Radial engines favored for powering the tanks & AFVs, 1935-45

[tomo pauk]

It doesn't change - radials aren't the right choice for AFVs.

Was that also the conclusion of the folks that drove and fought in the radial-powered tanks?

 

[Shortround6]

Was that also the conclusion of the folks that drove and fought in the radial-powered tanks?

Hard to say, for the Soviets it was radials vs diesels.
A lot of crewmen blamed the fuel for fires and not the ammunition so perceptions are screwed up.
British in NA were comparing good radials to really, really crappy Liberty V-12 installations. If fact the radials may have been only mediocre but compared to the Crusader tanks the Radials just looked good

It is worth noting that the US was still using radial engine vehicles in 1953 if not later but ALL of those were left over WW II production. Only the M36B2 shows up with the twin diesel engines.

 

[marathag]

The only new build M36 were the 187 M36B1 built Oct-Dec 1944 on M4A3 hulls, to make up the required contract numbers.

Fisher built 300 turretless M10A1 hulls Dec 1943-Jan 1944 which were used to produce the first M36 with the addition of a new turret with the 90mm gun. Attention then turned to reconditioning M10A1 TD retained with training units in the USA and replacing their turrets. And finally as M10A1s began to run out attention turned in May 1945 to reconditioning diesel engined M10s as the M36B2.

So no opportunity to redo the the M36 drivetrain without spending a lot of money.

You missed the point, I think.

The M10 should have just been an interim, for training and limited combat- Substitute Standard, in US Army speak.
Buick had the 76mm armed M18 in production at Flint in July, 1943 for initial Contract for 8986 units

However, only 2513 were built, production ending in October of 1944 from two far smaller production contracts.

This was mostly from McNair and AGF who (foolishly) wanted more towed AT guns than TDs, with the number of planned TD Battalions halved in number in late 1943

With the M18 in full production, Fisher could have retooled to make a proper low hull using M4 components.

The M18 could use the lower torque Radial successfully from the Torqmatic transmission

Let's throw out the diesel as its tough to compare very different fuels...

Had the V2 been set for Gasoline, it would have been a 700HP class engine. At the end of the day, Torque is all about the bore and stroke of its cylinders, and at what RPM they are operating at- not what hydrocarbon is in the combustion chamber

'No replacement for Displacement' is a valid saying.
It's the cheapest way to get torque.

People talk about HP, but they all drive by Torque.

 

[marathag]

And a tea kettle, right?

They weren't Barbarians, though had to live rough till the first 'civilized' Tank had one from the factory- the Centurion.

 

[Shortround6]

I would delete the Hall Scott engine from the list.
It was interesting and the right power but anybody who put it in a tank needed to be taken away to very quiet place with men in white coats to rest for a number of weeks/months.
It was a very good boat engine but a 3650lb engine should not be going in a tank.
Edit, Torque peak was down around 1400-1500rpm.

 

[marathag]

It was a very good boat engine but a 3650lb engine should not be going in a tank.

It's doable.

The Detroit Diesels in the M4A2 was nearly as heavy as the monstrosity from Chrysler- a monster that turned out to be extremely reliable in British service.

The Hall Scott, being a Marine or Industrial engine, was overbuilt to hold that rated HP continuously. Most of the other engine used in tanks couldn't operate wide open throttle for hours. The 3600 was one of the lighter H-S engines, some models of the V-12 were 4600 pounds

Doing a version in aluminum would shed a lot of weight, if that was needed- but since the other existing engines that were used were heavier, no need.

 

[marathag]

Back to the theory for more radial engines
The A-57.
a sorta-radial

 

[Elan Vital]

The R-975 started with not so good durability (mostly owing to lubrication faults and poorly designed parts for tanks), 100-150 hours back when an A-57 might be good for 225 hours. It was sensitive at high rpm. It also tended to consume oil and gasoline at a more significant rate than the other engines.

