Bluebird K7 Latest
Discussion
Jim H said:
Fantastic photo’s Mr BMW.
I really need to get up and have a look - soon!
Interesting looking at the Union Jack motif on the fin.
I remember watching footage when Bill Smith first discovered Bluebird underwater and he wiped off the algae from that part. I can only guess he’s preserved this aspect ??
Did anyone else spot that?
It looks like the paint on the flag here is untouched, yes. I really need to get up and have a look - soon!
Interesting looking at the Union Jack motif on the fin.
I remember watching footage when Bill Smith first discovered Bluebird underwater and he wiped off the algae from that part. I can only guess he’s preserved this aspect ??
Did anyone else spot that?
Turkish91 said:
Equus said:
Jim H said:
I’d be interested if you have any views or opinions on the accident itself?
Long, technical post: skip on by, if you're not interested.Occam's Razor applies.
I'm willing to believe that the lack of refueling was a combination of nerves, wanting to get the job done, and possibly a hope that he might make the return run before the first run's wash started bouncing back and forth and chopping up the surface (which from his commentary wasn't the best in any case). Whether the surface would have been any better had he paused to refuel is anyone's guess, though, so it's pointless speculating.
The fuel tank is (deliberately) located bang over K7's centre of gravity, so whilst she's a bit lighter overall with an empty tank, it doesn't really affect her trim (ie. pitch incidence), as such.
We know that her aerodynamics at 300mph (50mph above her design speed) were very marginal*. It's worth remembering, when considering this, that aerodynamic forces rise in proportion to the square of the increase in speed, so 50mph. over design speed is a much bigger margin than it might at first appear.
The following graphs are taken from a detailed technical article that the Norris brothers wrote for The Engineer (a professional journal for engineers), published in 1957 (ie. relating to her original, Beryl-engined design):
You'll note that they are taken at her 250mph design speed.
(ETA: in case its not obvious, for those unused to reading graphs, Bluebird does a somersault at the point where the two lines cross).
Broadly speakiing increasing the speed to the 300-325mph she was running on the fatal attempt would have the effect of moving the whole 'pitching moment' and 'lift' lines up the graphs, and not in a simple, linear relationship to the increase in speed. Note also the 'hump' in these lines. My understanding is that the Orpheus, whilst more powerful, was also a fair bit lighter than the Beryl (Wikipedia quotes 379kg. vs. 680kg., which if true is a not inconsiderable 300 kilos of difference!), so the 'restoring moment'/'weight of craft' lines on these two graphs would have moved down (and it's here that an empty fuel tank certainly doesn't help).
She had a well known habit of tramping** (rocking laterally from one sponson to the other) and we know both from the footage and Campbell's commentary that she was doing this badly on the return run. The effect of this is that the boat is rotated around a conical axis centered on the rear planing shoe, with the water line then forming the 'surface' line of the cone, which effectively pitches up her nose.
There's an addendum chapter by Graham Beech, in association with Ken Norris, in the reprinted version of 'With Campbell at Consiton' (retitled 'The Bluebird Years') where he extrapolates a version of the above graphs for the Orpheus and analyses the pitch effect of the tramping, but it's just a 'best guess' and FWIIW, I think it might be a bit optimistic. Beech/Norris guesstimated the effect on the graph as reducing the critical pitch to 6 degrees (already unacceptable, given her tendency to tramp), but due to the hump in the curve, it would take only a very slight error in their estimate and this would be cut to less than 3 degrees, at which point you can forget worrying about flame-outs - the tramping alone would have made the accident a virtual certainty.
TL:DR version: K7's stability at ~300mph+ was very marginal, so she was an accident waiting to happen. They just ran out of luck.
* One factor I've never seen discussed, here, is that whilst the addition of the Gnat tailfin for the '66/67 attempt will have aided her longitudinal stability, the additional drag on it, above the CoG, will have resulted in an additional moment tending to pitch her nose up which, whilst small, would be highly undesirable. The flat spray deflectors will similarly have tended to cause a small amount of additional lift ahead of the CoG. Even the damage to the front spar fairing caused by collision with a duck might have creeated turbulence, hence drag, that added to the pitch-up tendency... all small factors, but all tending to have an effect in the wrong direction, on a situation that was already unacceptable.
