Posts about: "Engine surge" [Posts: 41 Pages: 3]

Biggles78
I know these fuel flows seem crazy (If take-off fuel flows had been maintained the endurance of the aircraft would have been about 55 minutes!!). But as the majority of the flight was carried out at Mach 2 and above, with the relatively miniscule fuel flows, you can see how we were able to cross the Atlantic with relative ease. It was the subsonic bit that was the pain.
The powerplant was as you say truly amazing. We had an, as yet, unmatched engine/intake combination, with a variable primary and secondary nozzles. The variable intake allowed supersonic operation with maximum pressure recovery, minimum aerodynamic drag, as well as extreme operational stability. (Extreme temperature shears, that would have caused surge/unstarts in military installations) were dealt with as a total non event). It's astonishing to believe, but at Mach 2 cruise, the intake provided approximately 63% of the powerplant thrust. It was controlled by the world's first airborne digital control system. (The system computers were built by the Guided Weapons Division of what was then BAC). The combination of the variable intake, plus the LP and HP compressors gave an overall compression ratio of 80:1.
The engine itself, being supplied with air at an ideal pressure, could run at an almost conststant TET, thanks to the variable primary nozzle. This also allowed N1 and N2 (corrected for total temperature) to be controlled more or less independently and run as close as possible to their separate surge lines throughout the entire flight envelope.
The variable secondary nozzle (wide open above Mach 1.1) allowed the jet efflux to gently expand against a cushion of air that was passed over the rear ramp of the intake, through the engine bay and into the annulus of the nozzle itself. This prevented thrust being wasted by the jet efflux widely splaying as it met ambient air that was at a pressure of as little as 1.04 PSIA.
It was this integrated powerplant that made true supersonic cruise possible
The airframe life issue was sort of like 'how long is a piece of string?'. The airframes are lifed in supersonic cycles, (which had been extended before, with modifications) and studies were always underway as far as further life extensions were concerned. (Basically the airframe was as tough as a brick outhouse in structural terms). The only real area of concern was the crown area (the roof ). There was a design flaw here in that the structure had not been designed fail-safe (allegedly by designed a Korean designer at A\xe9rospatiale who, it was said, went a bit loopy). When the FAA evaluated the design (in order for the aircraft to be registered in the USA, for Braniff operations out of IAD) they wanted 'crown planking' to be fitted externally, which would have added over a tonne to the weight of the aircraft, as well as producing some not inconsiderable drag. Fortunately a compromise was reached and additional NDT inspections were carried out, as well as more limited structural modifications. There was a long term, cost effective solution being studied, which would have cured the problem altogether. (The changes would have been mandated, over new requirements for ageing aircraft)

Nick Thomas
Nick, the whole expansion issue was one of the biggest issues that had to be addressed. Wiring looms would 'snake' in some underfllor areas to take up expansion, but the biggest difficulty of all were the mulitudes of hydraulic lines. These required sliding expansion joints, with of course seals to prevent leakage. When a seal deteriorated YPU GOT A LEAK!! (Fluid at 4000 PSI tends torun for freedom very quickly ). As far as fittings go, ChristiaanJ is quite right, you tried to anchor at one end only. I seem to remember that the passenger seat rails travelled over a roller afair. Fuel lines wer less of a problem, because their relative lengths were less.
I also agree wholeheartedly with ChristiaansJ's explanation about the 'friction' thing, I never really liked those stories. As a matter of interest, 127 deg's, for Mach 2, that would be at ISA +5 (-51.5 deg's C). Any warmer than that and we could not achieve Mach 2, due to the Tmo limit of 127. I remember one year, for several weeks we had unusually high north Atlantic temperatures; these impacted both the flight time AND the fuel burn. The further away you were from Mach 2, the higher the fuel consumption. (The faster you flew, the less fuel you burnt. How's that for a paradox?).
At ISA (-56.5 deg's C) temperatures, the total temperature was at around 118 deg's C.

