1930-1945: alternative engines for military purposes (3 Viewers)

[ThomasP]

For the UK a tankerized Cheetah might have worked, at least for early war tanks if they were designed for the size of the radial.

In 1935, the unsupercharged Cheetah V with a CR of 5.2 it was rated at 270 BHP at 2100 rpm on 73 grade fuel. Dimensions were Ø48" x ~36" thick not counting the prop shaft, and weight was about 600 lbs. If they could retain the reliability of the aircraft engine at ~1000 hrs between overhauls? (The supercharged Cheetah X was rated at 1200 between overhauls in 1941.)

 

[tomo pauk]

Germans seem to be in their own world. A 12 liter V-12 of 265-300hp and using 6-10 gears maybe an elegant solution, but tanks are not elegant, they are brute force. Using larger engines but fewer gears may have given the same result and been cheaper. May depend on a nations gear cutting ability? I wonder how much swarf (Chips)
you get from 10 speed transmissions? And you have to use very good steel. Which turned out in Germany's case, to be in shorter supply than they thought.

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.

There certainly is more time and more room for better engines.
Problem with the French is that they were going in several different directions at once.
They weren't really trying to find the 'best' tank and them build a crap load of 2-3 models. They were trying to find usable tanks and provide employment to different factories and build up the manufacturing capabilities of some factories. A lot of politics involved which led to most factories wanting to use their own engine/s and not a standardized engine.
But even a 500-1000 tank order was not enough for a bespoke engine and they tried to use something either in stock or something they can pull other pieces for.

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 engine from a Char B1. Very much in the fashion of a split WW I V-12 aircraft engine. They seem to have added to both bore and stroke over the years but the sperate cylinders does show the dated design (Liberty was no better).

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.

 

[tomo pauk]

For the UK a tankerized Cheetah might have worked, at least for early war tanks if they were designed for the size of the radial.

In 1935, the unsupercharged Cheetah V with a CR of 5.2 it was rated at 270 BHP at 2100 rpm on 73 grade fuel. Dimensions were Ø48" x ~36" thick not counting the prop shaft, and weight was about 600 lbs. If they could retain the reliability of the aircraft engine at ~1000 hrs between overhauls? (The supercharged Cheetah X was rated at 1200 between overhauls in 1941.)

The twinned bus engine on the Matilda II was 57in long - so a good half a metre longer - and ~2650 lbs (1200kg). Also 58in tall.

 

[z42]

Were there other users of engines with similar requirements as tank engines, to get decent production volumes without having to make a lot of tanks? Beyond aircraft of course. I'd guess most civilian uses in the same size would prefer robustness and ease of maintenance over maximum power per volume. Maybe torpedo boats?

 

[Elan Vital]

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.

This is correct, the French concluded that V or W layouts were best for their battle and heavy tanks. The idea of using half of the battle tank engine in I or V form for the light tanks didn't happen until 1939, largely because the 1933 program light tanks were too light and small to make use of such an engine and the evolution towards 15-20 tonnes happened in 1939.

The G1 and heavy tanks all used V or W engines bar the transverse I6 in G1R, but it isn't until 1939 that a V engine was designed for B1 Ter, largely because it was originally expected to use a modified B1 Bis' engine at a lower combat weight.

 

[tomo pauk]

Sometimes, the engines land in one's lap. Like the case with Germany getting many hundreds of enignes when they annexed Czechoslovakia, hundreds of radials and W engines when they conquered Poland, and thousands more when they conquered France.
Apart from the HS 12Y-45, 49 and -51, the other HS 12Y will not be suitable for 1st line aircraft come 1941, but they might warrant a try in a tank or in a transport aircraft. The CR of 5.5 will allow for the fuel of the low octane rating to be used, with a bit of down-rating if/when required. Low weight is another boon, up to 500 kg vs. 950-1000 kg of the HL 210/230 series. Sizable displacement will bring good torque.
The smaller 12M and X might've been also interesting, and also being shorter than the big bore siblings 12N and Y; both the M and N will probably need to go lower compression.

