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Valentine Engine CompartmentWe can take a look at the Valentine tank. The engine bay was long enough for the 6-cyl diesel to fit, that went at 79 in long? The R-670 was under 35 in of lenght. Let's be conservative and have the radial engine of good power being 40 inches shorter - a full meter. In the time when tanks were 5+- meter long, that is a major thing. Even saving of 50cm leaves a lot of weight allowance to be used on other stuff.
Me neither. Just pointing out that engines, even from the same manufacturer, had wildly varying costs. So I don't think in general you can make the argument that a radial would be cheaper than a liquid-cooled inline, all else being equal.
I don't think you can attribute that 500kg (rough difference between BMW 132 and Maybach HL 230, if we're going by wikipedia numbers?) solely to cast iron vs aluminum. Or radial vs inline, for that matter.
Maybe? But maybe you instead lose by needing a higher hull, which adds weight by itself as well as being an easier target. If you look at the volume of the powerplant instead of focusing on any one particular dimension, I'm not sure the radial wins by that much, if at all, anymore. Also keep in mind the radial will need a large fan with assorted ducting for cooling, which will increase the length somewhat (of course the liquid cooled engine will need radiators and fans as well, but has a little more flexibility how these are placed). With a long and narrow engine like a V-12, maybe you can compensate with a lower hull, and by putting things like fuel tanks beside the engine bay?
The biggest downside was low torque output at low RPMs, that was overshadowed by the great Horsepower to weight ratings.In this comparison, my opinion is that the radial is a less costly choice, while also offering the knock-on effects wrt. tank weight/price/armor etc.
I've tried to make a comparison between a 9 cyl radial (often used on the US tanks/AFVs) vs. a 12 cyl liquid cooled engine (standard on German, Soviet and British tanks/AFVs worth speaking about) tanks, not just any radial vs. any liquid cooled engine.
In this comparison, my opinion is that the radial is a less costly choice, while also offering the knock-on effects wrt. tank weight/price/armor etc.
I'm not sure that I've simply attributed to the materials chosen the weight difference between the two engines. Iron/steel was possibly 'guilty' for 200+- kg weight creep on the HL 230 (that went to 1300 kg)?
1-row radials were very light for the power they were making, though. The BMW 132 was far lighter than the HL 230, possibly up to 900 kg when we also account for the cooling system.
Seems like that Valentine tank, that used the humble inline 6 engine, was tall to the roof same as the M3 light. It was also much wider. German tanks were also not known for their small height no width, especially the 'big cats'.
We can also see that a bit smarter packaging, like what the people that designed the M-18 Hellcat did, keeps the height within the modest proportions. It used the same engine as many of the M3s/M4s, yet it was a lot lower because there was the gearing added that kept the propeller shaft low.
In case that gearbox is at the back, as it was common on the French, British and Soviet tanks, even that gearing is not needed.
So limiting ourselves to single row radials, for instance, in 1944 a R-1820 (9-cyl radial) cost $8920, and a V-1710 cost $10565. So yes, the radial is slightly cheaper. OTOH the V-1710 makes a lot more power, so on a price/hp comparison I'd guess the win goes to the Allison. Of course both of these are way too big for a tank, but just as a data point.
My point is, aero engines in general were pretty light, both radials and inlines. But this did come at a cost. In a non-aero application, you're probably quite ready to sacrifice some weight for lower cost, general sturdiness, and lower maintenance requirements.
A low profile engine is a necessary but not sufficient condition for creating a low profile hull. There are certainly many other ways to fail!
You need to also take into consideration the weight of the engine, the radiator(s) and related plumbing plus the armor to protect the cooling system.So no, I don't think it's at all clear that a radial will automatically be cheaper.
As far as height goes, you need to remember that the M10, M36 & M18 were not tanks. They were tank destroyers. All had open topped turrets which also meant less of an issue accommodating the breech end of the gun as it was depressed.We can also see that a bit smarter packaging, like what the people that designed the M-18 Hellcat did, keeps the height within the modest proportions. It used the same engine as many of the M3s/M4s, yet it was a lot lower because there was the gearing added that kept the propeller shaft low.
In case that gearbox is at the back, as it was common on the French, British and Soviet tanks, even that gearing is not needed.
I don't think that I've ever specified the height of these vehicles, but the way that M18 specifically have had a device that lowered the propeller shaft.As far as height goes, you need to remember that the M10, M36 & M18 were not tanks. They were tank destroyers.
Okay. Even though I can't see that the roof being open or not had any bearing on the layout of the prop shaft.All had open topped turrets which also meant less of an issue accommodating the breech end of the gun as it was depressed.
It doesn't really. It may have an bearing on the overall height of the vehicle.Okay. Even though I can't see that the roof being open or not had any bearing on the layout of the prop shaft.
The M36 'Jackson' that the crews only called 'Slugger' should have been done this wayOpen topped vehicles could be shorter because they expected the crews to fight with the tops of their heads above the top level of the armor, at least a lot of the time, and only ducking when needed. Not fighting (or being in a danger area) for several hours.
Why is everyone saying the German V-12 have low torque??The biggest downside was low torque output at low RPMs, that was overshadowed by the great Horsepower to weight ratings.
Aircraft engine sit at cruise RPMs for most operations, where that low torque just never came into play.
The way to avoid all that, is adding the complexity of electric or even hydraulic drive, or what the Germans did with their high rpm, low torque V-12s, add more gears.
V-12 Engines of the WWII eraWhy is everyone saying the German V-12 have low torque??
I've stayed away from commenting previously about the proper(TM) design for a WWII tank gearbox being in the front as I felt this was aircraft forum, not armour.I think I've mentioned in multiple threads that IMHO, gearbox in the rear is the correct(TM) design for a tank, so no argument here.
Shermans had all gears but 1st and Reverse synchronized, so new drivers didn't have to worry about double clutching. Soviet Tankers didn't get that Bourgeois luxury unless they were in Lend Lease.Secondary reason - for manually shifted transmission, having short shift linkage is major advantage. >1/2 the recruits won't have seen an automotive vehicle - expecting them to operate/maintain a remote linkage/automatic transmission in the field is asking too much. Post war when you can provide proper training/users already have experience, it is whole different story.
The only new build M36 were the 187 M36B1 built Oct-Dec 1944 on M4A3 hulls, to make up the required contract numbers.The M36 'Jackson' that the crews only called 'Slugger' should have been done this way
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Let's throw out the diesel as its tough to compare very different fuels...V-12 Engines of the WWII era
Maybach HL230 1457 cubic inches 3000 rpm(2600 rec) 700HP Torque 1,364 ft. lbs@2100rpm
A-65 1568 cubic inch V-12 SOHC from Chrysler, 650HP@2600rpm Torque 1458 ft.lb. at 1600rpm
V-12 Hall-Scott 2181 cubic inches 575 BHP@2100 RPM brings ,1500 torque lb. ft.
Ford GAC V-12 1649 cubic inches max rpm 2800 Max torque 1560@1600
Lower RPMs for peak torque is better than higher 'Area under the Curve'.
German V-12 needed higher RPMS for top HP and torque than the others. To stay in the peak powerband, you need more gears.
And a tea kettle, right?...
British also went for even more luxury, pneumatic pre-selector shifting- almost automatic.