Idler 2.0 part III

Just a quick post today to close the loop with the idler saga. I fitted the KP4 bearings with the spacer in between. At first, when pressing the bearings in, they did not rotate freely due to residual load on the spacer. I took a screwdriver to play with the spacer radially and after a few cycles, the bearings rolled well. Here is the final product:

In position once all fasteners propely torqued:

I also fixed the new trim tab to the elevator for the first time today. Next step is to paint it and connect the trim tab wire!

Trim tab

At the end of my flying season in 2014, I found a crack on my trim tab during a preflight inspection. I stop-drilled it as a temporary measure, but promised myself to make a new one. Here is what my old trim tab looked like:

The trailing edge extension has been added at some point by one of the previous owners, but I'm not 100% sure why. The most probable cause is that it didn't have the full +7.5/-42 degrees travel recommended in the assembly manual so it was decided to add more surface.

Below is a better shot at the crack. The end of the control horn and the beginning of the trailing edge extension are almost on top of each other. This is certainly the main cause of the crack developing.

Without knowing the full story behind the trailing edge extension, I decided to err on the conservative side and make a one-piece type trim tab with the same area as the old one:

The brown block behing the control horn is phenolic. I read somewhere that some Pitts Model 12 are made that way and I thought it was a good idea to distribute the load more evenly along the chord of the tab. I also increased the depth of the control horn for the same reasons.

I went to my friend Paul's shop to build the parts. Big thanks to him for his great help! He machined the phenolic block to a perfect fit! The trailing edge bend was not straightforward to do. What we ended up doing is tack weld a rod on the edge of a flat plate and use this as a dye to press the metal sheet between two blocks of steel. I was very happy with the result.

Then I went to see my other friend Scott to use his press drill to make all the required holes. This is probably the most sheet metal work I'm ever going to do on this airplane:

Then  I cleaned all the parts and used Alumiprep/Alodyne to create a corrosion protection coat:

Finished the assembly using Avex rivets and AN525 8-32 screws for the control horn:

Next step will be the paint and installation on the airplane!

Idler 2.0 Part II

Finally had the chance to fit the new idler in the airplane with all the elevator control system connected from the sitck to the elevator. I wanted to do that before painting the idler in case i had trimming to do first.

On the first try, there was still a little restriction when deflecting the stick to the RH stop. I suspected the washers I added on each side of the rod end connected to the aft hole of the idler to be interfering with the bearings. I grinded the washers to allow more clearance and it helped, but didn't cure completely the problem. I used a belt grinder to remove material from the washers:

After a thorough inspection of the rod end clearances throughout the range of motion of the stick, I haven't found any fouling condition. I was puzzled. This meant that I was reaching the limit in twist of the rod ends.

I took a step back and realized that the stick had more travel on the RH side than the LH side... In fact, I had only one washer on the RH stop bolt vs two on the other side. Before changing anything, I measured the angle on each side and confirmed the RH travel was 24° vs 20° on the LH side. The travel recommended in the assembly manual is +/- 20° so I decided to add a washer on the RH stop bolt and get back to symmetrical travel. I was happy to find that the restriction was gone after that.

I removed the idler, cleaned, primed and painted. Next step is to fit new bearings and reinstall in the fuse!

Idler 2.0 part I

Quick post today: pick up my new, thicker idler today. The internal distance between faces went from 7/16 (first idler) to 17/32. This is going to allow rod end clearance adjustment using a standard washer on one side and a light washer on the other side.

If you wonder what the bushing on my cutting board is for, it's a spacer that goes between the two KP4 bearings so that they don't take axial load when torquing the axle bolt.