Gnat down at CarFest
There seem to be a surfeit of precious old vicars lurking on this thread. Humility dictates that we respect their opinions as they should respect ours.
Do forgive my temerity as a new poster but this is a good thread and a robust exchange of views should be defended from the tyranny of petty minds.
Do forgive my temerity as a new poster but this is a good thread and a robust exchange of views should be defended from the tyranny of petty minds.
Regrettably, some posters only come out of the woodwork to post about aircraft accidents - there's one, for example, whose 41 posts are 100% about accidents.
That's hardly 'speculation' - it's obsession.
As for
That would be a frankly absurd way of teaching a pilot new to type.....
That's hardly 'speculation' - it's obsession.
As for
Anyone with any tactical swept wing fighter time will have on their first dual sortie been instructed to pull to the buffet, then through the buffet into full departure before recovering several thousand feet below.
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I have to confess I tend to lurk and don't post much any more however I have taken an interest in this one as its rather close to home for a variety of reasons which I wont go into.
I've personally avoided speculating as the only jet I ever qualified on was the JP which is nothing to shout about, as part of the conversion onto type we were of course made aware of high speed stalls and even for civilian flying had to demo a pull to the buffet which makes me find the following statement very odd:
I would expect anyone tasked with actually fighting an aircraft to have a very thorough understanding of aerodynamics, AoA limitations and the results of exceeding them regardless of the speed at the time, indeed this is another part covered in the DA process.
As for the media, I've personally had quite a bit of exposure to them over the last 12 months having been described as everything from "Local Top Gun", "Lewis Hamilton of the skies", neither of which I am, and my aircraft referred to as a "Jet" multiple times despite having a ruddy great spinning thing on the front.
Alas Journo's nowadays are more interested in selling papers than being factually correct and the latter is often disregarded in favour of the former. Please therefore take any references to "RAF Ace" etc with a pinch of salt, having met Kev a few times however and knowing of his background outside of flying I've no doubt that had he put his mind to it he would have become all of the things the media described him as.
Regards
UA
I've personally avoided speculating as the only jet I ever qualified on was the JP which is nothing to shout about, as part of the conversion onto type we were of course made aware of high speed stalls and even for civilian flying had to demo a pull to the buffet which makes me find the following statement very odd:
And yet many pilots still do not understand that they can stall a fast jet or other aircraft doing 350 KIAS in a bank but level attitude (or any other configuration) by pure G loading. You have demonstrated that you understand this as do others here.
As for the media, I've personally had quite a bit of exposure to them over the last 12 months having been described as everything from "Local Top Gun", "Lewis Hamilton of the skies", neither of which I am, and my aircraft referred to as a "Jet" multiple times despite having a ruddy great spinning thing on the front.
Alas Journo's nowadays are more interested in selling papers than being factually correct and the latter is often disregarded in favour of the former. Please therefore take any references to "RAF Ace" etc with a pinch of salt, having met Kev a few times however and knowing of his background outside of flying I've no doubt that had he put his mind to it he would have become all of the things the media described him as.
Regards
UA
Terribly sad accident, but reminds me of a day in 1966 in Aunty Betty's Fun Jet: turning final at Valley, wind blowing towards the runway. W tightens turn, jet starts going down like a lift. Rhodesian accent from the back "I have control". Unloads, rolls wings level and overshoots. Voice from the back "If you had been on your own you would have been f@ck1ng well dead". Thanks Vic.
Busterbucani,
I appreciate your reply and stand guilty as charged of thread creep! However, if there are to be on-going discussions of accelerated stalling then a knowledge of the high altitude aspects, even if not relevant here, is a useful education. My use of the phrase 'not as simple as you implied' related to the complexities of stalling and not this accident. I would like to respond to a few of your points.
When converting to a swept wing jet a pilot will not practise taking it to the point of departure unless that is a cleared manoeuvre that is approved in the Flight Manual. I do not have a Gnat Manual to hand so cannot comment on that type but, for example, the Hunter was not cleared for intentional departures in service (although it was when specially instrumented in the flight test world).
Many (most?) display accidents, in piston engined aircraft, straight wing and swept wing jets, occur because there is insufficient height to execute a safe recovery from the aircraft's pitch and roll attitude. For example, being too low at the top of a loop, rolling with too low a nose attitude such that the nose drops to an irrecoverable dive angle.
The P-51 is one aircraft type that does have accelerated stall characteristics that can result in an inadvertent departure during a display. It has an essentially laminar flow wing which results in a very rapid right roll at the point of stall with no prior buffet (although a P-51C that I have flown did have a very narrow buffet margin when compared to the Ds that I have flown); in essence, it has no stall warning. The other type that I have displayed that has the same problem (albeit with not quite such a high roll rate at departure) is the Harvard/SNJ/T6. Most other aircraft, and especially swept wing ones including the Gnat, have some buffet margin to warn of the accelerated stall and in many aircraft the accelerated stall characteristics are actually quite benign.
