Friday, July 9, 2010

A Fitting End

Well, no, not really "a fitting end." More accurately, "fitting the end fittings."

The idea behind having a brake master cylinder and brake pedal on all four of the rudder pedals is to allow the brakes to be used from either seat. This is useful for instructing new pilots (don't you wish you had had a full set of controls when you were teaching your kids to drive? Same idea, higher stakes in the airplane.) The thing is, though, that even with two full sets of brake controls we are left with the inconvenient truth that there is only one set of brakes. To allow two sets of pedals to work with one pair of brakes, the master cylinders need to be tied together somehow. That 'somehow' is done by running lines between the master cylinders to share not only brake fluid but pressure applied thereto. I fabricated those lines tonight.

There are two types of brass fittings in use: 90 degree elbows and 45 degree elbows. The plans are clear about which goes where, but you do have to pay attention because there is an asymmetry here. The left (pilot's side) pair of cylinders use three 90's and a 45, while the right (screaming passenger's side) uses two 90's and two 45's. I did the pilot's side fittings first because really, it is all about me, isn't it?

I have to confess that I don't know the official answer as to how far these things are to be screwed in. The method that I have been using is to screw them in until I feel significant resistance, then go one more full turn.

UPDATE - Nov. 21, 2010: I suggest getting yourself some of this stuff (also available at car parts stores):

I re-did all of my fittings using this stuff and was able to easily get at least one more full turn on each fitting.

Here's the rider's side:

The two 45 degree elbows at the top will eventually pass through the firewall and attach to the brake fluid reservoir. The bottom 90's are the fittings for the crossovers. On both the pilot's and petrified rider's side, the 90's are deliberately canted inwards to allow the stiff plastic lines to pass between the other lines at the top of the cylinders.

So, now for the hard part. The lines need to be cut and have fittings put on. They're very much like the fuel lines in that way. The only real difference is that they are flexible and don't need to have bends put in them. The kit comes with two 15' lengths of line, and each 15' gets cut into three sections. I wrote the measurements of the six lengths into two columns and added them up to make sure I didn't end up running short of line in one of the lengths. You never know, right? There are a 180" in each 15' length, so if I cut them just like I wrote them down, everything should come out just fine. In theory, anyway. Time will be the final arbiter.

Just as with the fuel lines, the order of doing things is critically important. The nuts go on first, then the sleeves, then what passes for the flare. The flare in the fuel lines was created with a special tool. In these lines, it is done by shoving a little brass tube into the end of the line. For something that sounds so simple, it's surprising how difficult it can be. For the first one, anyway. Once I learned the tricks, the remaining three were simple.

So, the first order of business is putting on the sleeves and nuts.

The sleeve is supposed to end up 1/8" from the end of the line. I measured and marked the 1/8" point, slid the sleeve down the tube to the mark, and held it in place while getting the brass flare started. It takes quite a bit of a push to get the brass flare into the tube far enough to hold the sleeve into place, and once you do that's about all the further you can get it to go in no matter how hard you push.

This is where the plans suggest soaking the thing in boiling water for a minute, then pressing the flare the rest of the way in.

It sounded oh so easy. You have to consider, though, that the brass sleeve is going to be hot as blazes and the tube is going to be wet and hard to get a good grip on. After numerous (painful) tries, this was as close as I could get:

That's nowhere near good enough. Brakes are just one of those things that you want to work each and every time, preferably without spraying leaking brake fluid all over the place. I was going to have to figure out a way to get this to work. I boiled it down (heh!!) to two distinct possibilities:

  - if I could get the water hotter, it might loosen things up a bit,
  - and if I could find a way to exert pressure without having to try to get a grip on a wet, slippery plastic tube,

I just might have a chance.

First thing first: making water hotter than normal boiling. Two ways to do that: put it under pressure, or add impurities to the water. First one, hard. Second one, easy. I added a tablespoon of salt to the water. I doubt if it makes a whole lot of difference, but the placebo effect alone made it worth the effort. It worked for Dumbo, after all.

As far as finding a better way to apply the downward pressure, I realize that I could use the nut for that. As long as I didn't let it soak in the super-heated salt water, anyway. I don't know which of those (if not both) did the trick, but the trick was done.

The 45 degree elbow was a little trickier. The sleeve is permanently attached to the nut, so the entire process had to be modified. I had to be a little more careful about getting the sleeve's 1/8" gap from the end of the hose correct, and I had to wear a glove to press down on the nut since I had no choice but to allow the nut get heat soaked too. The concepts still worked, though.

With the fittings on, there's no difficulty whatsoever in getting the lines installed.

I sure wish there was a way to leak check them! They are never going to be this easy to get at again. If I ever have to tighten or replace one of these fittings, it's going to be done by crawling down in there. As I've learned with the RV-6, that's not a fitting end to any story.

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