While I have my KR at home for some electronics upgrade and paint
repairs,, I think I will put metal flexible lines on my brake calipers
John Shaffer, N455JS. Fremont, Ohio.
-----------------------------------------From: "Jeff Scott"
To: krnet@list.krnet.org
Cc:
Sent: Sunday April 18 2021 5:16:38PM
Subject: KR>Re: extended taxi test
I've seen numerous failures of the plastic brake lines due to heat.
One in a Rutan Defiant caused the loss of the aircraft due to a brake
fire while braking during rollout after landing. The other was a RV-4
that popped both brake lines after a long taxi causing no damage to
the plane, but ruining the fly-in weekend for the owner since she got
to spend the weekend searching for parts and bleeding brakes. The
nyloflow plastic tubing is rated for 1000 psi and holds up to braking
pressures reasonably well. However, it will not tolerate hot brakes if
the line is inside the wheel fairings or attached to an overheated
caliper. If one wants to use nylaflow, nylaseal, or polyflow brake
lines on your project (which makes for an easy installation), it is a
good practice to terminate the plastic line outside of the wheel
fairings and use aluminum, stainless, or properly rated pressure hose
the remaining few inches down to the brake calipers. That eliminates
any chance of having the brake
lines fail due to heating, and eliminates any chance for brake fire
with 5606 hydraulic fluid. Note that some builders choose to use
Skydrol (TM) Hydraulic fluid rather than 5606, but the vast majority
of light aircraft use 5606 and most FBOs will have 5606 in stock if
you ever need it and are unlikely to have Skydrol on hand. The two
fluids are not compatible and should not be mixed.
On my KR, I terminated the plastic lines at the bottom of the gear
leg and used aluminum lines inside the wheel pant. You'll see the
fitting location right at the top of the intersection fairing in this
photo:
/>
One other note on the plastic brake lines. The plastic lines do tend
to expand a bit under pressure. With the expansion comes a loss of
brake pressure. I have fixed a number of brake issues on Experimental
planes by swapping out the 1/4" Nyloflow brake lines for 3/16" lines.
I noted recently that the Aerion Lightning aircraft are now using 1/8"
Nyloflow lines for the brakes to prevent loss of brake pressure due to
the tubing expansion under pressure.
Jeff Scott
Arkansas Ozarks
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