The HS 12 engines would've been a very intersting choice for the French heavier tanks, too, at least teh yesterday's models so the price is not over the top.

 

[Elan Vital]

Sometimes, the engines land in one's lap. Like the case with Germany getting many hundreds of enignes when they annexed Czechoslovakia, hundreds of radials and W engines when they conquered Poland, and thousands more when they conquered France.
Apart from the HS 12Y-45, 49 and -51, the other HS 12Y will not be suitable for 1st line aircraft come 1941, but they might warrant a try in a tank or in a transport aircraft. The CR of 5.5 will allow for the fuel of the low octane rating to be used, with a bit of down-rating if/when required. Low weight is another boon, up to 500 kg vs. 950-1000 kg of the HL 210/230 series. Sizable displacement will bring good torque.
The smaller 12M and X might've been also interesting, and also being shorter than the big bore siblings 12N and Y; both the M and N will probably need to go lower compression.

The HS 12 engines would've been a very intersting choice for the French heavier tanks, too, at least teh yesterday's models so the price is not over the top.

I think the obstacle for Germany is that they wouldn't want their new medium and heavy tanks to rely on limited quantities of a foreign engine which is quite different in design to boot, and they didn't have much need for engines of this power class in less optimized gun carriers.

Use of the Hispano Suiza 12 was contemplated in the FCM F4/F1 fortification assault tank, first with the 12Mb delivering 560 hp at 2000 rpm, and then the 12Nb delivering 765 hp at 2000 rpm.

However, Hispano-Suiza replied in January 1939 that their capacity was completely absorbed by aircraft engine production programs so that they could neither modify nor provide any bench equipment, and the FCM would even have to to go to the Air Ministry to get 2 test engines. They could not make promises they knew they couldn't keep. By the time Hispano-Suiza may finally exceed its requirements for aircrafts, the French would already have had access to their bespoke engines in development.

In the end, the superheavy tanks used twin Renault 12KGM engines modified by the ARL for use in tanks which were from Air Ministry stocks, which could deliver 480 hp nominally and up to 550 hp, at least on 72 octane fuel (I have never found an archive stating if Renault finally confirmed performance on 65 octane).

 

[tomo pauk]

I think the obstacle for Germany is that they wouldn't want their new medium and heavy tanks to rely on limited quantities of a foreign engine which is quite different in design to boot, and they didn't have much need for engines of this power class in less optimized gun carriers.

Panther was a medium tank only if we believe the Germans
Production of the Tiger I was under 1500 pcs. IMO the supply of yesterday's HS 12Y engines - from -31 down - from Czech and French stocks would've met the needs of the program.

 

[Shortround6]

For the UK a tankerized Cheetah might have worked, at least for early war tanks if they were designed for the size of the radial.

It might have worked, but would it have worked well?

We often talk about derating engines to run on "pool" gasoline but that may have different meanings in different armies.
The US used a least two different grades of fuel in their vehicles. Most vehicles like cars, trucks, even 1/2 tracks ran on fuel of about 72-73 octane. The tanks ran on 80 octane which in some memoirs was called aviation fuel. It sure wasn't the fuel used in fighters or bombers (or most transports) but it was a common trainer fuel and it was not used in any land vehicles that were not tanks or built on tank chassis.
I believe (from previous threads on this site) that pool gasoline was about 74 octane? or a tiny bit lower. The Cheetah Va was an engine that used a rotating mixing fan at crankshaft revolutions and no boost. Tank engines often ran at closer to max power/ rpm than aircraft engines. Down grade as people see fit.
M3 Stuart used a 10.9 liter engine. 80 octane (?)
Cheetah was a 13.65 liter engine. ??? octane
M-3 Grant used a 15.9 liter engine. 80 octane for sure.