** At risk of digression, if you watch a video of Spirit of Australia on her record run, you'll see that she is tramping very badly indeed, too, albeit at a lower frequency than K7 used to. SoA was significantly narrower than K7, so the effect of this 'sponson walking' on her pitch stability will have been much less, and of course she also had a horizontal stabiliser to correct pitch, but if I'd have been Warby, I'd have been stting bricks, none the less.The guy had balls - you've got to give him that!
Edited by Equus on Thursday 15th February 13:45
Here is a brief summary of our findings, which do not directly contradict some of the previous postings, but may help clear up some misunderstandings that have arisen along the way.
1 At speeds in excess of 310mph, Bluebird K7 was only marginally stable. The additive factors of ground effect and port spar damage were such as to reduce the stability margin further to the point where recovery beyond that speed was impossible once moderating engine thrust was lost or reduced. Episodes of ‘hovering’ on the last runs have been identified and, indeed, confirmed throughout Bluebird’s operational life.
2 The hoped-for stability benefits of a further forward CG resulting from the Orpheus conversion were all but lost by the addition of the compensating ballast to facilitate planing.
3 The angle of the wedges incorporated as part of the original design brief to obtain 250mph were suboptimal for speeds above that and contributed to the additional drag experienced.
4 The strident ‘rooster-tail’ spray pattern, evident in smooth or rough running conditions implies that Bluebird was near or at its dynamic stability limit.
5 The first run on 4 January was not without incident as has been generally claimed but demonstrated evidence of instability at the climax of that run and catastrophe was only narrowly averted.
6 Application of the water-brake following the first run was less efficacious than that predicted in earlier lower speed runs due to dynamic instability / rear shoe ‘hop’.
7. Campbell used ‘sighting lines’ off K7’s sponsons to aid his positioning on the lake. He also proceeded far deeper into the southern bay of Coniston than has been previously appreciated. The separation / divergence of the tracks on the first and final runs has also been confirmed.
8. The ‘bouncing’ phenomena observed on the final run are physically distinct to that of ‘tramping’ as they have a different cyclic frequency and form. Tramping was only observed to occur on the initial run-up from Peel Island and played no part in the critical stages i.e. from point ‘A’. The water conditions over the central part of the lake including that of the timed km were good.
9. The speed profile of the latter part of the final run reveals a serious decelerating episode following bounce ‘3’.
10 Engine failure has been confirmed at around 7 seconds prior to impact
11 No evidence can be found to indicate that the water brake was deployed in the final seconds.
12. It is asserted that Donald Campbell’s strategy on the final runs was to exploit the benefits of a quick turn-round given the good conditions of the water and his knowledge of how K7 itself disturbed the water during such runs. This approach was not unprecedented as he had exploited it on various previous runs.
The Gnat tail fin produced less drag than the previous fin K7 was equipped with from 1958 to July 1966.
Our book was written with the direct involvement of Mr AE James - project manager of the K7 refit and Prof. John Stollery, Professor of Aerodynamics at Imperial College and consultant aerodynamicist to the Campbell / Norris team.
I would recommend Keith analysis to all our are interested in understanding the dynamics of Bluebird K7 and the events of those last two runs made by Donald Campbell.
Thank you for posting.
Engine failure 7 seconds prior to impact? How do you know this?
I don't mean to sound rude, and realise that sounds a bit accusatory, but it's a genuine question as I'm genuinely interested. From memory, the film doesn't appear to show that. But I'll be honest, I haven't the foggiest about jet engines.
I'm also intrigued as to how the rooster tail demonstrates she was at her stability limits. Can you explain in words with not many syllables for a layman please?
Engine failure 7 seconds prior to impact? How do you know this?
I don't mean to sound rude, and realise that sounds a bit accusatory, but it's a genuine question as I'm genuinely interested. From memory, the film doesn't appear to show that. But I'll be honest, I haven't the foggiest about jet engines.
I'm also intrigued as to how the rooster tail demonstrates she was at her stability limits. Can you explain in words with not many syllables for a layman please?
sheppane said:
The Gnat tail fin produced less drag than the previous fin K7 was equipped with from 1958 to July 1966.
