FAQ

Russ
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Re: FAQ

Post by Russ »

The FAQ's that I have are a bit more technical, but looking at the photos I'm left wondering how K7 worked. By that I mean;
How much of K7 was in contact with water when on the plane, and how far into the water did she sit?
How did the planing wedge work? In a "pic of the day" a while back it looks like an initial ramp and then level to the rear of the boat? That seems like a large area in contact with the water to be described as a "three-pointer", or have I mis-understood the photo?
Why was K7 so difficult to get on the plane?
How big is the deceleration when K7 comes off the plane? The recent photos of the deceleration give an indication of what she had to be built to withstand, but I wondered if it had ever been measured?
What are the acceleration / deceleration times and distances for say, 0-100, 100-200, 200-100, 100-0?
How does the water brake generate so much braking effect if it's only a 6" rod?
Why doesn't K7 have a water brake at the front as well to balance the retardation effect instead of it all being at the back and acting as another pivot point?
Why is the fin so effective, how does it acheive such a stabilising effect given that it presents such a narrow profile to the airflow?
Why didn't K7 have a tailplane fitted to generate downthrust and cancel out lift?

Renegadenemo; did you get the PMs I sent a couple of weeks ago about DVD3 and a BBP suggestion? I also sent one to Malcom last July responding to the Active support at Consiton 2011 thread; did that one get through?

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Renegadenemo
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Re: FAQ

Post by Renegadenemo »

Whoa! They're not FAQs at all so I'm giving that lot a body-swerve. Anyone?
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klingon
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Re: FAQ

Post by klingon »

I'll try a couple and mebbe someone can help with the rest!
How much in the water?--virtually nothing-just the "footprint" of the planing shoes on the sponsons which is very small and the planing surface of the main hull at the rear which is just as small-K7 "skated" on the surface to use common parlance.

Tailplane-not allowed at the time by the water speed record rules-no "variable lift surfaces"-(I think from what I can gather)

Acceleration-Check with the "anoraks" but I can't find figures anywhere-K7 was more just speed over a measured mile-not time in getting to that speed.
Front water brake-possibly a front brake either in conjunction with the back brake or singly would have tended to pitch K7 up on her nose in a forward roll-try slamming the front brake on on a bike and you'll see what I mean!-but again that's only a guess. :D
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Renegadenemo
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Re: FAQ

Post by Renegadenemo »

Just a daft point that would most likely be overlooked. Supposing a front brake was considered (and deploying such a thing would almost certainly result in a nasty accident) about the only place it could be mounted would be F-19 between Donald's feet with the ram on the inside running through a watertight lip seal to the outside. Because of the distance between the water and the underside of the boat in the planing position it would require a much longer ram than at the rear where it's mounted outside the boat and right down on the back of the planing shoe requiring minimal extension before it meets the water surface. The twisting loads would therefore be immense requiring substantial strengthening of the frame within the cockpit and if it did get loose it would impact squarely in the region of Donald's wedding vegetables... I suspect Mr Norris would have put that idea to bed pretty quickly.
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quicksilver-wsr
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Re: FAQ

Post by quicksilver-wsr »

I'll answer one ...

"How does the water-brake generate so much braking effect if it's only a 6" rod?"

The answer is that water is 800 times the density of air. It's very draggy and viscous. So you only need a device that's very small to create immense drag when the speeds are as high as they were with Bluebird.

Bear in mind that drag increases as the square of the speed. That means that the retardation force on the water-brake at, say, 200 mph isn't twice what it would be at 100 mph - it's four times as much!

This fact of physics tends to be overlooked by many, who simply don't appreciate the magnitude of the forces involved in going very, very fast on water.

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mtskull
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Re: FAQ

Post by mtskull »

Russ wrote: Why is the fin so effective, how does it acheive such a stabilising effect given that it presents such a narrow profile to the airflow?
It is a bit tricky to explain without the aid of diagrams, but here goes: Take a dart and hold it so the flights are vertical and horizontal; think of the fin as the flight that points vertically upwards. When the dart is flying straight it presents only its edge to the airflow and so creates very little drag, but if there is any sideways (yawing) movement, then the flight presents an angle of attack to the airflow and generates an aerodynamic force in the opposite direction, thus pushing the dart back into a straight line.

It's the same with Bluebird's fin; it only needs to be so thick as to be strong enough to do the job and would probably have been even thinner if it had been designed from scratch instead of being transplanted from the same aircraft that the engine was taken from.

Now, before someone points out that a dart also has flights on either side and above and below its shaft, the horizontal flights would be the equivalent of the tailplane (absent on Bluebird, as already discussed) and the role of the downward pointing flight is fulfilled by a tiny fin attached to Bluebird's transom.
The reason that it doesn't need to be anywhere near as big as the aerodynamic fin is due to the much greater density of water (as previously mentioned), enabling a much smaller fin to generate the equivalent stabilising force.
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polo
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Re: FAQ

Post by polo »

rudder drag = 2 x 1/2p[w]s[r] u xu [thats u squared]c[rf] according to Ken Warby.

symbols:
p[w] is the density of water
s[r] is the rudder wetted surface area, one side
u is the speed in metres per second
c[rf] is the rudder fricton coefficient[ this leads us into another equation]

so with my limited math, I would presume the brake would have the same or similar formulae.
The large bit of course is the speed in metres per second squared and at 500kph it is [according to Ken!] 139 x 139

I'll let you lot work it out.
All the calcs for Spirit are on Kens web page.

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Renegadenemo
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Re: FAQ

Post by Renegadenemo »

so with my limited math, I would presume the brake would have the same or similar formulae.
Reckon you'll have to brush up on your integral calculus to work out the varying drag around the front half of a circular piston rod. Plenty different to a rudder blade...
I'm only a plumber from Cannock...

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Russ
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Re: FAQ

Post by Russ »

Thanks to all who've explained in such detail, it's appreciated.

regards

Russ

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klingon
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Re: FAQ

Post by klingon »

No problem Russ- but one or two at a time eh?-our brains no function beer well without! :lol:
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