Archive for December, 2023

Brake fluid

Sunday, December 31st, 2023

Before filling the brake system with fluid, I removed the calipers and took out the pistons so I could install improved o-rings. These are necessary to take full advantage of the higher-temperature brake fluid available these days (MIL-PRF-83282D) and were quite difficult to find in small quantities in the correct temperature rating of -40º to +400ºF. I ended up ordering them from Van's, which took a while due to their current difficulties. I lubed the new o-rings and the caliper bore with silicone before installing.

It's funny that this is all the brakes you get to stop nearly a ton of airplane traveling at highway speeds. Small wonder I chose to use high-temp brake fluid, since these can get really hot under heavy use.

To bleed the brakes, I cobbled together this contraption from a small pump oiler and a special adapter designed to go on the bleeder fittings:

To catch the overflow from the brake reservoir, I plumbed a catch can using a coke bottle and some brass fittings. Additional details of how this works can be seen in the photos below:

Before starting, I put down some old t-shirts under all the potential leak spots, to hopefully keep the floor clean:

I recruited a friend to help pump brake fluid while I crawled inside checking for leaks and tapping on things to clear out air bubbles. Happily we had no leaks and – I think – ended up with a solid result. We went through a lot of paper towels and rubber gloves, and didn't take any pictures during the process, but you may assume it was messy despite our best efforts to be sanitary about it.

Clear tubing at the top of the reservoir allows air bubbles to be pumped out. We kept pumping fluid until the brakes were solid and bubbles stopped appearing in the tube:

The end result was a reservoir totally filled to the top, which is fuller than it needs to be. I used a syringe to siphon out about an inch of fluid before installing the vent cap.

All the accessories are stored inside a messy plastic bag for future brake work. From the quart can of brake fluid I opened, I ended up with about a pint left over, which is stored in a mason jar I stole from my wife's canning supplies.

Fuel caps

Sunday, December 24th, 2023

After sitting untouched for too many years, the fuel tank caps didn't want to come off immediately, but I got them loose eventually:

I disassembled the caps so I could clean out the old grease and replace the ancient o-rings:

Since I started this project, Vans has switched to a different style of fuel cap, so information about this type is getting harder to find. Click here for an exploded view.

I decided I wanted to improve the cosmetic appearance before engraving, so I got out my granite surface plate and wet-sanded the caps and levers using a series of progressively-finer grits. The hardest part was flattening the rough castings using 220 grit; each successive grit after that went pretty quickly.

I progressed to 600 grit, not quite a mirror polish, then applied a vertical brushed finish using a grey scotchbrite pad. I didn't worry about making this look perfect, since these will inevitably get scratched up, but I'm happy with the results:

After researching the fuel tank labeling requirements and the fuel type specifications for my engine, I sent the caps off to Aircraft Engravers. A few weeks later, they came back looking like this:

New o-rings installed and lubed, latches adjusted, and caps reinstalled on the (very dusty) tanks:

ELT service

Sunday, December 10th, 2023

I'm such a slow builder that the batteries in the ELT have timed out, so I need to replace them to be legal. There are three in total, starting with the one in the remote indicator in the panel:

In addition to making entries in the aircraft logs, I put stickers showing the battery expiration dates on the side of each component:

The main battery pack for the ELT itself is huge and expensive:

Despite the expense, a replacement ACK ELT battery pack doesn't come with the required o-ring, so I re-lubed and reused the old one:

The third battery is in the audio alert unit, which I quickly regretted installing on the aft side of the F-707 bulkhead where it couldn't be seen:

When I reinstalled all these units I moved the audio alert unit to the front side of the bulkhead, so it will be slightly easier to service next time:

And while I was crawling way back in the tailcone, I fitted the ELT antenna static suppressor that's now apparently required by a service bulletin: