Concorde engine intake "Thrust"
The Concorde laid the ground work for the scientific basis of some of our airworthiness assessments today.
To say it another way, since the airplane was so different in its enviroment, some extra thought went into how to make it safe.
Today when we look at supersonci high altitude flight, we also have to look at potential decompressions and how to get the plane down quick enough to save the passengers. No real harm in a few healthy passengers passing out, but we would like them to wake up for the landing. Thus the size of the hole that lets the air out has to be considered vs the probability of the hole being made.
So a consideration is made of uncontained engine failures as well as a window out, etc. Because of this a limitation had to be placed on the size of the engines in diameter, simply due to the size of an engine disk being ejected.
I suppose that other what ifs could enter into this but they would all be veted by the historical probability of them occurring.
That of course brings one back to the arguments was the Concorde really safe enough?
In my view it was considered a leader in safety for its design period, not withstanding a couple of surprises to us in its service life. It simply had less surprises.
To say it another way, since the airplane was so different in its enviroment, some extra thought went into how to make it safe.
Today when we look at supersonci high altitude flight, we also have to look at potential decompressions and how to get the plane down quick enough to save the passengers. No real harm in a few healthy passengers passing out, but we would like them to wake up for the landing. Thus the size of the hole that lets the air out has to be considered vs the probability of the hole being made.
So a consideration is made of uncontained engine failures as well as a window out, etc. Because of this a limitation had to be placed on the size of the engines in diameter, simply due to the size of an engine disk being ejected.
I suppose that other what ifs could enter into this but they would all be veted by the historical probability of them occurring.
That of course brings one back to the arguments was the Concorde really safe enough?
In my view it was considered a leader in safety for its design period, not withstanding a couple of surprises to us in its service life. It simply had less surprises.
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Decompression is already discussed in the other Concorde thread.
Have a look here :
Concorde question, post #68
and the few posts before and after that.
And yes, decompression was definitely taken into account!
The critical case was considered to be the loss of a cabin window with only three of the four air conditioning / pressurisation packs operating.
With a near-immediate emergency descent, cabin altitude would have reached 40,000 ft for about two minutes, which is survivable with pure oxygen without pressure breathing.
I wasn't personally involved, but obviously tests were performed to measure the air loss with the appropriate pressure differential.
And yes, that's why the windows are so small. They are slightly bigger on the prototypes, either because the tests hadn't been done before the construction of the prototypes started, or because the certification requirements were narrowed afterwards.
I don't know about the uncontained engine failure case (never happened either), but I suspect it was considered the resulting shrapnel would have resulted in several smaller holes, with a total area not bigger than that of a cabin window.
lomapaseo is right, in that many of the existing certification and airworthiness requirements for subsonic aircraft were either inapplicable or inadequate, and in the end a huge document, the TSS (Transport SuperSonique) Standards was written specially for Concorde.
CJ
Have a look here :
Concorde question, post #68
and the few posts before and after that.
And yes, decompression was definitely taken into account!
The critical case was considered to be the loss of a cabin window with only three of the four air conditioning / pressurisation packs operating.
With a near-immediate emergency descent, cabin altitude would have reached 40,000 ft for about two minutes, which is survivable with pure oxygen without pressure breathing.
I wasn't personally involved, but obviously tests were performed to measure the air loss with the appropriate pressure differential.
And yes, that's why the windows are so small. They are slightly bigger on the prototypes, either because the tests hadn't been done before the construction of the prototypes started, or because the certification requirements were narrowed afterwards.
I don't know about the uncontained engine failure case (never happened either), but I suspect it was considered the resulting shrapnel would have resulted in several smaller holes, with a total area not bigger than that of a cabin window.
lomapaseo is right, in that many of the existing certification and airworthiness requirements for subsonic aircraft were either inapplicable or inadequate, and in the end a huge document, the TSS (Transport SuperSonique) Standards was written specially for Concorde.
CJ
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RJTRT -
Yes, the flight crew had pressure breathing apparatus.
I believe the EROS masks we're all so familiar with were developed for Concorde??? Anyway - that's what we had, with the addition of a couple of supplementary 'pull' straps to ensure the mask remained firmly attached in pressure-breathing mode. The system was automatic - if the pressure altitude was above 42000' you were px breathing, below that you weren't.
Every other year we'd go on a rig during SEP to practice it, and it was really not that big a deal. A bit odd and a bit harder to speak but no issues.
There would have to have been a pretty serious event to the cabin to >42000', mind.
As for uncontained failures, don't forget the Olympus' were in pretty substantial housings - I know of one fairly severe fire which burned for a few minutes, resulting in huge damage inside the nacelle but none out of it.
Wasn't 202's divider robbed to go on AB after the latter had a fairly big failure of an engine? Again - no question of airfram damage outside the cowlings.
In this respect I reckon the Conc was more robust than many conventional designs.
Yes, the flight crew had pressure breathing apparatus.
I believe the EROS masks we're all so familiar with were developed for Concorde??? Anyway - that's what we had, with the addition of a couple of supplementary 'pull' straps to ensure the mask remained firmly attached in pressure-breathing mode. The system was automatic - if the pressure altitude was above 42000' you were px breathing, below that you weren't.
