AAIB investigation to Hawker Hunter T7 G-BXFI 22 August 2015
G0ULI, Out of interest, who was placing the blame? An insurance company or a court? I think many people have a low opinion of seemingly arbritary decisions made by car insurance companies that may/may not stand up in a court of law.
For those that say he was too slow in the inverted part of the Loop, I think you are missing the point that at slow airspeeds the radius of curvature will be SMALLER. So would have helped reduce the size of the loop.
Just to demonstrate the principle... Taken to the extreme, if his speed was over 500kts in the inverted, the possible radius of curvature would be enormous.
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Just to demonstrate the principle... Taken to the extreme, if his speed was over 500kts in the inverted, the possible radius of curvature would be enormous.
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It was generally me or forensic examiners who were responsible for establishing the sequence of events. The paperwork then went 'upstairs' for a decision to be made on what further action to take. Insurance companies were not involved until much later in proceedings and frequently not at all, because there was no policy in force.
Short of a tree, building or aircraft suddenly falling on a vehicle, nearly all accidents are avoidable if a vehicle is driven in a manner appropriate to the road conditions at the time.
I don't have any problem with 'enthusiastic' driving under the right circumstances, but drivers must accept it carries a risk to themselves and other road users.
Same thing goes for air displays. Operating an aircraft near the boundaries of its performance envelope requires minute attention to detail and a clear assessment of the potential risks to the aircraft and those on the ground. That clearly didn't happen at Shoreham, or the risks and consequences were grossly underestimated on the grounds that no incident involving mass casualties had happened for decades.
Short of a tree, building or aircraft suddenly falling on a vehicle, nearly all accidents are avoidable if a vehicle is driven in a manner appropriate to the road conditions at the time.
I don't have any problem with 'enthusiastic' driving under the right circumstances, but drivers must accept it carries a risk to themselves and other road users.
Same thing goes for air displays. Operating an aircraft near the boundaries of its performance envelope requires minute attention to detail and a clear assessment of the potential risks to the aircraft and those on the ground. That clearly didn't happen at Shoreham, or the risks and consequences were grossly underestimated on the grounds that no incident involving mass casualties had happened for decades.
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scifi
Correct but for the fact that a certain minimum airflow over the wings and control surfaces is needed for the aircraft to remain airborne and controllable. Swept wing aircraft need more airspeed to avoid stalling than conventional straight wings.
Correct but for the fact that a certain minimum airflow over the wings and control surfaces is needed for the aircraft to remain airborne and controllable. Swept wing aircraft need more airspeed to avoid stalling than conventional straight wings.
Really ? Aerodynamics as taught by the RAF and a million others, as well as a lot of personal hands -on experience, tells me that stalling is a function of angle of attack not airspeed or have I been in ignorance since I started flying in 1960 in swept and straight wing jets !
...............and I thought this was a professional site !
...............and I thought this was a professional site !
Scifi. The speed needed at the top of a loop is dictated by several factors. If too slow then as G0uli correctly stated it becomes harder to keep accurate control of the aircraft, even if the AoA remains very low by unloading. Gravity helps you at the top by providing a 'free' +1g even if you are fully unloaded, but then you'll need more than +1g to finish the loop so you'll need to accelerate to get more speed as you descend. Therefore you clearly can be too slow at the top of a loop.
However, as you eluded to, you can also be too fast. To a certain degree the faster you are the more g you can pull, but the radius also increases so there does become an upper limit. Minimum radius is probably what you are after. Therefore, the apex gate parameters will invariably have a minimum height and a min and max IAS. The Hunter was just above the minimum speed, but not too slow.
The actual speed at the apex will obviously be a function of entry parameters, induced drag and radius. To a certain degree you can pull harder and hence be lower but faster at apex. Alternatively, a slacker pull will give you more height but at the expense of speed. Had the Shoreham Hunter used much less pull on the way up it may have been a little higher but also slower. Entering the loop too slowly also had a significant effect. Of course the change in induced drag with AoA can be considerable in a swept wing machine.
RBaby, I think you know exactly what G0uli was eluding too!
However, as you eluded to, you can also be too fast. To a certain degree the faster you are the more g you can pull, but the radius also increases so there does become an upper limit. Minimum radius is probably what you are after. Therefore, the apex gate parameters will invariably have a minimum height and a min and max IAS. The Hunter was just above the minimum speed, but not too slow.
