Very good gentlemen. You're both close.
Our standard 199-109 wheel and brake kit (RV-3 through RV-9) comes with the very light (read "thin") #164-017 brake disk. The small disk mass doesn't allow much heat storage, which the FARs and brake literature call "kinetic energy capacity". The Cleveland-rated kinetic energy capacity of an 199-109 kit w/ a 164-017 lightweight disk is 117,500 ft-lbs.
There is, of course, a standard equation for the kinetic energy required to stop the airplane; it's found in FAR 23.735 or all brake manufacturer's literature:
(0.0443 x aircraft weight x velocity in knots^2) / # of brakes = KE
Turn it around to see how many knots your brakes will handle....
sqrt (rating x 2 / weight x .0443) = knots at start of braking
Go ahead, pick up a calculator. You'll find it's close to the accepted minimum (Vso or V1) for the 1800 lb gross models...one stop from 54 knots.
TSO C26 requires slowing the aircraft at a minimum
rate of 10 ft/sec^2 without exceeding the kinetic energy rating. The KE rating is a measure of energy storage capacity, while
brake torque is a measure of stopping power. Torque means
arm x
force, i.e. a
moment (thus the hint).
The thin disk heats very quickly. In general, as the disk temperature increases, so does the required pad pressure in order to maintain the same brake torque. Don't want to increase line pressure or caliper piston diameter? Well then, just reduce the
arm of the rotating assembly (tire rolling radius) by lowering the max tire pressure.
Doesn't add weight, which is how Cleveland keeps the 10.8 lb sales position for the 199-102 wheel and brake kit. The catch is
technically, tire pressure is restricted to 31 psi if you want to meet TSO C26. Best I can tell they bury that detail in drawing 50-76, which is not readily available on the Parker/Cleveland web site.
You can return to 50 psi and meet the TSO by installing a thicker disk, which doesn't get so hot soaking up the same kinetic energy. In our case it is conversion kit 199-200, a thicker disk (164-099), a caliper spacer, and two longer caliper bolts. You get an increased KE rating in the deal, to 155,000 ft-lbs
Or you can just run 50 psi and accept longer stopping distances, which is the considered compromise I currently accept. Eventually the disks will need replacing, and I'll install thicker 164-099's. I've installed them before, and under hard braking there is a noticeable reduction in required brake pressure near the end of the rollout.