The swept wing jets that I have departed (Hunter, Alpha Jet, F-16, F-18, Hawk intentionally, Tornado unintentionally!) invariably have a very rapid yaw off at the point of departure, often simultaneously with a roll off and pitch up. In the accident video it appears to me that the final motion that can be seen is a left roll from approximately 90 deg to around 120 - 130 deg bank angle with a simultaneous nose up pitch rate that was present before the roll occurred. I cannot see any noticeable yaw but that does not mean that there isn't a yaw rate developing. Draw your own conclusions, please.
Until the video is analysed fully in order to ascertain airspeed and pitch rate no-one can estimate the normal acceleration that the aircraft had just prior to impact. From memory I believe that the g limit in the Gnat was +7g (although I may be wrong) and the display sequence notes on the team's website mention 6g turns. Therefore, I think that any comments about +8g are not appropriate.
Unfortunately, there is one comment that I will take you to task about, your comment "I mourn the lost aircraft as I mourn its pilot". I find that extremely distasteful and disrespectful to his wife, family and friends. I fail to see how any sentient being could feel that way.
I appreciate your reply and stand guilty as charged of thread creep! However, if there are to be on-going discussions of accelerated stalling then a knowledge of the high altitude aspects, even if not relevant here, is a useful education. My use of the phrase 'not as simple as you implied' related to the complexities of stalling and not this accident. I would like to respond to a few of your points.
When converting to a swept wing jet a pilot will not practise taking it to the point of departure unless that is a cleared manoeuvre that is approved in the Flight Manual. I do not have a Gnat Manual to hand so cannot comment on that type but, for example, the Hunter was not cleared for intentional departures in service (although it was when specially instrumented in the flight test world).
Many (most?) display accidents, in piston engined aircraft, straight wing and swept wing jets, occur because there is insufficient height to execute a safe recovery from the aircraft's pitch and roll attitude. For example, being too low at the top of a loop, rolling with too low a nose attitude such that the nose drops to an irrecoverable dive angle.
The P-51 is one aircraft type that does have accelerated stall characteristics that can result in an inadvertent departure during a display. It has an essentially laminar flow wing which results in a very rapid right roll at the point of stall with no prior buffet (although a P-51C that I have flown did have a very narrow buffet margin when compared to the Ds that I have flown); in essence, it has no stall warning. The other type that I have displayed that has the same problem (albeit with not quite such a high roll rate at departure) is the Harvard/SNJ/T6. Most other aircraft, and especially swept wing ones including the Gnat, have some buffet margin to warn of the accelerated stall and in many aircraft the accelerated stall characteristics are actually quite benign.
The swept wing jets that I have departed (Hunter, Alpha Jet, F-16, F-18, Hawk intentionally, Tornado unintentionally!) invariably have a very rapid yaw off at the point of departure, often simultaneously with a roll off and pitch up. In the accident video it appears to me that the final motion that can be seen is a left roll from approximately 90 deg to around 120 - 130 deg bank angle with a simultaneous nose up pitch rate that was present before the roll occurred. I cannot see any noticeable yaw but that does not mean that there isn't a yaw rate developing. Draw your own conclusions, please.
Until the video is analysed fully in order to ascertain airspeed and pitch rate no-one can estimate the normal acceleration that the aircraft had just prior to impact. From memory I believe that the g limit in the Gnat was +7g (although I may be wrong) and the display sequence notes on the team's website mention 6g turns. Therefore, I think that any comments about +8g are not appropriate.
Unfortunately, there is one comment that I will take you to task about, your comment "I mourn the lost aircraft as I mourn its pilot". I find that extremely distasteful and disrespectful to his wife, family and friends. I fail to see how any sentient being could feel that way.
Last edited by LOMCEVAK; 5th Aug 2015 at 16:01.
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Everyone who flew the Gnat remembers the STUPRECC (or STUPRE for us older pre 399 generation) and hydraulic failure at any stage of flight should not have caused any serious embarrassment to a Valley QFI. It should be noted, however, that Mr. Petter’s pocket rocket could present one or two less well known and unrehearsed surprises. In 1967 & 68, during my tour at 4 FTS, I remember two occasions where QFIs were faced with malfunctions making the aircraft uncontrollable.
1. Gordon Allin’s longitudinal control ran away completely nose up and stayed there, causing the aircraft to repeatedly pitch up to the near vertical until apparently stalling into a dive; control inputs having no effect, he and his student ejected.
