back to article Latest F-35 bang seat* mods will stop them breaking pilots' necks, beams US

The American F-35 Joint Project Office says ejection seat and helmet modifications will stop emergency ejections from breaking petite pilots' necks. Pilots who weigh less than 62kg (9¾ stone, 136lb) are currently banned from flying the state-of-the-art F-35 fighter jet because an emergency ejection using the currently fitted …

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minimum weight

Can't they put adjustable weights in the chair, like a handicapped horse? Or is it that a man who weighs less than 9 stone is going to be flimsy and prone to falling apart?

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Re: minimum weight

Surely it can't be a simple weight switch; what if the pilot is pulling +g?

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Re: minimum weight

Well that's an interesting point.

G applies to the entire mass of the seat. Under +G the seat and pilot are "heavier" for the charge to get moving.

If one ejected under negative g, then the pilot and seat would be "lighter", meaning even the sturdiest pilot would come in "underweight".

One presumes the seat already has a g-meter to deal with such potential variation in ejection conditions, and the weight switch would inform it whether the pilot is lighter than the cut-off at a given g-rating.

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Re: minimum weight

Far simpler - perhaps the seat electronics take the weight of the pilot before takeoff and store that information until the plane has landed again?

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Re: minimum weight

If all the switch does is delay the parachute opening a little to allow the seat to slow down a little, why not just make the delay standard and do away with the switch?

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WTF?

Re: minimum weight

If you want a parachute to open, then the implication is that you are falling.

But delaying the parachute opening allows the seat to slow down a little??? What laws of physics are in operation here?

Also, bodies of different masses fall with the same acceleration. Some old Italian dude is credited with that one. So what difference does the pilot's weight make?

I suspect that something has been lost in the reporting...

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Re: minimum weight

"But delaying the parachute opening allows the seat to slow down a little??? "

Yes; as ejected, the seat is moving forward through the air at the same speed as the aircraft but is nowhere near as aerodynamically shaped. Hence, it slows down as time goes by. Opening a parachute on a forward moving seat will give a large force that causes the pilot's head to move forwards.

However, I still don't understand what the pilot's weight has to do with it. Unless a lower weight pilot results in a faster ejection (upwards) speed due to a lighter mass load on the ejection mechanism ...... I still don't get it.

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Anonymous Coward

Re: minimum weight

"There are no UK F-35 pilots affected by this issue"

Does this imply that they are all lard-arses?

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Re: minimum weight

"So what difference does the pilot's weight make?"

My guess is its more to do with the pilots build. A heavier pilot is more likely to have stronger neck muscles that can withstand the forces. Sure a fatty won't, but then they won't have got through the selection process to pilot a fast jet in the first place.

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Re: minimum weight

You're missing the atmosphere, mate.

Fighter jets travel fatser than the terminal velocity of a dude strapped into a chair, so when he's ejected he'll spend the first seconds slowing down.

Also, bodies of different masses fall with the same acceleration _in a vacuum_, but usually fall with different accelerations in an atmosphere, due to drag.

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Re: minimum weight

Pilot build does seem a likely problem, don't forget there's a lot of female fighter pilots out there.

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Unhappy

Re: minimum weight

Good idea.

BTW each helmet is apparently tuned to the pilots eyesight and eye motion tracking.

According to The Economist it takes 2 days for a helmet to be calibrated to a pilot.

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Coat

Re: minimum weight

fall with different accelerations in an atmosphere, due to drag.

Not very surprising, but I don't expect pilots to wear large billowing dresses very often.

The one with the 'Priscilla, Queen of the desert' DVD in the pocket, ta.

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Anonymous Coward

Re: minimum weight

Fighter jets travel fatser [sic] than the terminal velocity of a dude strapped into a chair, so when he's ejected he'll spend the first seconds slowing down.

Ah, but not if he's flying upside-down when he ejects.

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Re: minimum weight

"Can't they put adjustable weights in the chair, like a handicapped horse?"

I can see PETA's response now...

"While we applaud the military for not discriminating against handicapped horses, we strongly oppose putting a horse in a fighter jet."

:)

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Re: minimum weight

@Montreal

Damn you. I need a new keyboard.

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Re: minimum weight

This has to do with body mass and build and the spine and neck being able to support the helmet when the seat fires. I guess you've never read or heard about the violence that happens once someone pulled the eject lever?

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Re: minimum weight

Do you really want to delay the opening of the parachute if ejecting from ground level ? Take off and landing being the most dangerous phases of flight etc.

Maybe F1 style helmet brace would work.

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Re: minimum weight

I believe the issue is due to faster deceleration on the main parachute (same drag less mass pulling it down for lighter folks) while the pilot's head (and heavy helmet) suspended on the (weaker) neck continues down at original velocity (due to its own inertia). So for a moment there's potential for speed difference between the seat (and pilots body) and the head/helmet and resulting injuries. I'd guess that delayed opening of the main parachute let's the pilot-chute decelerate some of velocity though changes to helmet construction and neck brace (or whatever stabilizing device they implemented) would probably be of greater importance.

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Re: minimum weight

I've always wondered if there was an advantage to be "heavy" (which might be called "out of shape" in the military).

I'm around 100kg (15+ stone if I get the conversion right) at the moment, so I guess I'll do.

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Re: minimum weight

"I guess you've never read or heard about the violence that happens once someone pulled the eject lever?"

I have, enough to know I'd never want to do it unless there's no other choice.

A substantial proportion of pilots who eject spend the rest of their careers flying desks thanks to spinal damage.

The fact that this is related to the mass of the helmet indicates that this is related to the compression forces generated on cervical vertebrae when the eject rocket fires. Ejector seats clamp the pilot's head to the seat back during eject specifically to ensure that forces are vertical and to prevent whiplash injuries when the chutes open.

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Re: minimum weight

"Maybe F1 style helmet brace would work."

Unlike F1 drivers, pilots are expected to be able to look over their shoulders, etc.

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Re: minimum weight

Unlike F1 drivers, pilots are expected to be able to look over their shoulders, etc.

They could mount, err, wing mirrors. Just have to be careful of the blind spots...

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Re: FOV. F35 doesn't have one.

Could very nearly bolt the helmet to the seat and not affect the pilot's field of view significantly. He's supposed to use his HUD and something akin to Hololens.

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Re: minimum weight

It's probably something to do with design tradeoffs.

The problem is going to be that it's a zero, zero ejection seat. Meaning that should the F35 catchfire on the runway then the pilot can eject from zero altitude whilst stationary. This requires a fairly powerful explosive exit, followed by a very fast parachute deployment.

At a guess, the reason the timer is set to it's current setting is that if it's set to longer then if you do a zero zero eject then the seat could well hit the ground before deploying the chute, a not ideal situation.

If you then eject at speed, kicking out the parachute pretty much immediately is going to cause the ejection seat to go from the aircraft speed to a slow decent very quickly. So quickly that the helmet is going to cause the pilots head to get something like whiplash, which presumably has never been a problem previously because the helmets were just there to protect the pilots head, instead of having a ton of electronics attached.

They probably used a very, very simple fault impervious and time proven system like a burning fuse lit by the initial ejection charge because I suspect the Martin Baker engineers are probably more paranoid about system failure than most of EL Reg's readers. I guess somebody is having to design in a more untested and less fault tolerent workaround at the moment that checks how fast the seat is moving and how far it is from the ground etc.

The weight issue probably doesn't have much to do with weight in the seat per se, but how the pilot is built, ie people with strong neck muscles might get strained muscles, but slightly built pilots get broken necks. As telling people to measure people's neck with a tape measure is probably not an acceptable workaround, and given military fitness standards mean that body fat is not likely to be significant on pilots somebody probably figured that it wouldn't be an issue for >99% of people over $weight (+$FudgeFactor) as they probably have substantial enough neck muscles for this not to be an issue. Probably. Just guessing.

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Re: minimum weight

Worse. It means that there are no F35 aircraft in the UK.

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Re: minimum weight

> Does this imply that they are all lard-arses?

Or that no pilots are affected because they're not doing any flying due to a lack of planes.

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Re: minimum weight

Looks to me as it is the hard deceleration when the parachute opens that is the issue. Not the ejection per-se.

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Vic

Re: minimum weight

But delaying the parachute opening allows the seat to slow down a little??? What laws of physics are in operation here?

The seat has a two-stage parachute system: as the seat leaves the airframe, a rocket is fired from the top which putts a drogue chute out.The main chute is delayed by a fixed time delay and an air pressure switch (the barostat), preventing the chute from deploying if the seat is too high or travelling too fast.

Prior to the main chute being deployed, the drogue slows the descent of the seat. Once the barostat has fired, it then pulls the main chute out.

Also, bodies of different masses fall with the same acceleration. Some old Italian dude is credited with that one. So what difference does the pilot's weight make?

By the time the main chute deploys, the seat frame has been thrown away, and only the pilot's weight remains in the harness. The force exerted by the parachute is going to be pretty much constant for a given descent speed, and the resulting acceleration is given by Newton's second law. The heavier the pilot, the lower the deceleration.

Vic.

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Vic

Re: minimum weight

I have, enough to know I'd never want to do it unless there's no other choice.

I was reading an article a while back about that way of thinking; apparently, there is a real problem with civilians flying ex-military aircraft in that they really don't want to eject.

A substantial proportion of pilots who eject spend the rest of their careers flying desks thanks to spinal damage.

I think that might have been true for very early seats, but that was a long time ago. There's been lots of development on ejection seats.

The fact that this is related to the mass of the helmet indicates that this is related to the compression forces generated on cervical vertebrae when the eject rocket fires.

It;s the pilot's mass that is important. To my mind, that implies it's the deceleration on deployment that causes the problem.

Ejector seats clamp the pilot's head to the seat back during eject specifically to ensure that forces are vertical and to prevent whiplash injuries when the chutes open.

Errr - you sure about that? Because none of the seats I've played with do that...

Vic.

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Vic

Re: minimum weight

They probably used a very, very simple fault impervious and time proven system like a burning fuse lit by the initial ejection charge

They don't. They use a barostat. This contains a clockwork timer and a diaphragm pressure switch. Deployment is delayed until the timer has expired - so that the seat is clear of the airframe - and until the pressure is high enough. If the pressure is too low, then the seat might be too high, or else it is travelling too fast. In either case, it sits under the drogue until it reaches the correct height & speed, and then a clamp is released which allows the drogue chute cable to pull the main parachute out.

It's quite ingenious really.

Vic.

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Re: minimum weight

"I was reading an article a while back about that way of thinking; apparently, there is a real problem with civilians flying ex-military aircraft in that they really don't want to eject."

In many countries ex-military craft have the ejector seats removed so a civilian pilot can't eject even if (s)he wanted to (explosives being illegal in a non-military craft, etc). There's also the issue that being in the aircraft means that pilots tend to take more care about where it ends up when things go ultimately pear-shaped.

"I think that might have been true for very early seats, but that was a long time ago. There's been lots of development on ejection seats."

Indeed there have, but a 1 in 4 chance of permanent disability is still far too high for my liking. There are quite a few pilots who've ejected once and are still in cockpits but very few have ejected twice and been able to resume active duties.

WRT ejector seats and head clamps: Older ones don't. Newer ones do - along with the also-mentioned airbags to securely clamp the pilot in for the duration of the (short) ride. The issue at point in the F35 is excess helmet mass and I'm pretty sure that the pilot mass requirements are a kludge answer as neck strength and crush/whiplash resistance are wildly variable even for people at the same mass and fitness (Think wrestlers vs footballers)

Presumably the problem could be solved in the short term by moving as much of the mass of the helmet as possible somewhere else but dangling umbilical cables are going to be problematic and it means the ease of dropping a pilot into any available aircraft will be compromised (plus it's something else to go wrong in the field).

Longer term, lighter components will probably be available but by that point piloted craft will probably be obsolete.

In any case the F35 was never designed as an air-combat/air-superiority machine. That's a job for the F22. The F35 is too tubby, too underpowered and with too stubby wings to be an effective fighting machine(*)(**) and by the time it gets into the field its much-vaunted stealth(***) capabilities will be so hopelessly compromised by countermeasures that most of its armaments are likely to be on external hardpoints as there'll be no point hiding itself.

(*) Because the F22 will never be sold to other countries you can expect the Eurofighter and other aircraft to keep working alongside the F35 for a long time to come (assuming it isn't cancelled - and even the SDI got cancelled in the end on cost grounds despite massive multistate pork-barelling)

(**) These same features make it badly compromised as a ground-support aircraft. Short range and low carrying capacity mean it's less capable than what it replaces.

(***) F35 is ONLY stealthy on a 30 degree cone around the nose end of the longitudinal axis(+), ONLY stealthy at currently used SHF radar frequencies(++) and ONLY stealthy with the doors closed(+++)

(+) Networked detection systems can see it clearly from side or rear and transmit to AA batteries located along the flightline. Newer AA missiles can be guided from those side/rear radar systems rather than relying soley on the onboard smarts or controllers near the launch site. F22's role is to eliminate this threat but other countries won't have the F22

(++) Painting with VHF/UHF radar has been shown to work (UK air defence can see B2s even when they're fully stealthed up) and past US stealth tech has failed hoplessly when the wings are wet (which is how the F117 got shot down). Water is a pretty good reflector so all the matte paint in the world may not help much.

(+++) Neither of the above points matter much when you have a "stealth" aircraft so badly designed that the weapons bay (and other) doors need to be opened in flight every 10 minutes or less due to the avionics overheating and needing emergency cooling. At that point it'll cause even the dumbest radar systems to light up like a christmas tree.

The F35 is one of the most expensive clusterfucks the USA has ever engaged on and it's going to fuck their economy even worse than Ronnie RayGun's Star Wars program (which left the USA deeper in debt than it had ever been at any point in history). The best thing that any other country can do is hedge on purchases (many have already cancelled) and try to make as much money out of the program as possible in the meantime.

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Vic

Re: minimum weight

In many countries ex-military craft have the ejector seats removed so a civilian pilot can't eject even if (s)he wanted to (explosives being illegal in a non-military craft, etc).

Yes, but there are also countries where that isn't the case. The UK, for example, permits ex-military aircraft to carry original safety equipment.

There's also the issue that being in the aircraft means that pilots tend to take more care about where it ends up when things go ultimately pear-shaped.

If it's time to eject, that's actually a false premise - the pilot has already lost the ability to decide where the aircraft goes. The problem is that civilian pilots often try to fly through this situation - and invariably make the problem worse.

Indeed there have, but a 1 in 4 chance of permanent disability is still far too high for my liking. There are quite a few pilots who've ejected once and are still in cockpits but very few have ejected twice and been able to resume active duties

I suspect your data might be out of date. I fly with several pilots who have ejected many times - being close to ETPS means that several of my acquaintances are former test pilots. I know no-one who has been rendered disabled by ejection. I know several people who have ejected enough times that your 1-in-4 chance should likely have left them so, so I'm afraid I must disbelieve your statistic.

WRT ejector seats and head clamps: Older ones don't. Newer ones do

Do you have a citation for that? I've seen quite a few in-cockpit shots of Typhoon, and I've yet to see anything that could accomplish that.

In any case the F35 was never designed as an air-combat/air-superiority machine. That's a job for the F22.

Well the original description released for the F-35 was that is was a cost-down F-22. Given that the F-22 cost $150M each, this might still be true[1] - but is is a far inferior aircraft for that price tag.

The F35 is one of the most expensive clusterfucks the USA has ever engaged on and it's going to fuck their economy

It is - but look at what the UK has committed to buy as well. It's not just the US economy that buggered...

Vic.

[1] <a href="https://en.wikipedia.org/wiki/Lockheed_Martin_F-35_Lightning_II>Wikipedia</a> reckons the current F-35A costs $98M without engines. Whether this will make it cheaper overall than the F-22 is not a calculation I want to make right now...

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Re: minimum weight

Even if s/he's upside down his forward velocity will decreasing fairly violently if the aircraft was doing mach 2 when the handle was pulled

It's quite possible that drag will slow down the pilot vertically too - a bang seat will initially be accelerating at 20+G and won't take long to exceed the terminal velocity

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Handling the G's

I am surprised that anyone approaching the lower weight limit would be capable of handling the

G-force's that pilots sometime have to endure.

This is based on my personal assumption that the heaver and stronger that you are, the more G's you can handle.. Although I could be completely wrong on this point.

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Re: Handling the G's

IIRC, much to the annoyance of those in charge at the USAF, it was found a number of years ago that those best suited to handling G-forces were small, slightly overweight females. Not quite the all American jutting jaw hero type they try to portray.

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Re: Handling the G's

Actually smaller people and women particularly handle excess G better and less likely to black-out.

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Re: Handling the G's

"Actually smaller people and women particularly handle excess G better and less likely to black-out."

Which is more important, the fact that they are women or the fact that they are shorter ?

I can't find any serious article which states clearly that women are actually more capable, a reference anyone ?

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Re: Handling the G's

Same with the Astronauts, women were trained for Mercury Gemini but didn't fly probably for PC reasons :(

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Anonymous Coward

Re: Handling the G's

I can't find any serious article which states clearly that women are actually more capable, a reference anyone ?

You best ask a few women, but give me a moment to buy some popcorn first :)

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Re: Handling the G's

"Same with the Astronauts, women were trained for Mercury Gemini but didn't fly probably for PC reasons :("

Or maybe they just weren't good enough. I know, a shocking statement but it could just be true.

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Re: Handling the G's

It's largely a height issue but there's also a build issue. A short person who is well conditioned resists black-out better because in addition to the G-suit, which effectively squeezes the person, a short person has a shorter distance to pump blood to keep the brain in adequate oxygen supply. Being fat is bad and fit is better because in addition to the lower probability of restricted arteries a fat person isn't as capable of tightening their muscles to push as much blood toward their brain as a slender fit person and it comes down to only the suit squeezing the fat. In the end, your ideal fighter pilot would look a lot like a well toned jockey.

Of course, that isn't what the typical fighter pilot looks like and in order to accelerate the typical amount of beef of the larger pilots and clear the tail it has to be a rather good shove and you want the parachute to deploy quickly because you never know what orientation the plane will be in or how close it is to the ground, yes that would leave a mark. So you get a really healthy shove out followed by a quick jerk back which would likely break our jockey's neck. Delaying the rearward jerk while reducing whiplash will also increase the odds of splatting on the ground in the hopefully rare case of an inverted low altitude ejection. Perhaps a simple1 tether to the back of the helmet that goes taut when ejecting would ease the problem while keeping the quick chute deployment.

1. Simple in concept as I'm fairly sure it would require a bit more than installing a seat belt auto-tensioner since the "gravity" vector can change radically in a fighter aircraft.

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Re: Handling the G's

Perhaps a simple1 tether to the back of the helmet that goes taut when ejecting would ease the problem while keeping the quick chute deployment.

Has anybody done a cost benefit on not having ejector seats at all? Yes, you crash, you bought it, but there's a cost to the extra weight and complexity of ejectors, plus a small but notable number of accidents where poor buggers have been thrown out of serviceable aircraft by ejector related mishaps (and a fair few ejected crew are sufficiently injured that they never fly again).

Some will say that's a bit harsh, given that every hull loss would then mean a pilot loss. But demanding a lifeboat when you fly a ship specifically designed to rain death on people usually without suitable means of defence against your weaponry seems a tad rich, perhaps? Chopper pilots take more risk and have no escape options, why do the fast jet ponces seem to merit this pandering?

A quick scan of aircraft losses suggests that having no ejector seats on fast jets would have cost about ten additional lives in Afghanistan. Compared to the c3,000 allied troops killed (and 1,500 "contractors" about whom you can make your own mind up). Not to mention around 30,000 civilians.

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Re: Handling the G's

"Chopper pilots take more risk and have no escape options, why do the fast jet ponces seem to merit this pandering?"

Why shouldn't they when its possible to do so? Learning to fly a fast jet fighter is a long expensive process - the pilot is actually more valuable in real terms than the plane. Flying a chopper while tricky isn't in the same league and so I'm afraid the life of the pilot is basically worth less since chopper pilots are frankly ten a penny. That and the fact of building an ejector seat that could shoot someone through the rotor blades without turning them into mince is ... tricky.

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Re: Handling the G's / ejection seats for helicopters

There is a little comic by André Franquin about ejection seats for 'choppers'.

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Re: Handling the G's

"That and the fact of building an ejector seat that could shoot someone through the rotor blades without turning them into mince is ... tricky."

But remember the synchronised machine guns on WWI fighters that fired through the propeller.

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Re: Handling the G's

Good for the pilots but what about the crew/passengers? Think door-gunners and medics and wounded...or a load of infantry. The big issue is altitude. Most choppers, if they are about to fall out of the sky, are not at an altitude were parachutes are effective.

*I'm a former door gunner, Vietnam era.

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Re: Handling the G's

Explosives on the chopper blades worked in bond :p

Also autorotation landing if you are high enough and the pilot is alive, if you are that high I would prefer a parachute!

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Re: Handling the G's

> "Altitude" ..."I'm a former door gunner, Vietnam era."

More like 'Attitude': you must have been either extremely brave, or totally reckless. To the FNL* on the ground YOU, yes that body in the doorframe, were the TARGET.

* aka NLF

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