"Ejecting hazards"...question.

[NY3D]

I was having a conversation with some co-workers and we were on the subject of ejections.I heard that the human body can only withstand no more than 2 ejections in a pilots lifetime.Is this true? I didnt argue cause Im not sure myself,any experts here???:smartass:

[rogue_blade]

ppfff thats bull sh!t. thats like saying an F1 driver can only survive 2 crashes in a lifetime

[Kuky]

where do these people get their "information" from? :D

[NY3D]

That's what I thought, 2 ejections is nothing.Well I cant really say that cause Im not a pilot and have no clue what it feels like,however if you think about it ejections put a lot of strain on your neck,or other parts of your body,so there might be a specific number after all,but 2 i think is kinda low.

[NY3D]

Very interesting,thanx IguanaKing. Thanx for the input guys !:thumbup:

[Groove]

I think 3 ejections is all they let you have because of the spinal compression you get.

 

Besides, if you eject 2 times i bet there is no 3rd time for you ;) Of course in peace times.

[EscCtrl]

2 might screw your back up badly but there is no specific figure, it doesn't work like that :P

[jonnyB3]

I heard that every time you eject your rib cage moves slightly down and after three you cannot do it again because your ribs are too disported.

[jonob66]

Back compressions are not the only dangers. At high speed the wind force can do very serious damage.

[Frostie]

AFAIK 3 ejections is the limit in the RAF.

[Jester_159th]

AFAIK 3 ejections is the limit in the RAF.

 

I've heard the same thing. So I was suprised when I watched a video posted on these forums a few days back about ejections. In it an RAF wing commander talks about being ejected through the canopy of his Harrier after the det cord failed and the canopy didn't disintigrate. He made a comment about the experience (after corrective surgery) leaving him with one vertebra less than everyone else, but he was flying again after about 18 months. Now I only watched the video through once and I'm not sure if I misheard or misunderstood what he said, but I would have thought an injury like that would have immediately had him flying a desk rather than a Harrier.

[EscCtrl]

I've heard the same thing. So I was suprised when I watched a video posted on these forums a few days back about ejections. In it an RAF wing commander talks about being ejected through the canopy of his Harrier after the det cord failed and the canopy didn't disintigrate. He made a comment about the experience (after corrective surgery) leaving him with one vertebra less than everyone else, but he was flying again after about 18 months. Now I only watched the video through once and I'm not sure if I misheard or misunderstood what he said, but I would have thought an injury like that would have immediately had him flying a desk rather than a Harrier.

 

The RAF spend around a million pounds per pilot to train them to their standard, they will never write off a pilot that easily. I recall a harrier accident some years back where the plane tried to land but lost thrust somehow and it collapsed into the ground and the pilot lost the use of his legs. Worked out cheaper to convert the rudder pedals to a control he could use with his hands.

[Force_Feedback]

It depends on the type of ejection seat used. The age of that system, older systems generate ~22 vertical Gs for about 0.2 seconds, the windspeed, wether it was an ejection through the canopy or not. Most 'current' rocket assisted ejection seats (MB Mk. 14/16, ACES II, Zvezda K-36DM series 2) generate vertical acceleration loads of around 18G for 0.25-0.45 seconds. The actual load varies greatly, this due to the condition of the rocket pack and the type of catapult that is used prior to rocket ignition.

Then we have the forces of windblast and decelleration prior to main parachute deployment, as now known (due to a 10 year old documentary appearing on youtube :P) the forces of windblast are the real hazards of egress. For example, when ejecting at 600 kts at 25000 ft (numbers are rusty, but it was high and fast) the force needed to hold on to one ejection handle of the K-36. And let me remind you that the K-36 has two handles, so the forces per hand are lower compared to the 'D-ring' ejection handle used on most Martin Baker and ACES II seats. The conclusion from American military scientists is that the grip used on the K-36 is the best kind of grip configuration to reduce the grip strength needed.

 

I made a nice chart using some data from a test report, which was made with both Russian and American test equipment, the flight suit used was KKO-15. Only test 6 used the KKO-5 flight suit.

 

This will give you some detailed insight on what kind of forces are involved in a high speed ejection.

 

 

Here are the neck load limits during the entire ejection sequence, the -Z axis correponds with the vertical G loading.

[redeagleGER]

The RAF spend around a million pounds per pilot to train them to their standard, they will never write off a pilot that easily. I recall a harrier accident some years back where the plane tried to land but lost thrust somehow and it collapsed into the ground and the pilot lost the use of his legs. Worked out cheaper to convert the rudder pedals to a control he could use with his hands.

