Bluebird Archive Photos & Films

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KW Mitchell
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Re: A Picture paints a thousand words....

Post by KW Mitchell »

DMCK7 Fan wrote: This could lead to a particular person/persons or fault and after all this time I don't really think that would be fair, do you ?

I personally would rather not know ALL the details that could lead to the individual (s) involved, it's not a fair comparison doing this now when looking back to technologies involved between 53 - 67 is it ?

I'm happy to theorise but in all truth I'd rather never know the real reason or reasons, it was an ACCIDENT.
In the interests of fairness, I think it only right to point out that the issue of blame only arose in this debate when you, yourself, introduced it in your first posting ----------.

All other contributors have been happy to continue in the discussions, reflections - and yes, speculations - so that we might (hopefully) gain enlightenment/understanding as to the causes of one of the most traumatic episodes in British record braking history sans accusation or judgment.

Long may that continue ------------------!

DMCK7 Fan

Re: A Picture paints a thousand words....

Post by DMCK7 Fan »

While we are quoting, I also said
This COULD lead to AND I'm happy to theorise AND it was an ACCIDENT
No need to stick the knife in :o :shock:

And my other question still satnds.
Do we really want to know now what the failure or failures were that caused the accident ?
Obvioulsy from your reply YES but me, NO.

KW Mitchell
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Re: A Picture paints a thousand words....

Post by KW Mitchell »

Renegadenemo wrote:The problem is that it's natural to be curious and, like it or not, curious we will be.

Here's another thing. Someone kindly sent me enough information last night that I was finally able to find the reference in the first run to relighting the engine. I need to have another listen because it was late, my headphones were nowhere to be found and I didn't want to wake the house but it may well be correct. Knowing that the fuel system was a total abortion of a thing and having all of its components to hand it shouldn't be difficult to determine with reasonable certainty whether the engine was starved of fuel on the second run. It would explain a lot.
Bill - some questions:

1 - running a jet engine over max. rating to achieve extra thrust usually requires disproportionate amounts of fuel and very high jetpipe temp's. Might it be possible that the original estimates of fuel consumed could be too low?

2 - fuel starvation/air in fuel lines is a common cause for 'flame-out'. If the level was low in a gravity feed system - and in the presence of considerable agitation - then is there not the very increased likelihood of flame-out?

Keith

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Renegadenemo
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Re: A Picture paints a thousand words....

Post by Renegadenemo »

1 - running a jet engine over max. rating to achieve extra thrust usually requires disproportionate amounts of fuel and very high jetpipe temp's. Might it be possible that the original estimates of fuel consumed could be too low?

2 - fuel starvation/air in fuel lines is a common cause for 'flame-out'. If the level was low in a gravity feed system - and in the presence of considerable agitation - then is there not the very increased likelihood of flame-out?

The engine driven pump (so far as I can determine at this stage) was the correct one for the engine but I don't know how much extra fuel it was physically capable of delivering. It remains untouched until I can find a suitable rebuild facility to run it up and measure its output. We can accurately measure the fuel capacity of the three tanks and the fuel lines plus duration of the runs can be fairly well established from the recording of the radio traffic though we can't say how long the engine was idling before the first recorded transmission.

Now here's a curve ball for you. The system wasn't gravity at all fed. Fuel was siphoned from the main tank into a swirl pot with its own boost pump and from there into a second, auxilliary tank in the bottom of the hull - again with a boost pump - then into the engine. Because all the breather plumbing was thin-wall steel pipe it's long gone so we can't be sure how it was set up.
Both boost pumps were cobbled into the same electrical supply. The boat was set up in 66 with only the lower pump but when the second was added in place of the fuel filter they just lashed it into the same relay. K7 had no on board power generating equipment and so relied on a pair of batteries - condition unknown, as well as their state of charge.
It's entirely possible that the fuel system is the culprit.
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes.

'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler

jonwrightk7
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Re: A Picture paints a thousand words....

