Ejection Seat Question

[Compass Call]

I recently downloaded a video clip of a Harrier crashing into the sea just off a crowded beach. The Harrier was at very low level and appeared to be in the hover.
The pilot ejected and was propelled upwards & forwards away from the aircraft as it entered the sea. The seat and pilot separated and the seat fell into the sea in front of the aircraft. The pilots canopy deployed and seemed to be fully inflated as he landed in the sea, apparently on top of the wreckage. As this happened an object was seen to come down past him trailing what seemed to be a deflated parachute canopy or streamer.

I have two questions:

1) Is it normal for a pilot to land back in the wreckage after a very low level ejection?

2) What was this other object that came down?

:confused:

CC

[jimgriff]

The seat (Martin Baker Mk 12a) has an on board electronic sequencer.

Having seen the vid it would be safe to assume that the sequencer chose mode 1.
Mode 1 is designed for low-speed/low-altitude ejection conditions. The aim is to deploy the main parachute as soon as practicable after the seat has separated from the aircraft. A drogue deceleration phase is not required so the bridle releases are operated very quickly, thus ensuring that the deploying drogue and bridle assembly moves rapidly clear of the seat in readiness for the immediate main parachute deployment. Modes 2, 3, and 4 cater for high-speed ejections at low and medium altitudes. These ejection conditions require a delay before the parachute is deployed, to allow the velocity of the seat to reduce. The stabilizer drogue provides maximum deceleration while maintaining the seat in the optimum attitude for the occupant. The sequence timings of modes 2, 3, and 4 progressively extend the drogue phase with increasing speed and altitude so as to ensure that the parachute extractor is fired only when the seat velocity has reduced to a suitable level. The drogue bridle is jettisoned shortly after the parachute starts to deploy, both to avoid an entanglement and to allow the seat to fall clear of the occupant.

Mode 5 is the high-altitude ejection sequence, in which deployment of the main parachute is delayed until the drogue-stabilized seat falls through the 18,000-feet altitude boundary. This allows the occupant to be brought down to a safer atmospheric condition in the shortest possible time. Once the parachute deployment sequence is initiated, the seat performs in an identical manner to that of modes 2, 3, and 4.



Mode 1, low speed - low altitude. The drogue bridle is released, the parachute deployment rocket motor fires to deploy the personnel parachute, and the harness release system operates to free the occupant from the seat. The occupant is momentarily held in the seat bucket by the sticker straps.
During the ejection sequence, the parachute deployment rocket motor fires, extends the withdrawal line, and withdraws the parachute in its bag from the headbox of the seat. The parachute canopy emerges from the bag, periphery first, followed progressively by the remainder of the canopy and the drogue. The extractor rocket and bag clear the area. The drogue and crown bridle impart a force on the canopy, proportional to airspeed, to inhibit full canopy inflation until g-forces are reduced.



The "bit" that falls into the sea alongside the seat could be one of two things:
a) The seat drogue and bridle......or
b) The main parachute deployment rocket with associated webbing and bits attatched.

It is not unheard of for the pilot to fall onto the wreckage of the crashed a/c. Didnt an UAS stude land in the burning wreckage of a harrier a few years ago?

I hope I got the above info correct?

[Zoom]

Sounds good. In the early days of the F-14, the crew ejected at low level (during a display, I think) and the pilot descended onto his aeroplane's fireball, but the extremely hot air (!!) lifted him clear and he landed safely. All was caught on film.

[5 Forward 6 Back]

I should imagine it was the drogue. I wasn't aware that there was a "rocket" to deploy anything; the only rocket I can think of on my current seat is the one under me. The main chute's released by the drogue shackle withdrawing, allowing the drogue to head up and drag the main out of the seat box. If the Harrier seat's different, I don't know because I don't fly it :)

Didnt an UAS stude land in the burning wreckage of a harrier a few years ago?

The story at the time; I was on a UAS around then; was that she was too light and was outside seat parameters. Someone more qualified than me would be needed to say how that could affect her ejection.

[PPRuNeUser0172]

Sounds like someone has just cut and paste from the Martin Baker website!

The incident you refer sounds like the crash of the harrier display jet off Lowestoft in 2002??

You have kind of answered your own question about landing back on the wreckage. It was a low level ejection as you pointed out (100' ish?) and a pretty still wind day by the looks of it, where else is he going to go other than straight down??

