The Bluebird Project

'Water all over the place'

A pic taken in 57, with the shallow sponsons, to illustrate the water flow as K7 gets up on plane. For the Aix le Bains demo in 58 and the Swan river, Perth demo in 65, the area between the spars was covered over with an ally sheet, attached to the underside of the spars. This had three effects, more aero lift, less drag from the leading edge of the rear spar and better spray baffling. Just the job when you want to do low speed demo's....

K7, equipped for low speed running with ally sheet attached the the underside of the spars. Perth Jan 65

This had three effects, more aero lift, less drag from the leading edge of the rear spar and better spray baffling. Just the job when you want to do low speed demo's....

We considered this option for low speed demos but look again at the picture of K7 running. The rear spar is completely submerged as is the sponson. The water is only a few inches below the inlet deck so K7 must be dangerously deep in the water at this point. Hopefully things improved as she went faster but she'd be using a huge amount of engine thrust overcoming that lot so I'm unconvinced.

The pic' of bluebird taxi-ing also shows that the earlier curved perspex spray baffles weren't doing the job as water is clearly being ingested into the Orpheus' compressor. Interestingly a small amount of ingested water increases the mass flow - and hence thrust - and was used to do just that in military jet engines in the 50's and 60's. Too much of course and it puts the 'light' out!

I agree that the plate between the spar booms would provide little lift at low speeds. It would have had to have been well in excess of 100-150mph before having any effect.

Incidentally , Bluebird's thrust to mass ratio of ~ 1.00, is approaching that of high performance jet fighters. In theory it could have propelled the craft to 400mph or more or up to when drag limitations occurred. Stopping it from flying, however, would have been another matter and fate declared it's hand all those years ago ----------------!

I actually discussed the closed spaces between the sponsons with Prof John Stollery at Cranfield. He told me the boat needed a fair amount of way on her for the baffles to make a difference. 100mph +. Considering that the thrust / drag curves show K7 lifting at between 65 and 70mph I never quite understood what the baffles were designed to achieve. We've investigated everything from temporary hydrodynamic devices to redesigned planing surfaces to take some ofthe strain out of getting her onto the plane but the best option involves throwing off a lot of excess weight and moving the CofG aft a few feet. This has the effect of seriously reducing her potential top speed but that's not a bad thing either!

Renegadenemo wrote:I actually discussed the closed spaces between the sponsons with Prof John Stollery at Cranfield. He told me the boat needed a fair amount of way on her for the baffles to make a difference. 100mph +. Considering that the thrust / drag curves show K7 lifting at between 65 and 70mph I never quite understood what the baffles were designed to achieve. We've investigated everything from temporary hydrodynamic devices to redesigned planing surfaces to take some ofthe strain out of getting her onto the plane but the best option involves throwing off a lot of excess weight and moving the CofG aft a few feet. This has the effect of seriously reducing her potential top speed but that's not a bad thing either!

Not being a 'boat' man I might be very wrong, but to use the aircraft parallel, moving the CoG aft increases instability both in direction and pitch. Might this make Bluebird more difficult to control with a reduced stability margin?

I would also have thought that the consequences of the bow becoming lighter would have made it more vulnerable to choppy conditions ---------?

Aesthetically as well, tail heavy aircraft look less purposeful and realistic in the sky ; might Bluebird look the same in the tests if it's planing along 'a--e end' down?

Incidentally, I wonder if the real reason for uprating to the more powerful Orpheus from the Metrovic Beryl was the amount of thrust required to get the craft planing which, as you state, was very considerable. Forgive me; another aviation analogy: I was involved in an Airshow many years ago when the Red Arrows arrived the evening before and parked-up on the grass alongside the runway. Overnight it rained, and their wheels sunk in - they had to apply full power to extricate themselves from the 'clarts' (Red One was very embarrassed ------------!).

The Orpheus' extra thrust would certainly help in the initial high drag phase - which would be very useful on relatively short waters such as Coniston. Once on the plane, however, and with little drag I wonder whether the relative accelerations were that different ---------------?

Another one of Eddie Whitham's FANTASTIC photographs, taken on the 14th December 66, as K7 gets into her stride. A work of art... in all senses...
Photograph copyright: Eddie Whitham

And in that shot you can clearly see that the main spar is clear of the water. Incidentally, if you find a pic of the cockpit wall, and the one on the cover of 'With Campbell at Coniston' is a good example, you can see a diagonal line of screws going up the side of the boat. They're into captive nuts on the inside and don't attach to anything. I've always assumed they were to fix the baffles at their inboard edge. Perhaps Neil will post a pic?

abolutely! just stunning!!!

This one Bill I think you mean. I thought these fill in panels were used for two reasons, 1 to increase the hydrodynamic lift when getting on the plane and 2 to prevent water ingress into the intakes inless than suitable water conditions also when getting on the plane. I would have servere reservations on using these on a first time run due to decrease in the safety margin that would result. I know Ken Norris stated that the boat would flip at 150mph when this space is filled in, alittle to much throttle on a first time run and you could end up with another 04/01/67.