The centre of pressure of that drag, however, is higher up (creating a larger nose-up moment around the craft's CoG). It's not the drag that matters, it's the moment.I'm uncomfortable with the statement that tramping played no part in the critical stages. Even if the tramping had ceased (as it would of course, once the front planing shoes had lost meaningful contact with the water) by the time she passed the point of no return, it had already made a critical contribution to the pitch attitude of the boat. In plain English: once she'd started to pitch up, she tended to stay pitched up because there wasn't a whole lot to bring her back down. The only thing causing a nose down pitching moment was that part of the rear of the boat that was in contact with the water (the rear planing shoe and rudder), and that wasn't enough.
If you watch the film, she's tramping very noticeably (visibily rocking side to side) up until at most 3 seconds before she clearly passed the point of no return, so it would have taken some decisive dynamic factor in those few seconds to pull the nose back down, to overcome the harm that the tramping had already caused.
It's worth saying that, here in the UK, we tend to obsess about Bluebird's crash in isolation as though it was a unique, profound and unprecedented occurrence. If you spend any time watching American Unlimited Hydroplane racing (and I recommend that you do - it's quite an exciting sport to watch), you'll learn that 'blowovers' are relatively commonplace*, and you'll quickly learn to much more clearly read the signs from roostertails and the tramping/pitching movements of the boats that tell you things are getting out of hand. Having driven (much slower!) inboard-engined three-point hydroplanes in my youth, I can also tell you that once they start to 'hover' or 'float', there's not a whole lot you can do to stop them, other than to gently ease off and hope it sorts itself out**. The American Unlimited hydroplanes now have driver controlled front canards that give the driver a small amount of control, but such adjustable aerodynamic control surfaces used to be banned by the UIM.
I'd also say (having been through the same process myself) that it's easy to over-analyse film, beyond the resolution of its frame speed. You cannot fill the gaps between the individual frames, and it's particularly easy to be misled by cyclical motions (in the same way that the frame rate of a film will sometimes appear to make an aircraft propeller or wheel rotate backwards, or stand still, when in fact it's rotating forwards at many cycles per second). The film of John Cobb's crash in Crusader is a good example of this: from the film itself, you'd conclude that Crusader was pitching at a fairly slow rate, in terms of cycles per second. Because in that instance (and in contrast to Campbell's crash) we could see Cobbs head being thrown back and forth as he sat in the cockpit (with the motion of his head out of sync with the apparent pitching cycles, because of course it was accelerating and decelerating independently of the structure of the boat), it has been concluded that the pitching was actually occuring at a much higher frequency than the film suggested.
Because of all of the above, I'm afraid I'm somewhat sceptical of these sorts of 'expert' analyses: the very fact of wanting to present themselves as 'expert' means that very few are willing to say: 'actually, we don't know, because the evidence simply isn't good enough to reach a clear conclusion'. All we can say is that there were very probably a number of contributory factors, but if we try to pin their relative importance down too far, we're kidding ourselves. Sadly, such a conclusion doesn't sell books!
* and these days, now we have safety cockpits, fairly survivable: one of the characteristics of a 'blowover' is that, by definition, at some point in the loop (usually twice, in fact) the craft is presenting its whole plan area to the direction of travel, which results in enough drag to slow it down appreciably before it impacts the water. The damage is often quite limited, and on some freak occasions the boats actually manage to complete a near perfect loop, touch down and carry on almost as if nothing has happened.
** and even that would be less effective with a jet boat: with a prop-driven hydroplane, you rely on the drag of the slowing propeller to cause a nose-down moment to pull you back onto the water.
AW111 said:
I assume there's some rule-based reason WSR craft aren't true hydrofoils?
Nope. You're welcome to use hydrofoils if you think you can make one work.The record was once held by a hydrofoil (Alexander Graham Bell's 'Hydrodome', at 70mph):
The Norris brothers - who designed Bluebird K7- also designed a jet hydrofoil called White Hawk (note the similar 'fuselage' design to K7), but it failed miserably:
A certain Noel Edmonds was also conned into parting with large sums of money on an absurd design called 'Excalibur' that proposed a propeller-driven underwater unit that lifted the main hull clear of the water using hydrofoils (utter nonsense: the drag of the underwater unit would have been phenomenal). This shows the mock-up (the underwater unit with its hydrofoils is in the background and would have been joined to the cockpit section like the keel of a sailing boat):
If you Google 'Noel Edmonds Excalibur' you'll find a picture of Edmonds with a model, which makes more sense, but it's got Alamy copyright stamps all over it, so I'd better not link the image directly.