2. Al Holyoake’s Gnat decided of its own volition to enter a continuous roll and couldn’t be persuaded to stop. Al and his student (Dave Moss?) ejected.
I don’t know of any other instances of Hobson Motor or PFCU failures, but I think either of these, had they occurred at low level, particularly in a banked attitude might have left insufficient time to abandon the aircraft.
1. Gordon Allin’s longitudinal control ran away completely nose up and stayed there, causing the aircraft to repeatedly pitch up to the near vertical until apparently stalling into a dive; control inputs having no effect, he and his student ejected.
2. Al Holyoake’s Gnat decided of its own volition to enter a continuous roll and couldn’t be persuaded to stop. Al and his student (Dave Moss?) ejected.
I don’t know of any other instances of Hobson Motor or PFCU failures, but I think either of these, had they occurred at low level, particularly in a banked attitude might have left insufficient time to abandon the aircraft.
Last edited by NutherA2; 5th Aug 2015 at 18:14.
No, but it does look like he was turning very hard.
All these horror stories of the Gnat hyd system makes me grateful I did the last RAF Vampire course, and my QFI tour of the delightfully benign JP 4.
I still find it hard to understand the cause, frequency, of G -loc when guys are wearing G -suits. Never saw it on the JP, no G- suits and max rate turns at sustained 5.5/6 g on some quite old (ish) refresher students.
All these horror stories of the Gnat hyd system makes me grateful I did the last RAF Vampire course, and my QFI tour of the delightfully benign JP 4.
I still find it hard to understand the cause, frequency, of G -loc when guys are wearing G -suits. Never saw it on the JP, no G- suits and max rate turns at sustained 5.5/6 g on some quite old (ish) refresher students.
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As I understand it G-LOC occurs due to the rate of rise of G as well as the maximum value, rather than the sustained value.
Greying-out in a JP can be cured by relaxing the G, whereas G-LOC involves a period of unconsciousness and a loss of short-term memory on recovery.
Greying-out in a JP can be cured by relaxing the G, whereas G-LOC involves a period of unconsciousness and a loss of short-term memory on recovery.
There are also phenomena known as P-LOC (partial loss of consciousness) and A-LOC (almost loss of consciousness). These have been well researched and documented by the USAF/USN for many years but have only been introduced into high g training in the UK Military since the Red Arrows accident at Bournemouth. That accident report is worth a read regarding high g related loss of consciousness phenomena, as is the one pertaining to the L-M F-22 accident at Edwards a few years ago.
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HarryMann
I did bring up the possibility in post No 40 and it was picked up by Wingswinger in his post No 51.
I seem to recall (1966) that pulling +7 g max possible rate turns in the Gnat was unsurprisingly easier than pulling +6 g max possible rate turns in the JP due Gnat swept wing aerodynamics, raked (front) seating, g suit and responsive flight controls that lent themselves to the task and thus made sustained high g manoeuvres more comfortable compared with the JP.
Gnat QFIs I flew with would require of me sustained high g turns, which, age 20 and reasonably fit, I was happy to furnish them with but I did notice that after three or so rapid turn reversals of max possible rate (full thrust, quickly to max g [7] on the buffet, max IAS [360 kts, I think], bank angle approx 140 degrees and going down fast) I could still hold a conversation with the instructor but, meanwhile, had quickly and completely blacked out. A recovery was instantly effected by relaxing the g and applying a little aileron to roll some of the bank off - amount guessed at, as I was unable to see until vision returned - when a muffled instruction usually issued from the rear seat to fly S&L or commence a less bracing pastime.
Whilst never getting to a G-Loc situation during these or other medium level exercises (just black-out), I was damned careful never to pull anything like the same g values at low level, when, I figured, a very quick black-out would equally quickly end in disaster.
Has G-Loc been discussed ?
I seem to recall (1966) that pulling +7 g max possible rate turns in the Gnat was unsurprisingly easier than pulling +6 g max possible rate turns in the JP due Gnat swept wing aerodynamics, raked (front) seating, g suit and responsive flight controls that lent themselves to the task and thus made sustained high g manoeuvres more comfortable compared with the JP.
Gnat QFIs I flew with would require of me sustained high g turns, which, age 20 and reasonably fit, I was happy to furnish them with but I did notice that after three or so rapid turn reversals of max possible rate (full thrust, quickly to max g [7] on the buffet, max IAS [360 kts, I think], bank angle approx 140 degrees and going down fast) I could still hold a conversation with the instructor but, meanwhile, had quickly and completely blacked out. A recovery was instantly effected by relaxing the g and applying a little aileron to roll some of the bank off - amount guessed at, as I was unable to see until vision returned - when a muffled instruction usually issued from the rear seat to fly S&L or commence a less bracing pastime.
