This one has been puzzling me for some time…older passenger locos mostly had three axle trucks, but the ones in service today for, say, Amtrak, have two axle trucks - such as the EMD F40PH and F59PHI and the GE Dash 8-32BHW and the Genesis Series.
Is the change due to the fact that most of today’s U.S. passenger services have reasonable mountain work, or has technology changed to the extent that the later locos are lighter and don’t need to spread so much weight???
Dave
Kozzie:
(1) Welcome back. Had not heard from your side of the world in a while.
(2)http://www.hebners.net/amtrak/amtSDPe.html
(3) The HTC 3-axle truck caused some unwarranted paranoia in the 1980’s
(4) Wheel slip/ adhesion technology improved to the point that the advantages of starting a train with a three axle truck diminished and the efficiencies of the 2 axle truck at track speed took over the market
Thanks Mudchicken. Things have been a little hectic down here but now I have had a chance to touch base with all of you “up over” lot and I knew you lot could help me with this one…
Your info is very helpful. I thought technology had a fair bit to do with it…And, (pardon the cross reference here to model railroading) a good “spin off” from going to two axles is that when running models of these later ones, there seems to be less hassles with the sharper curves on the layouts…
Dave
Many of thr original 6 axel engines were only powered on 4 of the axels, the other two were idlers. Both emd and alco pa’s were a1a trucks to alow them to operate on line requiring a lighter axel load. All us passenger operations are on main lines with heavy rails and no such weight restrictions. this also alows all the locos weight to be applied to the drive axels.
Not all the early pasenger diesels had 6 wheel trucks.The Canadian roads only had 3 E-units (all on CPR) and the classic picture of the Super Chief shows F units.
Canadian National had a series of hood locos (GMD1, I think) where they swapped around B and A1A trucks when the locos moved around the country.
Hey people, I’m going to take this discussion a little farther.
Rrandb mentioned that the early EMD E and Alco PA locos had A1A trucks, which allowed them to operate on lines with a lighter axel load rating.
So, I’ve been thinking, yes, yes, dangerous, I know… but… were there any passenger diesels with 3 axel truck that had all 3 powered? What about those might Trainmasters that did so much work for SP in CA? Were they A1A as well? Or were all triple axel Pax locos A1A???
Dave
…I wonder also aren’t the newer passenger engines using the modern “steerable trucks”…which didn’t exist for older pass. engines…And hello Dave, I’m also glad to see you back on here and bringing words from down under…{You know Dave, It’s getting cold up here now…12 degrees F as I write at 11 Pm}…
PS…We’re also looking for our first significant snow fall starting about noon tomorrow…Anyware from 4 to 8" of the stuff…It was originally projected to go south of us but that has changed and looks like we’ll get the above amount…I’m still holding out for them to be a bit wrong in the info…Watch out east of Indiana as it is coming…It’s a fast moving one too or it would be dropping more on any one place…Your safe Dave as I know you folks down there are getting warmer and warmer…
Kozzie I know that baldwin produced some models that had more than two powered axel per truck. I beleive another reason for the A1A trucks is if you go from 4 to 6 powered axels you now need 50% more power and with early diesel engines that was no easy task. Baldwin tried using modular engines to boost power but were unsuccesful.
At one time, all of the 6-wheel trucks were A1A no matter if in freight or passenger. Originally, the 6-wheel truck was due to axel loading restrictions. It wasn’t until the advent of the SD-9, RS16 (AS-6-6-16), the RSD-15 and the H24-66 that powering all 6 axels on 6 axel locomotives became common practice.
At one time, Baldwin fielded a C-C passenger unit and the F-M’s on SP were all “6-motor hoods”, and if I remember correctly, FM’s C-Liner 5 axel units came with all axels powered or 4 axels - your choice (B-C or B-A1A )
I know of NO specifically Passenger diesel locomotives that had all three axles of one truck powered. All were designed as freight locomotives, although some may have been equipped with boilers or head end power for part-time use in passenger service. Incidentally, a commentary on Kalmbach’s excellent DIESEL VICTORY is that nearly all B&M passenger locomotives except the E’s saw part-time use in freight service. Examples are GP-7’s 1567 and 1568, listed in the book as passsenger power and equipped for suburban service. I regularly rode these locomotives on the 4pm North Station - Portsmouth passenger run and then returned with the same locomotives (use singly) and same crew on the Portsmouth - Sommerville Yard night freight.
