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"G" Suits

Old 17th Jan 2019, 08:34
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"G" Suits

Non military so please be gentle with me.
After watching the Channel 5 programme on the Red Arrows, it got me thinking about the g suits.
I presume they are inflated by air, if so, where does the air come from?,

1 Is it a dedicated air supply with it's own compressor, to a pressure vessel thus maintaining a constant available pressure
2. How is the g actually sensed when in high g turns, and I presume the pressure proportional to the amount of g being applied.
3 What pressure would the system be at in say a 6g turn
4. When the g comes off is the relief proportional to the lessening of g, and where does the air vent to.


Thanks

UpaCreak
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Old 17th Jan 2019, 08:49
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Without getting too technical....think of pressurised air coming from a compressor attached to the engine. The system works with increasing "G" acting vertically with the body of the pilot. There is a weight on a spring - the weight controlling the access of air into the G suit. Pull more G, and the weight depresses allowing air into the suit. Pull more G, and more air is sent into the suit etc.

I once had a G suit with a regulator with a sticky spring. No air until G really started to bite then "Wham" and it all came on at once which was most unpleasant. There were incidences of the suit over pressurising in flight, but that's why you carry a knife.

As an aside about "G".... We once had a visit to Lossiemouth by a Belgian Mirage Sqn - they brought a twin sticker, and one of the Shackleton rear crew was given a trip. Needless to say, he came back full of it and was later found in the crew room bragging that he had got into some unscheduled air/air with some F4s "...and at one stage we were pulling 8 G!!".

"Yes, but that was metric G and not imperial G".

Recognising the spoof, another chap chipped in "Yes - if you look in the Jag cockpit, you'll find the G meter is dual calibrated, being Anglo French. Metric G is about 2/3rds of Imperial G isn't it?"

"That's right, so "Bloggs" here was only pulling around 5 G."

Exit deflated rear crew chap until he comes storming back in a couple of minutes later - full glass in hand ready to disperse it in our direction.
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Old 17th Jan 2019, 08:59
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1 Is it a dedicated air supply with it's own compressor, to a pressure vessel thus maintaining a constant available pressure

No, it is a bleed from the compressor, variable according to G
2. How is the g actually sensed when in high g turns, and I presume the pressure proportional to the amount of g being applied.
As above, a valve actuated by a weight on a spring. In the Macchi, it was under the left elbow, and to amuse oneself, one could activate the valve and blow the suit up.

3 What pressure would the system be at in say a 6g turn

F*** knows, but the suit gets pretty tight. Makes you grunt and tighten the stomach muscles to fight it, stay conscious and avoid going a little grey. if you don't fight it, the pressure is a bit uncomfortable.

4. When the g comes off is the relief proportional to the lessening of g, and where does the air vent to.
Vents into the cockpit, it releases the pressure proportional to the g.
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Old 17th Jan 2019, 09:47
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Most fast jets use bleed air, but the Hunter used storage bottles. 2 bottles in the F6 and T7, but an extra one in the FGA9, IIRC? There was enough stored pressure for most trips, but it could run out when you were least expecting it - rather disconcerting if you were pulling out of a strafe pass at the time!

I gather the mighty Jaguar used oxygen from the LOX system for anti-g purposes - presumably because there was such little oomph from the engines that bleed air would have been less than desirable?
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Old 17th Jan 2019, 09:50
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One reason Bader was a good combat pilot, without legs he was more G tolerant than his counterparts who would have blood pool in their legs in high G manouevers and start to grey out earlier..

Yup, the Jag did from the LOX pots.
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Old 17th Jan 2019, 10:09
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I have not tested an anti G valve for some years now but doubt it would normally see more than about 10psi

There are a variety of sources on the internet...

But from personal experience - yes starts to inflate at approx 2/2.5 G,I used to turn mine off (as pax) on transits and then turn back on when I was expecting High G turns etc.
The 'bob' weight which operates the anti g valve needs to be very free to move during pre start checks as a 'sticky' weight is ultra uncomfortable as alluded to by Wensleydale.