Whilst never getting to a G-Loc situation during these or other medium level exercises (just black-out), I was damned careful never to pull anything like the same g values at low level, when, I figured, a very quick black-out would equally quickly end in disaster.
Gnat QFIs I flew with would require of me sustained high g turns, which, age 20 and reasonably fit, I was happy to furnish them with but I did notice that after three or so rapid turn reversals of max possible rate (full thrust, quickly to max g [7] on the buffet, max IAS [360 kts, I think], bank angle approx 140 degrees and going down fast) I could still hold a conversation with the instructor but, meanwhile, had quickly and completely blacked out.
Those max rate turning sorties were quite physically demanding - but great fun!
At least the Gnat had a proper anti-G system which used bleed air, rather than the bottled air of the Hunter. On some range sorties it was possible to run out of anti-G in the F6A / T7, but IIRC the FGA9 had an extra bottle. Running out of anti-G when you least expected it was very disconcerting! One of our course mates* remarked that he'd completely blacked out when it happened to him in the T7 - something of an unfortunate turn of phrase though, given that he was of Jamaican descent.
*Great chap - went on to higher things on the Jaguar.
One of our course mates* remarked that he'd completely blacked out when it happened to him in the T7 - something of an unfortunate turn of phrase though, given that he was of Jamaican descent.
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llamaman
I think the technical term for what you've just read is banter.
noun
the playful and friendly exchange of teasing remarks: there was much good natured banter
verb
exchange remarks in a good humoured teasing way: the men bantered with the waitress
I'm afraid it used to be like that, back in the sixties, before PC and taking grave exception to everything became the norm, so please, cut us some slack, leave us alone and go and get yourself ready for the next Jeremy Corbin rally.
I think the technical term for what you've just read is banter.
noun
the playful and friendly exchange of teasing remarks: there was much good natured banter
verb
exchange remarks in a good humoured teasing way: the men bantered with the waitress
I'm afraid it used to be like that, back in the sixties, before PC and taking grave exception to everything became the norm, so please, cut us some slack, leave us alone and go and get yourself ready for the next Jeremy Corbin rally.
The reason I wrote that he was a great chap who went on to better things on the Jaguar, was so that ex-Jag Mates would kNOw to whom I was referring.
We were at UAS, RAFC and 4FTS together - those who know him, know his fine sense of humour.
His "I completely blacked out" comment had the crewroom in stitches, including him. "Yeah, since birth, mate", was one reply.
When there are 6 of you still surviving the TWU course and you're all mates, banter flows pretty freely. I hope that's still the case in the anodyne PC world of today....
Anyway, back to the thread - the anti-G system in the Gnat was very reliable and I don't recall anyone having had a failure or an inadvertent turning-trousers disconnect. But if you're braced ready for the system to kick in and for some reason it doesn't, you will be highly likely to black out - but that's not the same as G-loc.
We were at UAS, RAFC and 4FTS together - those who know him, know his fine sense of humour.
His "I completely blacked out" comment had the crewroom in stitches, including him. "Yeah, since birth, mate", was one reply.
When there are 6 of you still surviving the TWU course and you're all mates, banter flows pretty freely. I hope that's still the case in the anodyne PC world of today....
Anyway, back to the thread - the anti-G system in the Gnat was very reliable and I don't recall anyone having had a failure or an inadvertent turning-trousers disconnect. But if you're braced ready for the system to kick in and for some reason it doesn't, you will be highly likely to black out - but that's not the same as G-loc.
Last edited by BEagle; 6th Aug 2015 at 06:53.
I recall one disconnection of a G-suit in the Funjet - the late CC was doing aeros somewhere over N Wales when the connection apparently popped out. CC blacked out and came to at a height that made him delighted he had not been aerobatting over Snowdon
Last edited by Wander00; 6th Aug 2015 at 09:19. Reason: Fingers/brain interface again
I'm not entirely sure that the recounting of a pilot's somewhat disconcerting physiological incident should somehow be linked to the colour of his skin (despite the condescending asterisk link to footnote explaining what a 'great chap' he was).
At the risk of thread creep, who normally looks after the civilian pilots survival equipment in these cases? Is there a CAA rule that it must be maintained regularly or is it a case of taking it into a friendly forces squipper if you happens to be passing a base? As noted earlier in the thread did the ex-Gnat fliers here all wear internal Anti-G trousers?
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One would assume that they are maintained and certified by a civil company specialising in Squipping like SES at Tetbury.