24th Oct 2010, 22:18
permalink Post: 602
Concorde Reheat
Consider it done Feathers.
As promised, here are a few diagrams of the Concorde reheat (afterburner, for our American friends) system. The ORIGINAL design was done by SNECMA, but due to them getting into all sorts of trouble with the fuel injection system and flame stabilisation, Rolls Royce baled them out, and it became a Rolls Royce/SNECMA design. (The core engine was a 100% Rolls design, with no French input whatsoever. However some engine sub-assembles were manufactured by SNECMA).
The basic way the afterburner worked was by spraying the fuel FORWARDS intially at high pressure, against the jet stram about one inch, until it hit the anvil. . As the fuel strikes the anvil it is blown back by the jet stram and atomises, passing over the of the spray ring and the over the flame holder. The ignition operated by passing 15KV across a dual cylindrical tube, the resulting arc was 'swirlied' into the fuel stream by blowing engine 5th stage HP compressor air into the tube (there were 7 stages in all).
The key to successful ignition was a healthy spark, a good supply of air to the ignitor and accurate scheduling of fuel flow. (This was scheduled against dry engine flow as a funtion of total temperature). The other important factor (as with any afterburner) was correct and rapid operation of the exhaust nozzle. Fortunately, Concorde used it's primary nozzle for control of engine N1 anyway, so adapting this to operate as an afterburning nozzle also was a relative walk in the park, and it operated superbly.
During the light up phase of 3.5 seconds, the fuel ratio is a fixed 0.45 (ie. reheat fuel is 45% of dry fuel). After the light up phase the full scheduling commenced. As far as the FLIGHT RATING figures go (not take-off) the ratios were 0.6 at a TAT of 54 deg's C, falling linearly to 0.3 at 107 deg's C and above. (Remember that Concorde used afterburning really sparingly, just for take-off and then transonic acceleration; cut off at Mach 1.7 altogether.
Dude
As promised, here are a few diagrams of the Concorde reheat (afterburner, for our American friends) system. The ORIGINAL design was done by SNECMA, but due to them getting into all sorts of trouble with the fuel injection system and flame stabilisation, Rolls Royce baled them out, and it became a Rolls Royce/SNECMA design. (The core engine was a 100% Rolls design, with no French input whatsoever. However some engine sub-assembles were manufactured by SNECMA).
The basic way the afterburner worked was by spraying the fuel FORWARDS intially at high pressure, against the jet stram about one inch, until it hit the anvil. . As the fuel strikes the anvil it is blown back by the jet stram and atomises, passing over the of the spray ring and the over the flame holder. The ignition operated by passing 15KV across a dual cylindrical tube, the resulting arc was 'swirlied' into the fuel stream by blowing engine 5th stage HP compressor air into the tube (there were 7 stages in all).
The key to successful ignition was a healthy spark, a good supply of air to the ignitor and accurate scheduling of fuel flow. (This was scheduled against dry engine flow as a funtion of total temperature). The other important factor (as with any afterburner) was correct and rapid operation of the exhaust nozzle. Fortunately, Concorde used it's primary nozzle for control of engine N1 anyway, so adapting this to operate as an afterburning nozzle also was a relative walk in the park, and it operated superbly.
During the light up phase of 3.5 seconds, the fuel ratio is a fixed 0.45 (ie. reheat fuel is 45% of dry fuel). After the light up phase the full scheduling commenced. As far as the FLIGHT RATING figures go (not take-off) the ratios were 0.6 at a TAT of 54 deg's C, falling linearly to 0.3 at 107 deg's C and above. (Remember that Concorde used afterburning really sparingly, just for take-off and then transonic acceleration; cut off at Mach 1.7 altogether.
Dude
27th Oct 2010, 05:52
permalink Post: 610
Very good photo Feathers. The reheat really was just about the most fragile part of the powerplant, and gave us numerous headaches throughout the service life of the aircraft. The most unreliable part of all was the ignition side of things; the ignition transformer itself being the main culprit here. Also the swirl ignitor itself was rather fragile, as the smallest blockage in the air supply would render the ignitor useless. The failure of the reheat system resulted in the majority of rejected take-offs in the service life of the aircraft. (Failures during transonic acceleration would sometimes respond to a second selection of reheat, but this was often due to spontaneous llight up, due to the much higher total temperatures at Mach 0.95, rather than a recovery of the ignition system itself).