Post by jonwrightk7 »

i would go along with you on that one bill. surely not re-fueling and then passing over badly disturbed water would adgitate the fuel more in a fuel tank which was ,lets say less than half full, than it would in a full tank. there would be more air in the tank to mix with the fuel. bit like shaking up a half full bottle of lemonade, it fizzes up a lot more than a full one. i would imagine the effect would be similar to a diesel engine just on the verge of running out of fuel. it runs, but only just and then cuts out!
The world is full of Kings and Queens; who blind your eyes, then steal your dreams..

KW Mitchell
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Re: A Picture paints a thousand words....

Post by KW Mitchell »

Renegadenemo wrote:
The engine driven pump (so far as I can determine at this stage) was the correct one for the engine but I don't know how much extra fuel it was physically capable of delivering. It remains untouched until I can find a suitable rebuild facility to run it up and measure its output. We can accurately measure the fuel capacity of the three tanks and the fuel lines plus duration of the runs can be fairly well established from the recording of the radio traffic though we can't say how long the engine was idling before the first recorded transmission.

Now here's a curve ball for you. The system wasn't gravity at all fed. Fuel was siphoned from the main tank into a swirl pot with its own boost pump and from there into a second, auxilliary tank in the bottom of the hull - again with a boost pump - then into the engine. Because all the breather plumbing was thin-wall steel pipe it's long gone so we can't be sure how it was set up.
Both boost pumps were cobbled into the same electrical supply. The boat was set up in 66 with only the lower pump but when the second was added in place of the fuel filter they just lashed it into the same relay. K7 had no on board power generating equipment and so relied on a pair of batteries - condition unknown, as well as their state of charge.
It's entirely possible that the fuel system is the culprit.
Bill - your last point regarding pump power and battery condition started me thinking as to how we might estimate the former and any potential effects on battery voltage.

The method I've used to assess this might seem obscure - and possibly tenuous - but here goes (for those not interested in technicalities, please go to the next post!) :-

The Orpheus had a specific fuel consumption (s.f.c.) of 1.06 (i.e. 1lb of thrust for 1 hour required 1.06lb of fuel). The Orpheus was running at max. + 10% = 5225lb.

Fuel consumption per minute was therefore 5225x1.06/60 = 92.3 lb/min i.e. 11.5 gall/min (assuming 1 gall. kerosene = 8lb).

I then took a look at my model jet engines (see below) and did the same calculation. Interestingly, their s.f.c. is not that far removed from the Orpheus being 1.35. Each engine produces 38lb max. thrust and to achieve this requires a pump power of 80 Watts.

Armed with this data it was then possible to calculate the total pump power required by the Orpheus on the basis of the relative thrusts corrected by the relative s.f.c's multiplied by 80.

Total Pump Power = (5225/38) x (1.06/1.35) x 80 = 8640W or 8.64kW. If the batteries were connected in series to give 2 x 12V = 24V (consistent with aero' systems at that time on 24V), the current drain would be 8640/24 = 360A.

Now in all this I'm making a pretty coarse assumption that the relative efficiencies of the Orpheus' pump(s) and my small ones are the same (??) but it does suggest that there are some mighty big currents being taken from those batteries. It also must have been some relay that was switching it --------!

So to the effects on Jan 4th. If, indeed, flame-out occurred at the end of the first run this could have been due to loading/partial discharge of the batteries reducing voltage, or, the relay could have dropped out altogether due to low voltage, thus terminating fuel flow.

I am sure you are also aware that there is an in-between situation in relay operation where a making/braking oscillation can occur caused by the battery voltage being loaded, the relay breaks, the voltage recovers, the relay makes - and so on. This would not necessarily have caused the engine to flame-out, but would certainly have reduced fuel flow and thereby, engine thrust --------.
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KW Mitchell
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Re: A Picture paints a thousand words....

Post by KW Mitchell »

Mike Bull wrote:The math lost me a bit, but overall, I actually understood that! :geek:
No doubt, Mike, I'll hear pronto from Das BootFührer Smitt if it's a load of b--ls!

K.

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Renegadenemo
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Re: A Picture paints a thousand words....

