REFLECTOR: Brake heating question

Al Gietzen ALVentures at cox.net
Wed Sep 23 12:06:02 CDT 2009


Drawing on my past experience in heat transfer analysis; I concluded that
the dominant heat transfer mode, for the RG, with the Matco brakes, is
radiant heat from the rotor to the leg. I'm sure there is also transfer
through the axle; however, that conductive transfer path from the rotor,
through the rim, and through the bearings to the axle is rather torturous,
so we'd expect that the temp drop from rotor to leg would likely be large.
Probably more likely to damage the tire at the bead before damaging the gear
leg.

 

Because of the air freely moving between the rotor and the leg on the RG,
conduction through the air to the leg is likely small.  The best way to stop
radiant transfer is with a reflective baffle, with air space behind.  A
reflective wrap on the leg is good, but the material is a conductive path
from the reflective surface, which will get hot.

 

With wheel pants the story is somewhat different because of the trapped air;
but I'd say a reflective baffle is still important, as are air vents in the
pants.

 

We have no experimental data on the heat flow paths, so my analysis could be
wrong.

 

OTOH; I've done 285 landings with my plane (SE RG), on various runway
lengths, and with the associated taxi maneuvering, without a problem. My SS
baffle (I think it is .016") attaches between the axle and leg, with no
other insulating material between.

 

FWIW,

 

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Wednesday, September 23, 2009 6:28 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Brake heating question

 

My question would be, what kind of heating are people talking about?

 

1.)  Heat build up inside wheel pants?

 

2.) Radiant heat from the disk transferring  through the air  onto the

exposed gear leg?

 

3.) Heat transfered from the disk, to the axle and then through the axle

into the gear leg?

 

1 & 2 seem to be the most likely and require different solutions.

 

I'm having a hard time seeing how #3 really happens.   Seems like that

amount of heat would really fry the bearings also.

 

Scott

 

David Ullman wrote:

> I frequently read on this site about brake heating problems.  Is this just

> with the larger craft?  I have an SE. Should I be installing a heat shield

> while I am building it?

>

> David G. Ullman 

> Robust Decisions

> ullman at robustdecisions.com

> 541-754-3609

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>  

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