Dude
Dude
2nd Dec 2010, 11:33
permalink Post: 823
howiehowie93
Welcome aboard and thank you for your kind words; I am so glad you enjoy our thread. You are in good company here also, many of the 'more mature' vintage Concorde people
(like me) are ex-RAF. (And some of the pilots were ex-RN also, but no one is perfect
... only joking guys).
It is a matter of pride/embarrassment for me that up to the end of 2003, I'd only ever really 'known' two aircraft; the C-130 and Concorde
.
I was really interested in some of the RB199/Olympus similarities; TBP was tried on the development aircraft for engine control TET calculation, but Rolls-Royce were unhappy with the performance and abandoned TBP in favour of indirectly computing TET as a function of T1 (intake TAT) and EGT (T7). (And this meant the removal of the four TBP amplifiers too... we had even more black boxes then.
As for the three 'control amps' you were speaking of, I'm 99% sure that A/C 101, G-AXDN still does have the units you described fitted. The ECUs (or ECAs as they were sometimes called) were a highly complex analog control unit built by Ultra Electronics. They could be quite a headache sometimes in terms of reliability, but would generally perform flawlessly in terms of engine control. As with any analog box, control law changes in the field were not too straightforward and a soldering iron was the flight test engineers best friend here. The Reheat Amp was built by ELECMA (the electronics arm of SNECMA) and unlike some of the other components in the reheat system, was a beautifully designed and constructed unit. Very few reheat failures (and there were many) were attributed to the 'box' itself. The main fragility with the reheat system was the ignition system used (a 20 KV swirl ignitor, which you will see is covered previously in the thread). We (BA/RR) were seriously looking at one point of investigatng the use of 'hot streak' injection as a backup ignition source, which I believe was used in the 199 (?), but it unfortunately never happened. The Plessey DECU that was tried on A/C 202 (G-BBDG) DID combine main engine control and reheat, but unfortunately was never taken up for the production A/C, and so we were left withe the '3 AMPS' as you so eloquently describe. We had a total of THIRTY ONE control units associated with powerplant control on Concorde; might be a little different now methinks
]
Thanks for some of the fascinating engine history snippets you shared with us, although purists might regard it as being 'off topic' I personally think this rather unique thread is all the better for your contribution here,
I think it is great that you are working with industrial Olympuses, all part of the family tree. I will dig out the verboten sustained N1 speed band for the 593, it certainly WAS a fact though.
Thanks from all of us for your contribution here Howie, keep on posting.
Regards
Dude
Welcome aboard and thank you for your kind words; I am so glad you enjoy our thread. You are in good company here also, many of the 'more mature' vintage Concorde people
(like me) are ex-RAF. (And some of the pilots were ex-RN also, but no one is perfect
... only joking guys).
It is a matter of pride/embarrassment for me that up to the end of 2003, I'd only ever really 'known' two aircraft; the C-130 and Concorde
.
I was really interested in some of the RB199/Olympus similarities; TBP was tried on the development aircraft for engine control TET calculation, but Rolls-Royce were unhappy with the performance and abandoned TBP in favour of indirectly computing TET as a function of T1 (intake TAT) and EGT (T7). (And this meant the removal of the four TBP amplifiers too... we had even more black boxes then.
