Ejection systems in Helicopters.

Helicopters and tilt-rotor aircraft
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dunnman19

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Unread post27 Sep 2006, 02:09

I was recently reading about a Russian attack helicopter that has an ejection seat. I was wondering if anyone had any input on why the US does not use ejection seats in the Apache and Cobra helos. Besides possibly ejecting up into the rotor blades in a worst case scenario. I would appreciate any info on this thanks.
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LinkF16SimDude

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Unread post27 Sep 2006, 03:48

My guess would be weight issues. A single ejection seat adds quite a bit of weight to any design, and in the Cobra and Apache doubly so. More weight means bigger engines which means more gas needed, etc. etc...

Both the Cobra and Apache were designed to fly low and fast. So instead of adding two ejection seats, the helos (and in particular the Apache) were designed to withstand enough large caliber direct fire to either bug out and go home, or if damaged enough to quit flying, to last long enough for the pilot to autorotate (if possible) to a forced landing.

As for helos with the ejection seats, AFAIK most designs use seperation charges in the rotor head to seperate the blades prior to the seats leaving. So they don't actually hit the blades on the way out (hopefully). :wink: Can't think of any American design that used this feature tho.
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snypa777

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Unread post27 Sep 2006, 08:30

dunnman19 wrote:I was recently reading about a Russian attack helicopter that has an ejection seat. I was wondering if anyone had any input on why the US does not use ejection seats in the Apache and Cobra helos. Besides possibly ejecting up into the rotor blades in a worst case scenario. I would appreciate any info on this thanks.



Time? Okay, you blow the rotor blades with charges, wait for the debris to clear, you still can`t be entirely sure where those still swirling blades will be when you punch out. Right then, the area is clear, time to get out....too late, you hit the ground very hard!

It would be interesting to see how the Russian bird gets around that? What type? Ka-50 Black-Shark?
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spectre184

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Unread post27 Sep 2006, 18:12

snypa777 wrote:
dunnman19 wrote: What type? Ka-50 Black-Shark?


That may be it http://www.fas.org/man/dod-101/sys/ac/row/ka-50.htm read 4th paragraph.
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skrip00

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Unread post27 Sep 2006, 18:22

USMC tried it with the AH-1W. Didnt like it so they scrapped the idea. Pilots survive better if they stay with the aircraft. Ejecting at low altitudes supposedly isnt fun at all.
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LinkF16SimDude

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Unread post27 Sep 2006, 22:54

snypa777 wrote:Time? Okay, you blow the rotor blades with charges, wait for the debris to clear, you still can`t be entirely sure where those still swirling blades will be.....

Well, would you consider this?:

Because of a certain law of rotational physics (the exact name escapes me right now), you do know at least what immediate direction the blades will take after they're blown. When an object attached to a central spinning point (in this case the blades and rotor hub) is suddenly released, it immediately moves away in the same plane but on a line perpendicular to the radius of rotation (the tangent). Kinda like a discus thrower when he/she lets one fly.

In other words, when the blades are released, their rotational velocity will take them horizontally away from the helo for some appreciable distance well before the seats leave. As long as you're not past 90 deg. of roll at the time of ejection and since the seats always eject 90 degrees to the rotor plane, they'll be well clear of any danger of blade collision.

Or am I being totally off the mark?
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dunnman19

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Unread post28 Sep 2006, 03:02

thanks guys i appreciate the info, i wonder if the marines ever released any info about the testing in the cobra?
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174wepsw

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Unread post28 Sep 2006, 14:44

LinkF16SimDude wrote:
Or am I being totally off the mark?


I agree 100 %. Due to velocity of a spinning object to suddenly let go, it will have a straight path. But what we also have to remember is the gravity and Air resistance. Gravity doesn't really need to be looked at since it wouldn't act on the blades so quickly near the helicopter. The rotor blades shape, could be a problem later on, but with a high velocity and them being suddenly blown off. I wouldn't think they'd be a problem near the aircraft.

It's simple physics, the rotor blades want to stay in a straight line all the time, but are being held back when on the helicopter.
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174wepsw

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Unread post28 Sep 2006, 14:45

LinkF16SimDude wrote:
Or am I being totally off the mark?


I agree 100 %. Due to velcity of a spinning object to suddenly let go, it will have a straight path. But what we also have to remember is the gravity and Air resistance. Gravity doesnt really need to be looked at since it wouldn't act on the blades so quickly near the helicopter. The rotor blades shape, could be a problem later on, but with a high velcoity and them being suddenly blown off. I dwouldnt think they'd be a problem near the aircraft.

