane.

I didn’t have any old floppydisks lying around (would you believe I threw them all away a few weeks ago?) , so I couldn’t cut the item myself. It turned out that in the shop they cost €1.20 (around $1.50 I think).

Basically what it is, is a small, thin, bendable piece of plastic that wants to bend back to its original straight position.

The use is not difficult once you know what to do.

Item list:

Plastic hingeflapthingies (I have no idea what they are actually called!)
Exacto knife/Stanley knife/scalpel (I actually used an operating scalpel)
CA glue
something to mark the locations (pen/pencil)
a ruler (although I eyeballed it and it turned out fine for me)

First make sure you remove any access foam sticking out and make both sides (plane and elevator) as smooth as possible. I did this by using my scalpel and cutting it.)

The plastic flaps are 2.5Cm long (1Inch). I decided I would use 5 millimeters as hingepoint and therefore marked 1Cm from both sides.

I then eyeballed the place where they had to go (it is important to get as straight a line as possible, since it needs to hinge as straight as possible.)
I had already decided that I wanted to use 4 on each side, so I started about 5 milimeters of both edges, then divided them over the area with more or less equal space between them.

I marked both sides of the plastic hinge with a little stripe on the elevator  (If you don’t want to do this, you can use a bit of tape or anything that will show a mark and can be removed).
I then marked off the depth I needed on the scalpel using a felt-marker. This way I would only cut as deep as absolutely needed and would leave as much of the structure intact as possible.

Once all the cuts were made, I put a little drop of CA glue on the end that I was going to insert into the cuts. When doing it this way, it smears the glue over the plastic and it gets a nice and even amount. Make sure not to touch it with your fingers, as it will instantly stick them together.
Any excess amount can be wiped off using a piece of old plastic or a tool. (make sure you use something you do not intend on keeping in mint condition ;) ) Do this for all hinges.

Now comes the tricky part: the other side. We now have one side that has all the hinges in place, but it is very important to have the same cuts on the plane too, since it needs to be as horizontal and symmetrical as possible.
What I did was mark the width of the plastic flaps on the other side, making sure I left enough room to not rub against each other while moving.
You can eyeball this part too (I am semi-sloppy/lazy) but in the end mine turned out fine.

Once you have made the cuts on the plane-side you apply the glue to the ends again, then insert them. The really tricky part here is that you need to get them all in at once, before they dry (making sure you don’t stick your fingers together!).

The end result is something that should resemble something like this:

I have flown mine a few times now and the result is absolutely marvelous. Not only does it strain your servos a lot less than the normal “pressure bend” that foamies have, it also has a much more linear throw.

If you have any questions, feel free to ask them in the comments, I will try and answer them as soon as possible.

One addition:
I used 4 on each side, after testing I saw I could have done with less, but I will leave it in place anyway (since it has been glued and all ;) )
Less hinges makes it move easier, but it will also make it more fragile, it is your own choice.

Also: you can cut these from old floppy disks, but for this price I just bought them and saved me a lot of work.