G limits without Anti G system active
Thread Starter
Joined: Jul 2003
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From: Canada
G limits without Anti G system active
Does anyone know of any guidance material for what are the max and min G limits that can be performed by a pilot with an aircrafts anti G system disabled.
The aircraft is limited to +7 and -3.5 G, but the anti G system will not be operational, however testing of the G indicator is required for verification.
I realise this is quite a subjective question but Im interested if there are any recommendations available for this.
The aircraft is limited to +7 and -3.5 G, but the anti G system will not be operational, however testing of the G indicator is required for verification.
I realise this is quite a subjective question but Im interested if there are any recommendations available for this.
Joined: Jan 2008
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From: Wichita, USA
G limits
Hi Nigd3,
The US Navy's Blue Angels carry out all their display manoeuvers without the benefit of G suit protection, however they are all relatively young and highly fit naval aviators and it's a strain even for them!
If you really need to go to +7 then you should be looking to think about the following as a minimum:
Age and fitness of the pilot - a standard medical doesn't cover nearly enough of the requirements for high G flight (for instance high blood pressure in this case is actually a good thing)
Previous experience with high G manoeuvers
And the big ones.... rate of G onset and duration - if the G comes on fast then GLOC is almost certain unless you're very good at G straining techniques, likewise the longer the duration the more likelihood of GLOC.
I'd seriously consider getting the anti-G system working and putting on your speed jeans. Even then you'll only get about another 1.5 to 2 G's worth of protection with the system active.
The US Navy's Blue Angels carry out all their display manoeuvers without the benefit of G suit protection, however they are all relatively young and highly fit naval aviators and it's a strain even for them!
If you really need to go to +7 then you should be looking to think about the following as a minimum:
Age and fitness of the pilot - a standard medical doesn't cover nearly enough of the requirements for high G flight (for instance high blood pressure in this case is actually a good thing)
Previous experience with high G manoeuvers
And the big ones.... rate of G onset and duration - if the G comes on fast then GLOC is almost certain unless you're very good at G straining techniques, likewise the longer the duration the more likelihood of GLOC.
I'd seriously consider getting the anti-G system working and putting on your speed jeans. Even then you'll only get about another 1.5 to 2 G's worth of protection with the system active.
Joined: Dec 2006
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From: The No Transgression Zone
On some top aerobatic competition planes I've seen limit loads of +/- 20G
and the aviators who fly them frequently pull 10/12g and -5/-8g [outside snaps
]
However, this is of very short duration and the practice is intense to maintain g tolerance...
Military aviators may have to pull a Sustained 5-- 7g as some of those babies can accelerate in a 6g turn!! hence the G suit
...
for the average person more than 4.5gs is pushing it ---for the uninitiated 5gs is about it, before G-LOC
and the aviators who fly them frequently pull 10/12g and -5/-8g [outside snaps
]However, this is of very short duration and the practice is intense to maintain g tolerance...
Military aviators may have to pull a Sustained 5-- 7g as some of those babies can accelerate in a 6g turn!! hence the G suit
...for the average person more than 4.5gs is pushing it ---for the uninitiated 5gs is about it, before G-LOC
Joined: Oct 2003
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From: Canberra Australia
Nigd3
Test your Accelerometer on the ground using a centrifuge.
At 7g you probably will not be able to read the instrument anyway because you will have blacked out, unless the g application is very short term.
If you do not already know the answers to your question YOU shouldn't be contemplating the test.
What will you be using as a calibrated standard?
The whole test looks like a can of worms!
Test your Accelerometer on the ground using a centrifuge.
At 7g you probably will not be able to read the instrument anyway because you will have blacked out, unless the g application is very short term.
If you do not already know the answers to your question YOU shouldn't be contemplating the test.
What will you be using as a calibrated standard?
The whole test looks like a can of worms!
Joined: Jun 2002
Aviation Qualifications: PPL
Posts: 5,103
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From: east ESSEX
Nigd3,what aircraft are you doing the tests on,as a starter. ?How do you know the accelerometer is accurate?Has it been calibrated? Why is the anti-g system u/s? Even so,it is most unusual to take an a/c to it`s max g on an airtest,unless it is a new type,and even if it is it is essential that it is done progressively.It sounds as though you are talking about an ex-mil jet,in which case you need to know about it`s stalling characteristics as well,under `g` loading.OTHERWISE YOU CAN COME UNSTUCK IN A SHORT SPACE OF TIME.
