I have a RS3 I don’t know the max speed of a RS3. What are the constraint limit the speed of a loco?
Usually the gearing determines the top speed. The traction motors and wheels have large gears attached to them, and the different number of teeth on the gear determines how fast the engine can go. Traction motors can only spin at a certain speed. Too fast, and they get damaged. Some RS3s were equipped for passenger service, so 85-90 mph would not be out of the question. Most were freight geared, with a max of 65-70 mph.
Track also plays into it. If the track is only good for 30 mph, that is as fast as you go. Trailing tonnage is also a factor. Too much, and you won’t be able to go past a certain speed. The speed varies with load, gradient, wind, etc.
Thank you so for the answer and the precision about freigt and passenger. I haven’t any idea of the difference between freigt loco and passenger loco. thank you
The difference between a freight loco and a passenger can be compared to the diferences between you auto and a small van and then on to compare to a panel vn, a small truck and a semi.
The difference between an RS3 geared for passenger and one geared for freight is similar to your car and the small van… basically your car might have a small turboed diesel with a high ratio gearbox and differential while the van will probably have a larger capacity diesel, may or may not be turboed and will have lower ratios in the gearbox and diff. Your car will get away quicker from lights but th e van will lug the load.
Speed is a secondary consideration for operating departments (although they are a big thing with the marketing people). In operations what counts is reliability and the ability to stop. Whether it’s a passenger or a freight you want it to get there and not block the line and you put on enough brake force to ensure that the train will stop when and where you want it to.
Maybe someone else with better knowledge than I have will explain brake force and train weight ratios. One thing… an RS3 will not have dynaic brakes so it will have less braking ability in its own right and depend more on the continuous brakes of the whole train.
The main constraints on loco speed are:-
- Contact between rail and wheel
- Horsepower
- Brakeforce
- Track Condition
- Gradient - DOWN
- Gradient - UP
- Line Curvature
- Legal restrictions (e.g. local laws on grade crossings)
- Train Loading
- Possibly others…
- Such as the ability of the crew to see the line ahead…
Another difference which would apply in the early RS3 period would be that some passenger locos were fitted with steam generators for train heating andsome had signal lines for communication between the conductor and the engineer.
Steam generators tended to be in high short hoods while signal lines appeared among the brake pipes an
Or to think of it another way, if you’re in your car pulling a load going uphill, you shift down to a lower gear to get more torque and better pull - but at a reduced speed. Once you’re back on flat ground you shift up and start going faster.
Diesel engines have something similar, only they are set in the shops and can’t be adjusted on the road…so if your railroad is going to assign an RS-3 to freight or switching duties, it will set it up with a gear ratio that allows it to develop maximum pulling power at the sacrifice of speed - kinda like your car always being in first gear. You could pull a heavy load up hill - just not very fast!!
If the RS-3 gets re-assigned to passenger service, the shopmen could change the gearing to ratio allowing the engine to go very fast - kinda like your car only being able to run in top gear - you can go very fast, but trying to start uphill with a trailer behind you is pretty unlikely to succeed.
Some railroads used RS-3’s in both service and put the gearing kinda in the middle so they could pull a decent sized freight train, but still fill in on passenger runs if needed.
In steam days, they had to design the engine from the start to be freight or passenger, since the ‘gearing’ was done by the size of the driver wheels. A freight engine like a 2-8-2 with 61" drivers could pull long trains but maybe only go 40-50 MPH doing it. A passenger 4-6-2 with 80" drivers could pull a passenger train at 80-90 MPH but probably couldn’t start as heavy a train as the low-drivered engine could.
Actually Dynamic brakes were an available option on RS3’s. The spotting feature is a lovered opening just in front of the cab on the side of the short hood. I have a picture of the RS3 Intersate #39 which is Dynamic brake equipped. Most RS3’s were built to operate long hood forward. Ones built before 1954 have louvers in the long hood. The 1954 RS3’s and up have bare filters in larger doors. A lengthwise exhaust stack indicates the original air-cooled turbo’s. A crosswise stack indicates the later water-cooled turbocharger that was retro-fitted to most Alco units. Another positive sign of a passenger unit was the underbelly water tank between the rear truck and the air resevoir. Freight units never had the water tank.
