While we’re down this rathole…
I would say that a propellor IS a fluid transmission. You DO have a standing start problem with an aircraft, but it’s solved by the fluid transmission provided by the propeller. Same with ships – the propeller/water combination is a fluid coupling.
The difference between diesel-hydraulic and diesel-mechanical is descriptive. In both cases the engine directly drives the wheels via some kind of gearing. Even “diesel mechanical” DMUs had a hydraulic coupling (in place of a friction clutch) – as did London buses (RT). The Western Region and German hydraulics had multiple torque converters, one per gear ratio, and changed gear by filling and emptying them, whereas diesel-hydraulic DMUs had a mechanical gearbox with a torque converter, just like a car automatic transmission.
Cars solve the standing start problem with a mechanical clutch, of course, which slips, allowing the engine to turn and still transmit power. It’s a good compromise for low power, but not a great idea for 2000 hp.
The Fell (10100) was an interesting idea. Just had to reread “LMS Diesel Locomotives” to remind myself of the details. It solved the standing start problem with torque converters. The Roots blowers were there so the engines produced high torque at low speed, which is a bit of an unnatural act for a diesel (or petrol) engine.
The drive arrangement was byzantinely complex. There were four traction engines. They were joined together and to the wheels by four differentials. Each one had its own torque converter, which could be filled or emptied. To get more power, you filled more of them, bringing more engines into service.
Despite all that, it did actually work, and ran pulling main line trains for several years. It was no less reliable than the other early diesels. BR lost interest in the idea, very sensibly preferring diesel electric (except Swindon). In the end it was a maintenance error that got it – someone forgot to put oil in the gearboxes.
changed gear by filling and emptying them
Whoever invented that deserves a prize!
johnh wrote:
The drive arrangement was byzantinely complex. There were four traction engines. They were joined together and to the wheels by four differentials. Each one had its own torque converter, which could be filled or emptied. To get more power, you filled more of them, bringing more engines into service.
Sounds far more French than English!
Sounds far more French than English!
Ca va pas, non? To te fous de ma gueule ou quoi?
( :-) )
johnh wrote:
The difference between diesel-hydraulic and diesel-mechanical is descriptive.
I think what sets them apart is how much the fluid coupling does. In a BR Sprinter, the engine winds up to redline and stays there at constant RPM until the train gets to about 50 mph, then it switches to a direct coupled mechanical transmission, and engine speed is directly related to road speed. But in the BR class 172, you can hear it going through 6 gears of the gearbox as it accelerates, with the engine speed a direct proportion of each gear with the exception of moving off from a standing start (so much more like a modern bus transmission). Similarly with the old heritage DMUs with the 4 speed manual gear boxes, they started off through a fluid coupling so as to not need a clutch, but once the thing was moving, the engine speed was a direct proportion of road speed for the gear you were in (and in 4th gear, the transmission was locked together). There’s a good video here,
– the juicy bits, showing how the gear box works, starts at around 9 minutes 30
https://www.euroga.org/forums/hangar-talk/12616-cars-all-fuels-and-electric/post/337460#337460
That reminded me of this and the old saying “it may work in practice but will never work in theory” 
Thinking about constant high power and gliders. I’m often going Trondheim-Oslo by plane (in the back of a B-737 ) The trip takes about 45-50-55 minutes from take off to landing. How do they fly it? Take off is the usual way up to 30k something feet. That takes what? 10-15 minutes. Then they cruise for an additional 10-15 minutes. Then throttle back and “glide” for the remaining 30-40 minutes. Only a small fraction of that time is used in cruise. High power is definitely used in climbing to 30k feet, but not for that long. More than half of the time they are mainly “gliding”. I’m not sure (don’t remember exactly), but 20-30 years ago I think the trip only took 40-45 minutes, and they cruised considerably longer before descending, and descended much faster. Obviously this “gliding” is the cheaper (sorry, greener ) way of flying, and the increase in time is negligible.
This is a naturally “hybrid” operation. Use the engines to increase the energy (potential and kinetic in this case), then use that energy to travel at least half the distance for “free”. Take this to the extreme, and we have a ballistic missile.
LeSving wrote:
Take this to the extreme, and we have a ballistic missile.
We can fire you from a cannon.
Trondheim to Oslo is 178 degrees true, just need to work out the necessary charge and elevation.
Graham wrote:
We can fire you from a cannon.
That sounds like a very hard take off
Cue very old joke:
Circus Ringmaster: Our human cannonball was killed in a tragic accident
Other person: Oh no, and men of his calibre are so hard to find