Engine in the Grant used engine oil to lubricate the rocker arms. The oil was supplied and there was a return system to send the oil back.
Bristol Mercury valve gear was exposed or not totally enclosed and lubrication was by grease gun.
I can't seem to find the lubrication on the Continental or A-S Cheetah engines. The valve gear was totally enclosed but this does not mean it used a pressure feed system from the engine standard oil system. Some companies were in transition and while they enclosed the valve system they lubricated them in various ways, Grease gun, oil-soaked pads, small reservoirs (?).
Many engines, including the Cheetah had hinged valve covers fastened with spring clips which certainly hints at frequent-periodic maintenance.
Lycoming on their R-680 9 cylinder used pressure fed oil and return sumps of valve system lubrication.

Unfortunately for some tankers, their army command did not put a lot of forethought in maintenance before adopting certain features.

 

[tomo pauk]

M3 Stuart used a 10.9 liter engine. 80 octane (?)
Cheetah was a 13.65 liter engine. ??? octane
M-3 Grant used a 15.9 liter engine. 80 octane for sure.

Per Lumsden, up until the Mk.VIA the fuel was 77 oct. Unsupecharged versions Mk.V version did 275 HP at 2100 rpm. The supercharged early versions did from more than 300 HP to 326.
Newer versions that used 87 oct were making fromn 360 to 400++ HP, and the last versions (with 100 oct fuel?) up to 475 HP.

He also notes the Bristol Aquila, on 73-77 oct fuel, max of 500 HP and 830 lbs.

 

[Shortround6]

I think the obstacle for Germany is that they wouldn't want their new medium and heavy tanks to rely on limited quantities of a foreign engine which is quite different in design to boot, and they didn't have much need for engines of this power class in less optimized gun carriers.

Post War H-S claimed they provided not a single engine, gun, or truck directly to the Germans. They built stuff for Vichy France and delayed and screwed up production to the Germans.
G-R claimed to have delivered about 25% capacity to the Germans. Germans hoped for a lot more than they got from captured factories/territory's.

With tanks it is just the engines. You need the entire drive system. Yanking a 250-300hp engine and dropping in a 500hp engine is not going to end well as many American hot rodders discovered from the 1950s on. Blown clutches, blown transmissions, blown rear ends, snapped drive shafts and snapped rear axles.
Tanks also use the tracks and track drive system for steering, so the system is handling larger loads while trying to turn corners even a low speeds. The Drive/steering system can often weigh as much as the engine and take up more room than the engine (minus the cooling system).

 

[tomo pauk]

Post War H-S claimed they provided not a single engine, gun, or truck directly to the Germans.

Cunning as they were, the management of H-S didn't have a say on the French military stocks after June of 1940, be these whole engines or the parts and tools. They also have had no say at what Germans can produce for themselves in the Avia factory in Bohemia.

 

[Shortround6]

He also notes the Bristol Aquila, on 73-77 oct fuel, max of 500 HP and 830 lbs.

They made 6-7 Aquila's total. Basically, a series of prototypes and actual performance varied. Manufacturing costs of sleeve valves means it was a very good thing that the Aquila was quicky forgotten about.

Per Lumsden, up until the Mk.VIA the fuel was 77 oct. Unsupecharged versions Mk.V version did 275 HP at 2100 rpm. The supercharged early versions did from more than 300 HP to 326.
Newer versions that used 87 oct were making fromn 360 to 400++ HP, and the last versions (with 100 oct fuel?) up to 475 HP.

When we go from octane to PN numbers we are dealing with
73=50.91
77=54.90
80=58.33
87=68.29
100=100

Octane is not linier; we are looking for performance differences.
compared to 73 octane, 77 is actually 7.8% better, not 5.5% better.
More importantly 80 octane is 14.5% better than 73 octane, not just 7 'points' or even 9.5% difference in the octane numbers.
87 octane fuel is whole new world but you are not going to get 87 octane in tanks in WW II.
87 octane/68.29 PN is 34% better at resisting pre-ignition/knocking than 73 octane (pool gas).

Tank engines are much more subject to abuse than aircraft engines from bad drivers. Using the wrong gear and lugging the engine and trying to gas pedal your way out instead of down shifting can easily leading to knocking.