Circumstances led the Americans to find themselves with radials as their tank engines at the start of the war so they had to make do with them as it took quite some time for the alternatives to replace it - the GAA was rushed into service but early problems were such its production was kept low for a time, the 6-71 was in high demand in quad form for the Navy. Only the A-57 was available in numbers, as the radial also started being demanded by the Air Force. But other countries that already had Vees or developped them during the war did not need to use radials, and more often than not their industry wasn't set up to make a surplus for tanks anyway, so domestic radial production was absorbed by their Air Forces. In comparison, the peculiar situation with US aircraft industry meant that high power Vees were not as obvious of a choice as radials as off-the-shelf tank engines.

Overall, other countries would have fared worse if they had gone with radials, and making them work probably took as much time as finding a suitable Vee, or even developping one almost from scratch*.
*that time argument was given even regarding conversions of aircraft Vees (Harry Ricardo re the British situation).

 

[tomo pauk]

Back to the theory for more radial engines
The A-57.
a sorta-radial

Seeing that, a 14 cyl radial does not look like a bad idea

A table taken from the Russian book about ww2 tanks:



A few details stand up. Like how he tiny the Valentine was, and especially it's turret. Or, that Cromwell didn't get even the 77mm HV, while the Sherman received the 17pdr despite the small turret. Or, that Panther's turret was just 2/3rds of the volume of the Tiger's turret.
The figures for the turret volume should be just for the 'real' part of the turret, ie. for what is above the hull roof.

The prop shaft that went under the turret basket and the transmission were still eating a lot of volume, even when the 'lowering gearbox' was used.

 

[marathag]

Seeing that, a 14 cyl radial does not look like a bad idea

A table taken from the Russian book about ww2 tanks:

View attachment 810310

A few details stand up. Like how he tiny the Valentine was, and especially it's turret. Or, that Cromwell didn't get even the 77mm HV, while the Sherman received the 17pdr despite the small turret. Or, that Panther's turret was just 2/3rds of the volume of the Tiger's turret.
The figures for the turret volume should be just for the 'real' part of the turret, ie. for what is above the hull roof.

The prop shaft that went under the turret basket and the transmission were still eating a lot of volume, even when the 'lowering gearbox' was used.

Type	Armored	Volume	in M3		Volume	of	Components
	Combat Weight	Hull	Turret	Total	Driver	Fighting Area	Engine Bay	Transmission
Valentine	17	5.8	1.1	6.9	1.2	2.6	2.1	1
Mk III	22	9	1.5	10.5	2.2	4.8	3.5	spread
Cromwell	28	9.7	1.9	11.6	2	4.9	3.4	1.3
M4A2 Sherman	31	11	1.8	12.8	3	6.9	2.9	spread
T-34/85	32	10.6	2	12.6	2.2	5.2	3.7	1.5
Panther	45	14.9	2.3	17.2	5	7.3	4.9	spread
Tiger I	56	14.8	3.4	18.2	4	9.6	4.6	spread

Edit: For others to use in the future

Note that you can see the trade off of sloped armor, more interior space is wasted from the angles, vs the 'bunch of boxes' exemplified by the Tiger and British, that tended to go for thicker vertical plates to protect a smaller volume.

You can see, the Panther was physically larger than it needed to be

 

[bf109xxl]

Hard to say, for the Soviets it was radials vs diesels.

That's a strange statement. The Soviets received just under 2000 tanks with radial engines. They produced/received under Lend-Lease many more tanks with inline/V-engines (both carbureted and diesel). Soviet tanks did not have radial engines at all.

A lot of crewmen blamed the fuel for fires and not the ammunition so perceptions are screwed up.

According to the results of the Battle of Kursk, the percentage of losses from fire caused by fuel ignition was about the same for diesel T-34s and gasoline-powered T-70s (the latter were even slightly lower). However, this was rather a consequence of the abominable manufacturing quality of the T-34's fuel lines and the presence of fuel tanks in the crew compartment.

 

[Elan Vital]

Valentine Engine Compartment
View attachment 810152
View attachment 810153
View attachment 810155

The thing with inline engines is that they are nearly the same length as their Vee derivatives with the same amount of cylinder lengths (eg I6 vs V12, I4 vs V8) - but obviously have only half the power. Or conversely that a Vee engine with the same amount of cylinders will be nearly half as long.

