RE: brakes???
Rocket City made a set of brakes that operated the way sdb-5 has described. The unit was a 1 inch drum with prongs on the side that attached to the spokes of the wheel, and had music wire wrapped around the drum so that it tightened when pressure was applied to the wire. I've used them for years on 60 size airplanes and they worked well. Have not seen them on the market lately and don't know if Rocket City is still in business. They may have cost about $5.00 a pair ten years ago.
Don't know if this is what you're looking for; but I've come across a design that works the same way and simple to build.
I get a kick out of just taxiing out on the runway, line up and apply brakes and stop momentarily, then apply throttle for takeoff. It also helps sometimes to shorten the landing roll.
I can post a drawing of it if you want, but forget it if you are using retracts on your P-38.
feihu