As for the three 'control amps' you were speaking of, I'm 99% sure that A/C 101, G-AXDN still does have the units you described fitted. The ECUs (or ECAs as they were sometimes called) were a highly complex analog control unit built by Ultra Electronics. They could be quite a headache sometimes in terms of reliability, but would generally perform flawlessly in terms of engine control. As with any analog box, control law changes in the field were not too straightforward and a soldering iron was the flight test engineers best friend here. The Reheat Amp was built by ELECMA (the electronics arm of SNECMA) and unlike some of the other components in the reheat system, was a beautifully designed and constructed unit. Very few reheat failures (and there were many) were attributed to the 'box' itself. The main fragility with the reheat system was the ignition system used (a 20 KV swirl ignitor, which you will see is covered previously in the thread). We (BA/RR) were seriously looking at one point of investigatng the use of 'hot streak' injection as a backup ignition source, which I believe was used in the 199 (?), but it unfortunately never happened. The Plessey DECU that was tried on A/C 202 (G-BBDG) DID combine main engine control and reheat, but unfortunately was never taken up for the production A/C, and so we were left withe the '3 AMPS' as you so eloquently describe. We had a total of THIRTY ONE control units associated with powerplant control on Concorde; might be a little different now methinks
]
Thanks for some of the fascinating engine history snippets you shared with us, although purists might regard it as being 'off topic' I personally think this rather unique thread is all the better for your contribution here,
I think it is great that you are working with industrial Olympuses, all part of the family tree. I will dig out the verboten sustained N1 speed band for the 593, it certainly WAS a fact though.
Thanks from all of us for your contribution here Howie, keep on posting.
Regards
Dude
4th Dec 2010, 09:17
permalink Post: 832
Bellerophon
Ahhh this 'other operator' (I'd quite forgotten our code for *** ******). And as for this obviously baseless story
.... er yes it did happen. I should really have qualified my post and said 'The controlled N1
as long as the aeroplane was operated
CORRECTLY
was always at least in the upper 90's, well away from our blade resonance area'. I don't quite recall after the engines were removed post-flight (At Rolls-Royce's insistance) whether the entire LP compressor sections or just the first few stages had to be replaced at the engine overhaul base. In either case it was a rather expensive piece of experimentation.
ChristiaanJ
Certainly my friend (but hey, remember that I'm an old Volts and Amps and Ohms ancient at heart too
).
The lighting of a reheat flame can be achieved in three ways:
1) By using an electric arc ignitor.. the least reliable system, although relatively simple in concept.
2) Catalytic ignition, where the reheat fuel is sprayed over a platinum based catalyst, spontaneously igniting. I recall that although generally reliable, eventually the catalyst compound erodes away and you are left with no ignition source.
3) Hot streak injection (or ignition). I this case a sizable jet of fuel is injected through a single injector placed the the combustion chamber of the engine, a powerful streak of flame then 'shoots out' of the turbine, and ignites the reheat fuel. Generally reliable as long as the injector itself does not carbon up (as our new friend Howiehowie93 pointed out). What amazed me with this system when we were looking at it for Concorde, was that the Olympus 593 designer I spoke to at Rolls-Royce told me that it has a negligible effect on turbine blade life, as the hottest part of the flame does not hit the blades themselves, and also of course it is a very short duration burn anyway (1 - 2 seconds).
And Christian my friend, you should indeed 'rabbit on' here about some of your observations regarding Concorde electronics technology, you have a unique insight here as (probably) the only Concorde systems designer that regularly visits 'here'. I'm sure I speak for many of us here when I say that your experiences are unique and your contributaions are always illuminating. Come on, let's have some Volts/Amps and Ohms
Best Regards
Dude
Quote:
| Deciding that they would like to maintain this groundspeed, they went ALT HOLD and MACH HOLD at around FL530. They maintained their groundspeed, so the story goes, but the autothrottle then progressively reduced the N1, as the aircraft weight reduced, over the next couple of hours, into the prohibited range!Did you ever hear of any such event? |
.... er yes it did happen. I should really have qualified my post and said 'The controlled N1
as long as the aeroplane was operated
CORRECTLY
was always at least in the upper 90's, well away from our blade resonance area'. I don't quite recall after the engines were removed post-flight (At Rolls-Royce's insistance) whether the entire LP compressor sections or just the first few stages had to be replaced at the engine overhaul base. In either case it was a rather expensive piece of experimentation.
ChristiaanJ
Quote:
| Can somebody explain to a "Volts and Amps and Ohms ancient" what "hotstreak injection" is/was (without getting scabrous)? |
).