In narrow tanks like all those relatively light tanks of early WW2, inline vs Vee may have to be assessed on a case by case basis, as the wider Vee might lead to similar overall hull length if you have to relocate other assemblies in front of/behind the engine instead of beside it. In the case of the Valentine, the situation is worse as the Detroit Diesel was not provided with the anti-vibration equipment to make its full power of 225hp, so it was getting the power of a 4-71 with the length of a 6-71.

However, it seems the case is more clear cut in favor of the Vees if you are allowed to go wider, as you can then have room to put the extra assemblies beside the Vee engine anyway, so at equal power to the inline solution you can:
- improve the length/width ratio by reducing total hull length AND/OR
- increase the turret ring diameter and crew compartment length while keeping a reasonable total hull length.

With potentially reduced height owing to the Vee as a bonus.

Of course, if you go wider but keep about the same engine length as your inline, you can simply swap to the Vee with double the amount of cylinders and get double the power without doubling the total tank weight. Naturally, in both of these cases you still had to accept some increase in total weight and size, but that comes with greater performance.

 

[Think Tanker]

That's a strange statement. The Soviets received just under 2000 tanks with radial engines. They produced/received under Lend-Lease many more tanks with inline/V-engines (both carbureted and diesel). Soviet tanks did not have radial engines at all.

According to the results of the Battle of Kursk, the percentage of losses from fire caused by fuel ignition was about the same for diesel T-34s and gasoline-powered T-70s (the latter were even slightly lower). However, this was rather a consequence of the abominable manufacturing quality of the T-34's fuel lines and the presence of fuel tanks in the crew compartment.

This isn't terribly surprising I suspect, as the largest culprit for tank 'brew ups' were from ammunition and not fuel at all. Still, it's a very intriguing datapoint.

Also worth noting in this regard the typical T-34, despite being diesel-fueled, had relatively sensitive propellants and charges for its ammunition, which resulted in fairly catastrophic conflagration or detonation upon the tank brewing up. Colonel Loza had some very interesting recollections on such instances, which you can find from his memoir "Commanding the Red Army's Sherman Tanks." For an easier-to-access reference though, here's a link to a prior interview:

Dmitriy Loza

For a long time after the war I sought an answer to one question. If a T-34 started burning, we tried to get as far away from it as possible, even though this was forbidden. The on-board ammunition exploded. For a brief period of time, perhaps six weeks, I fought on a T-34 around Smolensk. The commander of one of our companies was hit in his tank. The crew jumped out of the tank but were unable to run away from it because the Germans were pinning them down with machine gun fire. They lay there in the wheat field as the tank burned and blew up. By evening, when the battle had waned, we went to them. I found the company commander lying on the ground with a large piece of armor sticking out of his head. When a Sherman burned, the main gun ammunition did not explode. Why was this?

Such a case occurred once in Ukraine. Our tank was hit. We jumped out of it but the Germans were dropping mortar rounds around us. We lay under the tank as it burned. We laid there a long time with nowhere to go. The Germans were covering the empty field around the tank with machine gun and mortar fires. We lay there. The uniform on my back was beginning heating up from the burning tank. We thought we were finished! We would hear a big bang and it would all be over! A brother's grave! We heard many loud thumps coming from the turret. This was the armor-piercing rounds being blown out of their cases. Next the fire would reach the high explosive rounds and all hell would break loose! But nothing happened. Why not? Because our high explosive rounds detonated and the American rounds did not? In the end it was because the American ammunition had more refined explosives. Ours was some kind of component that increased the force of the explosion one and one-half times, at the same time increasing the risk of detonation of the ammunition.

This 'component' as referenced is a comparison of the Soviet preference for higher-yield charge compositions. Though there were also differences in the manufacture and production of the propellants themselves.

Also, I highly recommend for folks use and reference of the ORO-T-117 armor casualty report, as it compiles a lot of valuable information on these matters. But, the important factor here, is that the gasoline-fueled vehicles did not seem to correlate to any systemic increase or decrease in vehicle survivability, as the above quote notes. Instead, a variety of other contributing factors played their part in the relative safety, survivability, and 'burnability' of a vehicle.

