Thanks to all for helping with this question. You might be interested in what one writer from Ontario said on the railroad list:
Original questioner: >> Does anybody know how to convert "pounds thrust" to >> "horsepower". First respondent: > Horsepower is a measurement of work done per unit of time. > In Fred Flintstone units, one horsepower is 33,000 foot-pounds > (lbs-ft) of work per minute or approximately 746 watts. Second respondent (from Ontario): Right. > Thrust, on the other hand, has no time involved in its > measurement, Not so. One pound of thrust is the force needed to accelerate a mass of one pound by 32.174 feet per second per second. The dimensions of units of force are therefore mass * length / (time)^2. The dimensions of units of power are mass * (length)^2 / (time)^3. Note that pounds of mass and pounds of force are completely different units. They only have the same name because of the boundless stupidity of the Flinstone "system" of units. (Apologies to William Hanna and Joseph Barbera.) To avoid having that factor of 32.174 appearing in all your calculations, you need either to measure force in pounds of force and mass in slugs, or force in poundals and mass in pounds of mass. But who's even heard of slugs or poundals? None of these complications occur in SI, where a force of one newton on a mass of one kilogram gives a acceleration of one metre/second^2. > so foot-pounds of thrust Foot-pounds are a unit of work, not of force (thrust), which is measured in pounds. One pound of force acting through a distance of one foot does one foot-pound of work. > has no direct equivalent to horsepower. Right.