The problem with hydrofoils is that you get 'cavitation' on the upper (suction) surface of the foil section. Above a certain speed (typically 70+mph) the pressure becomes so low that a vapour bubble forms over the top surface, so you end up only getting lift from the lower surface of the foil: effectively the same as you'd get from a normal planing surface, but you're dragging along all the useless, turbulent flow over the top surface as well. People have dabbled with 'supercavitating' foil designs (basically a wedge section - similar to the sections you use for a supercavitating propeller) which raise the upper speed limit a bit further, but even they won't work much above 100mph.
Edited by Equus on Monday 15th April 11:21
Equus said:
sheppane said:
The Gnat tail fin produced less drag than the previous fin K7 was equipped with from 1958 to July 1966.
The centre of pressure of that drag, however, is higher up (creating a larger nose-up moment around the craft's CoG). It's not the drag that matters, it's the moment.I'm uncomfortable with the statement that tramping played no part in the critical stages. Even if the tramping had ceased (as it would of course, once the front planing shoes had lost meaningful contact with the water) by the time she passed the point of no return, it had already made a critical contribution to the pitch attitude of the boat. In plain English: once she'd started to pitch up, she tended to stay pitched up because there wasn't a whole lot to bring her back down. The only thing causing a nose down pitching moment was that part of the rear of the boat that was in contact with the water (the rear planing shoe and rudder), and that wasn't enough.
If you watch the film, she's tramping very noticeably (visibily rocking side to side) up until at most 3 seconds before she clearly passed the point of no return, so it would have taken some decisive dynamic factor in those few seconds to pull the nose back down, to overcome the harm that the tramping had already caused.
It's worth saying that, here in the UK, we tend to obsess about Bluebird's crash in isolation as though it was a unique, profound and unprecedented occurrence. If you spend any time watching American Unlimited Hydroplane racing (and I recommend that you do - it's quite an exciting sport to watch), you'll learn that 'blowovers' are relatively commonplace*, and you'll quickly learn to much more clearly read the signs from roostertails and the tramping/pitching movements of the boats that tell you things are getting out of hand. Having driven (much slower!) inboard-engined three-point hydroplanes in my youth, I can also tell you that once they start to 'hover' or 'float', there's not a whole lot you can do to stop them, other than to gently ease off and hope it sorts itself out**. The American Unlimited hydroplanes now have driver controlled front canards that give the driver a small amount of control, but such adjustable aerodynamic control surfaces used to be banned by the UIM.
I'd also say (having been through the same process myself) that it's easy to over-analyse film, beyond the resolution of its frame speed. You cannot fill the gaps between the individual frames, and it's particularly easy to be misled by cyclical motions (in the same way that the frame rate of a film will sometimes appear to make an aircraft propeller or wheel rotate backwards, or stand still, when in fact it's rotating forwards at many cycles per second). The film of John Cobb's crash in Crusader is a good example of this: from the film itself, you'd conclude that Crusader was pitching at a fairly slow rate, in terms of cycles per second. Because in that instance (and in contrast to Campbell's crash) we could see Cobbs head being thrown back and forth as he sat in the cockpit (with the motion of his head out of sync with the apparent pitching cycles, because of course it was accelerating and decelerating independently of the structure of the boat), it has been concluded that the pitching was actually occuring at a much higher frequency than the film suggested.
Because of all of the above, I'm afraid I'm somewhat sceptical of these sorts of 'expert' analyses: the very fact of wanting to present themselves as 'expert' means that very few are willing to say: 'actually, we don't know, because the evidence simply isn't good enough to reach a clear conclusion'. All we can say is that there were very probably a number of contributory factors, but if we try to pin their relative importance down too far, we're kidding ourselves. Sadly, such a conclusion doesn't sell books!
* and these days, now we have safety cockpits, fairly survivable: one of the characteristics of a 'blowover' is that, by definition, at some point in the loop (usually twice, in fact) the craft is presenting its whole plan area to the direction of travel, which results in enough drag to slow it down appreciably before it impacts the water. The damage is often quite limited, and on some freak occasions the boats actually manage to complete a near perfect loop, touch down and carry on almost as if nothing has happened.