As for the utility of the radials generally as discussed in this thread, they ended up (in the R-975C4 and similar) as dependable, reasonably-powerful, and crucially available engines when they were needed most. They existed out of a need for the repurposing, reusing and optimizations of existing industry, not as the 'best available' of all existing technology. However, I do think it is short-sighted to argue that the Sherman series should've abandoned the radials earlier to redesign and lower the hull profile of the tank--that is ostensibly a new tank design for very marginal advantages, while suffering demonstrable consequences.

The 'shift' towards a form-to-fit low-profile Sherman would also hinder one of the (arguably unintended) consequences of the R-975 installation in the Shermans: the impressive adaptability and modularity of the engine bay to receiving new powerplants and 'plumbing' with relatively minimal structural change to the vehicle.

To reuse an old refrain..."perfect is the enemy of good enough," and 'perfecting' a lower profile vehicle design would be at the precipitous cost of vehicle production, industry readiness as the world marches head-long into War, and consequently the diminishing readiness of armored units in the rapidly-expanding Allied armies. In this context, the R-975 was a suitable powerplant and fulfilled its purposes well.

 

[marathag]

This isn't terribly surprising I suspect, as the largest culprit for tank 'brew ups' were from ammunition and not fuel at all. Still, it's a very intriguing datapoint

US Tanks tended to use hydraulic motor for turret traverse, powered by electric pump- though some Shermans were direct Electric drive

That fluid, that was under high pressure, was very flammable. Nick a pressurized line, and tank fills with a flammable mist with a Flash point of 180 Degrees F.

Wasn't till the M60 for that to be investigated, after Israel noted the disparity in 1973 from damage reports from UK, Soviet and US types used.

UK Tanks used Hydraulic at the start of WWII, going to Electric for later AFVs for the Turret traverse. Soviets used Electric.

In WWII, the German Mk IV had Electric Traverse(powered by a small 500cc 2-stroke Pony Motor, not from the main Generator) , Mk III manual only, and the Big Cats direct Hydraulic, geared to engine RPM

 

[GrauGeist]

The US had used Radials for AFVs well before the war:
The Continental R-670 was used in the US M1, M2 and M3 light tanks as well as the LVTs employed by the USN, US Army and Canadian Army.

The Guibertson T-1020 diesel radial was also used in the US M3 light tank.

 

[bf109xxl]

This isn't terribly surprising I suspect, as the largest culprit for tank 'brew ups' were from ammunition and not fuel at all. Still, it's a very intriguing datapoint.

Normally, the secondary fragments ignite the fuel first, and then the munition detonates from the fire - only in the case of a shaped charge projectile the munition may detonate earlier. I was talking about statistics of tanks burned, not destroyed by internal explosion - those causes were considered separately AFAIK. It was fuel ignition that was the cause of tank loss. Due to poor workmanship and/or poor design of the T-34's fuel lines, which could not withstand the vibration and shaking when moving, fuel often leaked into the crew compartment. It could form puddles and soak tankers' clothes or rags - gasoline would evaporate in such conditions, while diesel fuel would not. And if it caught fire, it was more difficult to put it out than burning gasoline. As a result, the theoretically more fire-safe diesel tank revealed no difference from the theoretically more dangerous gasoline one.

Also worth noting in this regard the typical T-34, despite being diesel-fueled, had relatively sensitive propellants and charges for its ammunition, which resulted in fairly catastrophic conflagration or detonation upon the tank brewing up.

The cases (known to me) where a large percentage of tank losses were caused by exploding ammunition (e.g., the Rechitsa offensive) are related to the mass use of shaped charge shells/ mines/grenades. If the main losses were inflicted by AT artillery using conventional AP shells, ammunition explosions were much less frequent.

Colonel Loza had some very interesting recollections on such instances,

I read the book by Dmitry Loza, as well as many other recollections/books of Soviet tankers/self-propelled artillery men.

Also, I highly recommend for folks use and reference of the ORO-T-117 armor casualty report

I read several very detailed Soviets reports with the analysis of the Soviet armor losses.