Trim tab

I took a little time for shop clean up tonight, now that the engine is not hanging on the hoist anymore. After that I worked on reinstalling my new trim tab. As you can see on this post, I had to make a new one since the old tab was cracked due to a bad modification which led into fatigue.

Before installing the new tab on the airplane, I applied transparent polyeurethane erosion tape on the bottom since it is highly exposed to prop blast. Here is how the bottom of my old tab looked like when I removed it:

One other thing I realized when I removed the old tab was that the attachment holes on the piano hinge were badly ovalized:

Again, this demonstrated to me how little details can be very important. The old screws were standard AN526 SS screws with almost zero shank length. The S-1S parts catalog calls for screws with a small shank so that no shear load is applied on the thread. I'm pretty sure that if the correct fastener was used, my old aluminium piano hinge wouldn't be as bad. I decided to replace the crews with AN 525 washer screws. You can see the subtle difference between the two here:

Here is a shot of the final installation compared with the old tab.

Again, big thanks to my friend Paul who patiently helped me building the new tab. Thanks also to my friend Joe who helped me with the paint (I hate painting).

Finalizing the tail surfaces installation

Once all the tail surfaces were in place, I made initial measurements with a smart level as well as a conventional level to know how far I was from the desired 2 degrees of incidence on the stab as well as zero washout as suggested by Doug Sowder's article on Pitts rigging. I was quite happy to find that without any tension on the tail wires, I was very close to the target incidence, with a little washout on both sides.

I used a tool that my friend Paul Goyette and I made for tensioning the wires. It is similar to the one that Steen sells, but made out of nylon and with a cylindrical shape rather than cubical. I think this home made tool is even less prone to damaging the wires than aluminium and would also cause less damage should I mistakenly drop it on fabric. I have two of them, one for the tail and one for the wings.

I slowly increased the tension by adding 1/2 turn on all wires, measuring angles and repeating until getting in the middle of the target range of 250 to 325 lbf tension. As I approached the final tension I realized I was inducing anhedral to the stab by doing 1/2 turns everywhere at each iteration. This is probably due to the top wires being longer and therefore stretching more that the bottom wires. When I realized that, I did one round of tensioning the top wires only, which brought me back to zero dihedral.

I used the Holloway Engineering tool along with an electronic torque wrench to measure the tension. 

Thanks to my girlfriend Isabelle who helped during the final stage of the tail installation!

Rudder

Tonight my goal was to install the rudder. First, I connected both elevator surfaces together. It was much easier to do this without the rudder surface in the way. I connected the aft elevator pushrod at the same time.

The bottom bolt was not reacheable with my torque wrench so I counted the number of turns on the bolt above when properly torqued, then applied the same number of turns on the bottom one.

Once the three bolts torqued properly and sealed, I went up in a ladder to reach the rudder surface on a shelf. Removed dust and patched a few scratches with small doilies cut out of polyurethane tape. In a similar way than for the elevator gap seals, I lubricated the rudder seals and glued the one above the top hinge to the fin. Next step was to install the rudder surface by bolting the two hinges on the fin using new hardware. While torquing, It was a little tricky to make sure the tail wire attachment horns were on the proper orientation. Here's the result with the tail wires fitted, but not torqued:

Next step will be the tail rigging!

Elevator surfaces

Today I installed the elevator surfaces on the h-stab. First I cleaned up the gap seals and the lubricated them using lithium grease. I glued the seals outboard of the strap hinges to the stab so that they don't slide off in flight. I used one bead of Permatex weatherstrip adhesive for that. The two bolts on the pictures are the AN4-17A going through the strap hinges.

I installed two new KP4 bearings to the root of the elevator surfaces and then fitted the surface in place:

The lithium grease greatly reduced the friction when moving the elevator. Before that, it used to make the sound of an old door cracking. Now it's quiet and smooth.

Next time I plan to install the rudder surface and tail wires!

Horizontal Stab

Took a pause from the idler saga and reinstalled the horizontal stabilizer. I made paint touch ups and installed all new hardware:

I also repaired little nicks on the lower tail wires. Will replace the clevises with new:

 

Next step is to install the elevator surfaces!