In a manoeuvre, the valve should start functioning at about 2 G . The pressure should be such that at 1G it is zero and from then on the pressure varies at the rate of 1 p.s.i. per ‘G’. Thus at 2 G , pressure is p.s.i., at 4 G it is 2 p.s.i. etc.
.
G: range 1 to 10
G suit pressure: 0 to 11 psig (PSI Gauge).
Source pressure: 0 to 300 psig (from engine compressor)
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Old 17th Jan 2019, 10:22
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Most Anti G Valves will operate and look very similar to this one...
The pressure inlet is the air tapped from the engine compressor,through a pressure reducing valve and into the anti g valve where it will be regulated between zeroish and 10 psi - controlled by the weight operating against its return spring.The press to test button usually operates directly onto the weight so you push down on it to inflate suit and when you release it the suit should deflate.
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Old 17th Jan 2019, 11:55
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Thanks for the answers guys. It's as I thought, but great to have confirmation.

UpaCreak
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Old 17th Jan 2019, 11:59
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BEagle. Thanks for the explanation on why the Mighty Jaguar anti g system was an oxygen fuelled system. I didn't know that! I often wondered during my time on the worlds oldest and premier fixed wing Sqn fighting the Cold War. I was, however, aware that with the earlier models, reheat was used whilst taxiing to get up the hill to gold sector, and that in summer the traffic lights on the Venlo-Nijmegen road at Well had to be set to red when our jets were taking off to the West.

Happy days!

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Old 17th Jan 2019, 13:18
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reheat was used whilst taxiing to get up the hill to gold sector
Rumour had it that the Jaguar had trials using the Sea Harrier ski-jump ramp for take off. However, the Jag had to start at the top and run down the ramp to gain sufficient speed to get airborne before the curve of the earth ran out.
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Old 17th Jan 2019, 14:34
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Originally Posted by oldmansquipper View Post
BEagle. Thanks for the explanation on why the Mighty Jaguar anti g system was an oxygen fuelled system. I didn't know that! I often wondered during my time on the worlds oldest and premier fixed wing Sqn fighting the Cold War. I was, however, aware that with the earlier models, reheat was used whilst taxiing to get up the hill to gold sector, and that in summer the traffic lights on the Venlo-Nijmegen road at Well had to be set to red when our jets were taking off to the West.

Happy days!

��♊️(AC)


There wasn't a lot of space in the Jag for much else, even the Tbird had to give up a gun to fit all the avionics in its place when they were left without a home when the second seat was stuck in it. When you stand aside one it isn't that big, and the U/C takes up more than its fair share of room.
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Old 17th Jan 2019, 14:58
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Wensleydale. Another little known fact, thank you.

I recall a design feature of the Jag was its flat fuselage undersurface. Enabled it to fly lower.

Nutloose. Trials on the Squadron during my time established that the undercarriage was, in fact, not really necessary (although afterflight servicing could be lengthy) and that the recce pod worked just as well as a full set of Dunlops.

Great aircraft, great times!

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Old 17th Jan 2019, 15:38
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Trouble is landing on the centre pylon they twisted one fuselage, even then we were looking at savings, too many pilots were banging off stores as the whiff of a problem and we were running out of ECM pods, so they removed the carts so they couldn't..... however the rest remained so you would end up with an out of balance jet when the rest of the stores went. but hey ho thread drift
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Old 17th Jan 2019, 22:22
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Salute!
Some good stuff here, and I can prolly claim more time at 9 gees than most. So I have seen the suits and feel to comment.
The standard suit must have been around for about 30 - 40 years. Figure 60's to 200x or so. I wore my first one early 1972 and last one 1984.
The ones I wore did not change until the early 200x years when we had the Raptor and later model Vipers and Hornets. I was there for the first documented gee-loc events, and was in back seat for one. The Eagle and Viper provided us with extended high gee engagements -figure 4 or 5 minutes at almost constant 4,5 6 gees. The 9 gee bat turn we had in the Viper was good for a defensive move, but most engagements saw 6,7 gees for a good turn and then the lower gees for another two or three minutes. All those were sloppy engagements, as you shoukld not be turning and burning for 3 minutes unless you started completely on the defensive.