 

[Shortround6]

Cunning as they were, the management of H-S didn't have a say on the French military stocks after June of 1940, be these whole engines or the parts and tools. They also have had no say at what Germans can produce for themselves in the Avia factory in Bohemia.

No, they didn't and while the Germans were masters at cobbling together bits and pieces of this and that to the everlasting joy of model makers of many generations how effective some of that stuff was is subject to question.
And just because you have some engines, there is a judgement call on how much you modify them to suit a different purpose.
There certainly was a Czech factory that could make Hispano's, the question is "how many per month" vs the expected need.
If the Germans want to make 300 Panthers per month an engine factory that can only make 50 engines a month is a real problem, there is only so much you can do with extra shifts.
Maybe you can lengthen the Panther chassis to fit in an HS 12Y engine instead of the Maybach, but replacing a 23 liter 3000rpm engine with a 36 liter 22-2400rpm engine could be a problem. Changing or modifying the reduction gear leading from the engine to the transmission is one thing. Hoping the transmission can deal with the extra torque is another thing.
Panther transmissions had issues at it was. Are they going to take even an extra 10-20%? If you change the final drives to keep the vehicle speed the same the transmission is doing most of the work trying to handle the extra torque. If you change the drive shaft speed from the engine to the transmission you can lower the torque going through the transmission and clutches. Is it enough?
This assumes the mechanics can reach and adjust the 6 carbs on a Hispano engine while it is in a tank engine bay.
Or perhaps the Germans make manifolds to allow the carburetors be on top like the Maybach.

It could be done. Should they? New accessory case at rear (no supercharger) and new front case (no reduction gear or lower output shaft)
Hispanos have the intake and exhausts on the outside of the cylinder head. You can make new heads to solve that, but the expense is starting to go through the roof.

 

[tomo pauk]

There certainly was a Czech factory that could make Hispano's, the question is "how many per month" vs the expected need.
If the Germans want to make 300 Panthers per month an engine factory that can only make 50 engines a month is a real problem, there is only so much you can do with extra shifts.

That holds true for any factory, not just engine factory, and not only something in Czechia. Any factory that will be making 300 high-power engines a month will need new tooling, be that in old or new location, the workforce, energy and materials supply. But a more realistic approach would've been having at least two sources for these engines.

Maybe you can lengthen the Panther chassis to fit in an HS 12Y engine instead of the Maybach, but replacing a 23 liter 3000rpm engine with a 36 liter 22-2400rpm engine could be a problem. Changing or modifying the reduction gear leading from the engine to the transmission is one thing. Hoping the transmission can deal with the extra torque is another thing.

Don't change anything - just have the future Panther to be designed with a big engine in mind from the get-go. Be that engine fueled by gasoline, or, preferably, by diesel. Or by a radial engine.

Panther transmissions had issues at it was. Are they going to take even an extra 10-20%? If you change the final drives to keep the vehicle speed the same the transmission is doing most of the work trying to handle the extra torque. If you change the drive shaft speed from the engine to the transmission you can lower the torque going through the transmission and clutches. Is it enough?

As above - the design need to cater for these factors before it is made in mild steel. But I think that engine power as-is is okay on the Panther.

It could be done. Should they? New accessory case at rear (no supercharger) and new front case (no reduction gear or lower output shaft)
Hispanos have the intake and exhausts on the outside of the cylinder head. You can make new heads to solve that, but the expense is starting to go through the roof.

Comapred with cost of designing a whole new engine from get-go - no comparison

 

[GTX]

An interesting area in this discussion is the possible use of gas turbines for tanks. The Germans did seriously consider such with multiple designs investigated: GT101, GT102, GT103:

Initial GT 101 schematic diagram and installation concept in a Panther tank.

One of the advantages of such an arrangement over the standard Maybach HL230 V12 would be the gas turbine's greater ability to use multiple fuel options - something of especial benefit to Germany in the war. The power output would also be greatly increased: with the Maybach the Panther had a specific power of about 13.5 hp/ton, with the GT 101 this would improve to 27 hp/ton.