ChristiaanJ
I remember the 17.5 degree position on the nose; it always looked as if the aircraft was trying to eat ants to me . I can not recall personally anyone removing the 12.5 deg' stops for access, although this could of course have been done on your side of the 'puddle' I guess.
As far as the APU ducting issue goes (hee, hee, not often we disagree Christiaan ) we are just going to have to agree to disagee about this, although I accept that two 4" diameter pipes (PLUS THERMAL INSULATION) might have done it, BUT I still stand by the other points.

Stlton
Unfortunately not; the keel beam area was extremely thin and there was not anywhere near enough room. Interesting solution on the 727 though, I never knew that one.

Biggles78
You are right on the button. Under NORMAL circumstances, Concorde never flew supersonically in level flight. You would always follow the Vmo bug on the ASI during the supersonic climb. (The ASI pointer actually nudged into the bug; it was a beautiful design). Initially this would be at a constant Vc of 400 kts, the 400 KT segment then went off towards 530 KTS as you climbed. You then 'stuck' to 530 knots until a fraction over 50,000', when 530 KTS became Mach 2. You would then continue the climb at between Mach 2 and around Mach 2.02, depending on the temperature of the day. (the colder the temperature, the faster you tended to fly). There was an extremely complex AFCS mode for the supersonic climb, that I promise to cover in anaother post.
So yes, on the whole, TOC did equal TOD.
The 'subsonic climb' wasn't quite as you thought; you'd normally subsonic climb to FL280, staying there (at Mach 0.95) until the acceleration point. Mach 0.95 was 'subsonic cruise'. But you were on the right track.
Oh, and NOPE, they never boomed us either
Nick Thomas
Keeping the powerplants as separate as possible was a major design headache, but generally they were just that; there was a titanium centre wall between the two engines and a really substantial heatshield above the engine also, to protect the wing above. To give you an idea how all this worked in practice, in 1980 G-BOAF, flying at Mach 2 between JFK and LHR had a major failure of one of the engines, caused by a defective material ingot used in the forging of one of the 1st stage LP compressor blades; which was subsequently shed. (The analysis done by Rolls Royce ensured that no such incident ever happened again in the life of Concorde). The resulting mayhem terminated in a large amount of engine debris flying around, and a titanium fire burning in the engine bay also. The aircraft however decelerated and landed at Shannon safely. On inspection, although there was extensive damage found in the engine bay, the adjacent engine was completely unmarked, protected by the titanium centre wall, and more importantly, when the heat shield werer removed, the wing was found to be completely undamaged!
The only problem you ever had with the dual nacelle arrangement was if you had an engine surge above Mach 1.6 (These were relatively rare, but could happen with an engine or intake control system malfuntion). If one engine surged, the other would surge in sympathy, because of the shock system being expelled from one intake severely distorting the airflow into it's neighbour. These surges were loud, quite scary (to the crew that is, most passengers never noticed much), but in themselves did no damage at all. Delicate movement of the throttles (employed during the subsequent surge drill) would invariably restore peace and harmony again to all. (The intake on Concorde was self-starting, so no manual movement of the intake variable surfaces should be needed in this event). After this was over, normal flying was resumed again As I said before, these events were relatively rare, but when they did occur, they would be dealt with smartly and professionally; the engine and intake structure being undamaged. (Post surge inspetion checks were always carried out on the ground after an event, on both engine and intake, but nothing much was EVER found).
The reduction of fuel flow as you climbed was quite interesting. Although the throttles would be 'at the wall' (dry power remember), the electronic control system was constantly winding fuel off as a function of Static Air Temperature, as well as falling Total Pressure. The system was always 'tweaking' as you climbed, and you only used as much fuel as you really needed to stay at Mach 2. There were various ratings that would also be manually selected at various phases of flight; each rating change 'detuned' the engine slightly, so yes, you did not run the engine when flying fast at anywhere near the levels you did at lower speeds/altitudes. The engine final ratings were changed from 'Climb' to 'Cruise' manually at FL 500, just as you hit Mach 2).