The lighting of a reheat flame can be achieved in three ways:
1) By using an electric arc ignitor.. the least reliable system, although relatively simple in concept.
2) Catalytic ignition, where the reheat fuel is sprayed over a platinum based catalyst, spontaneously igniting. I recall that although generally reliable, eventually the catalyst compound erodes away and you are left with no ignition source.
3) Hot streak injection (or ignition). I this case a sizable jet of fuel is injected through a single injector placed the the combustion chamber of the engine, a powerful streak of flame then 'shoots out' of the turbine, and ignites the reheat fuel. Generally reliable as long as the injector itself does not carbon up (as our new friend Howiehowie93 pointed out). What amazed me with this system when we were looking at it for Concorde, was that the Olympus 593 designer I spoke to at Rolls-Royce told me that it has a negligible effect on turbine blade life, as the hottest part of the flame does not hit the blades themselves, and also of course it is a very short duration burn anyway (1 - 2 seconds).
And Christian my friend, you should indeed 'rabbit on' here about some of your observations regarding Concorde electronics technology, you have a unique insight here as (probably) the only Concorde systems designer that regularly visits 'here'. I'm sure I speak for many of us here when I say that your experiences are unique and your contributaions are always illuminating. Come on, let's have some Volts/Amps and Ohms
Best Regards
Dude
23rd Dec 2010, 18:54
permalink Post: 978
A couple of points on some of the latest entries
Discharge valves
We definately used alternating systems outbound and inbound and only No 1 system had thrust recuperators. I think the original idea was that No 1 system would be used always with No 2 sytem being a back up. However from the start BA operated as I said alternating per sector so as to be sure that both system were working. The same logic went for the engine starting ignitors which were used Lh or Rh per sector. This logic caused more problems with starting than any other although a way was found to over come this problem
under wing
Not sure if I am on the same thread as others but there were definately strengthening straps / doublers fitted on the underside of the wing outboard of the engines, which were on a wing root/wing tip alignment. This surprised everybody as they seemed to go against all the need for limiting drag that had been impressed on us during the lectures.
These strengthening straps were fitted a few years after the start of service due to small cracks appearing in the outer wing, and only seen on BA aircraft. This was put down to the fact that in the early years BA Concordes flew heavy and subsonic for extended periods across Europe, on their route to Bahrain, whereas Air France aircraft always accelerated shortly after take off
Also either side of the engines there were two tubes on the underwing which went fore /aft. These tubes were the drain outlet for their respective engine dry bay and directed any fluid to the trailing edge of the wing.
Mind you all this is some 30 years ago so the old grey matter could be playing me tricks
Discharge valves
We definately used alternating systems outbound and inbound and only No 1 system had thrust recuperators. I think the original idea was that No 1 system would be used always with No 2 sytem being a back up. However from the start BA operated as I said alternating per sector so as to be sure that both system were working. The same logic went for the engine starting ignitors which were used Lh or Rh per sector. This logic caused more problems with starting than any other although a way was found to over come this problem
under wing
Not sure if I am on the same thread as others but there were definately strengthening straps / doublers fitted on the underside of the wing outboard of the engines, which were on a wing root/wing tip alignment. This surprised everybody as they seemed to go against all the need for limiting drag that had been impressed on us during the lectures.
These strengthening straps were fitted a few years after the start of service due to small cracks appearing in the outer wing, and only seen on BA aircraft. This was put down to the fact that in the early years BA Concordes flew heavy and subsonic for extended periods across Europe, on their route to Bahrain, whereas Air France aircraft always accelerated shortly after take off
Also either side of the engines there were two tubes on the underwing which went fore /aft. These tubes were the drain outlet for their respective engine dry bay and directed any fluid to the trailing edge of the wing.
Mind you all this is some 30 years ago so the old grey matter could be playing me tricks
17th Jan 2011, 14:20
permalink Post: 1114
Brit312 wrote:
Really alternate side Ignitors? All RR aero engines I have worked on always sparked up both sides every time, well the Avon, Spey 202, RB199 & the Oly 20202 (Vulcan) and industrial Oly did. Would this have made a difficulty with starting logic??
