The Last run....

[mtskull]

the engine would have spooled down uncommandedly as the engine-driven piston pump cavitated causing a loss of thrust and the aerodynamic centre of pressure to move aft along the underside rather quickly.

The engine driven pump of a turbine engine doesn't depend on the booster pump(s) for the engine to run. It may well have been necessary for the booster pumps to run in order to achieve the absolute maximum thrust, but failure of one or more booster pumps would not have caused a catastrophic, sudden and total loss of thrust.

[Renegadenemo]

The engine driven pump of a turbine engine doesn't depend on the booster pump(s) for the engine to run. It may well have been necessary for the booster pumps to run in order to achieve the absolute maximum thrust, but failure of one or more booster pumps would not have caused a catastrophic, sudden and total loss of thrust.

I'll think you'll find in this case that it would. LP boost pressure on the Orph' installation was essential. In the Gnat the LP pumps are switched on until the engine spools up after which the tanks are pressurised by bleed air from the delivery case then the electric pumps go off again. The engine would doubtless start and run to a degree without the LP pumps or tank pressurisation but the piston pump is designed to run with an input pressure of around 25psi and will cavitate without it.
Now here's the scary part... It only takes an interruption in the supply for 1/10th of a second to flame out an Orph' at full throttle so losing the LP boost under those conditions would do very nicely indeed.

This was actually one of the first issues on the table when I first went in search of help with the fuel system; the engineers raised their eyebrows as one when I described the haphazard nature of K7's LP fuel setup, namely one boost pump hastily added along with a swirl-pot where the in line fuel filter had lived the day before and a second in a small, auxiliary fuel tank down in the bilges both wired together into a ropey-looking relay and then to a switch on the dash. Untried, untested and no tank pressurisation either.

Another consideration is that the fuel tank was never modified to suit the Orph'.
Look at pic's of the Beryl installation and you'll see that the main fuel line came out of the tank near the top then hopped a short distance aft to where it met the inlet of the Beryl fuel system - presumably a gear pump upstream of the main pressure pump. This wasn't altered for the Orph' meaning that fuel had to be siphoned from the tank. It wasn't even gravity fed so the pressure dropped from whatever head was created by the depth of fuel in the tank to zero at the outlet then back to whatever head it created back down at the aux' fuel tank so the chances of the system vapour-locking were greatly increased for no good reason. Nor did they bother fix this obvious problem when they broke the air intakes and had to gut the hull from F-10 to F-15, which means removing the fuel tank to shift the inlets. Having to siphon its fuel didn't seem to upset the Beryl but it was far from ideal considering the inlet requirements of the Lucas piston pump fitted to the Orph' and the submersible LP pumps designed to operate with a head of fuel above them.
The LP system offered a dozen ways to flame out the engine and may well have done so. As I said - let's get it all working again and find out how it performs.

[mtskull]

I'll get my coat....

Seriously, thanks for that Bill. I guess it was too great an assumption that a 1950's military turbojet with a lashed-up fuel system would behave in as predictable and benign a manner as a modern, twin spool turbofan equiped with nice things like variable stator vanes and FADEC.

Re. your description of the fuel system; that is just too scary for words!

[ace_chris]

"Now here's the scary part... It only takes an interruption in the supply for 1/10th of a second to flame out an Orph' at full throttle so losing the LP boost under those conditions would do very nicely indeed."

Having had some experience of miniature gas turbines, completely see where Bill is coming from. These are modern, FADEC controlled units not the lashed up Heath Robinson affair of the Orpheus and even they will flame out if their fuel supply is interupted.

However watching the film of the return run on 040167, I find it hard to see where the engine may have flamed out, but thats not to say it didnt happen! Chris

[Renegadenemo]

...which again brings us to the boat clearly producing no jet efflux as she stands on her tail. Among the theories and conjecture, that seems to me to be the one absolute fact?

