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Most military aircraft, for safety reasons, have their passenger seats reversed with respect to the direction of travel. I am wondering why this is a safer system.

(Please don't say it's because aircraft hardly ever reverse into mountains, that line has been around since the Wright brothers :)

This seat reversal system has been recommended for civilian aircraft many times, but mainly for psychological and financial reasons, it has never been adopted on a wide scale.

There is a reference here Aviation Stack Exchange but it does not explore the resultant forces involved in a collision.

My main point is that, the next 10 years, driverless cars will probably reach a large section of society, and for all but the human "supervisor", reversed seats may confer an additional safety advantages.

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My questions concerns the reasons why reversal of seats reduces / mitigates the impact forces involved in a collision.

I am trying to think through the difference in forces regarding say, reduction in neck injuries, but other than spreading the impact load through the larger surface area of the person's back, I can't come up with a fundamental reason based on forces and vectors, although I am fairly sure there is a connection, otherwise I would not asking this question.

Some clues may be given from the following extract.

From: Aerospace Magazine

Yet they also cite a 1958 accident involving an airliner in Munich, Germany, which crashed on takeoff with the Manchester United soccer team on board. Those in forward-facing seats were killed, and those in aft-facing seats were saved.

In 1983, Richard Snyder, a research scientist studying crash protection and transportation safety at the University of Michigan, published a paper titled “Impact Protection in Air Transport Passenger Seat Design.” Snyder wrote, “Data appear to overwhelmingly substantiate that the seated occupant can tolerate much higher crash forces when oriented in the rearward-facing position.”

EDIT From John Rennie's comment, (in case it gets deleted)

Isn't this obvious? Suppose you were to experience 50g. Would you prefer to do it lying on your back on a smooth surface or lying on your front supported only by two lengths of webbing?

I was looking for an answer in terms of some reduction in forces, but it is simply a spreading of the impact.

END EDIT

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  • $\begingroup$ Not so much the force as the impulse: same momentum change over a longer period of time. 'Slow' pressure of the seat vs fast snap of the neck or collision with the surface in front of you. Somewhat mitigated in cars with airbags. $\endgroup$
    – pjc50
    Sep 21, 2016 at 14:31
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    $\begingroup$ Isn't this obvious? Suppose you were to experience 50g. Would you prefer to do it lying on your back on a smooth surface or lying on your front supprted only by two lengths of webbing? $\endgroup$
    – John Rennie
    Sep 21, 2016 at 14:34
  • $\begingroup$ @JohnRennie yes, I am probably over thinking it, all right. I just remember John Stapps rocket sled experiment where he knew he would experience 50ish g and he still sat facing forward. But he was mimicking pilots and ejector seats. $\endgroup$
    – user108787
    Sep 21, 2016 at 14:54
  • $\begingroup$ @CountTo10 he was experiencing +50g ie pushing him BACK into the seat. If he had experienced -50g ie stopping and being thrown forward he would have preferred sitting backward. $\endgroup$
    – Martin Beckett
    Sep 21, 2016 at 16:38
  • $\begingroup$ @MartinBeckett I might salvage a small bit of dignity yet : ) I only read this 5 mins ago en.wikipedia.org/wiki/John_Stapp a total of 74 human runs had been made on the decelerator, 19 with the subjects in the backward position, and 55 in the forward position. Stapp's research on the decelerator had profound implications. For instance, the backward-facing seat concept, was given great impetus by research program. It proved beyond a doubt this position was the safest for aircraft passengers and required little harness support I should have done more research first $\endgroup$
    – user108787
    Sep 21, 2016 at 16:46

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I would have thought if you accelerate somebody at high g back into a chair that is supporting their full body and head and is already in contact with the body they are going to do better than throwing them forward and once they are moving try stopping them with a single belt across a part of their body while allowing their head and arms/legs to flail around and hit things.

Not sure if it is still as relevent with airbags.

edit. This assume a vehicle that experiences higher magnitude acceleration when stopping than when accelerating forward. I'm not sure if this is necessarily true for high performance military aircraft especially with a catapult.

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  • $\begingroup$ Thanks Martin, I think John Rennie's comment and your answer sort this out for me. I got the wrong end of the stick thinking about this in terms of reduced ( in some mysterious way) forces. Thanks. $\endgroup$
    – user108787
    Sep 21, 2016 at 14:59

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