Was there LH & RH Ignition selector switch maybe?
I hope I haven't missed further comment on this since page 50 but just back off my Hols and raced through to the end.
Also on a tangent a bit; the roll out picture further on was that a Nimrod's tail in the corner of the Hanger??
regards
Howie
Quote:
|
Discharge valves
The same logic went for the engine starting ignitors which were used Lh or Rh per sector. This logic caused more problems with starting than any other although a way was found to over come this problem |
Was there LH & RH Ignition selector switch maybe?
I hope I haven't missed further comment on this since page 50 but just back off my Hols and raced through to the end.
Also on a tangent a bit; the roll out picture further on was that a Nimrod's tail in the corner of the Hanger??
regards
Howie
17th Jan 2011, 18:40
permalink Post: 1117
Quote:
| For that reason, I believe, flight in mechanical signalling was removed from transonic flight on airtests and altogether from Base Training. The simulator was the only sensible way of trying to fly like that... |
Quote:
| Was there LH & RH Ignition selector switch maybe? |
Yes there was an Ignitor selector labelled LH--Both--RH, however the engines would be started using only one ignitor. This caused a few small but annoying delays as if the selected ignitor failed the start would have to be stopped the starter given a cooling period and then a further engine start using the other ignitor would be attempted, however it did give a running check that both ignitors were working.
This was not very popular with the crews and the ground engineers were persuaded to test the ignitors before presenting the aircraft for service. However due to the engine starting Fuel Pump switching, this resulted with a small fire in the hanger, and so the crews were back to starting on Lh or RH ignitors.
If I remember correctly the RR Conways on the VC-10 also had 2 ignitors per engine with a LH--Both-RH selector.
Quote:
| flying control pre-flight check! Learning it was a conversion course rite othat f |
If you remember, if something went wrong with the Flying control check the F/E was always busy. This gave him a chance to think up a suitable answer or even better the pilots did the check again and it now worked.
Quote:
| But the 'trainers' often used to come seek me out in the hangar and (over coffee, not beer I'm afraid) confer about various system quirks and nasties to use on you guys during the tech' refreshers |
Now I have to admit coming across the hanger to consult with you boys when preparing for a new sequence of F/E "Tech Knowledge Checks". Not that we did not understand it, you understand, but mainly to make sure that we were correct before some clever line F/E informed you of your error. Very embarrising that, and I should know
18th Jan 2011, 06:28
permalink Post: 1118
Good to have you back here again Howie
There was no automatic ignition selection logic as such built into the start sequence, but a manually selected L & R ignition selector switch. The reason of course to alternate L & R selection during starting was to detect otherwise dormant ignition failures if 'BOTH' was always selected. (Modern A/C with AUTOSTART do not have this problem, if an ignitor fails during the engine start sequence the other is automatically selected and an ignition status message is set on the lower EICAS screen). The ignition L/R selector switch was bypassed during engine operation by the auto-ignition system, where if the engine control unit detected a flame out (set at 58% N2) both ignitors would automatically fire up. The sequence would release onece the perceived N2 rose above 63%. The ignition system had several reliability issues, the first was the plugs themselves. Penetration into the 'can' was crucial; if it were more than about 130 thou', the tip would very quickly burn off. We soon learned that a penetration check was vital when fitting a plug and shims needed to be used to get the correct penetration. The other reliability issue was the ignition leads themselves; For the first 10 years of service they were a major pain until 'they' (Rolls-Royce) finally got it right. Also until Rolls modified the lead clipping, it could take 3 to 4 HOURS to change a lead. The dual channel HEIU itself was as good as gold, and seldom let us down, It was a very powerful 8 Joule 2KV beast, and you obviously treated it with utmost respect.