Common you dont even belive this yourself. A pilot has so much to do, especialy in a harrier that he cant afford to not use them :doh:

[EscCtrl]

Common you dont even belive this yourself. A pilot has so much to do, especialy in a harrier that he cant afford to not use them :doh:

 

It was on a TV show about the pilot. I swear!

 

Surely someone else saw it all that time ago?

[Pilotasso]

Hazards of ejecting? Do it too soon and youll disapoint the girl! :D

[Frostie]

I believe he was a test pilot during the original testing of the Harrier.

It had got about 15ft off the ground when things went wrong.

 

I think Health and Safety is priority for the RAF, and if its proven that a pilot can only take so many ejections before serious damage can happen then no amount of money is worth the pilots future..

 

Ive only ejected three times , unfortunately I ended up with three kids.:D

[Kuky]

...Ive only ejected three times , unfortunately I ended up with three kids.:D

 

LOL :megalol:

[Sytse]

I don't know much about ejections... How high are the G-forces?

 

Would be interesting to compare them to this:

 

Highest G-Force Endured Voluntarily: 82.6g for 0.04 seconds by American Eli L. Beeding Jr. in 1958. He spent three days in the hospital afterwards.

 

In February 1957 a chimpanzee riding a rocket-propelled sled on a 5,000 foot long track, braked to a stop, and survived a load of some 247 g for a millisecond, with a rate of onset of 16,000 g per second.

 

http://en.wikipedia.org/wiki/Eli_Beeding

[Force_Feedback]

In an ejection from a K-36DM series 2 seat, as seen above, the average G load from the ejection rocket is about 18G, but that is ~18G for about 0.35 seconds. The G value from the catapult alone, the thing that fires before the rocket initiates, is ~13G for about 0.18 seconds. The frontal windblast G load is around 19G in a Mach 1.1 ejection, and 35G in a Mach 2.51 ejection.

Mind you that these values only apply to the K-36. T

he ACES II for example has a low level delay of 1.17 seconds before the drogue chute is jettisoned, independant of the speed (ie ejecting at Mach 1.4 or ejecting at Mach 0.7, it doesn't matter, 1.17 seconds of decelleration). This is done to limit the horizontal displacement of the seat, but, in most cases (high Mach 90 degree dives excluded), the K-36 travels beteen 100 and 300 ft more in the horizontal plane than the ACES II.

The VS-2 seat for example on the L-39 is rated for 0 altitude and 150 km/h and more ejections, yet it has a Gz (rocket) loading of around 22 G. So the G-load varies greatly from seat to seat. A rough value of 16G for the ACES II, 18G for the K-36 classics, 20 G for the Mb mk. 10 can be used, but this is only for low speed ejections (under 250 knots IAS). The actual G-loading depend on the immobilizing mechanisms used in seats, and the use of nets (ACES II+, on the F-22), or windblast deflectors with nets (K-36 3.5 series), flight gear, decelleration methods (drogue chutes, stabilized drogue chutes, drogue booms) and the time those things are given.

IMHO it is better to decellerate the seat in a 'smooth' (highly relative!) manner than to decellerate from Mach 1 to Mach 0.05 in 1.5 seconds. As the last mentioned method will surely save the pilot, but will also break a lot of bones and leave potential brain trauma. 'Saving the pilot no matter the cost' is something I don't agree with, as having the man/woman spend 2 years in hospital afterwards will only make matters worse.

Also note that this 'slow decelleration' thing only applies to older seats. New seats with computerized sequencers and special algorythms can assertain the needed form of decelleration. So if a plane is about to lawn dart at high speed, it will deploy the main chute as fast as possible, and if ejection occurs at medium altitude, the seat will give more time to decellerate before firing the main chute.

[EscCtrl]

I don't know much about ejections... How high are the G-forces?

 

Would be interesting to compare them to this:

 

Highest G-Force Endured Voluntarily: 82.6g for 0.04 seconds by American Eli L. Beeding Jr. in 1958. He spent three days in the hospital afterwards.

 

In February 1957 a chimpanzee riding a rocket-propelled sled on a 5,000 foot long track, braked to a stop, and survived a load of some 247 g for a millisecond, with a rate of onset of 16,000 g per second.

 

http://en.wikipedia.org/wiki/Eli_Beeding

 

Chances are that g force was exerted forward, as opposed to the g you'd feel when ejecting which is upward. As it is in a different axis it effects the flow of blood to the head less and thus you can withstand much higher G loads hence the 80 or so g you stated whereas a pilot in a plane can only withstand under 20g ejecting upwards (for a very brief period of time though)