Every other year we'd go on a rig during SEP to practice it, and it was really not that big a deal. A bit odd and a bit harder to speak but no issues.
There would have to have been a pretty serious event to the cabin to >42000', mind.
As for uncontained failures, don't forget the Olympus' were in pretty substantial housings - I know of one fairly severe fire which burned for a few minutes, resulting in huge damage inside the nacelle but none out of it.
Wasn't 202's divider robbed to go on AB after the latter had a fairly big failure of an engine? Again - no question of airfram damage outside the cowlings.
In this respect I reckon the Conc was more robust than many conventional designs.
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When Intakes Go Wrong Part 1
When intakes go wrong
We've talked quite a bit here about surges and such, so I thought it might be useful to look at what was involved with Concorde 'when things went wrong', in that direction as well as a few other intake horror stories.
The variable air intake control system on any supersonic aircraft is fraught with pitfalls, and downright dangers, the main areas of concern are those of surge and unstart.
A surge, resulting from the breakdown of stable compressor flow, can occur in just about any type of gas turbine engine, however with a supersonic aircraft the effect are really dramatic; The typical characteristics can be really quite disturbing. We get a loss of thrust, an increase in turbine entry temperature and most alarmingly of all a short sharp inlet overpressure, followed by a fairly small longer duration under-pressure. The problem is with any such surge is that unless the cause of that surge is corrected, then the whole process can repeat again and again.
Unstart is far more serious than a simple surge; the inlet shock system is expelled forward of the inlet, with severe 'surge like' effects. Unless changes are made to the intake geometry itself AND ALSO engine demand is reduced, the inlet and engine will not recover and very severe cyclic yawing forces will continue to act on the airframe.
In the case of a Mach 2 surge on Concorde, the most commonly occurring event would be due to a control system malfunction. (The malfunction itself could be an intake ramp going slightly off schedule, a mis-matched engine N1 and N2 at a given temperature or even wing-induced flow distortions. Above Mach 1.6, a surging engine would always cause it's neighbour to surge also. The dynamics of all this, 'a typical surge' are as follows (again quoting from 'The Concorde AICS':
The surge drill used by Concorde crews involved reducing power on the affected engines, until the surging stopped, and when the power was re-applied this was done quite gingerly. (I will leave it to the guys to tell you all how not easy this wa, but the thing was that this well rehearsed drill did in fact work well, and normal service was normally resumed afterwards.
As far as unstart went on Concorde, well I#m pleased to say that there was no such thing
. The intake was designed from the outset to completely self-starting, and so unstarts were fortunately completely unheard of.
I'll continue the surging saga and things that went bang in the night in my next post.
Oh, and ps:
EXWOK
It was OAF, and you are quite right. (OAF's damaged titanium centre wall was removed, 202's was first modified to airline standard and fitted to OAF, the centre wall from the retired French pre-production aircraft 102 was fitted to 202 (to enable the aircraft to remain airworthy) and finally the damaged OAF centre wall fas fitted to 102 in the museum SO THAT THE ENGINE DOORS COULD AGAIN BE CLOSED. (A neat game of musical centre walls). I may have repeated in another thread that when this event happened (as the result of a first stage LP compressor blade loss in 1982 that an FAA inspector was quoted as saying the no other commercial aircraft could have survived the same titanium fire that OAF did.
EXWOK, as far as your statements regarding the safety of our aircraft go, I'm with you 1000%.
Dude
We've talked quite a bit here about surges and such, so I thought it might be useful to look at what was involved with Concorde 'when things went wrong', in that direction as well as a few other intake horror stories.
The variable air intake control system on any supersonic aircraft is fraught with pitfalls, and downright dangers, the main areas of concern are those of surge and unstart.
A surge, resulting from the breakdown of stable compressor flow, can occur in just about any type of gas turbine engine, however with a supersonic aircraft the effect are really dramatic; The typical characteristics can be really quite disturbing. We get a loss of thrust, an increase in turbine entry temperature and most alarmingly of all a short sharp inlet overpressure, followed by a fairly small longer duration under-pressure. The problem is with any such surge is that unless the cause of that surge is corrected, then the whole process can repeat again and again.
Unstart is far more serious than a simple surge; the inlet shock system is expelled forward of the inlet, with severe 'surge like' effects. Unless changes are made to the intake geometry itself AND ALSO engine demand is reduced, the inlet and engine will not recover and very severe cyclic yawing forces will continue to act on the airframe.