Hi M2Dude - keep it coming! I missed all this stuff from the early days......

Tim00 - good question, and very relevant.

It takes a lot to incapacitate a Flight Engineer - beer, cigars and scary women were no issue - they were definitely the most relaible part of the operation. (And arguably the least attractive.....)

If the unthinkable happened the First Officer would find himself on the FE's seat. We practised it less often than you might think, but thought about it a great deal. Especially the fuel system management.

Which brings me to your second point - yes, there was a preset for the 'automatic' fuel transfer system, although that wasn't the mechanism used for the pilots to 'take control' of the CG. The critical thing was to be able to get the CG forward if a rapid decel had to be made - for this reason there was an override switch above the First Officer which used various pumps and valves to txfr fwds - primarily by txfring from tank 11. It would be used in various recall checklists (supersonic 4-engine flameout and Continuous Ssurge at M>1.3 seem to register from the dim past) until the FE was able to take over the txfr system himself.

I didn't ever need it - in the surges I encountered the FE was always ready to manage the txfr before we needed the override.

Oooooooh!!!! There's a new topic for someone: Surges.

Theoretically the correct checklist to call for was the "Continuous Engine surge above M 1.3 Conditional Procedure, please". In reality the call was always much more succinct.

Monosyllabic, in fact................

I'm off to the pub, but I bet Bellerophon can speak with erudition on the operational aspects, and if M2Dude is who I suspect he is, I KNOW he'll be able to cover the technical aspects in great depth!

