Monday, 6 March 2017

American Ergonomics

Ergonomics in tanks is an important factor, one that I touched on previously in some detail. It turns out that despite certain prevalent stereotypes, the ergonomics of various tank schools are more complicated than many people believe. Having already applied Soviet ergonomics standards to a German design, let us hop across the pond and see what the Americans thought about the topic.

Thankfully, this time, the Fort Knox Medical Research Laboratory report "Adequate Head Room in Tanks" provides us proper measurements, which makes my job a lot easier. The adequate head room for a sitting crewman, excluding the upper and lower 5% of men, is stated as 34" to 38.25", or 86-97 cm. The Soviet "dimensions of an average man" define the same measurement to be 90 cm (35.4"), which falls pretty well in the middle of that range. The American tank helmet adds a whole 1.5" to the height of a tanker by his crash helmet, a thickness that is found to be excessive. At the time of the study (November 27th, 1942), a thinner helmet was already being tested.

Let's see how well average people could fit into American tanks.



Crewmen would have to be incredibly small to fit into the M5 Light Tank. A loader's lowered seat gives only 33.5" of height, excluding almost all men (99.82%) from serving comfortably in this position. The tank commander does a little better, but still only accommodating the shortest 5.53%. Compared to the turret crew, the hull crew lives in luxury, with 35.25" of head room, which is good enough for 26.41% of men according to the study. The study is very critical of the ergonomics of the M5: "It has been determined that the tank can be driven satisfactorily if the maximum required head room can be made available. A major change in seat design is required to effect this change."

The Soviets never ordered the M5 Light Tank, but experienced the same ergonomics issues on the M3A1, among others. 

Next, the Shermans. As expected, the medium M4A2 provides significantly more space for its crewmen than the light tank. The loader enjoys more room than anyone in the Stuart, which meets the Soviet requirement for an average man and allows for 42.30% of Americans sampled to serve in that position. Every other position in the Sherman is even roomier than that, and you can figure out who can fit into it on your own with the data from the report.


To finish off, let's go back to that German example. We already found it deficient by Soviet standards, but how many Americans would be fit to drive their tank?

The height of the driver's compartment is only 80 cm (31.5"). This is not only less than any position of the Stuart (a light tank!), but out of the 541 men sampled in the 1st Battalion, Armored Force Replacement Training center, not a single tanker would be capable of comfortably occupying this position.

The report also includes a diagram of the driver's seat in the Stuart, so let's see how well it does compared to the cramped Soviet driver measurements.


As we already knew, the driver's compartment isn't quite tall enough to fit an average Soviet driver. The leg room seems a bit tight as well compared to the Soviet standard (instead of the 58 required cm of leg room there is only 40), but far from the disaster we see in the German design. 

28 comments:

  1. "The American tank helmet adds a whole 1.5" to the height of a tanker by his crash helmet, a thickness that is found to be excessive." This statement has proved to be utter nonsense. Today the NFL football helmet is padded with 1.5" of foam and still does not prevent concussions.

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    1. Medieval greathelms - as in, helmet on helmet on serious padding - didn't either, which is why knights liked to whack each other on the head with maces. Blunt trauma is a bitch.

      The purpose is more to protect the head from incidental bumps anyway.

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    2. I didn't find it excessive, the American researchers did. Also I'm pretty sure the American tanker is subject to completely different stresses than the football player, so the helmet is going to be a little different.

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  2. If the goal is just to prevent cuts and bumps from light impacts then something lighter will suffice.

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    1. That's correct. No helmet can "prevent" concussions.

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    2. And there is the usual zero-sum game of protection versus comfort and practicality...

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    3. I'm reading "Panzer IV Sherman: France 1944" and it said that Sherman gunners had trouble with the new M55 gun sight because they tended to wear a steel helmet over their tanker helmet. So they really do need a lot of head room no matter what the researchers say.

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    4. Yes. That´s why I suggest to compare only engeneering drawings before jumping to conclusions.

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    5. The conclusions regarding the sufficiency of headroom in the Sherman is made by the Americans based on their measurements of the tanks. There are no engineering drawings involved here. Seems you are a much more eager writer than reader, as usual.