Look at it this way - a healthy 701 Orph' according to Bristol Siddeley's bumf should be making 4700lbs of thrust then they reckoned they'd turned the wick up a little so in theory she should've been making enough thrust to at least hold her own weight if not a little more. Now compare the effect below the jetpipe on the water surface with the jetpipe pointing straight down (or rather the lack of any) and the effect as the boat sets off with the efflux parallel to the water surface. The engine was definitely spooled right down when the boat took off. But that's not the best evidence. One of the first things Steve Moss said when he looked at the engine - something any trained air crash investigator (and Steve is one of the best) will spot instantly - is that the engine definitely not producing power when it crashed because jets ingesting a big mouthful of water pull their compressor blades off in a forwards direction in an effort to move a much heavier medium. All that had happened to K7's blades was that the first stage had flexed forward a little and rattled around the inside of the guide vane ring. No power, see?

[quicksilver-wsr]

Reference Mike's last remark ...

"...which again brings us to the boat clearly producing no jet efflux as she stands on her tail. Among the theories and conjecture, that seems to me to be the one absolute fact?"

(Bill, I see you have posted while I have been writing this, so my post makes no reference to yours.)

I'm confused as to why there is further conjecture on any of this, as Bill has stated quite categorically that the forward engine-mount failed during K7's final run. That one, single factor is more than enough to cause a catastrophic accident. So why the need for add-on theories, if the accident damage visible on the wreckage of K7 already presents an open-and-shut case for the cause of the accident?

Two points about K7's jet efflux not impinging on the water's surface as the boat reared up into the air ...

The first point is that Ken Norris was adamant that film analysis of K7's final run indicated that Donald was slowing down considerably in the latter part of the run, because he had hit rough water caused by his southbound pass and realised he needed to throttle back quickly if he was going to stand any chance of bringing the boat home in one piece.

A throttled-back engine would, of course, produce less jet-efflux impingement on the water's surface. Maybe none at all.

The second point, which seems to be overlooked time and time again by people debating the accident down the many decades, is that as soon as K7's nose raised more than a few degrees off the water, the air-intake would stall and the engine would then instantaneously start spooling down - again, producing significantly less jet-efflux impingement on the water's surface.

I'm not sure why people think the Orpheus would still be merrily thrusting away when it had been (a) throttled back considerably - and maybe completely - by a driver who, rightly, sensed disaster and (b) had been completely starved of air by a profoundly stalled intake.

But, as said, if the forward engine-mount broke, all is academic. The engine would have stopped producing thrust the moment it broke free inside the hull, and the accident would be in full train.

[Renegadenemo]

When we have one of ours running, I shall conduct experiments with a bowl of water.

I think it would be much funnier to conduct experiments with Mike tied to a stick...

[klingon]

Tried it-they turn into an A1 flavored fireball and vaporise! -hot dogs last a bit longer but boy do they get crispy!

[quicksilver-wsr]

I’ll concede that, Mike. What you say in your most recent post makes sense, logically.

I cannot argue with you, in any case, as no-one really knows how much efflux that engine was producing when Bluebird’s nose pointed straight up at the sky.

But my comments about Donald throttling back, and the air-intake stalling – I’ll put my Quicksilver team shirt on them. The first bit of information I got directly from Ken Norris, who studied the film and worked out the speeds. The second bit of information is just a well-known fact: that air-intakes stall when they are put at crazy angles.

(Unless, of course, they are super-duper intakes of the type seen on the MiG-29, which have astonishing high-alpha – meaning high nose-up – performance. But that was a long, long time after Bluebird, by which time intake design had progressed massively, and Bluebird wasn’t designed to perform at high-alpha angles – the MiG, of course, was).

Wasn’t the modern-day “accident report” on K7 ever published. By that I mean the report that resulted from analysis of the wreckage, as recovered? Surely, if that was in the public domain for everyone to see, it would lay to rest many of the unsubstantiated and half-baked theories as to why the accident occurred?

In the same way that the recovery of Donald’s body finally laid to rest the daft theory that he was sucked into the air-intake.

[rob565uk]

Looking at the performance graphs for the Orph' and extrapolating, I estimate a thrust of around 200 lbs at a distance of 2 feet when an Orph' is idling - which should have produced some visible effect on the water in my humble opinion. So I am with Mike on this one (unless Bill succeeds in tying him to a stick )