Post by Renegadenemo »

Keith,

Not sure whether you missed a piece of your fuel system... The electrically powered boost pumps only ensure a small positive pressure at the inlet of the engine driven pump and deliver the required volume thereafter. The beastie that does the work is a rotary, swashplate type pump made by Lucas driven directly off the ancilliary gearbox on the engine. With no fuel demand small doors lift in the boost pumps so the impellors aren't running under load. In the Gnat installation they are only used during startup until compressor bleed air is available to pressurise the main tanks. K7 had no tank pressurisation so far as we know so the pumps must've run continuously.

Here's one I've meant to ask you and I was reminded when you mentioned the Orpheus performance data. The figures assume no power takeoff - K7 ran a flow/return hyd system for the water brake but no generator - but they also assume no inlet losses. The inlet was designed to feed the old Beryl engine and until it came apart during engine testing it remained unmodified so the losses there will have been substantial. More to chew over... And another thing, the story goes that the engine was tweaked up by 10% but how did they gauge this? Fuel delivery pressure? Half a turn clockwise on the pressure regulator? Too many anecdotes and not enough facts for us to work with, in my opinion.
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes.

'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler

KW Mitchell
Posts: 195
Joined: Sun Jan 18, 2009 11:37 am

Re: A Picture paints a thousand words....

Post by KW Mitchell »

Renegadenemo wrote:Keith,

Not sure whether you missed a piece of your fuel system... The electrically powered boost pumps only ensure a small positive pressure at the inlet of the engine driven pump and deliver the required volume thereafter. The beastie that does the work is a rotary, swashplate type pump made by Lucas driven directly off the ancilliary gearbox on the engine. With no fuel demand small doors lift in the boost pumps so the impellors aren't running under load. In the Gnat installation they are only used during startup until compressor bleed air is available to pressurise the main tanks. K7 had no tank pressurisation so far as we know so the pumps must've run continuously.

Here's one I've meant to ask you and I was reminded when you mentioned the Orpheus performance data. The figures assume no power takeoff - K7 ran a flow/return hyd system for the water brake but no generator - but they also assume no inlet losses. The inlet was designed to feed the old Beryl engine and until it came apart during engine testing it remained unmodified so the losses there will have been substantial. More to chew over... And another thing, the story goes that the engine was tweaked up by 10% but how did they gauge this? Fuel delivery pressure? Half a turn clockwise on the pressure regulator? Too many anecdotes and not enough facts for us to work with, in my opinion.
I put my hands up, Bill - what I was suggesting was a load of b--ls! I hadn't realised that the electrical load was for the boost pumps only ----------------.

As for the collapsed inlet saga, all we have to go on from the BBY's is that they were '------ strengthened and modified -------'. What the latter means is difficult to assess. The inlet area was obviously too small for the increased mass flow of the Orpheus, but there was no means of increasing it without major redesign to that area of the craft. Looking at photo's it is difficult to see if there is any difference in the size and shape of the inlets, pre' and post the blow-up on Nov.5th.

All I can suggest here is merely qualitative. The most severe stresses on a jet engine inlet structure occur when it is running at full power and is stationary; the air entering the inlet obviously has to be accelerated from zero. This represents the highest load condition on the compressor. Non-optimal area inlets would cause problems but as long as this did not result in compressor blade stall ('surging') - and there is no evidence to suggest that it did - the problem would diminish as forward speed was increased and load on the compressor reduced due to the velocity of air entering the orifices.

As to the engine 'tweaking' I ain't got a clue - it's beyond my knowledge of the engine. As there probably aren't too many Bristol-Siddeley engineers around now who worked on that engine it could be difficult to find out. I believe that there are Orpheus Workshop Manuals available on the web, but whether they say anything ---------?

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sheppane
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Re: A Picture paints a thousand words....

Post by sheppane »

Leo and Maurie attending to the water brake in Dec 66. Note K7's stablising fin and the stiff rubber seal around the lower part of the jet pipe.
K7 Tail 66.jpg
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