Let's not twist again

A lot of RV airplane projects that aren't nearly as far along as mine have had their first flights, but I'm not ready to fly mine quite yet. I decided some time ago that I would complete the plane as far as possible before its flight test, even if some of the parts I'm working on will be removed for first flight.

Hello, gear leg fairings!

The fairings, which will not be installed for first flight, are usually left to the "I'll get around to it stage" of experimental aircraft projects. They're needed to provide a smoother air flow over the wheels and gear legs and increase speed by 5-10 knots, a helpful thing when you consider the current price of a gallon of 100LL fuel at Fleming Field (KSGS) is currently $5.19.

But the process of fitting them properly is painstakingly slow. By this point in the construction process, however, if you haven't learned patience, you probably shouldn't be building.

My pal, Chris Knauf, was good enough to do some of the construction in the gear leg fairings and he did a great job getting them trimmed and the hinges installed. All that's left to do is fit them properly.

A misfitting fairing can act like a rudder or aileron and change the direction the airplane wants to fly from straight-and-true to didn't-we-just-fly-over-here?

My job this week has been getting those fairings fitted properly. The right-side leg fairing fit pretty well-- a very minor twist that I can take care of easy enough.

Last night, I set the left-side fairing up. The process for this is pretty funky. You mark the centerline of the fuselage, then pick three points on the gear-leg fairing and make an "extended centerline" back to a point on the horizontal stabilizer. I'm using an advanced aviation tool to provide the marking of that point from the tail to the floor -- a broomstick; three actually.

Then I take dental floss (it doesn't sag like string and allows for more precise measurement, plus it makes the hangar smell minty fresh!) and attach it to one of the three points on the front of the fairing and run the string back to the broomstick, so you have two parallel lines of dental floss to the front of the fairing. This, basically, simulates airflow over the fairing.

The distance between the center of the aft end of the fairing and each piece of string should be the same, indicating that the fairing is perfectly centered in the airstream with regard to the centerline of the fuselage.

On this particular fairing, I adjusted the bottom of the fairing to make that distance about 15/32". The mark halfway up the fairing was a little more off, and the distance on one side of the top mark was about 14/32" and on the other side was about 27/32". This, you may have surmised is the dreaded "twisted fairing."

There's no real way to work this out because the fairing is only clamped at the very top. There's nothing -- without an intersection fairing -- to hold the bottom from moving in order to twist the top into position.

The solution? I don't know, but I assume I'm not the first one to experience this problem. I'll begin researching it and eventually solve the problem and include it in an article I'm writing for the RV Builder's Hotline.

I just need a little more patience.

Putting the brakes on spring

What a difference a week makes! Last week, when I put together the right landing gear components, it was in the '70s, gentle breezes, and perfect. Today it's in the '30s, a wicked wind, and some sections of the state picked up almost two feet of snow.

I'm down to the last couple of drops of kerosene in my heater; I'd rather not buy another 5 gallons at $4 a gallon (although who knows how much it'll be next year), so the cold snap may require more long underwear if I'm going to work at the hangar.

I worked on the left landing gear today and I'm pretty sure I'm missing something in assembling these things.

Here's why:



This is the bracket for the brakes all set to go. There are two enclosed holes onto which the caliper (which has two prongs) fits. What has me confused is there's nothing else in the system to hold the caliper firm.

Here is the setup being inserted. I've taken off the outside brake pad to fit it against the wheel.



After it's inserted, I put the inside brake pad back on.



Now the caliper enclosed the wheel, so it can't fall off. But, it can move since the two prongs (1) float inside their hole. As positioned, you can see that the brake pads ride just off the wheel (2), but there's play in the hole caliper, so it doesn't take much to have the pad rubbing on the wheel.

That's why I say I must be missing something. I know that the brake line offers some rigidity, but I can't image you want an aluminum line performing that task.

So tell me? What am I missing?

Update: One of my RV heroes -- Tom Berge -- took a look:

You are missing nothing. The caliper floats as you have noticed intentionally. Yes, the pads can hit the disc, but that is normal. If the caliper were to be mounted rigid, then as the pads wore, the brakes would no longer contact the disc as intended.

Make sure the piston is inserted correctly in the caliper and that the bolts holding on the other half of the pads are safety wired. The brake line should have a loop in it to allow stress relief. I believe the plans show this.