Luis & Fab's RV-7A Construction Log

After bending the flaps on each side, the next step is to attach the piece that will connect the trim tab to the servo inside the elevator. This allows us to trim the plane with the touch of a button.

This task was fairly easy, as three of the holes connecting the trim tab to the attach angles are already pre-drilled. It’s just a matter of clamping both pieces together and then match-drilling.

A lot of people seem to have trouble with bending tabs on the trim tab, just as with the elevator tabs. This didn’t turn out to be so bad, after doing a mediocre enough job on my elevator to warrant cutting them off and replacing them with a rib.

The main thing I learned when doing the elevator was to use something with sharper edges than a piece of 2×4. I decided to try to make the bending blocks with 3/4″ MDF, and was very pleased with the results.

The first picture shows the trim tab clamped in the bending blocks, and ready to have the bottom flap bent (the trim tab is upside down). I used a small piece of 2×4 to gradually bend the flap down. I started from the left side in the picture and made my way to the right, where the flap is really short. I got to the point where I couldn’t bend it any further, and it looked like the second picture below.

I realized the angle on the bending block was a bit too small, and the bottom flap was grinding against the unbent top flap. Rather than fabricate another set of blocks, I just sanded down the edge to clear the unbent flap, and then used my rivet gun with very low pressure to get a sharper bend. I used some painters tape on the rivet set to keep it from scratching the aluminum.

I repeated the process with the other flap, first bending with piece of 2×4 and then with the rivet gun.

And here is the result. Nice and sharp angles, no cracks in the aluminum, and both of the flaps didn’t get too beat up in the process.

This picture shows the other side of the trim tab. Basically the same process, but the two flaps are smaller.

These two pictures show how I used a piece of wood (in this case not a 2×4, but a smaller strip I had laying around) to do the initial bends, before using the rivet gun.

And here is the rivet gun again, being used to clean up the bends. The picture on the left shows the finished bends.

Finally, just to get a feel for where this piece fits on the plane, here is the left elevator with the trim tab sitting close to where it will be eventually attached.

Last week I finally got the replacement front spar, and spent some time dimpling/countersinking the holes. Today I put everything together and started riveting the elevator.

While waiting for the new parts from the factory, I decided to tackle the elevator tabs. These are two overhangs on the skin that need to be bent 90 degrees to cover the triangular gap where the trim-tab meets the elevator. Supposedly this is a pretty hard task to do without cracking the skin because of the sharp bend. Some people end up replacing the entire skin, which I REALLY don’t want to do. Another option is to just cut off the tabs and build a little rib to support he skin instead.

So, I decided to try my hand at bending some scrap sheet aluminum. What better than to try and make a little rib! I installed the little rear spar on the skin to keep the right shape, and then drew the outline of the rib on a piece of scrap 2×4. Using a miter saw, I cut a wedge out of the 2×4 with the same shape, and made sure it fit inside the skin. I then transferred the outline to one of the pieces of scrap 0.020 aluminum provided with the kit (same thickness as the skin). Then I drew two parallel lines about the same distance away from the wedge as the flanges on most ribs. Finally, I cut out the shape using tin snips and put the piece on the wood block.

I re-assembled the cut 2×4 and clamped it to the end of my table surface. I then used another piece of 2×4 to bend one of the flanges down. As you can see, it looks OK but not great.

As stated in the kit instructions I then finished up the bend by whacking it with my rivet gun and flush set. I set the pressure down to about 20psi and just ran the gun back and forth over the bent flange.

The result was actually a lot better than I had expected. Here’s a picture of the little rib after doing the other side with the same technique:

So, this wasn’t so bad. Sure, time consuming but not bad. So, I decided to go ahead and bend the real thing on the elevator. I fabricated another wood wedge to fit the constrained dimensions in the elevator and proceeded to bend the flanges. Well, I didn’t crack the skins, but honestly they turned out looking like crap. First, it was a lot harder to do the actual bends because the skin and the clamps can’t be moved out of the way like with the rib above. Second, the wood form was not cut from the ‘middle’ of a 2×4 piece like the one above. Rather, I used one of the ‘edges’ of the 2×4 for one of the bends. Needless to say, the edge on the 2×4 is rounded, and it’s impossible to get a good quality bend. So, the lesson here is to ALWAYS use wood forms with nice sharp edges.

So, considering how good my rib turned out and how crappy the actual bend ended up looking, I decided to just cut it off and use my rib! I used a dremel tool to cut off most of the flange, and then used snips to finish with a clean straight cut.

Here’s what the edges look like after a bit of filing and deburring..

I went ahead and dimpled both sides of the front spar (used to attach the trim tab). It turns out the top half needs to be countersunk so the piano hinge can later be match drilled. I would just dimple the piano hinge too (have done it before on a training project with no problems), but match drilling it to the already-dimpled holes of the skin and spar is going to be a major pain.

It’s not very expensive, so I just ordered another one from Van’s. I had a couple more things I needed anyway, so it’ll be (somewhat) worth the handling and shipping fee….

I’ve decided to install electric trim in my plane. Instead of messing with a wheel and a steel cable going from the cabin to the elevator, I’ll be messing with a motor, switches, and wire going to the trim assembly. I’ll have a nice switch on the stick that I can use to trim the plane.

The plate where the servo is mounted does not come pre-punched. The plan gives some approximate measurements of where the brackets holding the servo should go.

I marked the recommended distances, but decided to offset the bracket by just a little bit to keep the servo arm centered in the slot. The picture below shows my test fitting:

After drilling the first hole with a cleco clamp holding the bracket and plate together, I just used clecoes for the rest. The second bracket’s location was determined by putting in the servo and marking the location where the bracket falls.

As you can see in the picture above, the bracket on the left protrudes slightly from the open slot. This is not an issue since it doesn’t interfere with anything. I still decided to file it down to follow the contour of the place just so it looks pretty.

I’ve spent the last few days deburring the left elevator components. This time I drilled everything before deburring the two spars, the short rib, and the counterbalance skin. After drilling, I started deburring everything (i.e., edges and holes). I think this made things go faster, but I can see how it’s easier to get cut when working with the sharp aluminum edges.

No pictures this time, as deburring is pretty boring…

The left elevator has been coming along. I haven’t been spending much time on this lately, but I finally got the whole assembly clecloed and drilled tonight. Drilling the lead counterweights went MUCH easier this time, using drilling lubricant and turning the drill very slow.

After a business trip and some visiting family, I finally got back to working on the elevator.

Here’s a couple of pictures of the skeleton after being primed and riveted together.

Here’s the skin after riveting the strip that covers the counterbalance rib. Doing this first makes it possible to use no blind rivets.

Finally, here’s the elevator finished and ready to be stored for a couple of years 🙂

After bending the elevator in the home-made bending brake, here it is all clecoed together.

Next I’ll prime the skeleton…