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  3. "The height of the driver's compartment is only 80 cm (31.5"). This is not only less than any position of the Stuart (a light tank!), but out of the 541 men sampled in the 1st Battalion, Armored Force Replacement Training center, not a single tanker would be capable of comfortably occupying this position."

    Somebody can´t measure. I took the source image, rectified the image according to three lines given with measurements and when I measured the headroom, I found the claim of only 80cm headroom to be not confirmed by the drawing.

    The vertical distance from axes of seat to roof plate is 98cm, the slightly inclined axis from the bottom via head to the roof plate is 94.5cm in the VK45.03.

    Just because You don´t understand how to use a ruler doesn´t turn lies into truths...

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    1. I blew up the image to have 1 pixel = 1 mm and all of my measurements matched up.

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    2. I challenge Your assertion as incorrect. Either by mistake or deliberately misleading. The VK 45.03 can be scaled precisely, because it is an engeneering drawing. The russian drawing CAN NOT be scaled because it´s measurements are contradictory (compared foot pedal H=100mm with the seat backs at H=400mm), You will not be able to bring the russian sketch to one common level where all measurements agree.

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    3. Yes, the pedal is out of scale, but I didn't use the pedal to measure the height of the driver's compartment.

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    4. http://imgur.com/a/ivwsd

      blue: BAMA drawing
      red: soviet sketch

      all measurements after scaling using Auto CAD

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    5. Wow you're obsessed with that pedal, aren't you. I used the 400 mm seat to scale the image, the value that you yourself admit matches the scale. The pedal is not mentioned or used anywhere.

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    6. Taking into account a CAD drawing, and Your claim that You scaled by referencing the 400mm seat, I am convinced You made another error. If You had indeed scaled the 400mm seat, You would arrive exactly at my drawing which is using the reference of the 400mm seat as You can see.
      One source of error could be the VK drawing.
      Since the VK drawing is perfectly matching all reference lines, -as could be expected from an engeneering drawing- how come You claim only 80cm headroom when CAD measurements give 95cm?

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    7. Probably because headroom is traditionally measured vertically, not diagonally.

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    8. The difference in inclination is not enough to explain 15cm. Vertical distance between bottom and roofplate is 94cm, not 80cm(!). By my estimation, and using Your combined drawing, You appear not to have used the seat as reference but the horizontal distance between seat panel and pedal. If You scale from this reference line You can get within 99.4% of Your drawing. However, the vertical seat now is not 400mm anymore but 480mm, which means all vertical distances will be in error.

      If You hold that for correct, then You appear to have scaled from a reference line without mentioning the conflicts of other reference lines but to top that of, You seem to have used the (incorrect) vertical scale from the soviet drawing to measure the vertical distances in the VK 45.03 H, instead of using VK´s own measurements, which are perfectly scalable.

      Precious deception.

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    9. lol You're a real piece of work, aren't you?

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    10. Fact is he is wrong with the crampedness of the VK45.03 H. Fact is also, Peter lied about it by quoting a reference line which was deliberately not correct.

      I caution everybody to double check any claims made in this blog.

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  4. Plus, the russian drawing is demonstrably NOT an egneneering drawing and contains multiple contradictions in scales. It´s a sketch indicating *desired* sizes, not *actual* ones.

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    1. Yeah, the Soviet standard desires 58 cm of room, the Stuart only has 40 cm of leg room, therefore it is cramped. Anything else you need explained?

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  5. Replies
    1. I at least care for facts.

      While everybody can make an error, it is important to point out mistakes, particularely, if conclusions in comparative "crampedness" are extracted from incorrectly scaled drawings.

      But I guess, You don´t like people pointing out the errors made by this blog.

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    2. I don't particularly care for autistic monomaniacs.

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  6. I don´t care what You think I am. But You should ask Yourselfe the question whether or not You care for facts and if You can actually contribute anything factual to the dicussion. I mean, anything other than name calling or ad hominem attacks...

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    1. I've seen enough of your "facts" to conclude you're not worth the effort of engaging with, thanks. Especially without a decent BBS quoting interface.

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    2. So let me recapitulate it. You are not interested to check mistakes made by this blogger if they don´t fit Your´perception, comrade?

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