1930-1945: alternative engines for military purposes (1 Viewer)

[swampyankee]

Their 'small' V12s were compact and reliable engines, but there the benefits really stop. Something that is V6 sibling of a 30-35L V12* would've gotten them compactness and reliability, too, but also lower price and time to make the engines and gearboxes, easier maintenance in the field, and will require the shorter engine bay.

* Germans were thinking about the heavy tanks much before they gotten into that in reality, that a big V12 should be powering.



The French were designing and making heavy tanks in the 1920s and 30s. Them opting for V12s for these tanks, with en eye for V8 and/or V6 versions for the smaller tanks might've been both economicaly and military prudent.
Also - their heavy tanks were big and boxy. A good radial engine would not be too much for the hull to house these.


An inline 6 would've been an ideal engine if the tank has the 'Merkava' layout - engine sits besides the driver, front sprocket driving the tracks. While not common on tanks of the day, it was not unheard of - Vickers light tanks had that, so did a lot of Soviet light tanks, and so did the Elefant (but with the electric 'transmission'). Frees a hefty % of the hull length and volume, and the tank can be repurposed into a SP chassis in an elegant fashion.

Another way of making the engine+transmission bay a good deal shorter was to have the engine being installed in the transversal position. That 'trick' was done on the T-43 tank, making the tank much roomier. An inline 6 installed in such a fashion would've netted even greater benefits vs. the longitudinal installation.

Every configuration has its issues, and packaging is a worse problem for AFV than small weight increases.

Looking at 1930s technology levels, I think some options are unlikely, like Hyperbar engines or extreme levels of supercharging, as in MTU's modern tank engines.

Some possibilities:
Two stroke spark ignition engines. These would require direct fuel injection to be reasonably efficient, and that technology was bleading edge. Obviously, crankcase scavenging is out. Roots blower or stepped piston would be easiest, but a Lysholm compressor would likely be better. Schneurle porting would likely be best, as uniflow designs require valve gear, opposed piston, or split-single configuration. The last has been used in cars and motorcycles, that is small engines with up to about 4 cylinders. OP spark engines were uncommon but not unknown.

Radials are tall, which is a packaging issue, and air cooling complicates packaging. A liquid cooled radial won't be much more compact, but the separate radiators would ease packaging. So would mounting the engine with the crankshaft vertical. A two-row radial wouldn't benefit much from being laid down. This does limit size and thus output to about 400 hp.

For diesels with 1930s-era technology the best choice would probably be an opposed-piston two-stroke. Get Fairbanks-Morse on the phone.

The UK and US didn't really develop clean-sheet AFV engines pre-war. Both countries had the industrial base to do so.

AFV engines are useless without transmissions. Wheeled AFV (that don't use skid steer) transmissions are straightforward. Tanks, not so much. Rear-engine, front drive seems to be the worst possible arrangement in terms of volume.

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Transverse, OP 6 cylinder diesel, rear-engine, rear-drive tank would be interesting....

 

[tomo pauk]

Two stroke spark ignition engines. These would require direct fuel injection to be reasonably efficient, and that technology was bleading edge. Obviously, crankcase scavenging is out. Roots blower or stepped piston would be easiest, but a Lysholm compressor would likely be better. Schneurle porting would likely be best, as uniflow designs require valve gear, opposed piston, or split-single configuration. The last has been used in cars and motorcycles, that is small engines with up to about 4 cylinders. OP spark engines were uncommon but not unknown.

Not too bad idea for an aircraft engine, too...

 

[Shortround6]

What is the technology level/s of the time/s?

What they could do in 1944 was a lot more than they could to in 1932.
It is not just theory or ideas or even prototypes, it was the ability to make the hoped-for engine in quantity and had have it work and work one hundred hours (or more than a hundred) in use.
There were a lot of changes in materials (alloys) and some nations had material shortages (raw materials) that affected things.
Many nations made some pretty crappy tank engines. Even the US with all it's resources (and raw materials, both domestic and imported) could not build enough of the desired engines. Or at least didn't think they could and signed contracts for thousands of "substitute" standard engines. A lot of which were given away as Lend-lease.
Cadillac had made ohv V-12s and V-16s from 1930-31 to 1937 in ever diminishing numbers and even the 452cu/in V-16 was not powerful enough for a 15-20 ton tank (and was way too expensive) and Cadillac built a new 346 cu/in flat head starting 1936. This monoblock engine replaced the older V-8, the V-12 and the V-16, partially because of market conditions (no real market for V-16 cars) cost of production. Even the old flathead V-8 used separate crankcase and cylinder block/s construction. "New" flat head was lighter, cheaper to make.
Cadillac made over 16,000 cars in 1940. They had a production base. Military engines were down rated to 110hp from 135hp. One source claims the engine only had 3 main bearings. So did the Ford flathead V-8.
Getting heavy duty engines was often harder than just grabbing existing car or truck engines.
Boat engines were usually to large and heavy. Commercial boat engines (diesel was just beginning to take over, so not much help there) were often expected to last thousands of hours Years as fishing boat or tug).
A lot (most) WW II tank engines were not very good. Reliability and durability are not the same thing. Soviet V-2 engine increased engine life from around 100 hours to start to around 150hrs in 1943/44(?) Soviets also used a lot of Aluminum in the engine. Soviet supply of aluminum may have been better than Germany or Italy or Japan? Or Germany wanted to use their aluminum for airframes and not build wooden aircraft? Wooden aircraft need suitable wood, not just any wood.
The US GMC -71 series of engines is quite well known with production stopping (at least for road vehicles) in 1995 but it only started in 1938. Yes, they built about 39,000 of them for tank/afv use in WW II but they build 57,000 of them for use in landing craft. How many went into diesel generators? They bult 1, 2, 3, 4 and 6 cylinder in-lines. The V engines didn't show up until the Mid 50s. It seems like the V-6 and V-8 should have been no-brainer ideas but either there was no market (?) or there was problem putting two conrods on one crankpin.
Mid 1950s metallurgy was very different from 1938-41 metallurgy.
Diesels, at least high-power ones need either better metallurgy or a lot more weight or both to even get close to the same power as a gasoline engine. GM's diesel car engine fiasco of 1978-85 shows that rather well.