The Last run....

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Jordangbr
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Re: The Last run....

Post by Jordangbr »

Can anyone explain this manoeuvre in more detail and as to why it was done to get the boat up on the plane?

"This needs a delicate manoeuvre. We are doing seventy. Apply brake sharply, turn left just as sharply, and up comes the back of the boat."

I'm trying to imagine how this manoeuvre works in my mind. :?
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Renegadenemo
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Re: The Last run....

Post by Renegadenemo »

Turning left is using gyroscopic precession to pick up a sponson and unstick it. The only way I could see the brake helping to lift the back of the boat is if were to behave in the same way as a hydrodynamic device called an interceptor. It's basically a surface that sticks vertically down into the water. You'd imagine that would provide nothing but drag but what it actually does is push a wedge of water ahead of it forming a ramp that behaves as a lifting surface. Perhaps the brake at seventy behaved in this way and helped lift the back end.
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chrissie 123
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Re: The Last run....

Post by chrissie 123 »

hi i was there on the day ,and although i was only 9 at the time I dont remember any completed runs at all, all I remember was the first half of the run from coniston up the lake and then on the second half when the boat turned round heading back and that was the fateful one . Dont think the engine cut out .

Excelsior2007
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Re: The Last run....

Post by Excelsior2007 »

Renegadenemo wrote:I always thought it was a tall order, deploying the water brake in those circumstances, and that he was either onto it very soon in the upset that ended in the crash - in which case he didn't mention it and that's out of character - or he never got near it. Lew told me it inched into the water quite slowly because it was a violent contraption in how it affected the boat. These days I'm more inclined to believe that it deployed uncommanded after the crash.

Here's a wild theory possibly worth exploring. Two things to consider. One, I'm sure I've seen a pic of K7 in her boatshed with the water brake in the down position but I can't put my hands on it. Any takers? There'd be little reason, except possibly if something was being tested, to deploy the brake with the boat out of the water or to travel back to the slip with it extended. Two, doesn't it say on the startup checklist, 'brake up'? That seems an odd place in the operating procedure to put such a reminder. Surely it would be better included in the shutdown. Unless, of course, the brake was in the habit of lowering itself overnight from the accumulator pressure.
I think I might be able to help there. I think there's a picture of the water brake in either Leap into Legend or Donald Campbell: The Man Behind the Mask. I'm not sure which, because I currently do have access to them.

Excelsior2007
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Re: The Last run....

Post by Excelsior2007 »

Mike Bull wrote:
I think I might be able to help there. I think there's a picture of the water brake in either Leap into Legend or Donald Campbell: The Man Behind the Mask. I'm not sure which, because I currently do have access to them.
See my picture post on the previous page!
Sorry, Mike hadn't read the previous post. My bad.

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mtskull
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Re: The Last run....

Post by mtskull »

Renegadenemo wrote:Turning left is using gyroscopic precession to pick up a sponson and unstick it. The only way I could see the brake helping to lift the back of the boat is if were to behave in the same way as a hydrodynamic device called an interceptor. It's basically a surface that sticks vertically down into the water. You'd imagine that would provide nothing but drag but what it actually does is push a wedge of water ahead of it forming a ramp that behaves as a lifting surface. Perhaps the brake at seventy behaved in this way and helped lift the back end.
Sorry to be a smart*rse, but how can you use gyroscopic precession to pick up a sponson?

The only source of gyroscopic effect in Bluebird is the spool of the Orpheus, the axis of rotation being approximately in line with the longitudinal axis of the boat. Therefore, any gyroscopic effects can only manifest themselves around the other two axes; i.e. gyroscopic precession will cause a turning moment to have a secondary effect in pitch, and vice versa.

Correct me if I'm wrong, but as I understand it the Orpheus rotates anticlockwise when viewed from astern. Therefore, the secondary effect of a sharp left turn would be a tendency for the bow to pitch down and the stern to lift. Might this have been the intention all along, especially if the effect of the water brake on its own was insufficient to lift the stern?
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Renegadenemo
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Re: The Last run....

Post by Renegadenemo »

Sorry to be a smart*rse, but how can you use gyroscopic precession to pick up a sponson?
Turn right - I always get that arse about face - to pitch the bow up and as the Cof G is above the waterline the boat leaned out of the turns and would tend to pick the inboard sponson out of the water. That's how I've always assumed it to work.
I'm only a plumber from Cannock...

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bluebirdsback
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Re: The Last run....

Post by bluebirdsback »

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Renegadenemo
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Re: The Last run....

Post by Renegadenemo »

I've often wondered whether the gyroscopic effect played a part in the accident because at the end of the 297mph run Donald made a left hand turn and, as I can't imagine K7 having much rudder authority I've always assumed it was quite a wide turn, then he set off again. In his commentary he makes reference to, 'straightening up on track' and 'passing close to Peel Island' so he was clearly over to the east side of the lake and a short time later he'd have had to make a right steering input to begin tracking up the centreline, which would've tended to lift the nose and the right hand sponson. Considering he was on-limits this time... what if?
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes.

'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler

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mtskull
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Re: The Last run....

Post by mtskull »

Hopefully there might be an engineering/mathematical wizard watching this forum who can do a swift analysis of the rotating mass v. RPM of the Orpheus, then weigh in and tell us whether the gyroscopic effect was likely to have been significant.
-On second thoughts, I'm in a hotel in Toulouse that is full of Airbus boffins. Think I'll just nip down to the bar and ask one of them.....
(15 min later).... b*gger. Bar full of Airbus staff and not a single design engineer amongst them :(
Last edited by mtskull on Tue Mar 30, 2010 7:04 pm, edited 1 time in total.
Obstacles are those frightful things you see when you take your eyes off your goals.

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