Ejection systems in Helicopters.

Unread postPosted: 27 Sep 2006, 02:09
by dunnman19
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.

Unread postPosted: 27 Sep 2006, 03:48
by LinkF16SimDude
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.

Re: Ejection systems in Helicopters.

Unread postPosted: 27 Sep 2006, 08:30
by snypa777
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?

Re: Ejection systems in Helicopters.

Unread postPosted: 27 Sep 2006, 18:12
by spectre184
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.

RE: Re: Ejection systems in Helicopters.

Unread postPosted: 27 Sep 2006, 18:22
by skrip00
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.

Re: Ejection systems in Helicopters.

Unread postPosted: 27 Sep 2006, 22:54
by LinkF16SimDude
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?

Unread postPosted: 28 Sep 2006, 03:02
by dunnman19
thanks guys i appreciate the info, i wonder if the marines ever released any info about the testing in the cobra?

Re: Ejection systems in Helicopters.

Unread postPosted: 28 Sep 2006, 14:44
by 174wepsw
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.

Re: Ejection systems in Helicopters.

Unread postPosted: 28 Sep 2006, 14:45
by 174wepsw
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.

Unread postPosted: 28 Sep 2006, 16:09
by MKopack
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...?)

Mike

Unread postPosted: 28 Sep 2006, 16:57
by snypa777
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...

Unread postPosted: 28 Sep 2006, 19:24
by Guysmiley
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 $^%&!"

Unread postPosted: 28 Sep 2006, 19:43
by MKopack
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?

Mike

Unread postPosted: 29 Sep 2006, 02:55
by Roscoe
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..

Unread postPosted: 29 Sep 2006, 20:17
by RoAF
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

Unread postPosted: 29 Sep 2006, 21:08
by skrip00
Also, take into consideration those two choppers fly higher and faster than most normal choppers.

Unread postPosted: 29 Sep 2006, 23:09
by habu2
Six seconds sounds like a lifetime... (no pun intended)

Unread postPosted: 03 Oct 2006, 06:33
by kmceject
Ejection seats in helos were rejected for several of the reasons given above in US service. The main one is that it takes time to eject that you don't have at low level. Systems tested included jettisoning the entire crew module, jettisoning the seat, or rocket extraction. The K-37-800 is an extraction system.

All three cases depended on jettisoning the rotors first. This leads to a VERY rapid sink rate on a helo and that makes it likely that the ejection sequence would be interrupted by ground interface at low levels. Not to mention as RoAF said it would be rather hazardous to fly in tight formation as most pilots are taught to do so for mutual aid. In the 80s in NYC where I lived a helo had a mishap atop what was the Pan Am building at the time (Met Life now) and it shed a blade that flew about eight blocks before intersecting a pedestrian, literally...

MKopack- great points, but extraction seats are significantly lighter than ejection seats, less than 100lbs vs 150-250lbs for seats (crew capsules start around 450, modules way up from there...). When you consider the weight of an armored crew seat on a attack helo it isn't that great an excess weight, and with modern engines helos typically have enough torque to spare a little if needed.

One other quick point is the K-37-800 pulls the crew out at an angle, leading to potential injuries. That was a problem when they tested the YANKEE a long time ago in AH-1s. I have reports on this stuff somewhere, but haven't had time to review them.

Kevin
The Ejection Site

Unread postPosted: 10 Oct 2006, 18:44
by kmceject
Did a little review of a 1973 vintage publication (for NATO countries) on the issue. The authors investigated several different concepts and had some interesting things to say about the issue. Manual bailout was listed as a decent concept for a low cost retrofit, but the min altitude issue was very problematic given the statistics. Sideward extraction was also a retrofit possibility, but with issues. Should a two-man tandem design like the Apache be fitted with extraction systems for example the fastest method would be simultaneous extraction in opposite directions (hoping the rotor disk wasn't too low on one side...) This would be problematic in the position of the collective interfering with one crewman's extraction.

For new design/built aircraft investigation was done into upward ejection or extraction, sideward ejection with L-shaped trajectory, or escape capsule. For upward ejection/extraction the rotor severance issues come into play. Concepts were pretty interesting including severing the rotor mast (which they suggested would need a method to raise and lock the collective inputs prior to that to allow for a predictable flight path of the disk.) Others included sequenced and simultaneous severing of rotor blades. Vibration was an issue, as well as risk of entanglement with the egressing crew and other vehicles in the area. Testing was done on sequenced ejection of blades in a set azimuth. Don't be in a formation in that direction and you probably would be safe! Simultaneous blade severance came in two flavors- all at once or pairs (in even number blade disks only). Technically all these concepts were reasonably valid, but most required a significant test progam to validate.

