Pic of the Day

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mtskull
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Re: Pic of the Day

Post by mtskull »

Renegadenemo wrote:
I think this has been mentioned before but what was it that led to the conclusion that RPM gauge was originally under reading?
Basically, the generator is driven by the engine gearbox and geared to read from 0 to 10,000rpm but the indicator they used reads from 0-12,000. The generator is just that, a small 3-phase genny and the indicator is a small motor that runs in phase with it so it always indicates low on the 0-12,000 scale.
Hence all the carry on in 66/67 about the engine not giving its all and the Bristol Siddeley boys turning up the pump stroke until what likely happened is they ran the engine so hard that the indication was what they expected to see, the air intakes caved in and, eventually, the engine starved itself and flamed out on the first run.
Alternatively, it might have flamed out due to poor handling because its very basic pressure-ratio controller was found to be blanked off and isolated from the control loop so you'd have to be very careful on the throttle to avoid putting the fire out.
Fascinating stuff.
So, if I understand correctly, when they thought that the engine was finally giving its rated RPM, it was actually running at 20% above its normal maximum.
Has the possibility been considered or investigated that this might have had a detrimental effect on the engine, perhaps causing to the fatal flameout on the final run?
Is the engine in a condition such that it could be determined if a mechanical failure had occurred?
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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

Fascinating stuff.
So, if I understand correctly, when they thought that the engine was finally giving its rated RPM, it was actually running at 20% above its normal maximum.
Has the possibility been considered or investigated that this might have had a detrimental effect on the engine, perhaps causing to the fatal flameout on the final run?
Is the engine in a condition such that it could be determined if a mechanical failure had occurred?
That's about the size of it. The indication was wrong. The same gotcha caught the tribute act and we only picked up on it when trying to set up the start system when a laser tacho aimed at the turbine disagreed with the engine driven tacho.
The flameout seems most likely to have been caused by the poor design of the fuel system, poor handling of the engine or a combination of the two. The only physical damage to the original engine that we found was the 1st stage compressor blades bent forward as they tried to compress water.
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Richie
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Re: Pic of the Day

Post by Richie »

Not knowing the full history of the intro to the orph... It seemed to me like the team merely clashed the thing in, perhaps a case of get it to run and plane without fully understanding the intricacies of the unit.

That said, does the actual Gnat systems run accurately when onboard the aircraft ?
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Terminator
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Re: Pic of the Day

Post by Terminator »

Richie the other things you have to take into consideration and most people forget is all the pressure the team were under 48yrs ago . A lack of any really support "stuck in this god awful place" for nine whole weeks by a freezing lake with wind and rain howling down most of the time! The engine change put even more pressure on the team when the boat would not even plane, money was fast running out, his marriage on the rocks the tax man etc etc etc. So all things considered it was easy for them to miss the obvious or make mistakes given all that was upon them.
I would love to see a modern F1 team perform in those sort of conditions by the side of a lake in deepest winter and not Monaco in a nice clinically clean workshop with money dripping from every corner of the carriage.
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Speedfab
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Re: Pic of the Day

Post by Speedfab »

I assume you gentlemen have consulted with turbine technicians on the operation of these engines. The fact is, they don't just "flame out" and will continue running under a pretty wide range of air/fuel ratios. Once you have a turbine lit and running, the only things that will stop it are: Commanded fuel shutdown by the controls, Physical damage or internal breakage, or something else cutting the fuel (and drastically so at that). Water ingestion would have to be really substantial IMO, not just some spray from a sponson, and to choke its air would take a massive ducting structure failure. Otherwise it is no more likely to quit (far less in fact) than a torch with a nice rich flame. The Orpheus is a really simple well designed engine, it has just 7 compressor stages driven by a single turbine, connected by a huge tubular shaft running in just two bearings. It has a 7 injector can/annular (cannular) combustor wherein even if one or two were to lose fire they will relight from the others. It is about as simple and reliable as a turbojet gets.

I'd have to guess it was a fuel supply/pump failure issue, but there are plenty of people you could ask who know a hell of a lot more than me.

