trim tab – PH-MNX

Elevator Trim Tab

ph-mnx — Sun, 31 Dec 2017 18:32:16 +0000

At the last day of 2017, I decided to do several small left-overs on the Elevators. First up the tricky trailing edge rivets on both the right and left Elevator. These rivets do no have enough “room” to be able to squeeze them or even get the bucking bar in there. So I used the barn door hinge again as bucking bar. It doesn’t have enough “punch” so you need extra long riveting-time.

Also I can use the squeezer for the last millimeter to set the rivet just right.
About thirty years ago I studied at the mid-level technical school (MTS) and one of our assignments was to build a controllable transformer which allows both voltage and current regulation. It still works, so I used it to drive the Trim Tab servo. Set the voltage to 12V and keep the current on low to prevent damage.

There are two types of Trim Tab horns delivered with the kit. One specifically for the servo motor and one when using a Tram Tab cable control. I did several tests with both of them and my conclusion is that even though I have the servo motor, I will use the other horn. Reason is that the lower servo horn might damage the trim tab if set at the outer limits. The manual trim tab horn doesn’t, since it is higher and doesn’t touch anything if you let the servo go to both extremes.

The result will be that the Trim Tab will have just a little less range (3.5cm instead of 4.5cm), however the Trim Tab is seldom used all the way. That is a good argument to use the original one, but I also want to prevent damage in malfunction situations. Moreover I asked several RV-7 pilots in the Netherlands and they claim the Trim Tab is very sensitive. Using the higher horn also makes the Trim Tab less sensitive.

Result looks good, however I was short one blind rivet (MK-319-BS), which I ordered with the Wings.

Time: 3 Hours, Rivets: 34/4

Video

Elevators Bending

ph-mnx — Sun, 17 Dec 2017 21:04:27 +0000

To bend the trailing edge of the Elevator and the sides of the left Elevator and Trim tab, it’s a good idea to have two people. So I invited my dad again to help me with that. Here you can see we already bend the sides of the Trim tab and are now drilling holes in these sides to rivet them together.

The drawings call out for blind rivets, however I think I can manage to rivet them with “normal” flush rivets.
Bending the trailing edge requires considerable pressure. It’s important to bend it just enough. If you bend it too little, the edge will be concave. If you bend it too much it will turn out concave.

The intended result is that the trailing edge of the Elevator is exactly straight. Measuring it with a ruler, there should be no light between the ruler and the trailing edge. The control surfaces of the plane do not have a wing profile, they are completely straight.

while attaching the skin to the right Elevator I found a piece of Styrofoam still being in between the stiffeners. This time we could laugh about it, after riveting the skin to the understructure, it would not be as amusing.

Although I still don’t have the new piano hinge, I use tho old one (the one I screwed up) to fit the trim tab. The sides of the trim tab fit nice into the left Elevator.
Here we are drilling the piano hinge to the left Elevator.

Now we can fit the connecting rod from the servo motor to the trim tab. One of the NVAV members warned me that the distance between the servo motor and the brackets was too small for the rivets to set. He used washers between the servo motor and the brackets. I’ve decided to counter sink those two rivets instead of dimpling them. This worked great (thanks Victor).

We tested the servo motor and it works great. Next time I can start riveting the skins to the understructure.

Time: 4 Hours, Rivets: 18/0