REFLECTOR:Brake selection.

[Scott Baker]

    Somehow Rob's excellent suggestions on how to avoid prolonged over-use
and over-heating the brakes has turned into a question about judging the
stopping power of the MATCO brakes.
    I believe that Rob, in an earlier post, gave his opinion that the
MATCO's were sufficient for normal operations using the piloting techniques
that he uses.
    Your question about an aborted take off deals with an emergency stop
situation.  The ability of the brakes to bring the aircraft to a halt during
an emergency stop situation, and do so _without overheating_ is not the
principle criteria for judging brake effectiveness.  I love the documentary
on the certification of the Boeing 777 where the criteria for a "passing
grade" for the brakes following an aborted take off emergency stop situation
was that the aircraft fuselage doesn't catch on fire after 5-minutes.  The
program managers at Boeing told the support crew that they didn't want to do
the test twice because of the cost.  They expected the brakes and the tires
to be ruined following the test - which indeed happened.  Flames leapt from
the brakes and the tires literally melted following the emergency stop; but
the fuselage didn't catch fire and everyone was happy because of the
successful test.

Scott B.

----- Original Message ----- 
From: "Greg Poole" <gpoole@zeta.org.au>
To: <reflector@tvbf.org>
Sent: Tuesday, April 06, 2004 8:16 PM
Subject: Re: REFLECTOR:Brake selection.


> Dear Rob,
>
> Thanks for going to the trouble to detail your understanding of the brake
> situation....after what Scott B. confirmed (-everything?), I'm not exactly
> sure where that leaves the situation in terms of a missed takeoff and the
> ability of the brakes to pull up at full gross without overheating if we
all
> agree that that should be the principal criteria for judging brake
> effectiveness.
>
> Greg.
>
> ----- Original Message ----- 
> From: <RJohn15183@aol.com>
> To: <reflector@tvbf.org>
> Sent: Wednesday, April 07, 2004 4:58 AM
> Subject: Re: REFLECTOR:Brake selection.
>
>
> > In a message dated 4/5/2004 6:48:28 PM Eastern Standard Time,
> gpoole@zeta.org.au writes:
> >
> > > Have I got the general consensus right? ...and just how
> > > successful has modifications been to keep heat from the
> > > Matco's from affecting the main gear legs?
> >
> > Greg,
> >
> > IMHO and in my experience heating of the gear legs is a non-issue as
long
> as the proper pilot technique is used. IOW, simply don't ride the brakes!
> >
> > I don't think it is so much how hot you get the brakes it's how long you
> keep them hot and how much time the heat has to soak into the entire brake
> then wheel then axel then finally to the gear leg before. If the duration
of
> the heat event is short then the disc will quickly radiate the heat away
> long before all those other parts can soak up enough to hurt the gear leg.
> >
> > Riding a brake is a sure way to get the long term heat soak needed to
hurt
> the gear leg. I always simply pumped the brakes. e.g. taxiing in a cross
> wind: hit the down wind brake for a few seconds and get turned away from
the
> wind some then release the brake completely until the wind weather vanes
you
> the back into the wind. Then stab the upwind brake hard for few seconds,
> repeat as needed. You end up doing a slightly curvy path along taxiway but
> your brakes stay nice and cool and it's nothing compared to the S turns
tail
> dragger do to get to the runway.
> >
> > Take off in a cross wind? Taxi to the far upwind side of the runway and
> start your take off run with about a 15 degree (or so) angle towards the
> downwind side of the runway. The wind will gradually point you back toward
> the upwind side. After a while you get pretty good at picking the amount
of
> downwind angle to start your run with depending on the crosswind component
> and the width of the runway and you get to the point you can make a take
off
> in a heavy cross wind without touching the brakes at all. Its fun to make
> the wind work for you!
> >
> > Of course your take off roll is one big curve. I should add  I did not
do
> this so much for brake heating as I did it just to reduce my take off
> distance. As noted in the Velo POH riding a brake to fight a cross wind
can
> really extend your take off roll. Plus if you are in a retract as I was
you
> could just leave the gear down a bit longer after the take off roll to
cool
> them off if you felt you got the hot. I would assume that even with wheel
> pants on the fixed gear versions there is still enough air circulating
> through there to prevent heat soaking the gear leg? So heating was not
> behind that technique at all.
> >
> > Landing works the same way, land at a little bit of an angle across the
> runway and let the cross wind do the work for you.
> >
> > Every time I read an article in some magazine about how perfectly
tracking
> a centerline on taxi way and runway indicates a sharp pilot I kind of grit
> my teeth. No matter what you are doing in life, flying, building, working
in
> the garden anything- if you are *good* at it you effectively use *all* the
> resources at your disposal.
> >
> > If I can make the cross wind work for me I believe that makes me the
> better pilot than the guy who just mindlessly tracks the centerline and
> fights the wind and extends his take off roll and heats up his brake etc.
I
> am letting the cross wind work *for* me and that other guy is *fighting*
it
> tooth and nail all the way but he's the better pilot because he rode the
> centerline? Not in my world view. YMMV.
> >
> > DM Rob
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