Re: Ed, that is my experience,with the physics of choo-choo's as well.
>> And no, reversing the motors isn't a more effective brake than using brake shoes without the wheels sliding.
> Sorry Doc. Been there done that.
You may have done it, but so have I, many times with many different types of equipment. Sliding or spinning wheels = reduced braking power (reduced TE if in power throttle position).
> But then with a foot of snow over the top of the rail the physics might be altered.
What does this have to do with the price of eggs?
Start here:
[
books.google.com]
Synopsis of findings: when wheel is rolling on a rail, the friction between the two is static frcition. When the wheel's surface is moving with respect to the rail, this is dynamic friction. The G-W tests plainly demontrated that dynamic friction can be as little as 50% of static friction, which translates to "less stopping power" no matter how you look at it.
If by reversing the motors, it causes one set of wheels in a pair of motors to spin, which is virtually always the case, then the maximum stopping power of the two axles has been reduced by about 75%.
With EMD DC-drive electrical systems, to reverse the motors, all you have to do is move the reverse lever in the control stand, and the motors will slug (BTDT too). Subsequently opening the throttle will try to drive both motors backwards, increasing the possibilites of a TM flashover, and this will trip the ground relay. As Hot Water has mentioned, once the ground relay trips, the abilities of the TMs to engage any sort of braking vanishes.