Best regards
Dude
Quote:
| Really alternate side Ignitors? All RR aero engines I have worked on always sparked up both sides every time, well the Avon, Spey 202, RB199 & the Oly 20202 (Vulcan) and industrial Oly did. Would this have made a difficulty with starting logic?? Was there LH & RH Ignition selector switch maybe? |
There was no automatic ignition selection logic as such built into the start sequence, but a manually selected L & R ignition selector switch. The reason of course to alternate L & R selection during starting was to detect otherwise dormant ignition failures if 'BOTH' was always selected. (Modern A/C with AUTOSTART do not have this problem, if an ignitor fails during the engine start sequence the other is automatically selected and an ignition status message is set on the lower EICAS screen). The ignition L/R selector switch was bypassed during engine operation by the auto-ignition system, where if the engine control unit detected a flame out (set at 58% N2) both ignitors would automatically fire up. The sequence would release onece the perceived N2 rose above 63%. The ignition system had several reliability issues, the first was the plugs themselves. Penetration into the 'can' was crucial; if it were more than about 130 thou', the tip would very quickly burn off. We soon learned that a penetration check was vital when fitting a plug and shims needed to be used to get the correct penetration. The other reliability issue was the ignition leads themselves; For the first 10 years of service they were a major pain until 'they' (Rolls-Royce) finally got it right. Also until Rolls modified the lead clipping, it could take 3 to 4 HOURS to change a lead. The dual channel HEIU itself was as good as gold, and seldom let us down, It was a very powerful 8 Joule 2KV beast, and you obviously treated it with utmost respect.
Best regards
Dude
Last edited by M2dude; 18th Jan 2011 at 07:28 .
18th Jan 2011, 07:15
permalink Post: 1120
Brit312
The main problem with testing ignitors in the hangar was residual fuel. The LH ignitor sat right at the bottom of the can, and sometimes had a small puddle of fuel lying over it. This would produce a small 'whoof' of smoke out of the jet-pipe for about a second or two as the ignitors fired, but no more than that. The main danger was forgetting to trip the START PUMP C/Bs before you did the ignition check. If you did you had a guaranteed fire in the can (the pump would run as you know as soon as 'START' was selected and stayed running for 30 seconds after the start switch was returned to NORMAL) which was very messy (and scary as hell too). The only remedy was to grap a start truck, make sure the C/B is finally tripped and dry motor the engine until all the smokey stuff is gone. (It did no damage, but made a hell of a lot of smoke; the fire brigade were never best pleased). But provided the ignition checks were done correctly there was no ptoblem. (In nearly 30 years of doing ignition checks CORRECTLY, I never once saw a problem. Saw a few when people did forget to trip the start pump C/B however.
In any case as far as the 'ground engineers' doing the check of the ignitors, in my opinion if you are doing a pre-flight check, there is no point doing it unless it is pre-FLIGHT. Just about every other system on the aircraft got tested right up to when you boys arrived at the aircraft, but quite rightly you tested them again. (The whole point of 'us' testing systems was to pre-empting failures before they could impact the departure time).
If you even bothered to read what I wrote "But the 'trainers' often used to come seek me out in the hangar and .....confer about various system quirks and nasties....". I never suggested that anyone but the trainers themselves wrote the tech refreshers; but several of the guys (not you, obviously) waited 'til I was back from leave etc to ask away over coffee about some specific system QUOTE quirks and nasties UNQUOTE they figured I would know about and could use in their refresher.
Or perhaps you are suggesting that I am hallucinating or worse?
Dude
Quote:
| This was not very popular with the crews and the ground engineers were persuaded to test the ignitors before presenting the aircraft for service. However due to the engine starting Fuel Pump switching, this resulted with a small fire in the hanger, and so the crews were back to starting on Lh or RH ignitors. |
In any case as far as the 'ground engineers' doing the check of the ignitors, in my opinion if you are doing a pre-flight check, there is no point doing it unless it is pre-FLIGHT. Just about every other system on the aircraft got tested right up to when you boys arrived at the aircraft, but quite rightly you tested them again. (The whole point of 'us' testing systems was to pre-empting failures before they could impact the departure time).
Quote:
| No dude we never came to see you boys for the "Pilots Tech Refresher" as we always had to keep those lectures very simple as otherwise the pilots would go to sleep. |
Or perhaps you are suggesting that I am hallucinating or worse?
Dude
Last edited by M2dude; 18th Jan 2011 at 07:27 .