Thu Sep 23 2010

Pilot / pax heat control linkage

In order to make a nice pivoting linkage for the heater control, I decided to fabricate some 3/8 inch diameter washers from some 0.062 thick material. I'm glad I keep all the little bits and pieces of scrap for situations just like this.

I found this nice little mandrel with a 1/8 inch diameter screw. Chuck it up in the drill and hold the edge against the sanding disc while both are running and I've got a nice .375 diameter washer. A little polishing using the same technique with the scotchbrite wheel had the edge nice and smooth.

Three washers in total.

Next up was fabrication of the main bellcrank. 2 17/32 center to center as noted earlier. The bellcrank is 0.040 thick so there will be 0.022 of side clearance to avoid binding.

Two more washers for capturing the'll see what I mean soon.

Here is the little horizontal linkage, pivot washer, and capture washer.

Ok...this is what it'll look like when I've pulled the handle to shut off the pilot's side heater vents. The cable will be coming from the left in this picture, and will be attached to the bottom of the bellcrank. That'll cause the top of the bellcrank to push to the right of the picture (actually to the left side of the airplane), and close the vents. It's pretty confusing since we're viewing this as from the engine, looking aft.

And here's how it'll look in the normal operating position (control knob pushed in). I'll be joggling the bellcrank up to allow for attachment of the bugnut or B Nut and thus the control cable. This is pretty close to being done. I just need to make up a spacer for the center pivot of the bellcrank. It needs to be at least 0.080 thick due to the way the linkages overlap. Since I don't have any 0.080 thick material, maybe I'll stack two layers of 0.062 and an 0.020. Dunno.