The actual speed at the apex will obviously be a function of entry parameters, induced drag and radius. To a certain degree you can pull harder and hence be lower but faster at apex. Alternatively, a slacker pull will give you more height but at the expense of speed. Had the Shoreham Hunter used much less pull on the way up it may have been a little higher but also slower. Entering the loop too slowly also had a significant effect. Of course the change in induced drag with AoA can be considerable in a swept wing machine.
RBaby, I think you know exactly what G0uli was eluding too!
Theoretically, one's max rate turn is also one's min radius turn but for the inconvenience of compressibility. Yes, the radius of a turn will increase in relation to the speed of the aircraft if lift is not increased but the increase is linear. Up to the G limit of the aircraft at a fixed coefficient (fixed AoA if you like) however, the lift increases in relation to the square of the speed. So, while your speed may be increasing the size of your turn, the lift available to shrink it is increasing at a greater rate. So, min radius turn happens nowhere near the min flying speed, it happens at the point where max lift coefficient (light buffet) coincides with max structural load (g limit) when one is going very, very fast.
Too slow over the top is a very real problem because the lift formula being dominated by EAS squared and Lift Coefficient produces very little puff at low speed. Your 500kts scenario is also very bad though SciFi because at that speed the pilot would encounter structural limitations that precluded the achievement of max coefficient.
Too slow over the top is a very real problem because the lift formula being dominated by EAS squared and Lift Coefficient produces very little puff at low speed. Your 500kts scenario is also very bad though SciFi because at that speed the pilot would encounter structural limitations that precluded the achievement of max coefficient.
Which in turn raises the interesting scenario that the pilot may have been aware of both the low apex height and airspeed, but judged that the lower than planned height loss that would result from the low apex airspeed would still allow safe completion of the loop manoeuvre.
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But he would also have known that to achieve a best solution he would require max thrust. Which he didn't have.
I believe he was confused or unaware, for whatever reason, when he pulled through.
I believe he was confused or unaware, for whatever reason, when he pulled through.
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Originally Posted by sika hulmuta
I believe he was confused or unaware, for whatever reason, when he pulled through.
I may have missed it, but the accident report doesn't seem to cover the pilot's actions on the day of the accident leading up to the flight in great detail, specifically, when he ate, what he ate and how much time elapsed subsequently.
This can have a bearing on hypoglycemic events that some people will have a predisposition for.
I remember an interesting case of an F-8 wingman joining on the lead aircraft after takeoff from NAS Miramar, when he went blind during the rendezvous! Fortunately the lead got him in sight quickly and gave voice commands which he was able to follow. After a while, his vision began coming back and the aircraft was recovered into the arresting gear at NAS Miramar. The sawbones blamed the problem on hypoglycemia resulting from a coffee and donut fighter pilot breakfast.
Hmm Gouli. Locally some of our road accidents have involved incapacity (Parkinson's and a cardiac arrest) a falling tree and a patch of oil leading to loss of control at an unusually low speed.
Of course a lot of them have involved alcohol or exuberant driving as well but the idea that mishaps that are not due to driver error are rare seems to me to be incorrect.
Tbh the more I think about this event the more I feel that wipe-outs at low level are inevitable. It doesn't mean there are no improvements to be made in pilot performance, but perhaps air displays with jets should only take place over the coast or moors. Focusing unduly on the pilot seems to me, unproductive.
As a spectator I'd far rather some measured approach like this, than a blanket ban or overly restrictive minima leading to displays that are too far away to see.
Of course a lot of them have involved alcohol or exuberant driving as well but the idea that mishaps that are not due to driver error are rare seems to me to be incorrect.
Tbh the more I think about this event the more I feel that wipe-outs at low level are inevitable. It doesn't mean there are no improvements to be made in pilot performance, but perhaps air displays with jets should only take place over the coast or moors. Focusing unduly on the pilot seems to me, unproductive.
As a spectator I'd far rather some measured approach like this, than a blanket ban or overly restrictive minima leading to displays that are too far away to see.