`We`, of course can help/advise,so please fill in the gaps....Syc.
`We`, of course can help/advise,so please fill in the gaps....Syc.
Joined: Oct 2005
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From: Raincoast
Nigd3
This isn't something you wanna try without some practice! You may end up destroying yourself or the aircraft or both.
Get the G metre calibrated on the ground. If you don't have experience with high g forces in an aircraft, don't do this.
I routinely pulled +7 (and more) and -3.5g doing post maintenance and acceptance test flying when I was in the airforce. It was mandatory on full-card test flights. You definitely have to get used to this.
If you're hell bent on doing this, go to a club with aerobatic instruction and get yourself worked up by a professional to withstand G.
Good luck 'n happy contrails
k-o-t-s
This isn't something you wanna try without some practice! You may end up destroying yourself or the aircraft or both.
Get the G metre calibrated on the ground. If you don't have experience with high g forces in an aircraft, don't do this.
I routinely pulled +7 (and more) and -3.5g doing post maintenance and acceptance test flying when I was in the airforce. It was mandatory on full-card test flights. You definitely have to get used to this.
If you're hell bent on doing this, go to a club with aerobatic instruction and get yourself worked up by a professional to withstand G.
Good luck 'n happy contrails
k-o-t-s
Thread Starter
Joined: Jul 2003
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From: Canada
Hello gents
Thanks for the replies and here are a few clarifications:
- I will not be conducting the test. My flying experience is purely egg whisks where high G was not an issue and I dont fly any more anyway. I work as a systems engineer.
- A qualified ex-mil TP will be conducting the test. How fit and young they all are depends on how much you believe them.
- It is the G indicator, not the accelerometer itself that is being tested. The accelerometer is a known. However we have implemented new G limit warnings in the G indicator of the PFD and wish to give these a simple test (warning comes on 1g before max +ve and -ve G limit).
- The avionics rig is capable of supplying a databus signal to the PFD to simulate the accelerometer, however the rig is not certified and cannot be used for certification credit.
Nigd
Thanks for the replies and here are a few clarifications:
- I will not be conducting the test. My flying experience is purely egg whisks where high G was not an issue and I dont fly any more anyway. I work as a systems engineer.
- A qualified ex-mil TP will be conducting the test. How fit and young they all are depends on how much you believe them.
- It is the G indicator, not the accelerometer itself that is being tested. The accelerometer is a known. However we have implemented new G limit warnings in the G indicator of the PFD and wish to give these a simple test (warning comes on 1g before max +ve and -ve G limit).
- The avionics rig is capable of supplying a databus signal to the PFD to simulate the accelerometer, however the rig is not certified and cannot be used for certification credit.
Nigd
Joined: Apr 2004
Posts: 34
Likes: 1
From: England
Nigd,
Since you are working in Switzerland, have you considered using the Libelle g suit if you are getting anywhere near the limits where a g suit would be required. This suit does not need any interface with the aircraft, various pilots close to you already have experience with this g suit.
GF
Since you are working in Switzerland, have you considered using the Libelle g suit if you are getting anywhere near the limits where a g suit would be required. This suit does not need any interface with the aircraft, various pilots close to you already have experience with this g suit.
GF
Do a Hover - it avoids G
Joined: Oct 1999
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From: Chichester West Sussex UK
Sorry chaps, surely you are making a bit of a meal of this?
The momentary application of 7g is not a problem for an unprotected pilot. Problems from g only arise when it is maintained.
Historically (before we even fitted g meters to RAF aircraft) it was not uncommon for an ignorant snatch to damage an aircraft without the pilot realising he had overdone things because he did not 'grey out' let alone 'black out'.
Mind you with today's risk assessments and health and safety issues I am sure human physiology has changed resulting in the need for meetings, equipment,training, money and godness knows what else to go above 4.
JF
The momentary application of 7g is not a problem for an unprotected pilot. Problems from g only arise when it is maintained.
Historically (before we even fitted g meters to RAF aircraft) it was not uncommon for an ignorant snatch to damage an aircraft without the pilot realising he had overdone things because he did not 'grey out' let alone 'black out'.
Mind you with today's risk assessments and health and safety issues I am sure human physiology has changed resulting in the need for meetings, equipment,training, money and godness knows what else to go above 4.
