John Cobb- Crusader/Railton Special

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f1steveuk
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Re: John Cobb- Crusader/Railton Special

Post by f1steveuk » Tue Oct 02, 2012 1:10 pm

Evening!

The lines shown in the two stills are supposed to be there. I'll go through my picture file later for a close up.

Other than that, the front shoe wasn't a weak spot as such, but became problematical, and quickly worsened. I have copies of the original factory drawings, and quite a few unpublished pictures, of the area, plus there was one other factor that contributed other than the structure, the waves and the mix of construction materials.
Steve Holter, UK and France, and sometimes reality....................

Stuart Baker
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Re: John Cobb- Crusader/Railton Special

Post by Stuart Baker » Tue Oct 02, 2012 9:55 pm

KW Mitchell wrote:It is important to understand that Crusader fell foul of the little-known effects of dynamic instability. This was elegantly enunciated by the Norris brothers following analysis of cinematographic recordings of Crusader's demise (The Engineer, 1957).

They showed that the craft suffered violent pitching oscillations of 5-6Hz, initiated by swell, which led to the collapse of the front wedge. Such instability was shown to be related to the height of the CG above the wedges and their inherently large moments therein, plus factors relating to the 'spring-rate' of the wedges.

It is also possible to argue that even if Crusader's front wedge had been strengthened, such extreme forces on a single front wedge would have led to failure - and - even if Cobb had been able to run on perfect water that fateful day, a speed would have eventually been reached whereby the oscillation was inevitable.
Isn't this like having an out of balance wheel on your car? If you can quickly accelerate through the natural frequency of the oscillation, then you should be able to return to stability?

We use this technique to reduce machining cycle times. Traditional logic says that you increase cutter speeds until hitting a resonance and then back off. However, if you characterise the natural frquency of a tool / component / fixture combination, then it is possible to identify a much higher cutter speed that sits between harmonics of the natural frequency. The technique was pioneered by the Advanced Manufacturing Research Centre in Sheffield (who incidentally are also supporting the Bloodhound project http://www.amrc.co.uk/featuredstudy/bloodhound/).

S

KW Mitchell
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Re: John Cobb- Crusader/Railton Special

Post by KW Mitchell » Wed Oct 03, 2012 8:52 pm

The problem with the two analogies you give here, is that it is only part of the system that suffers the resonance. That means that the amplitude of oscillation is constrained by the wheel and its mountings within the car, or, the cutter/chuck etc. within the overall lathe structure/housing. The more apt analogy is to compare what would happen if the whole car oscillated or the whole lathe on it's mountings. If the amplitude at the resonance point was so large then the consequences can be well imagined.

Resonances of relatively low amplitude in hydroplanes can be 'punched' through by accelerating. There is no better example of this than K7 itself; DMC refers to it at 150mph on the first '67 run (see Neil's book, p246) when classical tramping was experienced and the natural damping of the boat limited this to controllable limits as the speed was approached and then exceeded.

Cobb experienced a longitudinal pitching oscillation of such magnitude - and at some 50mph more than K7 - which could not be constrained by the ability of the overall craft to absorb it (due to its design limitations), and, the strength of the most vulnerable part of the design i.e. the single front wedge, to withstand the loads.

As to speed, Cobb would be accelerating hard at that point hence there was no option to accelerate through it when the craft was pitching so violently and a key part catastrophically failed. If it hadn't failed, Crusader's limited dynamic stability would have eventually manifested itself and the craft would have become uncontrollable in pitch - albeit at a higher speed - but with the same disastrous consequences.

polo
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Re: John Cobb- Crusader/Railton Special

Post by polo » Thu Oct 11, 2012 5:45 pm

At a speed record week I spoke to Frank Lyall who was one of the observers / timekeepers at the Cobb/ Crusader trials. He told me that work had been carried out on the front planing shoe including the drilling of holes inside the bulkhead where the planing shoe was. He did not give a reason for it, he just said thats what they did.
If you look at the position of the rudder and its construction and attachment to the rear of the front shoe. it doesn't take a great deal of imagination to think that due to the oscillations that this could have been ripped off the boat due to the continuous resistance changes due to its depth in the water and the hammering the shoe was taking at the same time.
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f1steveuk
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Re: John Cobb- Crusader/Railton Special

Post by f1steveuk » Sun Oct 09, 2016 3:38 pm

Just to let you know. Manuscript 1st draft at the publishers
Steve Holter, UK and France, and sometimes reality....................

ron54
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Re: John Cobb- Crusader/Railton Special

Post by ron54 » Sun Oct 09, 2016 6:50 pm

Well done, looking forward to it.

Karl Ludvigsen
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Re: John Cobb- Crusader/Railton Special

Post by Karl Ludvigsen » Sat Dec 10, 2016 1:28 pm

New to this forum as I am, just a quick note to say that I'm the fellow working on the biography of Reid Railton, in which the Crusader naturally occupies a significant role. I'm closely cooperating with Steve in this endeavour, giving due acknowledgement to his profound knowledge of this and other maritime matters.

My story of course also includes the Malcolm Campbell boats, which are addressed elsewhere in the forum.

Thanks a lot for the many interesting comments made above. Now all I have to do is figure out why and how it happened!

conistoncollie
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Location: Worcestershire

Re: John Cobb- Crusader/Railton Special

Post by conistoncollie » Mon Dec 12, 2016 3:51 pm

Hello Karl,
Very much looking forward to your forthcoming book and wish you good luck.
I remember the Railton Special in the old Science Museum in Birmingham (before it all got moved to the trendy Think Tank).
The Railton Special was always a fascinating exhibit. If I recall correctly it even had a push-button which played some original (rather scratchy) audio tape.

Terminator
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Re: John Cobb- Crusader/Railton Special

Post by Terminator » Mon Dec 12, 2016 5:34 pm

I also recall the Railton Mobil Special being on display at the Old Science Museum were it had been seriously neglected! So much so the seat had to be removed from public display having deteriated very badly!! The seat was then packed away and hidden from view such was the embarresment It was said at the time! The R.M Special was then loaned to the Donnington Collection whilst the new building was sorted were it was given some much T.L.C by Kevin Wheatcroft and Co. And what a splendid job they made of it, the car once again displayed in all its glory. Not stuffed in some dust ridden corner and left to fall into neglect :shock: The Donnigton collection would have been a good home for it but now it is on display in the new building in Birmingham the name escapes me at this time but it was looking good last i saw it.
I wonder if they ever cracked what the lightweight removable body was made up of? Not just normal Ally as i recall. Kevin Wheatcroft had it tested and re-tested and it's make up bemused all at the time! :?:
Novie
"Never ride faster than your Angel can fly"

conistoncollie
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Location: Worcestershire

Re: John Cobb- Crusader/Railton Special

Post by conistoncollie » Tue Dec 13, 2016 6:18 pm

The Railton Mobil Special was acquired by Birmingham Science Museum from, I believe, Dunlop in 1955.
The old museum was a real Aladdin's Cave. Full of dusty corners to explore. And it was free.
The new museum costs around £13 per adult to get in.

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