The bit that was "dangling" was probably/almost certainly the PSP (personal survival pack) which is the box that contains the life raft and all other survival goodies which you sit on, and automatically separates from the seat.

Ejection seats, although incredibly sophisticated pieces of engineering are designed to save life and quite rightly come with a pretty serious "health warning". You will rarely use one and get away without some kind of compression/parachute landing incident or a couple of broken bones/burns from the MDC........

Hey but at least you are alive.

[5 Forward 6 Back]

Yup, always thought it'd be nicer than hitting a hill in a fireball, but not quite as nice as hopping out through an open canopy :)

The bit that was "dangling" was probably/almost certainly the PSP

Didn't he imply that the other object landed after the pilot? Surely the PSP would have auto-lowered and just dumped beneath him as he came down?

[Zoom]

Aren't the various chutes intially deployed by the drogue gun anymore, which was fired by a cartridge rather than a rocket?

[jimgriff]

Actually I cut and pasted from My website!!:8

Ejection seats (http://www.ejectorseats.co.uk/NACES.html)

The Mk 12 seat is a tad more adanced than the Mk 10 and I'm led to believe that the system of parachute deployment is similar to the US Navy NACES seat.

In all of the videos (there are 3 versions or views doing the rounds) the PSP does not have a chance to auto deploy and I doubt the pilot had the time to manually release the PSP. He is under the canopy for less than 4 seconds.

BUT
I stand to be corrected!!!

[Compass Call]

jimgriff

Thanks for a coprehensive and easy to understand explanation.

Dirty Sanchez

The object seen falling close to the pilot came from above him. I definately was not his PSP.


CC

[strake]

From the above explanation, Mode 5 would appear to give the unfortunate subject considerable time to reflect on "Life, The Universe etc" before the comforting floating sensation kicks in.....

Any experiences...??

[jimgriff]

I know I've asked before, but I would love to hear from anyone who has used an ejection seat. I'm updating the website and need some new content.

Stories, pics, links all welcome.

Thanks in advance

[Smurfjet]

An account of an ejection at 47,000' from an F8U can be found in 'The Man Who Rode the Thunder' by William H. Rankin.'

[littleme]

Just out of interest....ejection seats....if the crew member is too light, what are the likely outcomes? How would it affect that crew member?

Cheers

LM

[BootFlap]

The pilot involved in the Lowestoft display Crash only suffered minor injuries sustained from........ landing on the wreckage!

As to the UAS girly several years ago. She was indeed too light for the ejection seat and was unlucky enough to land back in the wreckage. The pilot, who landed close by, re-entered the burning wreckage to drag her out, both of them thereby sustaining burns.

Outcome of being too light for the ejection seat may mean that you do not clear the aircraft to the degree tested. Conversely, you can also be too heavy (pushing the aircraft away rather than being fired clear ;) don't take this last bit too seriously)

[Speed Twelve]

It's not an ejection seat in the video, it's an ejectable battery being fired from the model aircraft. :}

ST

Bootflap,

I would have thought that being too light for the seat would result in your clearing the aircraft by a larger margin not a smaller one???

I thought that one of the reasons for having seat weight limits was to do with CoG of the seat and the resultant thrust vector from the rocket.

ST

[BootFlap]

Speed Twelve

It has to do with momentum I believe. If you are lighter, you won't have as much momentum when the rocket stops firing (and it doesn't last long, trust me!).

Not having done Physics since A-Levels many moons ago (when they still meant something, b'ah!) I can not remember the equation, but I am sure some kind soul will post it, thereby demonstrating my failing and often frail memory.:ok:

bootflap

[Speed Twelve]

Bootflap,

I see where you're going with the momentum thing, but...

acceleration = force/mass

So for a given seat rocket impulse, the lighter bod on the seat = less mass = more acceleration. :8

The light occupant/seat combination will be going faster after the rocket impulse than a heavier one.

Momentum-wise, though, a heavier occupant/seat going at the same speed as a lighter one will have more momentum.

IIRC on the EA6 Prowler the seats were command-eject sequenced so that if one guy was lighter than the one next to them they wouldn't accelerate past their mate and torch them with rocket exhaust.

