REFLECTOR: Brake authority

[Scott Baker]

Don't forget the weight of the aircraft.
The XL GTOW is hundreds of pounds more than the SE and LW/173, which of 
course affects the stopping power of the brakes.
SB

----- Original Message ----- 
From: "Pat Shea" <xl340hp at yahoo.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Monday, June 04, 2007 3:02 PM
Subject: Re: REFLECTOR: Brake authority


> Hiroo,
>
> There are two issues at play here: Braking Capacity
> and Braking Power. Braking Capacity is the amount of
> work the brakes can do before they become saturated
> with heat and f-f-f-fade away. Braking Power is how
> much friction can be generated between the pads and
> discs. Limited Braking Power is an annoyance (i.e.
> can't hold the plane still during run-up). Limited
> Braking Capacity is a major safety issue (i.e. you
> can't stop or steer). If you have air in the lines,
> the brakes may feel spongy or soft an which can impact
> Braking Power, but it will not affect Braking
> Capacity.
>
> I'm using the Matco 600XT's on my XL. I maintain
> 85KIAS on final and based at a 3,200' airport. I've
> done a extensive testing with my brakes and there are
> some definite limitations which need to be contained
> by energy management on the part of the pilot.
>
> The bottom line is that the brakes are only good for
> one full stop with substantial braking if they are
> cool (ambient temp) to start with. If you want the
> ability to abort a take-off from Vr, your bakes will
> need to be ambient temp to start with. FYI - it takes
> about 15-20 minutes for your brakes to fully cool down
> from max temp (approx 700*).
>
> So, if yu come in for landing and have to stomp on the
> brakes right away and ride them down to a full stop,
> you're not going to have much braking capacity left
> for taxiing. Taxi with caution - take it slow for a
> few minutes, giving the brakes a chance to cool a bit
> so you have some capacity to work with.
>
> I've found the most challenging scenario to be a
> headwind with a x-wind component. If departing and you
> need to taxi to get to the departure end of the
> runway, it's difficult not to heat up the downwind
> brake. The wind is pushing and turning the plane. Take
> it slow. If landing, let the headwind slow you down on
> the runway because you're going to need some braking
> capacity to taxi back with that quartering tailwind...
>
> Pat
>
>> ----- Original Message -----
>> From: Hiroo Umeno<mailto:humeno at microsoft.com>
>> To: Velocity Aircraft Owners and Builders
>> list<mailto:reflector at tvbf.org>
>> Sent: Monday, June 04, 2007 11:57 AM
>> Subject: REFLECTOR: Brake authority
>>
>> I had a situation this weekend that heightened the
>> "pucker factor" a bit.
>>
>> It was a rather warm day (80 or so at sea level) and
>> I landed at a 3400ft long.  Upon touchdown, I braked
>> more firmly than normal since it was a bit shorter a
>> strip than normal.  About mid-way down the strip, I
>> noticed that the rate of deceleration has decreased
>> a bit.  I used the full length of the 3400ft to get
>> it stopped and turned off the active.  The parking
>> was at the other end of the field so I taxied back.
>> It was probably about 5 minutes in taxi and after
>> getting to the other end of the 3400ft strip, I
>> suddenly realized that I could only turn left.  To
>> make matter worse, once I got the nose cocked left,
>> I could not straighten it out, either.  I had to
>> shut down, push the plane to the ramp, let the
>> brakes cool off, then taxi.
>>
>> Now, I've always had an impression that the braking
>> on my plane was "softer" than other planes I have
>> flown in the past.  For example, on the Pipers with
>> castering nose gears, I could make a "pin-point
>> turn" by locking one wheel or another by standing on
>> the brake.  Not on my plane.  I have the let the
>> plane start rolling and then nudge the nose over
>> gradually.  Also at run-up, I can barely keep it
>> from creeping forward at higher RPMs.
>>
>> As I have the standard wing and fuselage (SUV), I
>> have the Matco brakes.  My understanding is that the
>> Cleveland upgrade is only necessary on the XL class
>> aircraft.
>>
>> How much brake effectiveness should I expect on
>> these Matcos?  I am starting to think I might have
>> an air bubble or two in my lines.
>>
>> Hiroo
>
>
>
>
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