Locomotive brake force

[Anonymous]

[:)] I am leaving in France, ... but yes I saw the article in April 04 issue.

I was speaking about the air brakes. I would know the brake ratio of locomotives: SD70, C44C-W, GP's, ...
Is there the same AAR rules than for wagons brake ratio?

JLC

[Randy Stahl]

My god this would be a long reply. there are so many things that play into braking effort such as type of brake shoes, number of brake shoes, number of brake cylinders, size of brake cylinders, length of throw on brake beams, weight on drivers (sliding wheels are poor ). How about blended brakes? On dynamic brakes , old locomotives had poor dynamic brakes compared to the newest SD90MAC. I can assure you that most locomotives have more than enough brakes to smash a freight train. On steam locomotives you had to be careful about heating up the tires on the drivers thereby causing them to fly off. I guess you really need to be specific about what locomotive you want the info on and answer the question regarding the equipment on the locomotive.
See if you can get the April issue of TRAINS, the author did a fine job and will likely answer your questions.
Randy

[Overmod]

This isn't a trick question, is it?

In almost all operations, the braking value of the locomotive is minimal. Most of the stopping force is implemented by the trainlined air brake, with the independent brake (separate locomotive brake) hardly if ever used.

There was a discussion, I think on one of these forums, about how long a train was required to give adequate braking for a steam locomotive running by itself. IIRC Norfolk Southern excursions would run a few freight cars -- in revenue service, effectively -- to provide the necessary brake power.

Randy probably has an exact number for the force exerted by each brake cylinder on a diesel locomotive, and perhaps also for the force exerted through the brake rigging to the shoes on each wheel.

An interesting locomotive-brake exception is the use of eddy-current braking on the wheel faces, in locomotives like the AEM-7. I believe it's possible to get substantial effective deceleration out of these systems, as they don't heat up the tread, foul up the characteristics of the suspension, or cause lockup or skidding of the wheels.

Randy will also describe the maximum deceleration possible for dynamic braking at given speeds. As he's mentioned already in another recent post, the amount of power is limited by the applied DB field current, and the current that can be safely passed through the motor armatures -- I think the grids are not the 'limiting factor' per se. Theoretically it's possible for a diesel-electric to exert considerably more braking force than tractive effort, for a number of reasons.

[Anonymous]

Do you mean dynamic brakes or air brakes?

[Anonymous]

[?] What is the locomotive brake force value, for modern and old diesel engines?
JLC