We discovered that "clinching" the chest right away and also the neck was the best defense agaist gee-loc. The lower body bladders helped during prolonged engagements, and we woukld use the "test" button to pre-inflate those suckers just prior to the merge or earlier if we were on the offense versus an ususpecting bandit.
The new gear has bladders up on the chest to help more blood staying in the brain and you don't have to "clinch" as hard. They are also faster to inflate.
Gums remembers....
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Old 17th Jan 2019, 22:48
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On 19 April 2007, a JAS 39C Gripen crashed at the Vidsel airfield in northern Sweden. The pilot, Capt. Stefan Kaarle, was involuntarily ejected out of the aircraft in mid-air while approaching the airstrip in order to land. He landed safely by parachute. All C/D Gripens were temporarily grounded.

The post investigation found that just before the surprise ejection, the pilot had taken the aircraft into a tight turn (run and break ?) thus causing the G-suit to activate. The G-suit had somehow got snagged on the ejection seat handle, (I read he went for a pee at some point, probably loosening his G-suit). As the G-suit inflated and deflated during the flight, it had ultimately exerted enough force on the handle to cause him to inadvertently bang out in the circuit .

Last edited by gr4techie; 18th Jan 2019 at 10:28.
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Old 18th Jan 2019, 11:00
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Originally Posted by UpaCreak View Post
Non military so please be gentle with me.
If you have ever had your blood pressure taken then you have felt the pressure applied by a typical g-suit. Just imagine that force being applied over most of your legs and your lower torso and that is about what you feel when the bladders inflate to their lowest pressure in order to restrict blood flow (human blood pressure at 1G peaks at just over 2 psi and drops to about 1.5 psi between beats).

As G increases, the apparent weight of the blood increases so the psi in the suit has to increase proportionally to counteract the increased head of pressure. This can be up to 5 times greater than the blood pressure cuff at your doctors. If your doc kept on pumping the cuff on your arm you would not thank him for it.

😊
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Old 18th Jan 2019, 16:27
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I believe that the French took a look at the Russian G suits from the the Mig29s that collided at Paris. I was told that they were different from Western g suits, but I wasn't told how.
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Old 18th Jan 2019, 16:42
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The Russians used (maybe still use) the Libelle g-suit, which covers from neck to ankle and is formed of fluid filled bladders. Not sure of the mechanics of operation, but believe it to have been quite effective, more so than a traditional air inflated suit.
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Old 18th Jan 2019, 20:48
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I remember only to well, that having finished my Varsity course in 1971, and holding at Oakington, I was 'volunteered' to go to Farnborough to test G suits.

We (there were 2 of us) were 'chosen' since we were big aeroplane men and therefore not conditioned to strain like hell when pulling G.

The first day we were kitted up in a G suit and placed in the centrifuge, (the well known vomit comet) and given a button to press and a light to look at. The machine was set in motion and when the light faded (usually around 3.5g with the suit inflating) we had to press the button. Sometimes the suit inflated and sometimes it did not. However, strict instructions were given not to tense up and just to let the suit do the business!

Twice a day for a week and then sent back to base. No one told us the results, but surely G suits were in service before 1971, and if so why were we there being sick twice a day.

Twice a day for a week. Still it was an experience.
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Old 19th Jan 2019, 12:07
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Originally Posted by 57mm View Post
The Russians used (maybe still use) the Libelle g-suit, which covers from neck to ankle and is formed of fluid filled bladders. Not sure of the mechanics of operation, but believe it to have been quite effective, more so than a traditional air inflated suit.
Just reading an autobiography of an FAA pilot from WW2, they trialled water filled g-suits, essentially as you pulled g the water was forced into the lower parts of the suit pressing against the legs. They didn't seem to have been in service long though, his suspicion being due to a fatality after a ditching with one on. The less dense fresh water in the suit caused the survivors legs to float to the surface eventually drowning him. There was also the disadvantage in hot climates that you soon found yourself wearing a few kilos of warm water.
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