Locomotives

blue streak 1:

It is time for our engineering minded posters to take out their power charts and figure out how much HP is needed to maintain a certain speed on say a 1% grade per 1000 ton train for various speeds and then addapt that to an amfleet trains. ie can 4000HP pull 7 cars at 80 mph, 5 at 110, 3 at 125 or what is the actual figures? Then we can better argue about the high speed diesels and their value. I seem to remember that the NE corridor NH - BOS always had two F40s pulling the 6 car trains befor the electrification was completed.  

 I live less than 5 miles from the NEC (in RI) and it was very common to see a single F40PH on many if not most trains. Obviously the speed limit north of New Haven (the old end of the New Haven electification) was much lower in those days. The PC/Amtrak Turbotrain sets did O.C run at high speeds on the corridor....

The quick answer is they are not. Gas Turbine-powered trains  run at 125 mph in France (they consider this normal speed) and the RTL Turboliners ran at 115 mph for 22 years on the Schenectady-New York City route, limited only by the track. The RTLIII trains, which Amtrack refused to run, were clocked at 140 mph during acceptance testing near Schenectady. To run fast, unsprung weight must be kept as low as possible to minimize "P" Forces that cause rapid roadbed distruction. Diesel locomotives, which are basically converted freight locomotives, can't meet this requirement and so are limited to lower speeds.

Bombardier's Gas Turbine-Electric locomotive weighs no more than the Acela electric locomotive and while it has been limited to 125 mph for basically political reasons, undoubtedly could run much faster. Given the right design and the right track, speed is a function of horsepower and the locomotive or power car does not care whether it is generated on board or comes from far away via transmission line and catenary.

carnej1: as those times I rode that section before the ROW upgrade there was only 1 F40.  However the 2 times I rode that segment while they were installing CAT the schedule had been reduced (too much I believe) and those 2 F40s accelerated us to their 110 MPH much faster.  

The Turboliners not only have lower axle loads than Diesel locomotives, they have hydraulic drive through Cardan shafts rather than nose-suspended traction motors (OK, the RTL's have traction motors, but aren't they feeding the drive system rather than hung on the trucks?)

The proponents of power electronics and electric drives talk about how mechanical drive trains are part of technological history, but if that is the case, why are the Europeans looking at quill drive if not to reduce unsprung mass for high speed operations?  And a quill drive is a form of an articulated mechanical coupling between a sprung motor and an unsprung axle, as are the Cardan joints, and drive shafts between the hydraulic transmission and the axle on the Turboliner.  As are the connecting rods on a steam locomotive.  Mechanical power transmission lives on in railroad applications.

Jerry Pier:

The quick answer is they are not. Gas Turbine-powered trains  run at 125 mph in France (they consider this normal speed) and the RTL Turboliners ran at 115 mph for 22 years on the Schenectady-New York City route, limited only by the track. The RTLIII trains, which Amtrack refused to run, were clocked at 140 mph during acceptance testing near Schenectady. To run fast, unsprung weight must be kept as low as possible to minimize "P" Forces that cause rapid roadbed distruction. Diesel locomotives, which are basically converted freight locomotives, can't meet this requirement and so are limited to lower speeds.

Correct, with the caveat that the French retired the last Gas-Turbine powered trains almost two years ago now.

Further exception is that not all diesel electrics use nose suspended traction motors, both Bombardier and Siemens offer quill drives on the passenger versions of their diesel electric road locomotives as an option.  Also the JT42HWs built by Alstom in Spain for EWS in England used frame mounted traction motors with Cardan Shafts driving the axles, these locomotives are rated at 125 mph, quite possibly the fastest EMD powered locomotives.

The traction motors on the JT42HW's seem to be similar to the arrangement on PCC streetcars and CTA's rapid transit equipment.  This arrangement reduces unsprung weight compared to nose-suspended traction motors.