WOK

ChristiaanJ
aaah yes, Max Climb/Max Cruise modes. I'd not forgotten this my friend, I was going to say a few words about that in a future post, but maybe we can do that now. (And I'd love to hear more of your comments on this here too, ChristiaanJ). The intake and autopilot modifications were in a way complimentary it's true, but really dealt with separate problems, at least in my view:
The intake control unit software change (a change to the control law that limited engine N1 as a function of intake local Mach number, Mo, and inlet total temperature, T1) was able to put an absolute limit on aircraft achievable Mach number during Mmo overshoots, but it would not PREVENT Mmo overshoots occurring altogether, it was more of a safety brake. This particular overspeed problem manifested itself well before route proving, and in fact the intake system 'fix' resulted in the Thrust Auto Reduce System being deleted, electronic control boxes and all. The TAR system was fitted on all development aircraft equiped with the digital intake system, and it tried (in vain) to limit extreme Mach overshoots. The production aircraft retained the TAR wiring and locked out circuit breakers, as well as two vacant spaces on the electronic racks. The prime reason for all these efforts were that some of the rapid excessive Mach overshoots quite often drove the intake into surge; the modification to this N1 limiter control enabled engine mass flow to be controlled in such a way that these surges could be prevented during temperature shears. The aircraft Mach limit was an extremely useful fringe benefit.
The AFCS mode change from what was Max Op and Max Op Soft (always loved that name) to Max Climb/Max Cruise was at a stroke able to deal with the regular Mmo overspeeds that kept on occuring during, as you say, the route proving trials of 1975, when British aircraft G-BOAC and the French aircrfraft F-BTSD carried out pre entry into service evaluation flights, SD sadly was the aircraft that was tragically lost at Gonez in July 2000). The Max Climb/Max Cruise AFCS mode combo is a mode like no other that I've personally seen before or since anywhere, (it for instance resulted an elsewhere taboo; an autopilot and an autothrotte working together IN A SPEED MODE).
This problem encountered primarily at lower lattitudes, (for example, G-BOAC doing route proving flights out of Singapore), occurring initially as the aircraft reached Mach 2. It was termed 'the insurmountable problem', but the AFCS designers (such as ChristiaanJ) fortunately did not have 'insurmountable problems' in their vocabulary. The issue was that the aircraft would have been climbing rapidly at Vmo of 530 KTS, with throttles at the gate as usual, At exactly 50,189' we hit what was known as 'the corner point' in the flight envelope, where 530 KTS IAS equated to Mach 2 exactly. Max Op mode would then 'let go' of the Vmo segment, and try and control the aircraft to Mach 2. (As the aircraft climbed, Vmo itself would progreesively decrease in order to equate to Mmo, or 2.04 Mach). But in very cold conditions, the aircraft still 'wanting' to accelerate, and the simple Max Op/Max Op Soft modes just could not cope with gentle pitch changes alone. The problem became even bigger during the cruise/climb when severe temperature shears occured, and routinely regular Mmo exceedences occured. Something had to be done, and something WAS done and how; enter Max Climb/Max Cruise. It was really a classic piece of design, where the aircraft would do the initial supersonic climb in Max Climb mode. This mode itself was relatively simple, in that it was more or less a Vmo -Vc hold mode. That meant that the difference at selection between indicated airspeed, Vc and Vmo would be maintained, with a vernier datum adjust to this being available. In practice this mode was selected pretty much at Vmo, so datum adjusting was not always required. Now comes the clever part; the autothrottle, this would operate in standy mode at this point, just waiting there doing nothing, with the throttles at maximum as before. So the aircraft would now climb as Vmo increased to 530 KTS, and then following a now constant Vmo of 530 KTS until the magic 'corner point' (51, 189' remember). Now all hell would break loose; the mode would automatically change to Max Cruise, the autothrottle would also be automaically selected to Mach Hold mode (initially datumed here to Mach 2) and the throttles would retard, attempting to hold this Mach 2 datum, and the autopilot is commands a 'fly up' signal, over a 20 second lag period to 600'/minute. Now comes an even cleverer (?) part; the autothrottle Mach Hold datum is gradually increased over a 100 second period towards Mach 2.02, and so in stable conditions the throttles would now gradually increase again until they once more reach the maximum limit. At this point, the autothrottles now come out of Mach Hold mode and back into the waiting in the wings standby mode. The autopilot would now cancel it's 600' fly up, demand, returning to a datum of Mach 2. There was a little more complexity built in also, where the difference between the 'commanded' and actual vertical speeds offset the autoplilot Mach 2 datum. This would apply whether the autothrottle had cut in (+600'/min demand) or with the throttles back at maximum (0'/minute demand. A positive climb error tweaked the cruise Mach up slightly, a negative error (eg. in a turn) the converse was true. The effect of all of this complexity was that the aircraft itself could 'scan' until it settled at a point where the throttles could be at maximum, and the speed between Mach 2 and 2.02. On the North Atlantic, with warmer ISA temperatures, there was usually just the initial routine with the autothrottle as you hit the corner point. However at lower lattitudes (eg. LHR BGI) there could be a few initial autothrottle intercepts before things settled down. This whole incredible routine completely took care of the insurmountable problem, a problem that was shown not only to be insurmountable, but was put to bed forever, by people like ChristiaanJ.
I hope that my explanation here does not sound too much like gibberish.

EXWOK
I think you've guessed right as far as my identity goes; it's great that it's not just Concorde pilots I can bore the socks off now
PS. I bet the ex-SEOs LOVED your comments

Dude

A great thread and it only goes to show that you can always learn even about a subject that you thought you knew quite a lot about

As M2Dude described the rearwards transfer of fuel during acceleration was meant to be an automated process but in reality there was a lot of manual input. The first requirement of the F/E was to match the rearwards movement of the C of G to that of the ever increasing Mach number. If this was proving to be no problem he would take over the transfer manually by switching off the pumps on one side of tank 9 or 10 so as to pump only to either tank 5 or 7. This was because if you transferred evenly to these tanks due to their different shape size and position the aircraft would go out of trim laterally so the F/E would pump rearward just to one tank so as to keep the C of G going aft whilst maintaining lateral trim.

Being Concorde nothing was straight forward , which meant that when Tanks 5 and 7 ran out and you started using tanks 6 and 8, their size shape and position,was exactly opposite to that of tanks 5 and 7 so it now required the F/E to pump fuel the opposite way across the ship, using various valves and pumps, so as to keep the aircraft in trim laterally.

All the time he had to maintain the trim so as to keep an elevon trim of \xbd deg down, which as fuel was burnt required him to trickle fuel forward from tank 11. On the longer trips such as those to and from BGI the fuel towards the end of cruise became quite low and to stop fuel in the collectors from dropping below 1000kgs each, fuel would be transferred from tank 11 into the collectors until the
C of G had reached it's forward limit at Mach 2.0 of 57.5 %. If then the collectors dropped to 1000kgs the aircraft had to descend to subsonic heights and speed.

Surges

Surges were not an uncommon or common event on Concorde,but when they happened as they usually affected both engines on that side the aircraft would lurch /yaw and everybody on board would know about it as \x93Her In Doors\x94 would testify to that when glasses full and otherwise ended up in her lap during the meal service when a surge occurred.

The drill required all engines to be throttled to a predetermined position and the intake and engine control switches moved to their other position. If this stopped the surge then the throttles were restored to their cruise power a pair at a time and if no surge re-occured then the aircraft would return to cruise / climb

The crews post surge action was normally to have a cup of tea and light up a cigarette.

In the early days on a flight between London and Bahrain when the aircraft was in supersonic cruise the F/E who was a mature and refined gentleman, had to go to the toilet, which was just behind the front galley, and whilst there the engines surged. He was seen running from the toilet to the flight deck with his trousers around his ankles, which was a hell of shock to his refined nature

Enough for now sorry about the length

Brit312
It's so great to have a Flight Engineer's input into this fascinating thread. Your write up on the complexities of managing the fuel system was something else; the best such description I've ever read. I'm still wetting myself with your story about the E/O coming out of the loo with his trolleys around his ankles after a surge. (Not you I hope ).
The original air intake that was in use for the first few years of airline operation was as you know far more prone to surging than the later modified intake with the thinned and lowered bottom lip, which was far more stable and forgiving. Not only was the 'new' intake more stable, a new leading edge fitted to the rear ramp as part of the same modification, at a stroke cured the very serious ramp vibration issue, that was causing intake structural problems at lower supersonic Mach numbers. The most impressive change of all was a fuel saving of around 1.5 Tonnes per Atlantic crossing, with even bigger improvements in cooler temperatures. A major software change obviously accompanied this modification.

ChristiaanJ

Quote:

The one I know about is the ADC/DAC board (analog-digital and digital-analog converter board). The supply of either ADCs or DACs ran out literaly worldwide, and the board had to be redesigned, requalified and recertified with more recent components, and a new batch manufactured. The cost, for the replacement of that board alone, came to about 3 million euros

YEP! I remember now, the ADC/DAC board definitely WAS one of the candidates that were modified.
I think you will find the tale about AICUs being removed after museum delivery flights was more urban myth. The only units that I can remember being removed or relocated were the ground power protection unit, the TCAS processors and the radar transceivers. (BA had retrofitted their aircraft with a superb Bendix system a few years earlier, and the same units (with windshear detection re-enabled) are used on other aircraft types).
As far as ferrite cores are concerned, asked by DozyWannabe , the original Delco C1VAC INS fitted to the BA Concorde aircraft did utilise ferrite cores. These were replaced with CMOS EPROMs when a modification was carried out in the early 90's, in which a navigation database was fitted to the units. The fuel consumed and total fuel remaining indicators definitely used a ferrite core memory. These electronic displays used an internal memory in case of power interrupts. As far as AFCS goes, can you check your records? Although, as you say, a completely analog system (with the exception of the ITEM test computers) I seem to remember that the Safety Flight Control Computer used a ferrite core for the flying control strain gauge null memory. I could be wrong here, but I can't remember any other NVM in use at the time.

Galaxy Flyer
I'll leave it to one of my pilot (or F/E) friends to answer this one it that's OK.

Dude

Brit312 at 19.39 yesterday has given us a clue.
Surges
3rd paragraph.

It was determined in a very early stage, that an engine surge or engine failure at supersonic speed would produce a very abrupt, inacceptable, and possibly dangerous, amount of yaw.

So the prototypes were equipped with "autorudder" computers. They used pressure sensors in the engines to detect engine failures, and they would then kick in a "pre-dosed" amount of rudder, that would then be "washed-out" gradually while the pilot dealt with the issue and added rudder trim.

They were manufactured by SFENA, and since I was their flight test support at Fairford, they became automatically my "babies".

The computers (analog, big boxes, the same size as the autopilots or air intake computers) were extremely reliable (we had only two passive faults during the entire flying career of 002).
Unfortunately the same could not be said of the pressure sensors, and since it was always easier to "pull" a computer than a pressure sensor, we found a computer on the bench every few weeks, which then had to be taken through a full test spec and sent back with "no fault found", before anybody was willing to look at the sensors.

Luckily a better solution was found, using a lateral accelerometer, and from the preprod aircraft onwards, each big separate autorudder computer was replaced by a single board tucked away in the autostab computer.

Since the function was always "on", there was no separate autorudder engage switch. Many years later, I discovered that several airline Concorde pilots did not even know the function existed....

CJ

Nick Thomas

...I just wondered how the engine was kept at a sub idle 30% N2?...

Just below each engine's individual start switch, there was a second switch, which would select the type of start required, either NORMAL or DEBOW.

When between ten minutes and five hours had elapsed since an engine was last run, a debow start was required. With a debow start selected, the engine was started normally, but the debow system automatically stabilised the engine at a sub-idle RPM, around 30% N2, whilst the interior engine temperatures became more uniform and the HP spool shaft re-aligned/straightened itself.

As to exactly how it did this, you're going to need a reply from an engineer not a pilot. As far as we were concerned, it was the PFM box in the engine start system!

After running for one minute stabilised in debow (or when the debow light came on) the F/E would return the debow switch to normal and check that the N2 returned to idle and the debow light went out. The F/E would monitor the N2 very carefully over these few seconds, as the engine came out of debow, to check that the engine cleared rotating stall.

If it didn't, two things would happen.

Firstly the F/E got fairly busy, trying to clear the engine out of rotating stall without causing it to surge, and secondly, as with any Concorde engine malfunction drill, I quietly give thanks that I was a pilot and not a F/E.

If a debow start was required, but somehow got missed, the engine could give a reasonable impression of an out-of-balance tumble drier, or so I'm told.

