Bluebird K7 Latest

[Equus]

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

[Turkish91]

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

Absolutely fascinating read.

[Jim H]

Equus,

Thank you very much, just exactly what I was hoping for.

I’ve often wondered also why the Folland Gnat fin was fitted, it’s not really covered in the books that I have - only that it was fitted.

My extremely limited knowledge of aero, I can consider that it certainly would have had some effect on longitudinal stability. However, one wonders how much actual consideration (overall) it’s inclusion had at the time on the overall dynamics of the boat.

Also, I’ve read a few articles regarding the duck strike on the spar, again overall perhaps another small contribution to the overall design being operated well above it’s safe envelope.

Many thanks again for your insightful knowledge.

[PinkTornado]

Jim H said:

Over the years it’s been analysed, the lack of jet thrust from Bluebird as it left the surface. Do you think the lack of refuelling affected the boats trim (over the still present wash? Could also have lead to the engine flaming out?

The engine also flamed out on smooth water as he was slowing down towards the end of the FIRST run. Campbell comments that he is 'relighting like mad' in his radio transcript, i.e, using the compressed air starter to spin the engine back up and get it re-established. This fact alone may have been why he did not refuel- he had, or thought he had, insufficient air left on board to start the engine again after a fuel stop.

In 2018 with all of Campbell's fuel set up the Bbp found that the boat could flame out even with fuel in it and postulated that this was possibly what happened in 67. Add that to all the excellent material that Equus posted above regarding the lack of stability and other factors and that's a bad morning out for Campbell.

Edited by PinkTornado on Thursday 15th February 14:58

[Equus]

Jim H said:

I’ve often wondered also why the Folland Gnat fin was fitted, it’s not really covered in the books that I have - only that it was fitted.

My extremely limited knowledge of aero, I can consider that it certainly would have had some effect on longitudinal stability. However, one wonders how much actual consideration (overall) it’s inclusion had at the time on the overall dynamics of the boat.

It does seem questionable and, like you, I've yet to come across a good explanation.... there are references to K7 having a slight tendency for snaking at times, but it doesn't seem to have been a pronounced issue.

One wonders (speculating) whether it might have been something to do with Campbell's crash in CN7, which definitely was caused by a lack of yaw stability and which had been corrected on the rebuilt version by fitting a large tailfin. Perhaps Campbell (who with due respect was only semi-educated on technical matters) might have insisted upon the addition to K7, for that reason?

[Jim H]

Equus said:

Jim H said:

I’ve often wondered also why the Folland Gnat fin was fitted, it’s not really covered in the books that I have - only that it was fitted.

My extremely limited knowledge of aero, I can consider that it certainly would have had some effect on longitudinal stability. However, one wonders how much actual consideration (overall) it’s inclusion had at the time on the overall dynamics of the boat.

It does seem questionable and, like you, I've yet to come across a good explanation.... there are references to K7 having a slight tendency for snaking at times, but it doesn't seem to have been a pronounced issue.

One wonders (speculating) whether it might have been something to do with Campbell's crash in CN7, which definitely was caused by a lack of yaw stability and which had been corrected on the rebuilt version by fitting a large tailfin. Perhaps Campbell (who with due respect was only semi-educated on technical matters) might have insisted upon the addition to K7, for that reason?

I’m just wracking my faded memory banks here? Didn’t the Gnatt fin become gratis with from one of the aircraft that was broken for one of Bluebirds engines.

I’m sure I read that somewhere.

However, I do agree, it’s installation could have been as a result of the CN7 crash.

[PinkTornado]

Jim H said:

I’m just wracking my faded memory banks here? Didn’t the Gnatt fin become gratis with from one of the aircraft that was broken for one of Bluebirds engines.

I’m sure I read that somewhere.
.

Yes, the fin came from the same donor prototype Gnat trainer as had one of Campbell's two Orpheus engines.

[Jordie Barretts sock]

Just catching up.