In the case of a Mach 2 surge on Concorde, the most commonly occurring event would be due to a control system malfunction. (The malfunction itself could be an intake ramp going slightly off schedule, a mis-matched engine N1 and N2 at a given temperature or even wing-induced flow distortions. Above Mach 1.6, a surging engine would always cause it's neighbour to surge also. The dynamics of all this, 'a typical surge' are as follows (again quoting from 'The Concorde AICS':
An engine surge is the result of a breakdown of stable airflow in the L/P or H/P compressor sections of an engine. Intake induced surges are exclusively L/P in nature and are brought about by excessive airflow distortions/induced turbulence that can be caused by a number of reasons. A surge will usually result in a sudden sharp rise in EGT, a brief dip in N1 and an almost total collapse of P7 (LP turbine exit total pressure). More dramatically some quite severe over-pressure pulses are generated, that travel forward, into and out of the front of the intake. (During Mach 2+ intake development flying, if an engine surged when the aircraft was operating in darkened conditions, balls of flame could be seen from the flight-deck that were actually OVERTAKING the aircraft at a colossal speed!!). A single surge is relatively short in duration, only about 200 m/sec' or so but can place both the engine and the intake structure under severe trauma. During a typical surge, there is an initial over-pressure of around 50 m/sec' duration that peaks at approx' 10 PSIG, being followed by an under-pressure of about 150 m/sec' duration, peaking at about -2 PSIG. After this point the engine will either recover or the surging will repeat, surges often do tend to be oscillatory in nature and typically repeat at about 8-10 Hz. When you consider the relatively high cross-sectional area of the ramp surfaces, it can be appreciated that very severe peak loads are induced into the whole ramp mechanism from these over-pressures. In the case of oscillatory surging, the effects are even more serious. (The ramps in this case being 'hammered' with severe oscillatory air loads that result in 'organ reed' vibrations of the ramps, at very high peak structural loads).
As far as unstart went on Concorde, well I#m pleased to say that there was no such thing
. The intake was designed from the outset to completely self-starting, and so unstarts were fortunately completely unheard of.I'll continue the surging saga and things that went bang in the night in my next post.
Oh, and ps:
EXWOK
Wasn't 202's divider robbed to go on AB after the latter had a fairly big failure of an engine? Again - no question of airfram damage outside the cowlings. In this respect I reckon the Conc was more robust than many conventional designs.
EXWOK, as far as your statements regarding the safety of our aircraft go, I'm with you 1000%.
Dude
Last edited by M2dude; 20th Sep 2010 at 03:18.
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M2dude
I know this is the CONCORDE thread, and Blackbird was a twin that operated at 3+, so I'll not stay long, but only share what her pilots have shared with me.
Bird burns a one-off fuel, I think J-8. It will not light on start up without a hypergolic chemical reaction with injected ethyl Borate. I am unfamiliar with airstart, but believe it to be impossible following an unstart. If one engine unstarts, the Yaw is nearly 90 degrees, and instantaneous. Rather than wanting to be in dense air, the only hope is to be at thin air, and hope the a/c does not tumble. I have heard estimates that after unstart, the event is 50% fatal. There is a "club" where one's trophy is the helmet, worn at loss of sym thrust. The helmet strikes the side glass and folds in two. I think it is the "crease club".
Her pilots, (there are but two seats) are well trained for all possibilities, and have an edge over CONCORDE in that they have weighed the odds. The commercial ship is engineered to closer risk taking, and her limits also dance at the "edge".
One last SR-71's Size. Don't get the impression she is dainty, she has the shadow of a 727 classic. The Blackbird may have wider limits, but the Concorde put money in the Bank. The Blackbird "stole" two or three Banks per mission.
I know this is the CONCORDE thread, and Blackbird was a twin that operated at 3+, so I'll not stay long, but only share what her pilots have shared with me.
Bird burns a one-off fuel, I think J-8. It will not light on start up without a hypergolic chemical reaction with injected ethyl Borate. I am unfamiliar with airstart, but believe it to be impossible following an unstart. If one engine unstarts, the Yaw is nearly 90 degrees, and instantaneous. Rather than wanting to be in dense air, the only hope is to be at thin air, and hope the a/c does not tumble. I have heard estimates that after unstart, the event is 50% fatal. There is a "club" where one's trophy is the helmet, worn at loss of sym thrust. The helmet strikes the side glass and folds in two. I think it is the "crease club".
Her pilots, (there are but two seats) are well trained for all possibilities, and have an edge over CONCORDE in that they have weighed the odds. The commercial ship is engineered to closer risk taking, and her limits also dance at the "edge".
One last SR-71's Size. Don't get the impression she is dainty, she has the shadow of a 727 classic. The Blackbird may have wider limits, but the Concorde put money in the Bank. The Blackbird "stole" two or three Banks per mission.
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I was always impressed with the groundschool's instructors comment that the a/c could maintain (*maintain*!) a cabin altitude of 15,000' with the a/c at FL600 and 2 windows blown out (all 4 airgroups working). Would've been a bit breezy I should imagine.
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It's not impossible that your instructors were wrong....
This graph is from Chris Orlebar's book "The Concorde Story" (redrawn by me, because the original was too pale to scan properly).
It tells a very different story... after a window blowout you very quickly started an emergency descent, and in the worst case (only 3 airgroups working), the cabin altitude would still peak at about 40,000 ft for about 2 minutes.
I think we'll have to look at our flying manuals to setlle the question!
CJ
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Christiaan - possibly. But even Chris's book's (4-groups working) graph shows the cabin peaking only at just above F220: and that's with the engines at idle with the resultant low bleed pressures. At full dry power, FL600, I could believe the manufacturer's claims on this one. It doesn't really matter - the point is they designed the aircraft not to be exposed to rapid depress to FL600 as that wouldn't be survivable - the small windows and over-engineered air groups meant that the only way the cabin would "pop" to zero diff at ceiling would be following a structural failure the like of which would make what happened next moot...