Best Regards

Bellerophon

Nick Thomas
Just like Christiaanj I'm trying to dig up an accurate flight envelope diagram. (A lot of my Concorde 'technical library' is out on long term loan), but I would suggest that anywhere within Concorde's published flight envelope you never hit any equivilant to Coffin Corner, a la' U2. The whole issue is really one of air DENSITY, rather that pressure, where as you climb at a given Mach Number, your Indicated airspeed (IAS) falls away with altitude. (Velocity of sound being primarily tied to static air temperature). Now if you are climbing in the stratosphere, where temperature is more or less constant up to around 65,000', you can say that your TRUE Airspeed (TAS) is also constant with climb at a given Mach number. But lift and drag are functions of IAS (the equivalent airspeed that the aircraft would 'feel' at sea level) and not TAS. Because the U2 had a very low Maximum allowable Mach number (Mmo) as IAS fell away with altitude, it would get to the point where it's lowest permitted airspeed (we called this VLA) got to within a few knots of Mmo and severe aerodynamic buffering. i.e. you were screwed with nowhere to go but down .
In the case of Concorde, Mach 2 at FL500 was 530KTS, falling to 430KTS at FL600. Although we have less lift due to 100KTS lower IAS, the aircraft is now much lighter (this is the whole principal of cruise/climb) which keeps the universe in balance, but drag is now significantly lower too, getting us better MPG .
On the ASI, the only limitation displayed was Vmo; however the Machmeter did display fwd and aft CG limits at a given Mach number. The ONLY time that Concorde would experience relatively low speeds at altitude was at Top of Descent. I'm a little fuzzy here how it all worked exactly (it's an age thing you know), I'm sure one of the pilots can correct me, but I seem to remember that the autothrottle was disconnected, ALTITUDE HOLD was selected on the AFCS, and the throttles slowly retarded. (If you pulled back too far you'd often get a gentle 'pop surge' from the engines, and you had also to be wary of equipment cooling airflow too). The aircraft was then allowed to gently decelerate, still at TOD altitude, until Mach 1.6, when power was tweaked to give 350KTS IAS and IAS HOLD was selected. The aircraft was now free to carry out her loooong descent to 'normal' altitudes. VLA on Concorde was not directly displayed as you never flew anywhere near it, and also every pilot knew his VLA . (Stray into this and you'd get a 'stick' shaker warning.
I hope this blurb helps Nick

Dude

The deceleration would be like very hard braking after landing, so - yes.

The drag incurred flying supersonic was once described to me as like flying through wood, not air. The only times I ever closed all 4 throttles at M2 was dealing with surges (see earlier posts on the subject). While not quite like flying into teak, the decel was very impressive - it more than once resulted in a member of cabin crew appearing in the flt deck in a semi-seated position, grimly trying to stop a fully loaded galley cart.......

As for four-engine flameouts - perish the thought. The checklists, like many, depended on flight phase;

Above M1.2 it was expected that windmilling would provide adequate eletric and hydraulic power so the c/list aimed to start a fuel txfr forward, use the spare hydraulic system to drive half the PFCUs, ensure a fuel supply to the engs and ensure cooling to equipment.

Below M1.2 the RAT would be deployed, it was less likely that the standard means of fuel txfr would work so valves were overridden and the hydraulic fuel pumps brought into use, and the Mach fell further the PFCUs were put on half-body use only, using the stby hydraulic system.

You weren't far from the ground, in time, at this stage so it was a good time to get an engine relit!

Given the Olympus' auto-relight capability a four engine loss was going to be caused by something fairly drastic.

Brit312
mm I guess they were not to blame for flying for over one hour with a red throttle light on (the engine is under no electronic control), resulting in the severe engine overspeed (N1 overspeed protection amplifier already disabled) and the subsequent scrapping (on the orders of Rolls Royce) of the entire rotating assembly of the engine. Or for omitting TWO intake trunnion blocks during a ramp actuator replacement, and then the E/O continually and cyclically operating the intake lane selector switch, following a spill door runaway, until he manages a double engine surge and near destruction of the 'forgotton parts' intake and engine also. I suppose they are not to blame for the experimental tripping of the LPOG circuit breaker by the E/O, during an engine power mismatch, resulting in serious damage to the engine and intake due to the resulting massive over-fueling surge. I suppose again, that they were not to blame for ignoring for over 6 months a simple electrical load defect, eventually resulting in a not too minor fire in the electronics racks that had to be extinguished by the crew with extinguishers. And yet again, I suppose they are not to blame for putting skydrol into Concorde hydraulics systems, almost resulting in the loss of the aircraft, as well as a 9 month grounding while all of the hydraulic components were replaced. And it was not Air France that hammered Fox Delta twice into the runway at Dacca, resulting in so much airframe distortion that the aircraft performance was seriously compromised (and eventually broken up). And of course they were not responsible for the technical and operational failures, including the (forgotton AGAIN ) missing spacer and overweight take-off etc.) on 25th July 2000. Silly me.
And although I might have said 'precautionary engine shut-down', we are talking about a quite an eventful episode here indeed, you can NOT excuse the further mistakes made on that day, 'just because they are poor old Air France. With the greatest of respect Brit, there are 3 crew members on that flight deck, do you not think that the loss of over over 5 tonnes of fuel over a period of time might just be noticed????? The subsonic 3 engined leg was carried out for quite a time before it computed to them that they were still losing fuel. There is no excuse for flying with your eyes closed, I'm sorry.
For goodness sake, this is probably the biggest single episode that was behind the demise of Concorde, poor Air France my eye!!!