Equus, I knew she tramped, but is it not also correct she lifted and dropped on the two sponsors together? I'm not explaining myself well, but basically also 'rocked' fore and aft as well as side to side? Which is why she back flipped? As in, the lift on the bow got larger and larger and running over her own wake effectively gave her the 'leg up' she needed?

[dukeboy749r]

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

Absolutely fascinating read.

Indeed. Thank you @Equus

[99hjhm]

The sad thing about all the many previous removed Pistonheads threads on K7 is the loss of all the knowledgeable posts of Equus and a couple of others that posted regularly on many aspects of the K7 saga and its history.

Ref the Senna/Imola posts, fully understand, even BBP spent many years fighting to run K7 on Coniston, so I guess they had the approval of the Campbell family in doing this. The Aston Martin Simonson lost his life in at Le Mans in 2013 (GTE-004) also appeared at Le Mans in (2014?), 2015, 2016 and 2017, with his co drivers still racing the car!

[Equus]

Jordie Barretts sock said:

Equus, I knew she tramped, but is it not also correct she lifted and dropped on the two sponsors together?

Not as far as I am aware. What you're describing (straightforward pitching) is known as 'porpoising'. It's what killed John Cobb, in Crusader (ultimately because of structural failure, though it's been postulated that the violence of the porpoising was such that he was already unconscious before the hull failed... but that's another long and interesting story).

You need at least one fixed point (or axis) for the 'bouncing' end of the boat to react against, so you tend to get either tramping or porpoising. Both together would be what we'd refer to technically as 'bouncing around all over the fking place' and would be so messy that it wouldn't maintain a cyclical rhythm long enough for anyone to recognise it as cyclical before the boat tumbled and destroyed itself.

It's difficult to describe (I tried to do so above, with the description of rotation around a conical axis), but tramping results in a nose-up pitch of the boat anyway, though. Water offers so much resistance at that speed that the sponsons can only bounce 'up' and not 'down', on average, if that makes sense, so the effect of tramping is to pitch the hull up.

As a general rule, porpoising seems to afflict reverse ('tricycle') three-pointers more (and monohulls, of course), whereas conventional three pointers tend to suffer from tramping/sponson-walking in the same circumstances. It presumably stems from whether it's the single planing surface or the two that are 'excited' into oscillation first, although it's not well understood even today.

[Jordie Barretts sock]

Pitching. That's it.

Thanks again Equus.

[Jim H]

Morning again Gents,

Just another quick question which has puzzled me. When the runs were carried out at Bute, Bluebird ran without the K7 Infinity / Unlimited roundel markings on the sponsons. Was there any particular reasons for that?

After such a lengthy and involved restoration, I can’t believe it was an omission, or would have been that difficult to recreate?

[PinkTornado]

Jim H said:

Morning again Gents,

Just another quick question which has puzzled me. When the runs were carried out at Bute, Bluebird ran without the K7 Infinity / Unlimited roundel markings on the sponsons. Was there any particular reasons for that?

After such a lengthy and involved restoration, I can’t believe it was an omission, or would have been that difficult to recreate?

It simply wasn't finished, but has them now.

[DP14]

On the DM website today: https://www.dailymail.co.uk/news/article-13146489/...

[Jim H]

That was quick.. https://www.bbc.co.uk/news/articles/c6p49xypgv2o

[Jordie Barretts sock]

Excellent news.

[MB140]

Jim H said:

That was quick.. https://www.bbc.co.uk/news/articles/c6p49xypgv2o

There’s a long time between now and then for there to be an accident. Or something go wrong. I will believe it when it’s reported as journey complete and the craft is in the correct condition.

[MarkwG]

Updated - https://www.bbc.co.uk/news/uk-england-68434707

[ecsrobin]

I never knew this bit:

His initial plan had been to "nick the tail".

"It's true... I fully intended to hack it off and add it to my trophies, but I couldn't find the wreck immediately and in the four years it took I fell in love with [Bluebird] K7."

Says all you need to know about the guy, what other trophies has he stolen?