JF
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From: UK
Well said JF.
The RAF's Tincano is operated to +6/-3 without the aid of any form of anti-g system and whilst some of my less fond memories of flight testing involved cross-calibrating the front versus rear cockpit g-meters in stages , the only time I recall any physiological problems was in a sudden reversal (whilst recovering from an oscillatory inverted spin) from about -2½g to +4g; but that sort of reversal would probably get you with a g-suit also.
Re: health and safety committees. A simulator system well known to myself and JF is, in one location, set to nominally simulate a PA28-161; the aircraft has +3.8/-1.5 limits which it manages quite happily with a 3-point car type harness. The simulator on the other hand has a 4 point aerobatic harness because, apparently, a health and safety assessment decided that the 3-point in a simulator with fairly motion capability, was inadequate. I recall making my views on that fairly forcibly when told that after I'd raised the incorrect harness in my criticisms during a cockpit assessment.
G
The RAF's Tincano is operated to +6/-3 without the aid of any form of anti-g system and whilst some of my less fond memories of flight testing involved cross-calibrating the front versus rear cockpit g-meters in stages , the only time I recall any physiological problems was in a sudden reversal (whilst recovering from an oscillatory inverted spin) from about -2½g to +4g; but that sort of reversal would probably get you with a g-suit also.
Re: health and safety committees. A simulator system well known to myself and JF is, in one location, set to nominally simulate a PA28-161; the aircraft has +3.8/-1.5 limits which it manages quite happily with a 3-point car type harness. The simulator on the other hand has a 4 point aerobatic harness because, apparently, a health and safety assessment decided that the 3-point in a simulator with fairly motion capability, was inadequate. I recall making my views on that fairly forcibly when told that after I'd raised the incorrect harness in my criticisms during a cockpit assessment.
G
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Genghis
That's a shocking lapse of judgement on the part of those carrying out the H&S risk assessment on that simulator - surely it should have a 5-point harness? Don't they realise they're exposing themselves to the risk of litigation in the event of a negative-g related injury? Tut tut
That's a shocking lapse of judgement on the part of those carrying out the H&S risk assessment on that simulator - surely it should have a 5-point harness? Don't they realise they're exposing themselves to the risk of litigation in the event of a negative-g related injury? Tut tut
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Joined: Feb 2000
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From: UK
Well, longitudinal g strictly for the torpedoing effect that you need a crotch strap for (or parachuting, but it was fitted on the ground floor so I think that you can discount that).
G
G
Do a Hover - it avoids G
Joined: Oct 1999
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From: Chichester West Sussex UK
I am not surprised that as a pax you greyed out doing a 4.5 g loop.
Please read the earlier posts about the effects of time.
The fact of the matter is you could have been taken to 10 g without any visual effects if the duration was short enough. You might have tweaked your neck though!
Please read the earlier posts about the effects of time.
The fact of the matter is you could have been taken to 10 g without any visual effects if the duration was short enough. You might have tweaked your neck though!
Joined: Oct 2003
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From: Canberra Australia
My first experience with high g was during a mock dogfight with another student in a Wirraway/T6/Harvard. No g meter so number unknown. Guess it was about 5g.
Faded quickly into unconsciousness during which my back pressure on the stick relaxed. Came to all confused believing that I had fallen asleep on my motorcycle. Groped around the cockpit desperately trying to find handlebars. Took a few seconds to recognise I was supposed to be flying an aircraft.
I think it caused me to lose the dogfight!
It's fascinating how your eyes perform during g onset. Encroaching tunnel vision is accompanied by decreasing colour perception. With tunnel vision down to about 30 degrees there is no colour - called greyout - closely followed by GLOC or unconsciousness.
Extent of brain damage? Who knows? It still seems to work OK.
Faded quickly into unconsciousness during which my back pressure on the stick relaxed. Came to all confused believing that I had fallen asleep on my motorcycle. Groped around the cockpit desperately trying to find handlebars. Took a few seconds to recognise I was supposed to be flying an aircraft.
I think it caused me to lose the dogfight!
It's fascinating how your eyes perform during g onset. Encroaching tunnel vision is accompanied by decreasing colour perception. With tunnel vision down to about 30 degrees there is no colour - called greyout - closely followed by GLOC or unconsciousness.
Extent of brain damage? Who knows? It still seems to work OK.
Last edited by Milt; 19th February 2008 at 21:24.