Your statement seems at odds with the test flying reports that, once at the apex, thrust setting makes no significant difference to the height required for recovery:
"... the minimum radius loop tests showed that power had little measurable effect on looping radius during the downward porttion when flown with an AOA for maximum usable lift"
"... at the apex the power was varied between idle, which was less than in the accident manoeuvre, and maximum which, in the F Mk58, was greater than that available in G-BXFI. Significant differences (80 KIAS) were seen in the speed at the end of the manoeuvres as a function of power setting past the apex but power did not have any significant effect on the height loss with the exception of the final loop with 2 notches of flap when maximum power may have reduced the height loss slightly"
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GOULI
I agree that having an excess of speed over the top would have given AH increased options to abort the bent loop. I.e. more lateral control to roll out without the same risk of an inverted departure....
Too slow and the radius of the last quarter increases and one is left with no control other than to mush into the ground which is what sadly happened.
The only thing that might have saved the situation might have been to jettison the 100 gal droppies which still contained fuel. But they would have landed on the innocent victims in much the same location as where the Ac crashed.....
MB
I agree that having an excess of speed over the top would have given AH increased options to abort the bent loop. I.e. more lateral control to roll out without the same risk of an inverted departure....
Too slow and the radius of the last quarter increases and one is left with no control other than to mush into the ground which is what sadly happened.
The only thing that might have saved the situation might have been to jettison the 100 gal droppies which still contained fuel. But they would have landed on the innocent victims in much the same location as where the Ac crashed.....MB
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abgd
I agree that there is always going to be some element of risk inherent in air displays. I certainly don't want to see a ban either. Part of the excitement, to me, is the perception that there is a slight element of danger, as a spectator. It is no different to some of the more extreme rides at amusement parks. The element of danger to the riders appears far greater than it actually is. But we do not expect parts of these rides to fall onto spectators away from the immediate ride area, or outside the boundary fence of the amusement park.
Technical failures happen, pilots make errors of judgement. It is up to the organisers of air displays to ensure that where an accident happens, the effects are contained within the airfield boundaries or over unpopulated areas such as the sea or open farm land. This will inevitably affect the ability of some airfields to be able to hold air displays at all due to urban developers tendency to build right up to airfield boundaries.
Commercial aviation is by no means free from similar failings as demonstrated at Kegworth and Heathrow, where busy motorways run directly across the main runway approaches.
I agree that there is always going to be some element of risk inherent in air displays. I certainly don't want to see a ban either. Part of the excitement, to me, is the perception that there is a slight element of danger, as a spectator. It is no different to some of the more extreme rides at amusement parks. The element of danger to the riders appears far greater than it actually is. But we do not expect parts of these rides to fall onto spectators away from the immediate ride area, or outside the boundary fence of the amusement park.
Technical failures happen, pilots make errors of judgement. It is up to the organisers of air displays to ensure that where an accident happens, the effects are contained within the airfield boundaries or over unpopulated areas such as the sea or open farm land. This will inevitably affect the ability of some airfields to be able to hold air displays at all due to urban developers tendency to build right up to airfield boundaries.
Commercial aviation is by no means free from similar failings as demonstrated at Kegworth and Heathrow, where busy motorways run directly across the main runway approaches.
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Neil Williams crash 11Dec1977
I was flying all that day at Blackbushe when the news came in. Doug Arnold had been driving up the runway and taxiway in his Roller, setting fire to some dead grass. He was a very unusual man. I found him easy to do business with as long as you did as he told you
Neil was due in with Doug's latest acquisition for War Birds of Great Britain, a Spanish-built He 111. I didn't know that Neil was due in, but during the day RT with the tower became more tense.
Neil Williams was regarded as one of the finest pilots in the world. He flew his aircraft into the ground. No survivors. Here's a thread from another forum Neil Williams crash 11Dec1977 It's bad form and etiquette to post a link to a competitor forum so I quite understand if mods and admin here on Pprune delete it. However, it does tell a story that is relevant to this thread and for those who don't know the story, it is worth a read.
