Thank you for directing me to that. Why was the explanation amongst your preparations for the pre trial and not included in the diary that recorded the actual event? I have another question if I may. I read with interest your mention of the holes beside the head rest being there in 1967 and that they were gradually enlarged and that Donald Campbell's mechanics were addressing some related issue. Did you ever deduce what this was?
Fair questions. The description of the canopy failure was written a long time ahead of the new Bute diaries and included in our preparations to have it explained as one or two false rumours (nowt new there) were floating about and it seemed appropriate to set the record straight. But it wasn't uploaded until much later than expected and then the Bute diaries came soon after so I just left things as they were on the basis that by the time the Bute diary that included the canopy loss came along the story of why we lost it would still be fresh in readers' minds. Really ought to copy it into the other one now that you've mentioned it, just in case.
As regards the holes in the headrest plates, that remains a theory to be tested- well spotted. We noticed that they were modified as time went on, so we drilled them circular based on one photo then, in another, we saw that they had been roughly filed to a larger size and modified them to suit - but what could it mean?
The 1966 crew presumably had a good reason for doing this and also we can presume that the holes were there to allow air to pass through the bulkhead one way or the other so based on that the questions are then then, which way was the air going, how did they know and why did they need to flow more of it?
If it was coming into the cockpit from behind and pressurising the cabin, as we assumed initially, then where was it coming from, how did they know it wanted in and why would they let it in?
The inlets were all sealed up back then with no passage from the bifurcated duct through which the engine actually breathes to the central plenum that remains at ambient pressure - or at least they were supposed to be, especially after the inlets were strengthened. Most of that part of the inlet couldn't be re-used and if it was leaking significantly the crash damage precluded any meaningful investigation but if it was leaking, did they discover this and choose to vent it into the cockpit and if so why didn't it blow the canopy off in 66/67?
We recovered the entire front edge of the canopy opening and it bears absolutely no hint of any extra device that may have tied down the front edge of the canopy with it in the closed position and that is backed up by the photo evidence. Our belief then and now is that the canopy was held down by outside air pressure only.
If there was excess pressure in the plenum it should have vented through a hole in the top provided for cooling the radio equipment that was originally housed in there so unless there was lots
of pressure you'd never know.
They knew that the plenum exploded in the failure that wrecked their engine, but only because the ducts either side of it had the air pressure reduced by the engine at full throttle but it's not inconceivable that someone got their thinking wrong and thought that with a few holes popped in it, it wouldn't explode again but then what could happen to convince them that the holes weren't big enough and that filing them out was required? And then you still need a considerable leak in a structure that had just been heavily modified or, as we provided, a deliberate pathway but we saw no evidence of one.
Nothing really fits without asking more questions so let's look at it the other way and question whether the cabin was pressurising from without and the holes were to let the air escape into
the plenum and thence out though the vent in the top. That would be easy enough to detect. Ted described the pressure building on his chest. So here's an alternate theory but it's virtually 100% speculation except for the fact that there were ever expanding holes in the headrest plate.
When the boat was re-engined in 66 there are pictures of it ready to leave Hayward's Heath quite clearly showing that there are no holes in that plate so they came after the Orph' conversion had been tested on water and by the time of the accident they'd been drilled then enlarged with a file so drilling them hadn't been enough. Bearing in mind that the only aerodynamic change was the Orph' and therefore, potentially what went on ahead of the inlets when the throttle was closed, so let's speculate that an area of high pressure air was building up around the inlet openings and forcing itself under the cockpit rails and that this effect was less pronounced or even absent completely with the Beryl engine. Perhaps air would still vent through the Beryl compressor but the Orph' offered much greater resistance. Then add in the much longer spray baffles and thickened inlet lips and you have to wonder whether these changes would make matters worse.
So now what do we have... Donald coming in from a run and reporting that his ears are popping when he comes out of the throttle so Leo decides a few holes in the headrest plate either side of his head will dump the pressure and allow it to vent through the top of the plenum. But Donald goes out again and complains that it's still happening - file the holes bigger.
It all fits - except the next question has to be, why did our canopy blow off and his didn't?
The simple answer to that - again, speculating here - is that the filed out holes were doing the job. Air was streaming into the cabin under the side rails of the cockpit where they aren't sealed from an area of high pressure air formed ahead of the inlets and partially trapped by the longer spray baffles whilst the lid was being held down by air pressure from above due to the forward motion. But the vent holes won the day and it all stayed down.
So what did we go and do? We deliberately created a passage from inside the inlets to inside the cabin via those same holes that didn't just eliminate the pressure gradient between cabin and plenum that would allow the cabin to vent, it actually increased the pressure in the plenum such that air began coming in the other way adding to the problem and at that point the canopy stood no chance. It would appear that as speed decayed the ram-air pressure within the inlet that we allowed all the way to the cockpit overcame the aerodynamic forces keeping the canopy down and off it went.
Another happening that initially confused us but which fits the above speculation perfectly is that we drilled those vent holes in the sides of the new canopy to make sure any pressure inside the cabin would vent out easily, yet both pilots reported the canopy attempting to lift against the bungees when slowing down. It was inconceivable that we'd not provided enough venting until you look at it from the opposite direction and realise that those vent holes - if the high pressure air ahead of the inlets theory is correct - were in fact perfectly placed such that instead of letting air out, they were actually letting more in!
All guesswork but it all hangs together nicely together and remains a fascinating puzzle to solve next time we run.
I'm only a plumber from Cannock...
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'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler