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From: Gary Casey <glcasey@adelphia.net>
Subject: Re: carbon-carbon composites

At Bendix many years ago we built some of the first carbon-carbon  
brakes for aircraft.  Being a car nut, of course I asked why not use  
them for cars.  There turns out to be a good reason and it would also  
apply to our aircraft.  On large aircraft the requirement is to make  
one stop and then it's allowed to wait at least 30 minutes for the  
brakes to cool before another takeoff is attempted.  Consequently the  
brakes are "full-diameter" alternating stationary and rotating  
disks.  There is very little air contact and therefore little  
oxidation.  A car or our planes need to have significant heat  
transfer capability to the air so that the brakes can cool more  
quickly after a stop.  Or in our case allow taxiing with more brake  
application.  The rotor, being carbon, will oxidize (burn), gradually  
eroding itself away.  Race cars don't have that problem because the  
owners are willing to replace the rotors often.  commercial airliners  
also get rotors replaced fairly often, but their rotors are protected  
from exposure to air.  I'm afraid carbon rotors aren't in the cards.   
And yes, while they are very strong are probably very brittle.   
Aluminum, on the other hand, could be used, but that's another story.
Gary
On Apr 14, 2008, at 3:01 AM, Lancair Mailing List wrote:
>
> Posted for "Dan Schaefer" <dfs155@roadrunner.com>:
>
> Fred,
>
> Question here regarding a carbon brake disk.
>
> Would a carbon disk be brittle or easily damaged by impact on the  
> edge? The
> reason I ask is that, on my older 235 (original brakes), when  
> experiencing a
> flat tire during roll-out, the edge of the disk sustained damage  
> around the
> entire outside diameter from contact with the runway surface.  
> Obviously, the
> steel can take it without shattering - but, in your opinion, how  
> might a
> carbon disk fare?
>
> Dan Schaefer
> Early LNC2 N235SP
>