Ejection Seats and Operating Envelopes

[Fonsini]

I was reading the thread regarding the tragic Greek F-16 crash and the subsequent accident report and let me say that I'm just trying to learn something here, there is absolutely no intention on my part to second guess the chain of events.

Firstly I had no idea that trim could have such a huge impact on aircraft handling at takeoff, that was a big learning point for me - I always assumed that standard control inputs always trump trim settings, even without the use of any rudder (in this case). Now I know better.

But the crash report also specified that the ejection seats were "outside their operating envelope" at the time of the accident and that's the part I'm trying to understand. With maybe 150 knots IAS and 50 feet AGL with no option for sink rate being an issue I would have thought the seats would be right in their envelope - could this have referred to the aircraft having rolled past 90 degrees or is there another seat operating parameter that I'm totally missing.

Just trying to understand what happened and not disrespect the fallen, if I'm out of line asking this just let me know.

[Bob Viking]

Fonsini

It certainly looks like an honest question to me. I haven't read the full report yet but aside from RoD there are other parameters that must be considered. Rate of roll is probably relevant in this case.

Assuming they ejected at less than 90 AOB (it would obviously be a problem to eject from such a low altitude with more than that) then you must consider the flight parameters. When the seat leaves the aircraft it is imparted with a vector from the aircraft it has just left. For instance (not in this case) but a large RoD needs to be mitigated against by ejecting far earlier than in S&L flight. If the jet was rolling rapidly towards the ground this vector would be applied to the seat with tragic consequences. The differing angle of ejection for front seat and rear seat can also play a part (like in the Navy T8 accident involving Jack London) although in this case since they both died that would appear to not be the case.

Hope that makes sense.

BV

[KenV]

Aircraft pitch and roll angle play a huge role in the trajectory of the seat upon ejection. That combined with sink rate and low altitude (50 ft AGL is very low) can put the seat outside safe ejection envelope. That does not mean the seat failed to function in any way, but that the velocity vector present at the time of ejection meant that the seat did not have the ability (energy potential) to prevent impact with the ground shortly after rocket motor burn out. Basically, an ejection seat has a fixed amount of energy in the rocket motor. If the energy required to change an unsafe velocity vector into a safe velocity vector exceeds the energy available, the ejection is outside the envelope of the seat.

Other factors (not present here) include airspeed and altitude. If flying at high speed upon ejection the seat may function just fine, but the pilot might not survive the resulting airblast. Flailing injuries can result, and those injuries may be fatal. At very high altitude the seat may also function just fine, but the pilot may not survive the outside environment (very cold and very thin air.) So an airplane may be able to supercruise at 60K, but what happens if the pilot has to eject during such a supercruise?

[Fox3WheresMyBanana]

From the report, the ejection was initiated only 3.7 seconds after lift-off, by which time the aircraft had already past 60 degrees of bank and had started descending. The canopy jettison activated 0.3 seconds later at 69 degrees of bank. The height is not specifically mentioned, but it wouldn't have been much given the impact was only 4 seconds after ejection initiation.
Allowing for human reaction time, the only option for survival would have been recognition that rudder input was required to correct the situation, or unloading the aircraft with max left roll. The board makes clear why neither of these options would have seemed obvious at the time.

[NutLoose]

Firstly I had no idea that trim could have such a huge impact on aircraft handling at takeoff, that was a big learning point for me - I always assumed that standard control inputs always trump trim settings, even without the use of any rudder (in this case). Now I know better.

Even on the light stuff it catches you out, there was a fatal crash in the UK on a new build Cessna 182s

See

https://assets.digital.cabinet-offic...pdf_501522.pdf

[Fox3WheresMyBanana]

Putting the trim out of whack was a favourite among my QFIs when giving Unusual Positions to recover from during Instrument Flying training. You rapidly realised you were f#cked if you didn't sort the trim out pretty sharpish.

[glad rag]

ejection vectors...video usual disclaimers..

[Fonsini]

Excellent replies as ever - thanks guys. Rolling vectors and their effect on the seat parameters is the part I was missing.

Once again, respect to those killed and injured in this tragic incident.

[Fox3WheresMyBanana]

As ballpark figures:
Inverted at 400 feet, no descent rate,and the seat will save you.
Ejections at up to 60 degrees of bank aren't too much of a problem (assuming this doesn't stick you straight into the valley wall, which has happened) - you still have half the seat rocket thrust upwards, but it gets rapidly worse with just a bit more bank.
Altitude = at least 1/10 rate of descent (units per minute) and the seat will save you. So, supersonic straight down (e.g. post hole manoeuvre) and you must be out by 6,000 feet at the latest, preferably 10,000 feet. And that's AGL of course - gets scary in the mountains.
Rate of descent builds up rapidly and has an increasing effect on survivability at very low altitudes. The advice on the Harrier was Red Caption in the Hover - Eject. By the time one had worked out that there was an engine problem, it could have been too late to eject.

[Woff1965]

I found all of the above interesting as I had not really thought about ejection seats in such detail previously. When a seat is described as zero-zero I hadn't considered what that really meant.