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bearfoil
Thanks for you interesting post regarding the 'HABU', just like Concorde the SR-71 deserves and has it's own truly unique place in the realms of aviation history. (It really IS my second favourite aircraft of all time). We were always told that the 'I survived an unstart' club was called the Split Helmet Club; any S-R71 guys around can maybe clear this one up. I think that you will find that the fuel was JP-7; your points regarding igniting the stuff are I think correct, at least that's what I read.
The first really good look that I got of an SR-71 was at the Smithsonian hangar at IAD, before it was opened to the general public, and I have to admit that I was surprised what a big beasty she is. (But an absolutely awesome one too).
Please feel free to chip in here anything that you'd like to about the SR-71, I'm sure readers of this particular thread will find it as fascinating as I do.
Dude
Thanks for you interesting post regarding the 'HABU', just like Concorde the SR-71 deserves and has it's own truly unique place in the realms of aviation history. (It really IS my second favourite aircraft of all time). We were always told that the 'I survived an unstart' club was called the Split Helmet Club; any S-R71 guys around can maybe clear this one up. I think that you will find that the fuel was JP-7; your points regarding igniting the stuff are I think correct, at least that's what I read.
The first really good look that I got of an SR-71 was at the Smithsonian hangar at IAD, before it was opened to the general public, and I have to admit that I was surprised what a big beasty she is. (But an absolutely awesome one too).
Please feel free to chip in here anything that you'd like to about the SR-71, I'm sure readers of this particular thread will find it as fascinating as I do.
Dude
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NW1
It always amazed me just how 'tight' the airframe was in this regard. I remember that during construcion we used to do a pressure sustained leak check at 15 PSIG!!! (No one on board of course). She was totally amazing structurally , and if you were lucky enough to do any C of A renewal test flights you'll remember just how long that cabin altitude could be maintained at a fairly comfortable level with ALL air groups (packs to the rest of the world) shut down.
For pressure control, instead of using the 'traditional' motorised Boeing type outflow valve, she used four (I know, we only used two at a time) wonderfully designed pneumatically operated Normalair Garret (now part of the American Honeywell Group) discharge valves. These were not only lighter and far more elegant than the 'modern' units, they were INFINATELY more reliable than the units fitted to the 744 and 777. (As a 777 driver I'm sure you agree). But the real beauty with these things is in the deatail; for example if for some God-forsaken and unknown reason the entire 'guts' of the valve blew out at 60,000', the cabin altitude would be limited to no more than 15,000', due to the design of the frame of the outlet nozzle. (The flow of air through the divergent nozzle section produced. yes you've guessed it, a normal SHOCKWAVE across the divergent neck, choking down the flow).
Yes, they really DID think of everything with our wonderful aeroplane.
Dude
It always amazed me just how 'tight' the airframe was in this regard. I remember that during construcion we used to do a pressure sustained leak check at 15 PSIG!!! (No one on board of course). She was totally amazing structurally , and if you were lucky enough to do any C of A renewal test flights you'll remember just how long that cabin altitude could be maintained at a fairly comfortable level with ALL air groups (packs to the rest of the world) shut down.
For pressure control, instead of using the 'traditional' motorised Boeing type outflow valve, she used four (I know, we only used two at a time) wonderfully designed pneumatically operated Normalair Garret (now part of the American Honeywell Group) discharge valves. These were not only lighter and far more elegant than the 'modern' units, they were INFINATELY more reliable than the units fitted to the 744 and 777. (As a 777 driver I'm sure you agree). But the real beauty with these things is in the deatail; for example if for some God-forsaken and unknown reason the entire 'guts' of the valve blew out at 60,000', the cabin altitude would be limited to no more than 15,000', due to the design of the frame of the outlet nozzle. (The flow of air through the divergent nozzle section produced. yes you've guessed it, a normal SHOCKWAVE across the divergent neck, choking down the flow).
Yes, they really DID think of everything with our wonderful aeroplane.
Dude
Last edited by M2dude; 21st Sep 2010 at 18:34.
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Re the SR-71 JP-7 fuel I cheated, and copied Wikipedia, but it explains an issue mentioned earlier about relights.
"When the engines of the aircraft were started, puffs of triethylborane (TEB), which ignites on contact with air, were injected into the engines to produce temperatures high enough to ignite the JP-7 initially. The TEB produced a characteristic puff of greenish flame that could often be seen as the engines were ignited. TEB was also used to ignite the afterburners. The aircraft had only 20 fluid ounces (600 ml) of TEB on board for each engine, enough for at least 16 injections (a counter advised the pilot of the number of TEB injections remaining), but this was more than enough for the requirements of any missions it was likely to carry out."
She's 107.5 feet long, just over half a Concorde....
But yes, dainty she isn't.
And for my UK friends (or rather the few who may not know this yet), the only SR-71 in a museum outside the US is at Duxford in the American Air Museum.
And very much worth a visit.
CJ
"When the engines of the aircraft were started, puffs of triethylborane (TEB), which ignites on contact with air, were injected into the engines to produce temperatures high enough to ignite the JP-7 initially. The TEB produced a characteristic puff of greenish flame that could often be seen as the engines were ignited. TEB was also used to ignite the afterburners. The aircraft had only 20 fluid ounces (600 ml) of TEB on board for each engine, enough for at least 16 injections (a counter advised the pilot of the number of TEB injections remaining), but this was more than enough for the requirements of any missions it was likely to carry out."