There are excellent descriptions of train handling and brake systems on A.A. Krug’s website.
How do we tell if they were built to operate long hood forward? The ones I knew would go either way, but I seem to recall them normally favouring short hood forward. They were built before 1954, but by MLW in Canada.
I am in the middle of building one from a kit, hence my interest in your comment. However, I am certain that I remember them operating short hood forward more often than long hood forward.[%-)]
PS (edit) They have that “cow catcher” below the coupler at the short hood end, but not at the long hood end. Hence I conclude these ones were built to run short hood forward.
There is a small “F” denoting front of engine.
Dont forget the “Hotel Power” on the engine such as cooling, heating, drive train etc. A certain amount of power is lost right away to keep the system running.
Of the 1370 RS3’s built from 5/50 to 8/56 only 98 were built for Canadian RR’s. MLW built 128 RS10’s that look almost identical to an RS3’s and were more common north of the boarder. The engines could be ordered either end foward. Long hood was just more popular at this time. The small “F” is the only way to tell for sure but the pilot is a good clue. The spotting feature for an RS10 are a square joint where the end and the top of the hood meet and also the intercooler at the top of the hood just aft of the radiator shutters. The intercooler panel looks like it is raised out from the hood futher than the radiators. It looks like the Alco in your photo has buffers. Where is it from?
These ran in NSW Australia. The first class of diesels introduced to run main line traffic, built at MLW. The first entered service 30 November 1951. I always thought they were equivalent of RS3, but with a modified cab to fit the loading gauge, buffers for the old stock still running at the time and variations to the pilots to suit local conditions. Also six axles, but they were A-1-A, A-1-A unfortunately. All subsequent main line diesels had all axles driving.
Top speed, which was the original question? I don’t know. They ran fast freight or light passenger trains, so I would take a guess they were fitted with one of the intermediate ratio gear sets.
The “F” is on the sidesill as close as possible to the front of the engine, usually on an RS-3 up by the steps. BTW the way an earlier post read, it sounded like dynamic brakes and passenger service were connected, but they weren’t. An RS-3 set up for passenger service would normally have to have a small steam boiler included to allow it to create steam for heating etc. for the passenger cars (hence the water tank mentioned in an earlier post). I believe the CNW had some “hammerhead” passenger RS-3’s that had a low long hood per usual, but a high short hood to accomodate the steam generator…kinda like if you took the long hood of an RS-3 and the shorthood of a high hood RS-11 and put them on the same loco !!
It would be very unusual to see an RS with both PSG and DB on the same unit. Beside the difficulty of fitting them both in the high short hood, they (dynamic brakes) were primarily used for freight service. DB was rare on passenger service. I suppose someone could have ordered a mixed use RS3 with both but I am unaware that any were made as such.
Some RS3 had both. Called Hammerheads, the Short hood was the same height as the cab. Maybe 10 total were built, most were built with one or the other, but not both.
Traction motors are the same between frieght and passenger versions. The gearing determined how fast you could go. Kinda like a car stuck in a gear. If stuck in 2nd, go up to 65-70 mph, with decent acceleration and power – frieght gearing. If stuck in 3rd or 4th, more top end, but less grunt – passenger gearing. The motors can only spin so fast before they fail. There is also a minimum speed to take into account. If the motor turns too slowly under a heavy load, it could fail from overheating. Passenger units have a higher minimum continuous speed than frieght motors.
Their top speed was 65mph. Just found it in Wikipedia.
Something else to watch for is what you double head with. I don’t know if it was common to all RS3s, but these RSC-3s had something strange about the MU setup. I don’t recall what it was, but they were predominantly seen as pairs. Rarely with another type, and if my memory is not wrong they had to be coupled as the lead engine. No doubt some ex-railway men (or still active railway men) out there can correct me or fill in the actual limitation.[?]