The model boat programme
As ThrustSSC aerodynamicist Ron Ayers once said, the problem with record breaking vehicles is that they are both the prototype and the finished vehicle – which means that no matter how much research you do, when you’ve built the vehicle the only way to prove the design is to run it. If you’ve got it wrong it’ll be hugely expensive and even worse, potentially very dangerous.
But there is a way to test theories and collect data and it’s one that goes back to the very earliest days – use powered scale models. Just about every form of advanced vehicle design has been tested in model form – the larger the scale the better. To be really useful, the model must be a “true scale model” not just a representation by taking into account size, power, weight, materials and the actual test environment.
There are equations and rules to determine this, many of which can thankfully be discounted for our purposes. Railton and Vospers built a number of test models before the original K6 Crusader design was finalised so all we have to do is scale down that design.
Len Newton has done exactly that to magnificent effect. And for the follow up design which we have designated C2 for simplicity, we have the large scale wooden test model that remained largely unknown about until it came into Richard Noble’s possession. Is that Railton’s final design or just the start point? We have no real way of knowing until we build and test that model to run alongside the existing K6 Crusader.
So, although we will use an engine of identical power and consider how we might equalise weight if needed, the later model is of composite construction. This means that as we test, collect results and draw up conclusions, we can if necessary evolve that shape more easily in a way that Railton himself might have done.
Here from builder Len Newton is an explanation of each of the test boat engines:
The boats are named and referenced according to their type, method of construction and power plant. The LN 78 RIF using a code given to my engines by James Hill of the Gas Turbine Builders Association as these are constructed using the core of a commercial turbo charger – which means the compressor and the turbine share a shaft which connects the two. The rest of the engine including the hybrid ceramic bearings, combustion chamber, nozzle guide vanes etc are all home built. The engine produces approximately 30lbs of thrust at 90,000 rpm. The LN80 denotes my initials plus 80 as the diameter of the compressor. RIF is Radial Inflow. Most or nearly all commercial turbines are axial flow turbines. LN 80 RIF is a variation of the same type of home built engine.
I have built a few of these but the turbines do not cope well with the heat made from cutting and twisting a disk nemonic instead of inconel. So I decided to go with a turbocharger core as this was designed for the heat and the stresses incurred. The only difference is that the combustion gasses are re directed from the annular combustion chamber into the turbine wheel centre by the guide veins, hence Radial Inflow. The Crusader 1 and Crusader 2 carbon fibre test boats use versions of my engines.
The Crusader 2 fibreglass test boat is heavier and so requires a more powerful engine. The Mammoth engine was commercially available, produces 50lbs of thrust and is also slightly lighter. To reduce weight even more, I built a lightweight jet pipe from rolled and spot welded titanium to withstand the heat.
My interest in such things came from my father-in-law who was of the De Havilland Boys and assigned to John Cobb’s Crusader team to look after the Ghost engine that powered it. I have one of their original pulse jets in my garage which we managed to get running – you think gas turbines are noisy! I also have lots of small black and white pictures of this engine powering a plane and flying on a control line at Hatfield in 1948. He told me that they build a small gas turbine, but it didn’t run very well. All this pioneering work was what got me interested and I’ve been building engines for the last 25 years or so. Many ended up as glorified blow torches while some ran with difficulty – all to do with fluid dynamics. I still have development work to do with the 80 size engine. Although it’s a direct copy of the 78 it doesn’t yet self to self sustain. Small changes will no doubt overcome the issue which just needs lots of time to modify and test. But we have other engines already until then.
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