** and even that would be less effective with a jet boat: with a prop-driven hydroplane, you rely on the drag of the slowing propeller to cause a nose-down moment to pull you back onto the water.
With regards to tramping, that on K7 was at about 5-6 hz per second. The bouncing exhibited by in the K7 before it took off was a totally different phenomena, at around 0.8hz per second and should not be referred to as tramping.
K7 was also equipped with a fixed stabilising fin at the transom.
Have you read the analysis? I believe you would find it informative. I'm not saying it has all the answers, but I am saying, and various experienced individuals have agreed, that it does substantially inform the debate about DMC tragic accident.
By all means visit my Facebook page https://www.facebook.com/bluebirdk7 and DM if you would like to correspond further on this.
sheppane said:
I'm uncomfortable getting into debate with a party that does not identify themselves I'm afraid.
With regards to tramping, that on K7 was at about 5-6 hz per second. The bouncing exhibited by in the K7 before it took off was a totally different phenomena, at around 0.8hz per second and should not be referred to as tramping.
K7 was also equipped with a fixed stabilising fin at the transom.
Have you read the analysis? I believe you would find it informative. I'm not saying it has all the answers, but I am saying, and various experienced individuals have agreed, that it does substantially inform the debate about DMC tragic accident.
By all means visit my Facebook page https://www.facebook.com/bluebirdk7 and DM if you would like to correspond further on this.
We're all unidentified here mate. I'm certainly not a NZ All Blacks player's sock. With regards to tramping, that on K7 was at about 5-6 hz per second. The bouncing exhibited by in the K7 before it took off was a totally different phenomena, at around 0.8hz per second and should not be referred to as tramping.
K7 was also equipped with a fixed stabilising fin at the transom.
Have you read the analysis? I believe you would find it informative. I'm not saying it has all the answers, but I am saying, and various experienced individuals have agreed, that it does substantially inform the debate about DMC tragic accident.
By all means visit my Facebook page https://www.facebook.com/bluebirdk7 and DM if you would like to correspond further on this.
We are all very much adults too and can have a very informed debate without getting punchy. Equus is a very well informed poster who has made some very valuable and insightful posts on here. I wouldn't shy away from questioning him, and I know sweet FA! He always takes the time to explain.
Here is a photograph that exhibits tramping with K7. At 5 cycles per second you can calculate the distance travelled by K7 in that time, and if the background enables measurement through landmarks, the speed of K7 at the point of photography. The typical tramping frequency was five cycles per second and examination of one of the images shows that the distance covered during that five-cycle period of one second was
approximately 115 metres, as she passed Land’s Point. 115 metres per second equates to a speed of around 257mph.
approximately 115 metres, as she passed Land’s Point. 115 metres per second equates to a speed of around 257mph.
sheppane said:
I'm uncomfortable getting into debate with a party that does not identify themselves I'm afraid.
My website is on my profile; you can identify me easily enough from there, if you wish, though I struggle to see why you consider it important: either an argument is supportable or it isn't. Bill Smith once convinced himself on here that I was Jim Noone, which I found hysterically funny.
sheppane said:
With regards to tramping, that on K7 was at about 5-6 hz per second. The bouncing exhibited by in the K7 before it took off was a totally different phenomena, at around 0.8hz per second and should not be referred to as tramping.
K7 was also equipped with a fixed stabilising fin at the transom.
None of which I dispute (though as I have said, you should be wary of trying to accurately assess the frequency of an oscillation when your source data itself only has a very limited bandwidth... that's a lesson I've learned by much broader analyses than just the film of one specific accident). K7 was also equipped with a fixed stabilising fin at the transom.
I'm simply saying that the fact that she was no longer tramping immediately before she took off is not to say that the tramping that had occurred prior to that had had no effect on her stability, or did not affect the outcome.
sheppane said:
Have you read the analysis?
Yes.I've read lots of analyses of the accident, each of them by someone who had doubtless convinced himself that his was the best and most informative possible.