It's simple physics, the rotor blades want to stay in a straight line all the time, but are being held back when on the helicopter.
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MKopack

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Unread post28 Sep 2006, 16:09

As everyone has said, when you drop the blades they're going to leave the vicinity of the helo pretty quickly, so hitting them shouldn't be a problem.

But:
#1 - At low altitude you would still need time to drop the blades and eject. Most helos operate at 'low' altitude, at the very highest.

#2 - Ejection seats are heavy. Many, if not must helos are pretty 'lightweight' structurally (strong, but lightweight) especially when compared to normal aircraft - they have to be, to lift off vertically with their loads. Adding the weight of a couple of bang seats to the nose would required balanced weight to be added to the rear, and probably even more so than with conventional aircraft, every pound counts, if you add something, you're replacing either fuel, weapons, or payload.

#3 - Helos crashes tend to be pretty survivable. Look at the Army's safety statistics, although it's MUCH better than in the past their 'crash' rate is VERY high (of course when you're flying 'b*lls out' at 50 feet at night on goggles, it's understandable...) but their accidents don't make that much news, because in many cases, the crews are able to walk away.

That having been said, while the Russian Ka-50/2 does have ejection seats, like many of the other Russian 'airshow' aircraft, it is currently little more than a technology demonstrator - sort of like the B-1A with the F-111 style escape capsule. The Ka-50 will likely never be built in anything resembling operational numbers, and if it is, it's still to be seen whether the ejections seats would be incorporated. (Engineer / designer / salesman thought: "Hmmm, if we removed 400 pounds of seats from the nose, how much more fuel / weapons could we add...?)

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snypa777

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Unread post28 Sep 2006, 16:57

Great replies guys. The rotors would move away from the helo` just fine and you would be clear of "spinning death"!..Great if you assume the aircraft is flying straight and level and not rolling....depends which way you ejected also, 90 degrees away from the plane the blades move in would be a good start!...
Link, that would be centrifugal force by the way. still think it would take too long, low level environment being the limiting factor...
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Guysmiley

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Unread post28 Sep 2006, 19:24

MKopack wrote:#3 - Helos crashes tend to be pretty survivable. Look at the Army's safety statistics, although it's MUCH better than in the past their 'crash' rate is VERY high (of course when you're flying 'b*lls out' at 50 feet at night on goggles, it's understandable...) but their accidents don't make that much news, because in many cases, the crews are able to walk away.


To your point #3: http://www.youtube.com/watch?v=jix7N-uT0J0 AH-64 tree strike, safe landing.

(In truth there wasn't much altitude to descend... helo pilots are nuts) The audio is priceless (and thank God McD built those beasts to take a beating)

Pilot: "Think we can make it?"

CP/G: "Nope"

Pilot: "Oh, ye of little faith"

Pilot: "Oh $^%&!"
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MKopack

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Unread post28 Sep 2006, 19:43

Damn, and that wasn't even a tall tree...

Take a look at this: http://www.youtube.com/watch?v=3F2k-GWKW-w&mode=related&search= Have read that everyone survived, with the one guy that 'exits early' (watch the video, you'll see) having minor injuries. Can anyone confirm?

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Unread post29 Sep 2006, 02:55

Saw a lecture in college (early 80's) about that very issue. Ejection seats were too heavy, so they tried a different path. A rocket would fire upwards trailing a bungee-like cord (shock absorber) and pull the guy out. Obviously the rotors had to be addressed. The put explosive bolts at the base so they would fly away radially just as described above. Problem was that the spinning inertia was so high that when they came off at separate time (even milliseconds) the helicopter would tear itself apart. Or they wouldn't come off and the guy (test dummy) would die..
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Unread post29 Sep 2006, 20:17

The only operational helos with ejection seats are the Russian Ka-50 (single seater) and Ka-52 (two-seater, side by side).
The seat is Zvezda K-37-800 (a variant of the K-36). Officially it'a an H=0, V=0 seat, but in real life it's effective at 100 meters (300 feet) plus altitude.
After pulling the handle the top of the cockpit is blown out, just like one blade from each rotor (Ka-50/52 use 2 counter-rotating main rotors with 3 blades each. Than a drogue rocket blasts upwards towing a cable which pulls the seat out of the airframe. The whole sequence takes 6 seconds.

Only 2 Ka-50 have crashed so far (a prototype and a serial production), the seat wasn't used in neither of the 2 mishaps.

Due to the dynamics of the separated blades, Ka-50s have to fly with at least 150m (450feet) separation between them on the horizontal, for the reason explained by LinkF16Simdude in his second post on this thread
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