Originally Posted by bearfoil
One last SR-71's Size. Don't get the impression she is dainty, she has the shadow of a 727 classic.
But yes, dainty she isn't.
And for my UK friends (or rather the few who may not know this yet), the only SR-71 in a museum outside the US is at Duxford in the American Air Museum.
And very much worth a visit.
CJ
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When Intakes Go Wrong Part 2
There were many concerns regarding the design integrity of the system, where performance and stability had to be both predictable and safe. The designers at British Aerospace (and to an extent Rolls Royce also) had hundreds and HUNDREDS of flight test hours ahead of them; remembering also that a digital control system had to be 'invented' and flight testing begun in less than two and a half years; the original analog system being totally discarded as far as development went.
The biggest worry for the intake design team was however the STRUCURAL integrity of the intake itself, in the event of engine surging, and this was a worry that was well justified by events. In 1971, the French prototype 001 was undergoing tests when on cancelling reheat (At Mach 1.9, not 1.7 as was the eventual 'norm') the associated engine suffered an N1 overspeed and surged, along with it's neighbour. (001 like it's British sister 002 used the original Ultra Electronics constructed analog intake control system; the digital system being still two years away from taking to the air). Unfortunately in the case of this surge, the intake design was found to be seriously under engineered and the surge over-pressure spike caused the failure of the entire forward ramp attachment assembly. A large section of the forward ramp was blown forward and over the top of the wing (we are doing Mach 1.9 remember) and pieces of the rear ramp were swallowed by the engine, which was already in deep surge. The engine was seriously damaged and flamed out, but miraculously was re-lit at Mach 1.5, of course only to surge again, and was then shut down manually.
After the above event the structure was substantially improved mechanically, in order to prevent any such surges causing failures within the linkages and hinges. The biggest surge fear was always the over-fuelling surge which produced the highest overpressures of all, and it was always a concern that the structure could suffer terribly from such an event. Although the electronic engine control system was carefully designed to avoid such a thing, in normal airline operation it was hoped that this would never happen; IT DID!!:
In early 1977 a Concorde (NOT British Airways) was flying at Mach 2 when the crew noticed a mismatch on engine parameters; the fuel flow of one of the engines was depressed compared to the other three. Unfortunately it was decided instead of following normal procedures that a little 'experimentation' would be tried, and the F/E pulled the N1 overspeed protection system circuit breaker. There was a loud bang, and the aircraft was buffeted by some quite severe yawing forces, the autostabilisation system working flat out to prevent violent yawing of the aircraft. The engine was subsequently shut down as a precautionary measure and luckily the aircraft landed safely. Although there was a little damage to the frame of the intake, generally the structure had stood up well to a very serious event brought about quite honestly by abject stupidity. (There was a malfunction of the overspeed system, causing the system's own 'butterfly’ valve' to partially close off from it's normal wide open position in order to limit the fuel flow. In response the 'normal' engine control system's butterfly progressively opened to attempt to keep N2 on schedule. The overall effect was a wide open normal fuel valve and the overspeed one, in 'series' with the other guy partially closed off. When the F/E tripped the C/B the overspeed valve, that for obvious reasons was not rate limited in any way, to fly back to it's normal wide open position in about 150 milliseconds. So we have two valves, and both of them are wide open, and before the 'normal' valve has a chance to react, MAXIMUM fuel flow is fed to the engine, hence the violent surge.
There was another violent event that was in many ways far more serious: In late 1977 another NOT BA aircraft was undergoing maintenance at CDG, and part of this maintenance input was to replace an intake hydraulic actuator. Now this rather substantial unit lived high in the roof of the intake, just above the forward ramp and drove two screw jacks, winding in and out at ether side. The two screw jacks were coupled to the twin torque tubes (that rotated and subsequently moved the ramps up and down) with a pair of trunnion blocks, these being secured to the screw jacks with a large nut and bolt. The trunnion blocks were very substantial, being designed to absorb any shock loads that an engine surge could provide. Unfortunately the engineers in Paris forgot to fit, yes THEY LEFT OUT the two trunnion blocks, and the only thing attaching the two torque tubed to the actuator were the nut and bolt. (In this condition the thing would have rattled around like crazy, it's a 'surprise' that no one spotted it. (Or even not to mention followed the maintenance manual). The aircraft departed from CDG for JFK, and miraculously attained Mach 2 cruise without incident, that is until there was a system defect on the adjacent intake; this defect was a failure of the servo valve that operated the spill door that was located in the floor of the intake. (There were several servo valve failures in the early years of operation until modifications remedied the problem). The spill door would normally only ever open at top of descent when the throttles were reduced for decelleration, or in the event of an engine shutting down. Now the control system had quite adequate and sophisticated protection for such an falure event, and, due to the same spill door servo being mechanically common to both control channels, (but with independent control windings) froze the intake as both channels failed, preventing any further movement of the surfaces. I seem to remember that the crew drills just allowed a single reset attempt; every time you did a reset, all failure were over-ridden for just over 100 milliseconds, to give the system a chance to get online. While this time delay is in effect, the door was allowed to drive open, before the protection system freezing things up again. Unfortunately, the F/E performed a completely unauthorised rapid series of multiple resets, ech time the door travelling downwards, each time pushing the terminal shock system further aft in the intake, until the inevitable happened and the engine surged. Quite naturally this induced a 'sympathy' surge into it's neighbour intake, the one with the trunnion blocks missing. The surge loads hit the ramps, and without the two vital trunnion blocks in place, the two attachment bolts (which were never designed to absorb such punishment) sheared. The two ramps then freely fell downwards, the front ramp hitting the floor of the intake violently, shattering the honeycomb structure as well as seriously damaging the intake lower lip. Pieces of intake went straight into the compressor, taking out the engine and it's associated temperature probe. (Which unfortunately at the time was being used by the adjacent engine). Fortunately the aircraft, although with serious intake damage, was close enough to JFK to make an emergency descent, and land safely. The intake itself was so badly damaged that is had to be returned to Filton for repair. (Where all Concorde intakes for both countries were built on a separate production line, and fortunately in this case that line was still making intakes). It was highly fortunate that the intakes were still being constructed in late 1977; the wrecked assembly spent several weeks back in the assembly jigs. But things could have been far worse; it was lucky in this event that this pattern of poor maintenance and airmanship did not cause more serious damage.