I was flying all that day at Blackbushe when the news came in. Doug Arnold had been driving up the runway and taxiway in his Roller, setting fire to some dead grass. He was a very unusual man. I found him easy to do business with as long as you did as he told you
Neil was due in with Doug's latest acquisition for War Birds of Great Britain, a Spanish-built He 111. I didn't know that Neil was due in, but during the day RT with the tower became more tense. Neil Williams was regarded as one of the finest pilots in the world. He flew his aircraft into the ground. No survivors. Here's a thread from another forum Neil Williams crash 11Dec1977 It's bad form and etiquette to post a link to a competitor forum so I quite understand if mods and admin here on Pprune delete it. However, it does tell a story that is relevant to this thread and for those who don't know the story, it is worth a read.
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Can an experienced display pilot explain the following :-
[FONT=Arial][SIZE=3][COLOR=#231f20][FONT=Arial][SIZE=3][COLOR=#231f20]The resultant periods between the pull-up and the apex at the Shoreham 2014 and 2015 Airshows overlap.
However, when the videos of the ‘bent loop’ manoeuvres were viewed side by side, it was observed that the first half of the Shoreham 2014 ‘bent loop’ had a slightly higher pitch rate and was completed in a slightly shorter time than the first half of the Shoreham 2015 ‘bent loop’.
Engine speed during the loop at Duxford in 2014 was approximately the
maximum allowable throughout the climb. The Shoreham 2014 manoeuvre was initiated with a low engine speed which then stepped up in two stages, levelling at slightly under 8,000 rpm for the last part of the climb. The climb for the accident manoeuvre was initiated with an engine rpm approximately half way between the initial engine rpms of the other two manoeuvres. The engine speed then reduced to below 7,000 rpm, recovered to and briefly heldat 7,250 rpm, and then reduced further, passing below 7,000 rpm at the apex.
At the apex of the accident manoeuvre, the engine speed was approximately 1,000 rpm lower than for the other two manoeuvres. A further distinction of the accident manoeuvre is that the engine speed increased during the descent whereas during the other two comparison manoeuvres the general trend was a reduction in engine speed.
Would an experienced pilot changed the way he was controlling the throttle during a manoeuvre so that it was nearly the opposite. As far as I can tell this indicates to me that AH was not flying as 'usual' or there were other factors involved, which haven't been identified as yet.
[FONT=Arial][SIZE=3][COLOR=#231f20][FONT=Arial][SIZE=3][COLOR=#231f20]The resultant periods between the pull-up and the apex at the Shoreham 2014 and 2015 Airshows overlap.
However, when the videos of the ‘bent loop’ manoeuvres were viewed side by side, it was observed that the first half of the Shoreham 2014 ‘bent loop’ had a slightly higher pitch rate and was completed in a slightly shorter time than the first half of the Shoreham 2015 ‘bent loop’.
Engine speed during the loop at Duxford in 2014 was approximately the
maximum allowable throughout the climb. The Shoreham 2014 manoeuvre was initiated with a low engine speed which then stepped up in two stages, levelling at slightly under 8,000 rpm for the last part of the climb. The climb for the accident manoeuvre was initiated with an engine rpm approximately half way between the initial engine rpms of the other two manoeuvres. The engine speed then reduced to below 7,000 rpm, recovered to and briefly heldat 7,250 rpm, and then reduced further, passing below 7,000 rpm at the apex.
At the apex of the accident manoeuvre, the engine speed was approximately 1,000 rpm lower than for the other two manoeuvres. A further distinction of the accident manoeuvre is that the engine speed increased during the descent whereas during the other two comparison manoeuvres the general trend was a reduction in engine speed.
Would an experienced pilot changed the way he was controlling the throttle during a manoeuvre so that it was nearly the opposite. As far as I can tell this indicates to me that AH was not flying as 'usual' or there were other factors involved, which haven't been identified as yet.
To bring some sense into the discussion about the effects of speed in relation to turn radius.
http://people.clarkson.edu/~pmarzocc.../AE-429-12.pdf
http://people.clarkson.edu/~pmarzocc.../AE-429-12.pdf
Lemain,
You say "I personally don't believe the AAIB report goes far enough". Within the remit of AAIB reports, which present data and analyse it, what else do you think should have been included? Opinion and speculation are quite deliberately, and correctly, not included in their reports.
You say "I personally don't believe the AAIB report goes far enough". Within the remit of AAIB reports, which present data and analyse it, what else do you think should have been included? Opinion and speculation are quite deliberately, and correctly, not included in their reports.
