Getting back to the intriguing business of constructing model boats, we've been asked to make a functioning RC one that is a little out of the ordinary. HMS Hood could achieve 28 knots. SS United States at least 35 knots, maybe 40. That's fast. But this original for this new commission was a little faster. Close to 300 knots.
Earlier this month there was considerable media interest in the 50th anniversary of Donald Campbell's final attempt to raise the World Water Speed Record in Bluebird K7, a hydroplane built around a ridiculously powerful Orpheus turbojet engine borrowed from a Folland Gnat military aircraft. Driven by the outstanding achievements of his father, Sir Malcolm Campbell, Donald took 'Risk Management' to a whole new level. Freudian psychologists would have a field day with this. Disregarding the doubts of the designers and engineers of the K7, he maintained that in order to go faster on water than man had ever done before, conservative thinking was worthless. The boat was fast because at high speed only small parts of the frontal sponsons and the stern rudder and guide vanes were in contact with the water surface. Bluebird was actually more about aerodynamics than hydrodynamics. And in the 1960's these sciences were far less developed than today. Donald Campbell was pushing his luck.
Officially recognised World Record Speed attempts require two runs in opposite directions within a limited time. Bluebird was taken to the Lake District for the attempt. The safe option was to make one run, wait for the water surface to settle, then do the other. Campbell preferred to use a different approach, turning around quickly and making the return run immediately, before the boat's wash had reflected back into the centre of the lake. This was based on the risky assumption the the engine would have enough fuel for the whole exercise. The Orpheus didn't only drive the boat forward, but its high thrust line kept the nose of the craft down. If power failed at high speed the vessel could 'go ballistic'. The strategy had worked before. But, on a cold grey morning on Coniston Water, Donald Campbell's luck ran out.
The actual K7 was raised from the lake bed 15 years ago and is nearing the end of a painstaking restoration. The plan is to use the craft for close up shots, and scenes of it moving at up to 75 knots. But it won't be able to go any faster, so for shots of the high speed runs we'll need a model. A really fast one.
These days, hydroplane racing is a sophisticated sport, but the craft are generally powered by high-performance outboard motors. That's not going to look right for a working K7 model. We'll need to use jet or rocket propulsion to get realistic imagery, with the exhaust plume, the heat haze and other crucial characteristics. In the USA amateur rocketry is a popular, if rather scary, pastime. And real working jet engines have been built in quite small sizes: for example in the movie '11 Days' - about the Cuban Missile Crisis - the 1:6 scale models of Lockheed U2 aircraft were RC controlled and jet powered. So it's not entirely 'uncharted territory'
The initial idea is that the model will be filmed on real water, possibly back at Coniston. We are taking advice on the most practical model scale, which has to provide authentic stability and 'scale effect' but also keep the weight as low as possible. Bearing in mind that the model may be risking the same fate as the full size boat, it's been suggested that we guide it along a very long carbon fibre monofilament line, which would be invisible on film and be stretched just above the water surface. To make the hull and sponsons, we'd probably make wooden 'bucks' and use these to vacuum form the shapes. For rigidity and 'unsinkability' we could fill the sections with lightweight polyurethane foam. My guess is we would need quite a few hulls, to cope with 'mishaps'...
I'm not aware if anything like this has been done before, so I don't know if it's really feasible, and any info or ideas would be welcomed.