The intake things that went bang in the night story IS TO BE CONTINUED
Dude
The biggest worry for the intake design team was however the STRUCURAL integrity of the intake itself, in the event of engine surging, and this was a worry that was well justified by events. In 1971, the French prototype 001 was undergoing tests when on cancelling reheat (At Mach 1.9, not 1.7 as was the eventual 'norm') the associated engine suffered an N1 overspeed and surged, along with it's neighbour. (001 like it's British sister 002 used the original Ultra Electronics constructed analog intake control system; the digital system being still two years away from taking to the air). Unfortunately in the case of this surge, the intake design was found to be seriously under engineered and the surge over-pressure spike caused the failure of the entire forward ramp attachment assembly. A large section of the forward ramp was blown forward and over the top of the wing (we are doing Mach 1.9 remember) and pieces of the rear ramp were swallowed by the engine, which was already in deep surge. The engine was seriously damaged and flamed out, but miraculously was re-lit at Mach 1.5, of course only to surge again, and was then shut down manually.
After the above event the structure was substantially improved mechanically, in order to prevent any such surges causing failures within the linkages and hinges. The biggest surge fear was always the over-fuelling surge which produced the highest overpressures of all, and it was always a concern that the structure could suffer terribly from such an event. Although the electronic engine control system was carefully designed to avoid such a thing, in normal airline operation it was hoped that this would never happen; IT DID!!:
In early 1977 a Concorde (NOT British Airways) was flying at Mach 2 when the crew noticed a mismatch on engine parameters; the fuel flow of one of the engines was depressed compared to the other three. Unfortunately it was decided instead of following normal procedures that a little 'experimentation' would be tried, and the F/E pulled the N1 overspeed protection system circuit breaker. There was a loud bang, and the aircraft was buffeted by some quite severe yawing forces, the autostabilisation system working flat out to prevent violent yawing of the aircraft. The engine was subsequently shut down as a precautionary measure and luckily the aircraft landed safely. Although there was a little damage to the frame of the intake, generally the structure had stood up well to a very serious event brought about quite honestly by abject stupidity. (There was a malfunction of the overspeed system, causing the system's own 'butterfly’ valve' to partially close off from it's normal wide open position in order to limit the fuel flow. In response the 'normal' engine control system's butterfly progressively opened to attempt to keep N2 on schedule. The overall effect was a wide open normal fuel valve and the overspeed one, in 'series' with the other guy partially closed off. When the F/E tripped the C/B the overspeed valve, that for obvious reasons was not rate limited in any way, to fly back to it's normal wide open position in about 150 milliseconds. So we have two valves, and both of them are wide open, and before the 'normal' valve has a chance to react, MAXIMUM fuel flow is fed to the engine, hence the violent surge.
