REFLECTOR: Brake performance

Brian Michalk michalk at awpi.com
Sun Mar 17 12:55:25 CDT 2013


Thanks.
That brings the horizontal braking force down to 716lbf per wheel.  Just 
under my estimated 750lbf vertical force.  With a surface/tire friction 
number below .95, I should still be able to lock up the wheels.

I used to direct the skid number data collection program at TxDOT, and 
we also measured a lot of runways.  Skid numbers below 32 (.32 friction 
number) were generally considered low and in possible need of a 
resurfacing*.  Non-polished surfaces (like shoulders) could easily score 
into the 80's, and runways would score pretty well unless they had a lot 
of rubber buildup.


* This is a gross generalization.  Lot's of other factors came into play 
like braking requirements, data distribution, accident statistics and so 
forth.


On 03/16/2013 12:18 PM, Laurence Coen wrote:
> Brian,
> A 600x6 is 18" in diameter for a 9" radius. 6" diameter wheel plus two 
> 6" sidewalls.  The RG has a smaller tire that is 15" diameter and a 
> 7.5" radius.
> Larry Coen
> N136LC
>
> *From:* Brian Michalk <mailto:michalk at awpi.com>
> *Sent:* Saturday, March 16, 2013 10:26 AM
> *To:* Velocity Aircraft Owners and Builders list 
> <mailto:reflector at tvbf.org>
> *Subject:* REFLECTOR: Brake performance
>
> I just looked up the Matco specifications for the WHLW600XTE
> http://www.matcomfg.com/WHLBRKASSY600X6TRPLeXtraTorqueEnergy-idv-3801-4.html
>
> I don't know how the number match dimensionally, but I assume a 6.00-6 
> wheel has a six inch radius?
>
> Assuming the wheel above, a 5/8 bore master cylinder and their specs of:
> Static Capacity 	1860 LBS
> Load Limit 	5580 LBS
> Maximum Accelerate/Stop Kinetic Energy 	450500 ft-lb
> Torque Rating (@450 PSI) 	6441 in-lb
>
>
> For 450 PSI, I would need to press on the master cylinder a force of 
> 138lbf, which I am certainly capable of, and feel that I can generate 
> this much force without too much effort.  There is perhaps a 3X 
> mechanical advantage in the pedal arrangement.
>
> Their torque rating, with the wheel above shows that it could provide 
> 1074lbf to a wheel weighted to approximately 750lbf. Horizontal force 
> is higher than vertical force, indicating a friction number greater 
> than 1.0 is needed.
>
> This tells me that with very little effort, one should be able to lock 
> up the wheels while taxiing in their airplane.  I have the original 
> brakes, the W600XT, which have identical torque performance, but 
> different kinetic energy numbers.  I don't need higher energy, I want 
> better torque.  I do not think I am getting the performance indicated 
> in these specifications.  Is my math wrong?
>
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