The L-shaped ejection path was one of the most interesting, but probably psycologically impossible one to accept. Rather than jettisoning the rotor, the seat would fire sideways (at up to 11G) and fly horizontally until it cleared the rotor disk, then rocket upwards for clearance. Technology for this existed in '73, but would have required a long, expensive test program to make it worthwhile. It also would require significant design changes to the cockpit to allow for the ejection path. (Stowing of cyclic/collective and side consoles, etc.) In the 1990s the CREST and 4th Generation Ejection Seat programs showed that complete trajectory control of a seat (with accelleration rate controls too) could be accomplished if desired so this concept would be easier to do now if the requirement came up.

Escape capsules as defined in the publication would be severance of non-essential portions of the vehicle and recovery of the crew areas by parachute cluster. This would have to be a blank blueprint incorporated design, and would have had many issues that would make it difficult. The diagrams in the report of a CH-47-class bird with six parachutes or the CH-53-class design with six parachutes and a huge group of airbags below is rather interesting.

Beyond this report I reviewed a video I have of a test using a CH-53-class bird on a rocket sled at Holloman AFB (846th Test Squadron) using a YANKEE or RANGER Extraction system. The sled seems to be moving at a low (100kt or less) rate and the rotors are spinning. They are severed on an azimuth of about 2 o'clock sequentially then the roof seems to explode in shards of plexiglass and the two rockets are simultaneously launched out by catapult. The ignite at the end of the 3 meter lanyards and extract the two 'pilots'. It is a very quick clip so I can't tell much more than that, but I'd say there were no rotor entanglement issues (although the trajectories were not stable), and the extractions appeared clean.

I know AH-1 Cobras were similarly tested and the system was found to work reasonably well. I am not in the 'know' on why they were not produced but seat manufacturers have told me that they could make a system IF a requirement ever came along from the 'customer'.

By the way, the report conclusion is very intense on its insistance that an escape capability should be provided as soon as possible. I do know that crew seat improvements have made it significantly more safe to crash land than the versions available when the report was written. Most ejection seatseat manufacturers have designed impact absorbant crew seats for helicoptors for example...

Kevin
The Ejection Site
ps as to weight increases they list some 60kg per crewman for ejection seats and less than that for extraction systems. These weights were for 1973 technology though. The McDonnell-Douglas Minipac and Martin-Baker Mk 15s were designed later and are significantly lighter/smaller ejection seats for trainers and for consideration for helicopter use.

Unread postPosted: 11 Oct 2006, 16:04
by Roscoe
That Holloman video you describe was one of several that were shown at the college lecture I mentioned...all the others were abysmal failures. As a tester and engineer I accept that failures often happen on the road to success, but those were brutal, the failure mechanisms were different in every case, and the final one that eventually worked was deemed to be "lucky" by the lecturer. An analysis was then done to see how many crews would actually be saved even if it did work as designed...it was never intended nor possible to be a zero-zero system so there were a lot of flight conditions where it simply would not help and the crews had a better chance of surviving if they would try to set it down instead. Turned out to not be a worthwile investment.

Unread postPosted: 11 Oct 2006, 17:45
by kmceject
Roscoe,

Just to be clear, your earlier post seemed to indicate the blade sep method was the problem. The YANKEE is a proven system, and I have several 0-0 videos of it so I know that works for fixed wing. It was even live tested as the 'away' system in the days before manikins got all the fun jobs. The issue to me is more that the rotors were always the main problem.

Kevin
The Ejection Site

Unread postPosted: 11 Oct 2006, 23:07
by LWF
Besides, most helicopters don't need ejection seats since they do better by auto-rotating down. Unless the tail is taken out, then they spin down.

Unread postPosted: 12 Oct 2006, 04:32
by Roscoe
That's how it was presented. But that was also over 20 years ago so I trust your judgement on this one. Either way, it came down to a business case that it wasn't worth it. Any Helo so beat up you can't autorotate will probably not be stable enough to allow aircrew extraction.