Brake Failure

David-aviator · #1 09-01-2009, 08:31 PM

I've been wondering when an aluminum brake line would fail and it did yesterday after about 6 years of service. A leak developed at the flared tube where it goes into the brake assembly. The B nut was tightened and the leak stopped but when reinstalling the gear faring and repositioning the line slightly, it broke some more and leaked worse than at first. I do believe it is time to install a flex line since the aluminum tube seems to have become slightly brittle in this area.

The plan is to use the 1/4" brake hose (VA-118-1) from Van's and run it up the gear strut as far as it will go and connect it to the aluminum line coming down from the fuselage.

I know this is not the first aluminum line failure. What have others done to get more flex at the brake assembly?

gasman · #2 09-02-2009, 02:43 AM

You won't have room to couple it in the gear strut cover. Best to run it into the fuselage. And 1/4" is way too big for this. Best to have them made by BONACO.

Jaknjoan · #3 09-02-2009, 07:56 AM

I have always used 3/16 inch stainless braided flex line because it is smaller and takes up less room. You will need #3 flared fittings, including a #3 to #4 transition fitting where you change from 1/4 inch to 3/16 inch. The end fittings are all steel that you make yourself. They are rated to 3,000 psi.

I have always purchase the raw flex line and fittings from Columbia Airmotive located in Troutdale, Oregon. They have a website.

JT

David-aviator · #4 09-02-2009, 08:17 AM

Thanks for the info, guys. I need to do some measuring of area between the strut leg and cover. It looked like the 1/4" hose would fit nicely but the -4 coupling going from tube to hose may not.

Based on the response here, it would appear not many people have had a problem with the aluminum lines as per the plan. I may just replace that line with a careful loop and flare.

N941WR · #5 09-02-2009, 08:26 AM

David,

They are correct. When I first built my lines I put a union on the gear leg and 18" of flex line to the brake. Sure enough, the fairings wouldn't go over the union. The fix was to run the flex line all the way from the firewall down to the brake.

Here is a picture:

And here is the solution:

Beancounter · #6 09-02-2009, 10:40 AM

For what its worth I used the whip meant for the end of a grease gun. They are rated for petroleum products (DUH) and something like 2300 psi if I recall correctly. I was able to make the connection from the alu line to the flex line just below the gear fairing, thus avoiding the fit issues you are experiencing. Just anothe inexpensive alternative.

David-aviator · #7 09-19-2009, 02:28 PM

Quote:

Originally Posted by David-aviator

The plan is to use the 1/4" brake hose (VA-118-1) from Van's and run it up the gear strut as far as it will go and connect it to the aluminum line coming down from the fuselage.

After some delay due to family commitments, the beast is finally air worthy again. I flew yesterday and today with 8 landings around the area and no leaks so far.

I ended up using the 1/4" (VA-118-1) hose after all to replace the aluminum tube as per the plans. While it may not fit inside some RV gear leg fairings, it does fit under the the -7A fairing. It runs up the front of the gear strut to about 6" from the fuselage and is connected to the aluminum tube with AN4 fittings. The gentle turn to the brake mechanism allows for relatively free caliper action and it works.

Right brake fixed....and on to better stuff.

I sure enjoy flying this light weight machine. Today I came across KSUS from the south at the required 1800' for a left down wind to 8L. A close in descending full flap 180 degree turn to final at 65 knots made it a nice tight close in approach. The key is getting the speed back before starting the descent. A friend was on the down wind a mile behind and I was off the runway before he turned final.

Here at our 2200' grass strip, I've been working on a 60-62 knot approach with full flaps over some trees on the west end. (The runway length lost due to the height of the trees is about 500').

Again, the key is speed control on the descent. It's easy to see it increase to 70 knots if one doesn't pay attention. That extra speed is totally not needed going into the flare. Also, most helpful is the Dynon AOA system. I had a friend in the right seat yesterday and that device does work. It called for slightly higher airspeed than I normally see when solo. The AOA also is good indicator as to increased stall speed in a low speed turn.