I think this was true of most railroads, the Norfolk & Western’s red G-9’s included.
Electrics were a different matter, the New Haven’s EP-5’s were C - C locomotives, as one example. (Two three-motor, six-wheel trucks).
To me the big difference between earlier and later passenger diesels was the change from real streamlining to shapes more related to road-switcher design, reversed now with the latest lovomotives, but none as beautiful as the E’s and PA’s.
Note also that the B&M, the AT&SF, and others bought F units specifically for passenger service. The Candian Alco FA’s were noted above. Again, many saw part-time use in freight service as well. The last passenger EMD Bulldog locomotive bult was the New Haven FL-9. B - A1A.
If the loco can do the job (modern wheelslip control helps a lot) then a 2 x 2 axle design should be cheaper to build and maintain.
Modern diesel engines have a much better power to weight ratio, so it’s possible to put 4000hp in a 4 axle loco with sensible axle loadings, and it’s generally easier to make a 2 axle truck ride properly at high speed.
Tony
The EMD E units had to carry alot of weight to begin with, a few thousand gallons of water , steam generator etc. Spreading the weight out over 6 axles was a good plan , after all until the 60s alot of secondary mainlines were ( and some still are ) 100 lb rail. The passenger locomotives were heavy. There are significant limitations as far as outputs of the main generators as well, they simply did not have the capacity to operate 6 motors in many cases.
Randy
No, no, no. Not true. What about all of the RSD1’s of the 1941 to 1945 period? What about all of the DRS 6-6-1500, DT 6-6-2000, RSD4, RSD5, and H16-66 locomotives of the late 1940s? None of those locomotives were A1A. The DT 6-6-2000 and H16-66 were not built for light axle loadings. They were used on very heavy, but slow speed operations. Likewise the RSD4 and RSD5 were often used in mountain territory where they could apply more hosepower to the rail at low speeds than could the contemporary 4 axle machines.
Not only were the E’s loaded with fuel and water - they each had two complete engine/generator sets (1200 hp each). Gets pretty heavy… The UP E’s have been repowered and are now essentially GP38’s in E’s clothing.
I certainly can’t discount the axle loading concept, but I had stuck in the back of my mind that the extra axle on the E’s was in part for a smoother ride as it applied to passenger comfort.
I think – but I’d hate to sit here and pontificate (you’d hate me for it, too!) – that the main consideration was axle loading. As noted above (Larry) the GMD E’s were heavy beasts, and the PA’s weren’t a whole lot lighter, nor were the various FM’s of the day. And track then was a lot lighter – 100 pound rail was normal, and there were a number of passenger lines just after WWII (particularly in the south) where rail as slim as 70 pounds was still in use.
The clearest way to see the influence of axle loading, though, seems to me to be the FL-9s used for decades in operations out of Grand Central Station, New York. These critters were basically an F unit (F-9), but equipped to take power from a third rail. The hitch was that there was a great big heavy transformer required to take the third rail juice and use it in the regular traction motors – and that upped the weight enough so that the FL-9s had to use a three axle truck at the rear.
Thanks to everyone for your comments - (I’ve only just now been able to come back on-line again), it’s all been very helpful in understanding passenger diesel development. Much appreciated.
I particularly found interesting Dave’s comments on how passeneger locos have almost gone full circle with later designs returning to a form of streamlining.
Quentin, I don’t suppose you could send some of that snow WAY down south could you? We’re getting days with maximums in low nineties (ugh)!
Dave
Uh…Dave, I’d say you might have a bit of fresh air now as it’s about your bed time…near midnight…Snow…Wish we could send it all down to you Dave…I’m tired of it already…I’m afraid it would melt before it reaches you…
The FP45 and the SDP35 were 6 axle powered passenger units also.
I am probably wrong, but I thought that the U30CGs and the P30CHs also had all 6 axles powered.