Wednesday, 27 November 2013

Ergonomics

The idea that Soviet tank designers gave no thought to ergonomics is very common in Western media, but it is simply not true. Soviet designers were taught to take ergonomics into account, as illustrated in a chapter of Engineer-Colonel Samusenko's book Foundations of Design of Armament for Self Propelled Guns and Tanks. I'm not going to translate the entire chapter, but it contains some useful data.

"In order to avoid [crewmen] hitting the roof when traversing bumpy terrain, the height of the roof must be 900-980 mm above the seat. The upper limit is for a gunner of above average height (175 cm) in a sitting position (fig. 10).

Figure 10. A gunner sitting.

Since the loader's position changes based on remaining ammunition locations, his body moves during his work, and the indicated numbers do not provide him with a comfortable work environment. A loader requires at least 1450-1500 mm (halfway between standing and sitting), or 1750-1800 mm for only standing (fig. 11). The absolute minimum height of the fighting compartment is only acceptable when the loader has shells delivered to him from the ammunition rack by an automatic mechanism, and can remain sitting.

Figure 11. The size of an average person.

Figure 12 shows the comfortable position of a driver in low spaces.

Figure 12. A driver in cramped conditions.

With a low breech axis, when the breech is lower than the loader's elbow, a vertical breech is more convenient. With a high breech axis (950-1000 mm or more), a horizontal breech is more convenient, pointed towards the loader's side.

The fighting compartment must connect with the driver's compartment for communication and interchangeability of crew members. The hatches should be positioned comfortably, and be 500-600 mm in width."

The textbook also contains some crew space numbers, for reference.


The table lists the tanks in this order: MkIV (Churchill), Cromwell, T-34 (numbers indicate that this is the T-34-85), IS-2, PzIII, PzIV, M4A2 Sherman, Panther, Tiger.

The first column is the sequential number, the second is the tank's name. The third is the tank's mass in tons. The fourth is the location of the transmission: the first 4 tanks have it in the rear, the rest in the front. The fifth is the caliber of the gun on the tank. The sixth is the number of crewmen in the turret. The seventh is the diameter of the turret ring in millimeters. The eight is the width of the gunner's space. The ninth is the size of the loader's space. The tenth is the height of the fighting compartment, from floor to turret ceiling. The eleventh is the size of the fighting compartment, in meters cubed. The twelfth and thirteenth are the same for hull and turret respectively. The last is volume occupied by crew and components.

The table after contains similar data for some SPGs: the SU-100 and ISU-152.


The first column is the name of the SPG, the second is the total fighting compartment volume, then the space occupied by ammunition, crew, and equipment. The fourth column contains the number of crewmen. The fifth contains the volume necessary for the crew to move around. The last column is the "comfort coefficient", the total volume divided by consumed volume. The textbook warns that a high comfort coefficient provides the crew with comfortable working conditions, but a coefficient that is too high is indicative of an inefficient design.

Let's compare the numbers of these vehicles. Despite the accusations of uncomfortable Soviet tanks, the Churchill's crew is the one with the least space. The gunner only has 460 mm of space, a centimeter more than the average shoulder span of a Soviet tank crewman. Harsh. Everyone else enjoys approximately the same amount of space, with the Panther going slightly above the mean. Certain posters from the World of Tanks forums will be delighted to learn that the Sherman was, indeed, the most comfortable tank in this list for the gunner. 

The loader's position varies a little more. The Churchill's loader is ridiculously constricted, and the Cromwell's isn't doing much better. The T-34-85's loader has almost as much space to work in as the PzIII's loader, and lives a life of luxury compared to the PzIV's loader. The PzIII and Sherman are tied for the most room for the loader among the medium tanks. The IS-2 and Tiger, as the largest tanks on the list, have the most room for their loaders.

The height of the fighting compartment is where the Churchill shines: that is the only tank where the statistically average Soviet crewman can stand to full height, followed shortly by the PzIII and the Cromwell. In the rest of the tanks, he must sit. The PzIV has a pretty abysmal fighting compartment height, even less than the Soviet requirement for a half-standing loader, which bodes ill for the crew's comfort. Sadly, the space used for crew movement is not given in this table, making calculation of a comfort coefficient impossible.

In conclusion, this book teaches us two things. One is that Soviet engineers cared about ergonomics too. The second is that British people are apparently very tall and disproportionately narrow. 

6 comments:

  1. I really like your conclusion ;)

    But be careful: Indeed the different Nations populations might have had different physical attributes. What this calculations show is how different tanks compare to Soviet average crews.

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    1. Average height is primarily a function of nutrition levels (which is why that of formerly piss-poor backwaters has soared since the end of the War, including where I live) and AFAIK eg. Britons and Germans weren't really that much better off than Soviet citizens in that regard. I understand the tallest rank and file of the period would have been the relatively affluent US and overseas Commonwealth ones, which isn't surprising when you recall that those parts were where the European surplus populace migrated to in search of greener pastures.

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    2. What a narrow view you have, there are various factors that could make a population grow large or small. Japanese people are not as tall as Americans yet the Japanese are five billion times better off and have allot more healthier food than Americans.

      Growing large or not does not really tell much about whether the country is poor or not.

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    3. Sorry, but beside "healthier food" you also need it in adequate quantities. And in case of Japan this is only post-WW2 phenomenon - which is the reason why Japanese are much taller now.

      And yes, being tall or short is one of the indicators of country being poor or not.

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  2. Is there a way to find/get Samusenko's book?

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    1. Not an easy way, it's not on militera, at least. Yuri Pasholok has this part scanned here: http://yuripasholok.livejournal.com/2440403.html

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