Now back to those diary entries... :mrgreen:

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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

I assume you gentlemen have consulted with turbine technicians on the operation of these engines.
Yes, we're in the very safest of hands on that subject. The matter of ingesting water came when the boat crashed and the fact that the blades were merely tweaked and not ripped off at the roots testified to there being very little or no power on the turbine at the time (Steve Moss from AAIB told us that). The flameout could have been caused by the woeful fuel system or poor handling as the module that watched the engine's pressure ratio was found intentionally disabled.

As for the diary entry - it's about half done with not enough hours in the day but it's incoming. I've not forgotten.
I'm only a plumber from Cannock...

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Speedfab
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Re: Pic of the Day

Post by Speedfab »

Renegadenemo wrote: the module that watched the engine's pressure ratio was found intentionally disabled.
There isn't much need for altitude compensated fueling on a land/water bound turbine. Bristol Siddeley engineers may well have told them to do so for simplicity and/or weight savings. As to bent first stage compressor impeller blades, I am sure that is just the result of their meeting with a near incompressible fluid whilst still turning at tremendous speed.
As for the diary entry - it's about half done with not enough hours in the day but it's incoming. I've not forgotten.
I will ship you some spare hours as soon as I find a reliable source for myself.

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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

There isn't much need for altitude compensated fueling on a land/water bound turbine. Bristol Siddeley engineers may well have told them to do so for simplicity and/or weight savings.
In actual fact it was present and blanked off. It was an experimental 'lash-up' (that's how it is described on the archive drawing) and the maker's plate says 'built to lab report No. xxxx' (can't remember the number). It was one of only two ever built by Lucas and its history was traced by AEC for us. It wasn't necessarily there for altitude correction, it was there for handling the engine even on the ground to maintain a healthy pressure ratio when spooling up or down.
For those who don't know anything about these engines, you have to make sure the pressure in the front of the engine is always greater than that in the back or the fire will come out the wrong end of the engine (surge). Throw in a load of fuel by opening the throttle too fast and the combustion pressure will overcome the compressor and surge the engine. Likewise, cut the fuel too quickly and the still spinning compressor might blow out the fire out so there's a module in the fuel control loop that watches the PR and plays with the pump stroke to avoid either condition.
I was visiting with the Red Arrows last week and discovered that the fuel system on their jets is modified to give them better throttle response for formation aerobatics but the price they pay is the need for very careful handling of the engines because they're especially easy to surge so the problem remains to this day despite the advance of technology.
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Speedfab
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Re: Pic of the Day

Post by Speedfab »

Renegadenemo wrote:In actual fact it was present and blanked off. It was an experimental 'lash-up' (that's how it is described on the archive drawing) and the maker's plate says 'built to lab report No. xxxx' (can't remember the number). It was one of only two ever built by Lucas and its history was traced by AEC for us. It wasn't necessarily there for altitude correction, it was there for handling the engine even on the ground to maintain a healthy pressure ratio when spooling up or down.
Ah... you are talking about a more fundamental fuel control component, most likely the fuel control unit itself or at least some portion thereof. If the pilot has near full mechanical control of fueling to the turbine, a number of unpleasant situations could occur, such as a leanout drastic enough to kill the fire or a sudden enrichment causing compressor stall. In other words, sudden throttle(fueling) movements in either direction could easily exceed the ability of the engine to react.

What I thought you were referring to was this: To my knowledge all aircraft turbojet engines have an aneroid type device to control fuel enleanment at altitude to account for decreasing air density. On an engine designed before the age of electronic controls, this is purely mechanical as is the rest of the fuel system.

Extremely interesting information. Thank you Bill.

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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

Ah... you are talking about a more fundamental fuel control component, most likely the fuel control unit itself or at least some portion thereof.
The fuel control unit or CCU (Combined Control Unit) administers to what, in theory, ought to be a linear control curve of RPM against fuel requirement and it includes compensation for altitude by comparing atmospheric with delivery (the pressure where the air leaves the compressor for the combustion chamber) pressure (P1 /P2)
Additional modules in the system watch the fuel/air ratio and the pressure ratio. There's a third module called the Pressure Ratio Switch that introduces a step into the control curve dependent on altitude.
Altitude compensation obviously isn't needed for ground running but it's integral to the control system so, as the engineers who rebuilt it pointed out, if it's in there it had better be working properly!
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