All of them, in my opinion, over-extrapolate the available evidence and reach conclusions that present themselves as less speculative than they really are... but I appreciate that's the nature of the game. As I said, you don't sell books by admitting that you don't really have the answers.
Equus said:
sheppane said:
I'm uncomfortable getting into debate with a party that does not identify themselves I'm afraid.
My website is on my profile; you can identify me easily enough from there, if you wish, though I struggle to see why you consider it important: either an argument is supportable or it isn't. Bill Smith once convinced himself on here that I was Jim Noone, which I found hysterically funny.
sheppane said:
With regards to tramping, that on K7 was at about 5-6 hz per second. The bouncing exhibited by in the K7 before it took off was a totally different phenomena, at around 0.8hz per second and should not be referred to as tramping.
K7 was also equipped with a fixed stabilising fin at the transom.
None of which I dispute (though as I have said, you should be wary of trying to accurately assess the frequency of an oscillation when your source data itself only has a very limited bandwidth... that's a lesson I've learned by much broader analyses than just the film of one specific accident). K7 was also equipped with a fixed stabilising fin at the transom.
I'm simply saying that the fact that she was no longer tramping immediately before she took off is not to say that the tramping that had occurred prior to that had had no effect on her stability, or did not affect the outcome.
sheppane said:
Have you read the analysis?
Yes.I've read lots of analyses of the accident, each of them by someone who had doubtless convinced himself that his was the best and most informative possible.
All of them, in my opinion, over-extrapolate the available evidence and reach conclusions that present themselves as less speculative than they really are... but I appreciate that's the nature of the game. As I said, you don't sell books by admitting that you don't really have the answers.
sheppane said:
The reason I like to ID people is my preference to correspond with people who are happy to go on the record. There are too many social media platforms where people converse in a way under the cloak of disguise...
As Jordie Barretts Sock has said, whether you like it or not, PistonHeads is one of them. In fact, we have specific rules (4 and 7) that prohibit individual members sharing their own personal information - even if they want to - or from trying to determine the identity of others.
If you don't like that, I can only suggest that you stick to other social media platforms: you signed up to the rules of this one when you created your profile.
Edited by Equus on Monday 15th April 14:13
Back on topic:
One thing that I have noticed from viewing dozens of blowover accidents is that they seldom or never occur very suddenly - you can usually tell several long seconds before the boat reaches the obvious 'point of no return' that things are getting out of hand. The reasons that people pin on the accident are frequently only the straw that broke the camel's back, on top of a cumulation of other adverse circumstances.
By modern standards, the quality of film footage of K7's accident is relatively poor and makes analysis difficult (and we have no datalogging as we'd have on a modern unlimited, of course), but for this reason, again, I wouldn't restrict my analysis to the final moments only.
The Craig Arfons crash is another good example: LINK. The footage here (starting at about 1:26) doesn't show enough of the lead-in, but it's clear that he was in big trouble already, by that point, and probably had been for many seconds.
Speculative, of course, but engine 'failure' 7 seconds before impact (not take-off, mind you... impact... she was in the air for 3 seconds or so) would say to me that K7 was already likely in deep st, by that point, and Campbell would have known it. I'd therefore take some convincing that that any 'failure' wasn't simply as a result of him lifting off the throttle.
One thing that I have noticed from viewing dozens of blowover accidents is that they seldom or never occur very suddenly - you can usually tell several long seconds before the boat reaches the obvious 'point of no return' that things are getting out of hand. The reasons that people pin on the accident are frequently only the straw that broke the camel's back, on top of a cumulation of other adverse circumstances.
By modern standards, the quality of film footage of K7's accident is relatively poor and makes analysis difficult (and we have no datalogging as we'd have on a modern unlimited, of course), but for this reason, again, I wouldn't restrict my analysis to the final moments only.
The Craig Arfons crash is another good example: LINK. The footage here (starting at about 1:26) doesn't show enough of the lead-in, but it's clear that he was in big trouble already, by that point, and probably had been for many seconds.
Speculative, of course, but engine 'failure' 7 seconds before impact (not take-off, mind you... impact... she was in the air for 3 seconds or so) would say to me that K7 was already likely in deep st, by that point, and Campbell would have known it. I'd therefore take some convincing that that any 'failure' wasn't simply as a result of him lifting off the throttle.
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