rob565uk wrote:I agree that the Beryl powered version of the boat has a good overall look to the way it performs. I recall reading somewhere that it was once timed at around 285 mph when the pitot was blocked or failed and Donald couldn't determine his true speed. It kind of makes one wonder if he might have been better keeping the Beryl for the final attempt. Leo and the Team understood that setup very well and given some time and resource, could have really fine-tuned it to extract the maximum performance. Must admit though, I haven't done the maths and don't know if the nominal 3750 lb max thrust of the Beryl would have got K7 over the 300 mark. Unless some kind of additional short term boost could have been engineered - rather like that on the Orpheus version.
Re K7's top speed with the Beyrl, we calculated when doing the book that a bare 300mph was the absolute limit. Given K7's average of 286 on the first run in 1956 and 283 on the first run of the 64 record, the peak on both runs would have been just short of 300mph. The team were well aware of the knife edge they were operating on in terms of Bluebird's tendency to climb off the planes and run in ground effect. This tendency was less marked in higher operating temps, with less lift, but also lower engine thrust. In 56, K7 took flight as DC backed out of the throttle at the end of run one, and gave DC one hell of a fright. The ambient temp that September was in the mid teens in centigrade. In 1957, at near zero temp, K7 was on the fins at anything over 260mph. In 64, with a better configuration afforded by the fixed stabilising fin and revised sponson fairings, and a higher ambient temp, K7's performance was just about perfect. The higher ambient temp in the mid twenties centigrade helped make the difference.
Contrast that with low single figure ambient temp on Jan 4th 67, more thrust and a much higher peak speed, K7 had reached the edge and crossed over its safe operating envelope.
Ted makes a good point about K7 appearing to perform that much better with the Beyrl than the Orpheus. This is indeed something which we noticed when doing the book, and I think the team were becoming very aware of the different running characteristics, and that running in very low ambient temp did pose some potential issues.
It's perhaps for that reason that DC always preferred, if it had been possible to go back to Dumbleyung for the attempt on the 300. The lack of finance never allowed that to be a realistic option. The original plan of Coniston in September 66 would have to be the compromise. Little did they know they would still be there in January 1967...