There was another violent event that was in many ways far more serious: In late 1977 another NOT BA aircraft was undergoing maintenance at CDG, and part of this maintenance input was to replace an intake hydraulic actuator. Now this rather substantial unit lived high in the roof of the intake, just above the forward ramp and drove two screw jacks, winding in and out at ether side. The two screw jacks were coupled to the twin torque tubes (that rotated and subsequently moved the ramps up and down) with a pair of trunnion blocks, these being secured to the screw jacks with a large nut and bolt. The trunnion blocks were very substantial, being designed to absorb any shock loads that an engine surge could provide. Unfortunately the engineers in Paris forgot to fit, yes THEY LEFT OUT the two trunnion blocks, and the only thing attaching the two torque tubed to the actuator were the nut and bolt. (In this condition the thing would have rattled around like crazy, it's a 'surprise' that no one spotted it. (Or even not to mention followed the maintenance manual). The aircraft departed from CDG for JFK, and miraculously attained Mach 2 cruise without incident, that is until there was a system defect on the adjacent intake; this defect was a failure of the servo valve that operated the spill door that was located in the floor of the intake. (There were several servo valve failures in the early years of operation until modifications remedied the problem). The spill door would normally only ever open at top of descent when the throttles were reduced for decelleration, or in the event of an engine shutting down. Now the control system had quite adequate and sophisticated protection for such an falure event, and, due to the same spill door servo being mechanically common to both control channels, (but with independent control windings) froze the intake as both channels failed, preventing any further movement of the surfaces. I seem to remember that the crew drills just allowed a single reset attempt; every time you did a reset, all failure were over-ridden for just over 100 milliseconds, to give the system a chance to get online. While this time delay is in effect, the door was allowed to drive open, before the protection system freezing things up again. Unfortunately, the F/E performed a completely unauthorised rapid series of multiple resets, ech time the door travelling downwards, each time pushing the terminal shock system further aft in the intake, until the inevitable happened and the engine surged. Quite naturally this induced a 'sympathy' surge into it's neighbour intake, the one with the trunnion blocks missing. The surge loads hit the ramps, and without the two vital trunnion blocks in place, the two attachment bolts (which were never designed to absorb such punishment) sheared. The two ramps then freely fell downwards, the front ramp hitting the floor of the intake violently, shattering the honeycomb structure as well as seriously damaging the intake lower lip. Pieces of intake went straight into the compressor, taking out the engine and it's associated temperature probe. (Which unfortunately at the time was being used by the adjacent engine). Fortunately the aircraft, although with serious intake damage, was close enough to JFK to make an emergency descent, and land safely. The intake itself was so badly damaged that is had to be returned to Filton for repair. (Where all Concorde intakes for both countries were built on a separate production line, and fortunately in this case that line was still making intakes). It was highly fortunate that the intakes were still being constructed in late 1977; the wrecked assembly spent several weeks back in the assembly jigs. But things could have been far worse; it was lucky in this event that this pattern of poor maintenance and airmanship did not cause more serious damage.
The intake things that went bang in the night story IS TO BE CONTINUED
Dude
Last edited by M2dude; 24th Sep 2010 at 14:55.
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When Intakes Go Wrong Part 3
BA themselves had a serious incident, but unlike the OTHER airline this was not as a result of pathetically poor maintenance or airmanship, but of a strange defect coupled with a design anomaly. In the early 1990’s the ramp actuator brake assembly of #2 intake of G-BOAD detached in flight and travelled rearwards, seriously damaging the engine itself, which of course had to be shut down. This defect had never happened before and was attributed to a random failure, until three weeks later the same thing happened again. The aircraft was of course grounded until a fix was found (we could not even find out why this happened). It was known that a feature of the system called ‘HOLD’ would freeze the intake for a brief period (400 milliseconds) in the case of certain failures, inhibiting failure indications and control lane switching at the same time and it was postulated that maybe here maybe lay a clue. (just a theory at this point). Although no static failures could be detected (using specific electronic test equipment) we tried it during an engine run, and found that with a little vibration there was a high frequency repetitive failure of the spill door position resolver, which was replaced. The subsequent engine run proved good, with no further failure indications, and a test flight carried out with the same test equipment fitted, again with without any further failure indications. (It was a great flight too, just me, the three crew and my very large yellow test box at the rear of the aircraft). The aircraft was now allowed safely back into service, and when the offending spill door resolver pack was inspected in the overhaul workshop, a dry soldered joint was confirmed. Analysis showed that the failures were at just the right frequency to allow the ramp actuator brake to be applied, but after the HOLD time delay period expired the failure had cleared, and so the brake was released again, with no other indications, but a fraction of a second later the process would repeat itself. It was estimated that in the three week period between failures over a quarter of a million brake applications had been made, eventually the attachment bolts of the brake assembly failed as a result of metal fatigue. It was a horrible coincidence that this one little soldered joint could fail at just the right frequency to cause such mayhem; eventually stronger bolts were fitted to all aircraft and regular bolt replacements were routinely implemented.
During the first couple of years of Concorde airline operation there was a serious structural issue regarding the intake assemblies. Serious cracking was discovered at the ramp hinge area, and the cause was found to be an aerodynamic resonance issue in the Mach 1.4 to 1.8 flight regime. A short term fix was to strengthen the structure, coupled with a change to the control laws in this speed band. (The change to the intake software did have a performance penalty however). The long term fix was a profiled rear ramp leading edge, and more software changes coupled with a performance enhancing modification to fit a lower, thinned bottom lip to the intake.
The intake was nothing more than an aerodynamic balancing act, where you not only knew and controlled the position of the terminal shock system to within fractions of an inch you also hat to ensure that maintaining critical operation (the normal shock being at the narrowest part of the intake convergent/divergent duct) did not compromise other factors such as ramp angle and control schedule limits variable limits that could result in flow distortion and surge. The system always controlled everything to give you maximum performance, but would move slightly away from this point when necessary to preserve engine flow stability and safety; as was said before, a surge was always the result of something going slightly off 'tune' and was never just ‘one of those things’.
To find the root cause of a surge required a fair bit of forensic analysis; unlike AF, BA had a superb Plessey PVs1580 digital flight data acquisition and recorder (AIDS) system that monitored all the intake parameters; this enabled us to find the cause most of the time, by reading data from the Quick Access Recorder after the flight. (A fair bit of Midnight oil burned though; I still have bags under my eyes ). I remember that originally the singular most important parameter, inlet void pressure, was only sampled once every four seconds by the AIDS system, but once we showed that this was like an ETERNITY when you were trying to track down an engine 'hiccup', we got the sampling rate increased to once per second. Although even this was not ideal, it generally did prove to be sufficient for us.