So, given all of that there must logically be issues with the crew members weight. Would I be right in thinking that if a pilot is over a certain weight the ejection would not be "clean", also if the pilot was small and light then would that not be a problem too?

Normally, I would not ask but as some of you are in a mood to educate I thought I might take advantage

[Bob Viking]

Woff.

The short answer is yes. To both. The upper limit is for the obvious reason. The lower limit is to avoid injury to slightly built people.

Some people have had waivers granted. Heavy guys have been known to have a zero/70 limit instead of zero/zero. Meaning they need 70 knots before they can safely eject. A standing start might not give their parachute time to inflate correctly.

BV

[Swil]

All correct above about weight but another issue is that it affects the seat trajectory to the extent that the clearance over the empennage could become a factor for Mr Chubby. However, most two seaters have seats that diverge slightly thus reducing problem with fin. Also, for Mr Featherweight the problem could also be chute design factors such as stability or chute opening shock.

Remember that seats/chutes are designed for an envelope and generally speaking this means that they were tested and confirmed suitable for that envelope. This includes who is going to use it in terms of weight and anthropometric info and believe it or not, the height/weight data used back in the 90s was based on data gathered back in the 50s of the averages across a sample group of bods. Don't know if this has been updated yet to reflect the modern man/miss.

All that said, when I pulled the black and yellow they said I didn't go up, the aircraft got pushed down, something to do every action blah, blah.

[Woff1965]

Thanks for the prompt reply.

[KenV]

So, given all of that there must logically be issues with the crew members weight. Would I be right in thinking that if a pilot is over a certain weight the ejection would not be "clean", also if the pilot was small and light then would that not be a problem too?

The relationships are complex, but yes, pilot weight makes a difference. I'm short statured and was flying an A-4 on a sandblower mission. At 100ft AGL and 400KIAS the power turbine failed catastrophically and I had to eject. The combination of airspeed and my weight and weight distribution made the ESCAPAC seat unstable. Things did not go well. After recovering, USN prohibited me from flying ejection seat aircraft and I flew P-3s for awhile. Later, USN bought a cool new jet called the Hornet which had a new fangled Martin Baker ejection seat. This was the first aircraft USN bought that was designed for pilots ranging from the 95th percentile male to the 40th percentile female (anthropometrically I'm pretty close to a 50th percentile female in most measures). The seat could adjust to compensate for pilot weight and was stable over a wider speed and CG range. So they reassigned me to fly Hornets. I never needed to find out if the Martin Baker seat worked as advertized. But the bottom line is that modern ejection seats have much more capability, including having the ability to steer and alter their trajectories dynamically. They don't just fly in a straight line. I understand that some of the newest Russian seats are especially impressive in that regard.

[JointShiteFighter]

Sorry to ask such a question on this thread (if you don't ask, you don't learn), but KenV and Swil, how did the ejection its self feel? Was it painful? Or didn't you feel much due to being pumped full of adrenaline?

[KenV]

Sorry to ask such a question on this thread (if you don't ask, you don't learn), but KenV and Swil, how did the ejection its self feel? Was it painful? Or didn't you feel much due to being pumped full of adrenaline?

Very hard to describe. Time dilation was huge for me. When I pulled the face curtain (upper handles on the ESCAPAC seat) it seemed like it took forever for the canopy to jettison and the seat to fire. The ride up the tube (the ESCAPAC rides on a sort of extending tube the first few feet) seemed slow. After that everything is a blur because my body hit the airstream and started flailing and the seat went unstable and began a tumble. But seat/man separation was successful as was drogue and then chute deployment. The sensation was nothing like the ejection seat simulators we were required to ride annually. But I did have the presence of mind to remember post ejection procedures after the chute opened, although I did not have time to complete them. Those procedures vary depending on whether you eject over land or over water.

Visor: down overland, up overwater
Oxygen mask: loose/off overland, cinched tight overwater
Gloves: on overland, off overwater.
Seat pan: release both overland or overwater.

I think there was another procedure when ejecting underwater, but for the life of me I can't remember it.

Here's a link to an old training film about making the ejection decision and why you don't want to wait too long.
https://www.youtube.com/watch?v=Aa1Ba_NEobs

[JointShiteFighter]

Thanks, Ken.

[Swil]

Pulled the seat handle just as Hawk was departing flight at very low level. Acceleration from aircraft obviously very rapid and I seem to recal both initial cartridge firing followed by rocket pack. Chute opened just about immediately, saw feet pointing at horizon, swung once in chute over aircraft wreckage on the ground and hit ground like sack of spuds 50ft away, no time to think about anything during ejection sequence and automatics worked as advertised. Ran over to student, both of us ok so cracked open the survival packs and waited for Helo pick up. Great seat, cheers once again MB.

Only injuries were slightly twisted knee due to landing and minor facial cuts due to canopy Miniature Detonatig Cord "splatter" on parts of face not covered by visor or o2 mask.

[JointShiteFighter]

Thanks, Swil.

Where and when was this? I presume not RAF Valley otherwise you could have walked back to base instead of waiting for Helo pick-up.

[Swil]

At Mona just down the road, SOP to scramble the SAR Wessex with doc on board if crash site was within range, then back to Valley for check up.