January 27, 2020

New Fuel System Components and Autopilot Servo Pushrods Story

My special-order fuel selector valve from Andair arrived yesterday. I’m pretty impressed with the build quality, it certainly seems worth the price. I opted for a remote install version due to the solid fuel lines I’m running. The remote version comes with an extension bar and a u-joint. Now that I have the valve, my next task is to figure out exactly where to put it, and fabricate a bracket for it.

The valve selector knob
Fuel selector valve body, with AN6 flare fittings all around

I also found a replacement parking brake valve through Grainger – not my usual supplier for airplane stuff, but they had a nice valve with the correct size and thread fittings. This particular valve is designed to be panel mounted, so it has a little jam nut to secure it. It feels a lot more substantial than the Alpha Fittings valve that was included with the kit. I have to upsize the hole on the throttle panel slightly for the new valve, it needs a 9/16” hole (about 15mm) vs the 12mm hole provided on the panel.

Grainger valve on top vs the Alpha valve on bottom
The Grainger valve also has a larger handle made of metal vs a plastic handle

Next is a cool little story about my autopilot servos. When I received my TAF finishing kit a few weeks ago, I discovered that the kit doesn’t include pushrods for the autopilot servos. Fortunately, Garmin does offer a generic push-pull pushrod install kit, but the pushrod included is just a hair too short – 8” vs 8.5” (215mm) required. The Garmin pushrods are also just bare aluminum bar stock – it’s up to you to cut them to length and then thread the ends with a 10-32 tap.

A tap is easy enough to buy, but to properly drill the hole in the end of the bar you need a metal lathe, which I don’t own… and didn’t feel like buying for this small task. It’s also easy enough to buy a longer bar of 6061 aluminum, but again I would need to cut it to length and still have to drill and tap the ends.

Another Sling 4 builder (Rodney L) ran into the same dilemma. Rodney’s solution was to find a local metal shop to machine the rods for him.

I decided to do the same. My hometown conveniently has two metal shops, so I contacted both. Unfortunately they were both big production houses, and my one-off job wouldn’t be worth their time. But the owner of one shop put me in contact with a friend of his – Mike – that happens to live nearby at the Brookline Airport (NH16), and he was happy to help me out!

I provided Mike with a drawing for the pushrod, and a few days later he showed up at my house with a pair of beautiful anodized aluminum pushrods, ready to install. I have a few pics below of the pitch servo pushrod loosely installed to check fit. Mike is also a pilot and is really interested in my plane. He has built two planes himself, so I look forward to getting to know him better, maybe learning a thing or two.

I’ll be away for the next few days visiting family and friends for Christmas, but I have a pile of work for me when I return. Happy Holidays!

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