One small drawback of the thinned and lowered bottom lip was a susceptibility to small pop surges at top of descent, when the throttles were retarded. You just had to be a little careful, and I seem to recall that the initial 'throttle back' minimum limit was 18 degrees throttle angle; zero being max throttle. These surges were very mild and did no damage, but as with all surges post flight engine and intake inspections were required, (no problems werer ever found) together with the usual forensic investigations, ‘just in case’.
Dude
During the first couple of years of Concorde airline operation there was a serious structural issue regarding the intake assemblies. Serious cracking was discovered at the ramp hinge area, and the cause was found to be an aerodynamic resonance issue in the Mach 1.4 to 1.8 flight regime. A short term fix was to strengthen the structure, coupled with a change to the control laws in this speed band. (The change to the intake software did have a performance penalty however). The long term fix was a profiled rear ramp leading edge, and more software changes coupled with a performance enhancing modification to fit a lower, thinned bottom lip to the intake.
The intake was nothing more than an aerodynamic balancing act, where you not only knew and controlled the position of the terminal shock system to within fractions of an inch you also hat to ensure that maintaining critical operation (the normal shock being at the narrowest part of the intake convergent/divergent duct) did not compromise other factors such as ramp angle and control schedule limits variable limits that could result in flow distortion and surge. The system always controlled everything to give you maximum performance, but would move slightly away from this point when necessary to preserve engine flow stability and safety; as was said before, a surge was always the result of something going slightly off 'tune' and was never just ‘one of those things’.
To find the root cause of a surge required a fair bit of forensic analysis; unlike AF, BA had a superb Plessey PVs1580 digital flight data acquisition and recorder (AIDS) system that monitored all the intake parameters; this enabled us to find the cause most of the time, by reading data from the Quick Access Recorder after the flight. (A fair bit of Midnight oil burned though; I still have bags under my eyes ). I remember that originally the singular most important parameter, inlet void pressure, was only sampled once every four seconds by the AIDS system, but once we showed that this was like an ETERNITY when you were trying to track down an engine 'hiccup', we got the sampling rate increased to once per second. Although even this was not ideal, it generally did prove to be sufficient for us.
One small drawback of the thinned and lowered bottom lip was a susceptibility to small pop surges at top of descent, when the throttles were retarded. You just had to be a little careful, and I seem to recall that the initial 'throttle back' minimum limit was 18 degrees throttle angle; zero being max throttle. These surges were very mild and did no damage, but as with all surges post flight engine and intake inspections were required, (no problems werer ever found) together with the usual forensic investigations, ‘just in case’.
Dude
Last edited by M2dude; 24th Sep 2010 at 14:54.
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Just found this thread after a pointer in another Conc thread.
In all the 40 years I've been reading about Concorde, I've never found any of this sort of information before.
Seriously this all needs to be copied over to one of the specialist Concorde sites and tidied up for permanent display. It's a complete treasure trove and it needs preserving.
Amazing information about the SR-71 too, I've been a 'Sled' fan for a very long time too....
In all the 40 years I've been reading about Concorde, I've never found any of this sort of information before.
Seriously this all needs to be copied over to one of the specialist Concorde sites and tidied up for permanent display. It's a complete treasure trove and it needs preserving.
Amazing information about the SR-71 too, I've been a 'Sled' fan for a very long time too....
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Thanks Feathers, glad you enjoyed the thread. The 'black art' of Concorde always was a fascinating subject. I always found ithe idea numbing that this more or less 'set it and forget it' system could achieve so much and contribute so much to the performance of Concorde. Never in the world both before or since could a variable intake give such a large amount of stability and efficiency, time after time. A tribute to the twelve British and two French designers; well done lads and lass. (The two Aerospatiale guys were responsible for the intake/wing aerodynamic interface, true masters of their craft).
Dude
Dude
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I suppose that with the exception of the the SR-71 engine installation, no other aircraft had need of an intake control system that maintained performance in such a tight set of constraints. But yes, truly an impressive piece of engineering and all done with a tiny fraction of the computing power available to the modern designer.
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Yes, in the sense that just about any aircraft going up to Mach 2 and beyond needs some type of variable intake system.
No, in the sense that most of them have a far less sophisticated intake control system than Concorde or SR-71, with only Mach number and throttle setting as inputs.
The Tornado was originally designed for Mach 2+ and used variable intakes. Legend had it that the Tornado AICS had a family relation with the system on Concorde, but since it was developped by a German firm (Nord Micro), that's unlikely.
Also, most of the later Tornados were limited to Mach 1.3, so the AICS and the ramp actuators were removed.
CJ
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The Tornado was originally designed for Mach 2+ and used variable intakes. Legend had it that the Tornado AICS had a family relation with the system on Concorde, but since it was developped by a German firm (Nord Micro), that's unlikely.
(Not sure if this was done with the F3 though).
Fortunately for the western world, the Tornado was (and still is) a superb low level performer, but would have been a so much better Mach 2 aircraft if the powerplant (including the intake) was left to expertise and not politics.
Dude
Last edited by M2dude; 3rd Nov 2010 at 21:48.