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

Shortround6 said:

None of the these engines were really suitable for tanks (power to weight and/or power to volume). I would also note that some of the big industrial/marine engine builders (size of engines) actually were not high volume manufacturers. Maybe a few dozen engines a month in a good month?

Perhaps somebody could make a tank specific radial using more steel and less aluminum and using less intensive machining. But you might as well start over on much of the engine design (keep bore and stroke?), which means you don't get to tool up right away.

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Best 1930s engine of the power required was probably the SOHC V-12 from Hall Scott

2181 cubic inches 5 3/4" Bore x 7" Stroke, Net Weight for the Models 2268, 2269 is 3600 Pounds. Models 3368, 3369 is 4125 Pounds, Models 2286, 2287 is 4600 Pounds. Most were cast iron, other had some aluminum, depending on application

Model 2269, Industrial gas engine, 2181 ci. 5 3/4" x 7" @ 2100 RPM brings 575 BHP,
1500 torque lb. ft. 3600 pound weight.

Other had a supercharger for more power.

Most were set for Marine use. Using half of the V-12 as a straight Six, those were built by Hudson to get production numbers up for landing craft, crash boats and heavy trucks.

So decision to have some other factory to subcontract more engines would be needed. The US just wasn't thinking about the vast numbers of 400HP+ engines needed for a large AFV force before Pearl Harbor.

Admiral Beez said:

The German penchant for torsion bar suspension took up a lot of hull space.

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In German tanks and any other tanks with front drives, the driveshaft is a far bigger driver of hull height than the torsion bars (which take typically under 20cm). Sometimes with optimized placement of the bars and components, it is possible to fit them in a neat gap such that hull height may not have to be increased much, at least in certain areas of the hull. That said, the German torsion bar installation wasn't as compact as the setups made in later tanks.

Most modern tanks use torsion bars but still are able to work properly with notably lower hulls than many WW2 medium and heavy tanks. Some of the increased hull armor/structural weight can be offset by the lower weight of torsion bar suspension compared to bogies or independent external coil springs, with the former being unable to match the ride performance of properly made torsion bars anyway.

I must state that air-cooled vs water-cooled in tanks isn't a straightforward win in weight for the former. You may be able to delete the radiators themselves, but you need to offset the loss in cooling efficiency with much more extensive grating (let alone when the radiators used higher pressure water to increase boiling temp) and/or more powerful fans (which will eat more gross power from your engine). You also remove the ability to consistently cool even poorly accessible parts of the engine (a notable issue in the AVCR-1360), and you often are forced to increase the spacing between cylinders to provide proper air-cooling. As such, an air-cooled tank powerplant might end up with a notably bigger engine, bigger fans and more extensive grating to achieve the same net power, and not save much if any weight.

Elan Vital said:

In German tanks and any other tanks with front drives, the driveshaft is a far bigger driver of hull height than the torsion bars (which take typically under 20cm). Sometimes with optimized placement of the bars and components, it is possible to fit them in a neat gap such that hull height may not have to be increased much, at least in certain areas of the hull. That said, the German torsion bar installation wasn't as compact as the setups made in later tanks.

Most modern tanks use torsion bars but still are able to work properly with notably lower hulls than many WW2 medium and heavy tanks.

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The big reduction in postwar AFV has been to minimize the area above the track run, the Sponson, to keep low, along with rear drive.

Tiger got a triple hit to height, Torsion bar runs at the bottom, clearance for drive shaft, and then sponsons for ammo storage.
This layout was started by the Mark III

but here, the Ammo stowage wasn't in the Sponson area, with ammo locker low agains the rear firewall on both sides

Elan Vital said:

I must state that air-cooled vs water-cooled in tanks isn't a straightforward win in weight for the former. You may be able to delete the radiators themselves, but you need to offset the loss in cooling efficiency with much more extensive grating (let alone when the radiators used higher pressure water to increase boiling temp) and/or more powerful fans (which will eat more gross power from your engine). You also remove the ability to consistently cool even poorly accessible parts of the engine (a notable issue in the AVCR-1360), and you often are forced to increase the spacing between cylinders to provide proper air-cooling. As such, an air-cooled tank powerplant might end up with a notably bigger engine, bigger fans and more extensive grating to achieve the same net power, and not save much if any weight.

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Thread is focused towards the radial engines' 'branch' of the air cooled engines. Adding an air-cooled V engine to the equation kinda misses the point?

It Does address, sort of, the difference in problems of cooling between liquid and air cooled engines.
Arrangement of cylinders doesn't change the amount of cooling air needed by a great amount for a given amount of power generated.

There are/were problems with radial engines. Some things can be fixed, but at a cost.
Airflow through a box that is sealed at the bottom and partway up the sides (you do want to be able to wade through 3-4 ft of water right?) requires some ducting.
Actual dimensions of the cylinder assembly is only fraction of the volume in the engine compartment.

Shortround6 said:

It Does address, sort of, the difference in problems of cooling between liquid and air cooled engines.
Arrangement of cylinders doesn't change the amount of cooling air needed by a great amount for a given amount of power generated.

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Arangement and number of cylinders certainly play the part in design and excecution of fan cooling.

Shortround6 said:

Actual dimensions of the cylinder assembly is only fraction of the volume in the engine compartment.

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Of course.
A dimension that can have a good deal of influence on the design of the tank is engine's length. For the power levels of 300-500 HP, a 1-row radial is great.