ST

[SirToppamHat]

An interesting one this, as I am sure it was an issue when it was first suggested females were to be trained as FJ crews.

I have asked the experts if they can provide an answer, and will report back if MB respond. I suspect there are 2 issues here:

1. Might the reduction in weight might actually increase the likeliehood of injury from the actual ejection? Light weight = greater acceleration forces = greater possibility of injury due to compression:

Force = 900N X Acceleration (15 stone person)

Force = 600N X Acceleration (10 stone person)

If force is constant, the rate of acceleration for the lighter person will be half as much again for the lighter person. Now, I believe the weight of the occupant is 'dialled-in' on modern ejection seats, presumably to compensate for this, but there must be limits as to how much the seat can compensate?

2. For specific areas of the flight envelope, the seat behaves in different ways, as explained by jimgriff on his website. However, for a particular situation, the seats must be expected to perform in a given manner. I suspect that the manufacturers 'guarantee' that the seat will perform correctly within certain limits, and outside those limits there are no guarantees. Perhaps they haven't been tested outside a given range of weights? Given 'Duty of Care', I doubt the RAF/RN will risk it.

Waits to be shot down by those who know far more about such things!

[Tarnished]

I'm pretty sure the subject of the original question in this case is the drogue billet which is fired to pull out the main chute from its container. The container actually forms the head box of the seat. The drogue fires in the slow speed/ low altitude modes to speed up the time to obtaining a full chute.

The pilot lands back on the jet as a victim of circumstance in this case. There is an on-shore breeze blowing, he was pretty much in the hover with no speed over the ground and he ejected after a slight nose down pitch and a bit of right roll. All the vectors and forces conspired to bring pilot and aircraft back together again. If he has any more forward speed on the jet at the tiemof ejection he would most likely have been OK.

T

[BEagle]

Regarding the weight of the seat occupant, I was under the impression that the 'dialled in' value ensured that the centre of gravity of the seat + occupant was correctly established in order to make sure that the post ejection trajectory was also correct by aligning the rocket ports correctly?

Wasn't there also quite a happy ending to the story of the young lady UAS student who suffered burn injuries after her ejection from that Harrier?

[5 Forward 6 Back]

Yup, the weight dial affects rocket angle after you've left the jet.

[Captain Kirk]

So you mean...cranking up the seat weight won't get me out faster/further??? Damn, all these years....

[VP959]

IIRC there were two primary issues when lightweight female FJ bods came along. Firstly the "dial your weight" range didn't go low enough (my failing memory tells me that the lowest number was around 60kg on the Hawk) and secondly that the ergonomics were wrong, in that the leg length, body length, arm length ratios were sufficiently different as to cause some problems with posture.

As for the purpose of the "dial you weight", it's as stated, just to alter the rocket angle to ensure the optimal trajectory on the way out.

VP

[jimgriff]

The CofG changes with weight,
The dial in your weight alters the angle of thrust for the given weight and therefore ensures that the thrust is constant and optimal against the "all up" weight of the seat and pilot compined.
If you exceed the min or max design spec for the seat you risk the thrust not going through the CofG and the seat could tumble like a catherine wheel firework and the drogues and main chute will tangle.

:8

[caspertheghost]

On the seat in question there is no facility to dial in your weight, the seat is clever enough to tell just how fat you are!

[Trumpet_trousers]

IIRC there were two primary issues when lightweight female FJ bods came along. Firstly the "dial your weight" range didn't go low enough (my failing memory tells me that the lowest number was around 60kg on the Hawk)

...a simple solution....give all lightweight female bods free/gratis/for nothing "fun-bags" implants, courtesy of Aunty B, and everyone is happy! :E

[BOAC]

.and so, T_T, I think the boys will be too!:D

[jimgriff]

Addition to previous answer:

I have checked the hi res vid I have of the ejection in question and one can see that the main chute is pulled out verticaly from the seat by a rocket. There is no drogue gun as on seats up to and incl the Mk 10 fitted to this seat.

The seat stability drogue is not deployed on a low and slow ejection (mode 1) and therefore this is not seen on the vid and cannot be the item that is seen to fall into sea near the seat.

In the vid the item that falls into sea is followed by some white webbing / deployment bag that is attatched to it and is therefore the parachute rocket and bits as described.

Any stories anyone???? Pretty please!!:O