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This question got me thinking. Ejecting from a helicopter is necessarily more complicated than ejecting from a fighter jet or other fixed-wing aircraft. The answer to this question states that ejection-capable helicopters blow the blades first, then the canopy, then eject the passengers.

This seems to me like a lot of explosions above your head, which seems only slightly preferable. Why not eject the passengers either sideways or forwards?

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    $\begingroup$ This would not work so well at low altitudes, especially at the strange attitudes a helicopter requiring ejection would probably be in. $\endgroup$ – fooot Aug 28 '17 at 15:49
  • $\begingroup$ There are a lot of trade offs here, like space, weight, cost ,reliability, and use constraints, injuries to the person. Honestly, it's quite controversial whether ejection would help much in a helicopter at all, or under what conditions ejection has the advantage over not to eject. In reality most of the unconventional eject directions (down wards, side ways) usually have very tight use conditions and high failure rates. $\endgroup$ – user3528438 Aug 28 '17 at 15:50
  • $\begingroup$ If your question is specifically about Ka50, then a reasonable guess is, this use case is targeting low altitude usage (it's an attack helicopter) so you need to maximize altitude to deploy parachute reliably. $\endgroup$ – user3528438 Aug 28 '17 at 15:55
  • $\begingroup$ I wouldn't like to be in this helicopter in a nose-down position at low altitude when ejecting forward $\endgroup$ – Manu H Aug 28 '17 at 17:05
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    $\begingroup$ Good way to paralyze somebody, snap their neck moving sideways at quite an incredible speed. Spinal injuries are relatively common in normal ejections going straight up where the force vector is basically in-line with the spine. It would be like being kicked in the head by a professional soccer player. $\endgroup$ – Ron Beyer Aug 28 '17 at 19:23
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Well to me it seems that in your question you consider the helicopter flying straight and level and clear of any terrain. Well that's not true so let's take each case separately:

Eject forward

That seems like the most dangerous option to me. What if you are into CFIT? The ejection system will actually "spit" you into terrain with your helicopter's speed plus the speed of the acceleration. Ouch. Even if you survive this, the point is to escape the helicopter. And guess what its trajectory is: forward.

Also consider that the free stream works against you so you will need more acceleration to get away of the incoming helicopter.

Finally, right in front of you there is equipment like dashboards machine guns sensors et al. that need to get out of your way before you go.

Eject sideways

That sounds a least dangerous option. But what if the helicopter is banking to one of the sides? If the crew is seated side by side do they have time or even the option, "I go first you go after"?

Also bear in mind that attack helicopters' nature is to fly low and maneuver a lot. So there are high chances to be low and bank at the same time when in need to eject.

So the above 2 leave you with one option: eject upwards. But then you have one (or maybe 2) big propellers rotating above your head. But that's "easy": you get rid of them the same way you get rid of the canopy and then eject. Once the blades are released, the centrifugal will do what it knows best and the blades will be out of your way in no time. Well, hopefully.

Considering the "too many explosives above ones head", it's not rare practice to use explosives to get rid of things that are in the pilot's way like for example the canopy. That's been around for a while. But changing the trajectory of escape that will be a new concept and it will need lot's of testing.

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    $\begingroup$ This is a very well thought out answer that explains it in laymens terms. I'd +2 if I could $\endgroup$ – Sidney Aug 28 '17 at 16:33
  • $\begingroup$ @Sidney thanks, glad I've helped. $\endgroup$ – Stelios Adamantidis Aug 28 '17 at 16:39
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    $\begingroup$ I'd also say that the human body will survive a forward acceleration quite well, while upwards can result in serious injuries. But sidewards sounds really sad. $\endgroup$ – sweber Aug 28 '17 at 16:56
  • $\begingroup$ Also, I can think of a few scenarios where a forward ejection, even if it successfully ejected you forwards and safely deployed the canopy, the helicopter which might have been traveling forwards, could quickly catch up with the occupants, and if the rotors don't get the canopy, the body of the aircraft could also hit anyone that was ejected into the flight path of the disabled helicopter. $\endgroup$ – Devil07 Aug 28 '17 at 18:04
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    $\begingroup$ @JollyJoker good question! But you should really ask the OP! :) I quote: "Why not eject the passengers either sideways or forward" $\endgroup$ – Stelios Adamantidis Aug 29 '17 at 7:48
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Because of a high chance of being launched into terrain, not because it would be worse for the body.

The human body can actually withstand more g's in forward and sideways acceleration than in upwards acceleration. When accelerated upwards, the blood cannot reach the brain and eyes and very soon a glucose deficit will cause loss of vision and/or of conscience. Colonel John Stapp pioneered building up this knowledge between 1945 and 1958, by exposing first a dummy and then himself to accelerations up to 46.2 g. From this fascinating article:

Stapp was subjected to tortuous conditions, but more importantly, he survived. His team showed that humans could withstand forces in excess of 30G deceleration and just as importantly showed that seats, harnesses, and cockpits should be designed to withstand these forces as well.

And

Stapp had suffered a complete red out and was just barely conscious. The jolt burst nearly every capillary in his eyeballs, he was blinded, but his retinas did not detach. He slowly regained his bearings and within a day his vision was back to normal.

Results of the research of this brave man:

  • Forward acceleration up to 20G is perfectly survivable.
  • Backward acceleration is much more taxing to the body.
  • Sideways acceleration has little influence on consciousness, but does have significant impact on supporting muscles for the head. So the head must be fixed in sideways position before ejection.
  • Upward acceleration is more taxing than in x- or y-direction, with problems occurring at 4-5 g depending on onset and duration. A typical Martin Baker seat creates accelerations of 12-14g but for a very short time.
  • Downward acceleration is tolerated the least well by the body.

enter image description hereImage source

So for the body, x- and y-accelerations pose fewer problems than z-accelerations, provided that the head is supported for sideways acceleration - the Formula 1 style may be too restrictive for helicopter pilots though.

The first F-104 Starfighters had downward facing ejection to avoid the T-tail, however they fly quite a bit higher than a typical helicopter. The main practical problems are therefore altitude and attitude. Upwards is a better direction!

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    $\begingroup$ While it's true that being unconscious generally tends to disable one's conscience, I'm thinking that you meant to say "consciousness" instead? $\endgroup$ – Sean Nov 1 '18 at 0:33
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In both cases, you must be sure to "outrun" the helicopter blade. Your seat must go fast enough to avoid you getting a new haircut. This might be problematic because of violence of the acceleration, especially if you eject sideways.

In addition, helicopters tend to fly low so you might hit terrain or simply not have enough altitude to land safely.

I'd rather have explosions above my head and eject safely than ending like a pancake or minced meat.

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