Matt's RV-7 Project

Brake fluid

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.

Posted in Fuselage, Landing gear

Fuel caps

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:

Posted in Fuel Tanks, Wings

ELT service

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:

Posted in Electrical/Panel

Cowl fasteners

November 19th, 2023

I have been putting off finishing the cowl fasteners for no good reason, so I decided to tackle this job at last. I am using the standard hinges on the vertical portions of the lower cowl at the firewall, machine screws behind the spinner, and Skybolt quarter-turn fasteners everywhere else. In total I needed 42 sets of studs and receptacles to attach my cowl:

I put the cowl on the airplane, made sure everything was still fitting well, and drilled the existing pilot holes up to #30:

Then I removed the upper flanges from the firewall, and used the provided templates to drill all the required holes. Drilling the center holes from #30 to 11/16" with the unibit generated a tremendous amount of shavings, and required some concentration to keep the bit from wandering off-center:

After preparing the flanges, I riveted everything to the firewall. Afterwards I realized that this might be the very last structural riveting of the whole project… sure there will be additional rivets for nutplates and so forth, but I think this is the last bit of primary structure that was still left un-riveted.

Due to the limited space available in places, I chose to attach the Skybolt receptacles to the flanges with countersunk blind rivets:

Back to the upper cowl, I drilled the #30 pilot holes along the aft edge up to 15/32", again watching to make sure the unibit didn't wander:

After installing the studs and grommets in the upper cowl, I did a test fit and was happy to see that I had everything lining up well so far:

Since the mounting flanges along the bottom of the lower cowl were already riveted to the firewall, I had to drill the holes in-place:

To avoid drilling through the engine mount or various nearby components, I made the above holes using a 5/8" Rotabroach cutter, with a washer and a rubber o-ring acting as a makeshift drill stop:

Using the Rotabroach cutter for the bottom flange holes gave me an idea for a better way to drill the holes in the fiberglass cowl. Instead of separately drilling the holes in the cowl and the underlying flange and then hoping they line up, I realized that I actually had a way to make these holes perfectly concentric.

On the cowl side flanges, I used the Skybolt template to drill the #30 holes for the rivets and lock pin, but I left the center hole at #30:

(yes I realize the edge distance is not great at the front, but it's too late to extend these flanges now)

Here's the entire process in one image: I installed the cowl with clecoes, then removed one cleco, cut through the fiberglass using the ejector pin on the Roatabroach as a pilot, and replaced the cleco with a 1/8" fender washer underneath. Repeating this process for every fastener location gave me a row of perfectly-placed holes in the cowl, even where the holes in the fiberglass were wonky or buggered up.

The Skybolt grommets require a 15/32" hole and the closest Rotabroach cutter I have is 7/16", so I cut all these holes slightly undersized in-place and then enlarged them the last 1/32" on the workbench with a unibit. Then I removed the lower cowl and used a 5/8" Rotabroach cutter to make the holes in the flanges for the receptacles:

Doing it this way guarantees concentric holes, since you're using the same pilot hole to guide the cutter in both cases… really a special kind of match-drilling.

After deburring everything, I riveted the remaining receptacles to the lower cowl, and installed it back on the airplane:

And sure enough, every one of my fastener studs engages perfectly with its receptacle:

Adjusting the depth of the receptacle inserts takes some trial and error. You have to install the cowl, mark the ones that are too high or too low, remove the cowl, unclip and adjust each receptacle, and repeat. Each half-turn of a receptacle adjusts the depth by 1/64", so although you can't get every one perfectly flush, you can get pretty close:

After finishing the Skybolt fasteners, I bent the ends of the lower cowl hinge pins upwards, and riveted these little clips to the inside of the cowl flanges. Now the pins are secured from rotating or backing out, but they can easily be sprung loose when required:

The airplane looks pretty good with the cowl attached. I still have some minor fiberglass work to do, but that job will wait for a future work session:

Posted in Cowl, Firewall Forward

Wingtip lighting & final installation

October 1st, 2023

I spent a couple evenings installing the eighty or so nutplates that will be used to attach the wingtips. Once again I slightly under-squeezed the rivets to avoid cracking the fiberglass, and I was none too picky about achieving countersinking perfection. These holes will all be hidden when in use, so as long as everything fits together and the nutplates are nominally attached, it will be good enough:

The Whelen nav/strobe heads are designed to be screwed to a mounting plate, which is in turn affixed to the wingtip. However, they don't give you much of a hole for the wiring, which is sort of annoying. I passed the wires through the mounting plates, then installed Deutsch DTM connectors, which will have to be de-pinned if I ever want to separate these components:

I have known about Deutsch connectors for a long time, but only recently picked some up to play with. Once you understand the installation process, these connectors are just as easy to use as Molex connectors, and are apparently vastly more reliable. Over time I'll probably replace any problematic Molex connectors with Deutsch, but I can't be bothered to go back and redo any of my old work at the moment.

I cut holes in the wingtips to allow the connector to pass through. Luckily this will be hidden behind the mounting plate, as will the extra hole I previously drilled to help with fitting the lenses:

I attached the mounting plates to the wingtips with large-area washers so the fiberglass won't crack. Since rough fiberglass is abrasive, I used some snake skin on the exposed wires to prevent chafing:

With zip ties, grommets, snake skin, and clamps, I cleaned up and secured the wingtip wiring. Later I realized that these might actually have been the very last wires I needed to finish on the whole airplane: