The basic RV-8 design does not have a parking brake. I thought about adding one, but couldn't come up with a simple way to add one. The recommended routing of the brake system holes is very nicely laid out, and I didn't want to add several feet of hose to go to a parking brake valve.

But, I eventually realized that I really should have a parking brake, as I plan to do a fair bit of traveling, and that means some times I will end up on a sloping ramp, or with lots of wind. I would be a real trick to leap out of the aircraft quickly enough to stop it from rolling too far.

A few weeks ago I saw a message on theVAF WWW forumsfrom Mickey Coggins describing a very nice way toinsert a parking brake valveinto Van's recommended hose layout. I decided to order aMatco parking brake valveand add it to the system.

The first task was to remove the old bracket that held some elbows in the brake system hoses, and manufacture a new bracket to put the parking brake valve in this location. This sounds simple enough, but I was trying to do it on 31 Dec, and we had done a bit of a work up for New Year's Eve the evening before. I made two minor screw ups, then decided that maybe this was not a good day to be working on the aircraft. We didn't hit it too hard on New Year's Eve, so I was able to finish the bracket and paint it on New Year's Day.

This shows how the bracket fits against the valve.

Here is a shot from the front baggage door area showing the fittings going into the front side of the parking brake valve.

After I put the bracket in place, I saw a problem that I hadn't expected. The 45 deg angled fittings at the top of the valve forced the brake lines high enough that they would interfere with some other stuff I had installed on that bulkhead. Big depression. I needed to have 90 degree elbows there, but there wasn't room to screw the second elbow in without it hitting the first one.

I went back into the house, and started flipping through my Aircraft Spruce catalog, hoping for a revelation. I stumbled across the AN914 elbow, which is much more compact than the AN822 elbow that I would normally have used. This elbow was short enough that it could be screwed in place without hitting the other elbow. I would need to then install straight nipple in the elbow, but that was OK. The AN914 elbow reminded me of a Street Elbow, used in automotive fuel systems. I rushed to the aviation aisle at Canadian Tire, and purchased two brass Street Elbows.

Here is the parking brake valve after replacing the 45 deg elbows with street elbows and straight nipples.

Next, I removed the section of aluminum tubing that went from the parking brake valve area down into the right landing gear box. I shortened it a bit, and flared the end to match up with the parking brake valve. But, when removing it, I had managed to bend the part that went down into the landing gear box. I straightened it out, but I didn't quite get the same angle. There was hardly any room to work down in the landing gear box, so I was working by feel. I spent hours trying to get the fitting to screw back onto the elbow at the bottom of the landing gear box. I couldn't get it line up perfectly, so it wouldn't go. Arrgh.

Today I finally realized that I could loosen the nut holding that elbow in place at the bottom of the landing gear box so I could wiggle it around into different orientations. I was finally able to get the fitting to screw onto the elbow. Whew! I'll attempt to modify the tubing on the other side without removing from that fitting. Lesson learned.

The orientation of the control arm on the parking brake valve is such that a push-pull cable from the top would work in the sense of Pull to release the parking brake, and Push to engage it. This is not acceptable. I would need to add a bellcrank to reverse the motion of the cable. Too heavy and too complicated. Fortunately I can reach the control arm by leaning forward a bit and reaching under the instrument panel. So, I will not install a Bowden cable to control it. I will need to install a spring-loaded clip to hold the control arm in the OFF position, to ensure that the parking brake does not get engaged when I don't want it.