Dude

NW1
I do remember well that the AF incident was as a result of severe vibration, that was what I was (not very elequently) eluding to in my previous post. The engine shut down was due to these vibrations, not because of any fuel loss. According to Rolls Royce the fuel pipe fracture ended up being as a result of an engine build failure, on the part of the AF sub-contractors. However my 'eyes closed' comment still holds here I'm afraid, it's basic situational awareness folks. And I'm not jumping to any conclusions here , I helped investigate the first of the serious errors (the experimental c/b tripping/overfuel surge incident) when I was still at British Aerospace in early 1977 and learned long ago to get my facts straight as far as possible in these things.
As a grotty old engineer I tend to lack the subtlety and diplomatic skills of you guys, but this coming at the end of such a long catalogue of gross errors, this possibly last straw in the life of Concorde was in my view also the very last straw in terms of these serious procedural failures too.
There are so many events in Concorde's history that we would like to 'roll back the clock' on, but this extremely pivotal one has to be just about at the top of a very big pile (save of course for the Gonesse tragedy).

Dude

NW1 and ChristiaanJ
Ahh yes, the super hi-tech 'HUD'. It was right up there with the 'eye level datum' indicator and not to forget, the reheat capabiliy indicator in terms of sophistication. (Extremely reliable though ).
As far as 3 engined ferries went; well NW1, not sure if you'd call me seasoned or just just clapped out and wrinkly, but it did happen a very few times in days of yore, mostly from SNN back to LHR. There were at least two; OAF in 1980 when she had the infamous LP1 blade fail (and Monty Burton's immortal words during the 'event' "what *** ing drill?). The second one that I can remember was OAA in 1991 when there was another far less serious compressor blade failure. In each case for the ferry flight, the broken engine was 'swaged' to prevent it windmilling and the aircraft would be flown back to the LHR garage by a management crew. There was however another required ferry measure as well as the engine swaging, this measure was to prevent the good engines going into contingency, due to the very slightly flamed out dead 'donk'. This procedure required the Engine Speed Unit to be removed from the electronics rack and a special jumper plug fitted in it's place (without the jumper fitted the start switch would never latch in. In this case also the E/O would also need to manually disengage the start switch at 25% N2). I have to admit that I never in my life ever saw this jumper plug, and in the cases that I can remember the aircraft departed SNN with the three engines at contingency. I remember that the case of OAA back in '91 most certainly was; I was flown out to SNN equiped with a pile of circuit diagrams and test boxes to investigate what we all thought was just a surge related engine shutdown. only to find a slightly more hairy state of afairs, with a very broken engine indeed. As a matter of interest, this particular failure was the only one ever in the history of Concorde in BA attributed to the engine having run for a protracted time in rotating stall. (This had happened on the previous day). A lot was learned by both BA and Rolls Royce after this event, and this failure never occured again.

Dude

Oh darn it Feathers, if you insist (LOL).
First of all, what is rotating stall? All gas turbine engines are prone to this to some degree or another, the Olympus was particularly prone (so we discovered to our cost). What happens is that extremely LOW figures of N2, small cells of stalled air rotate around the anulus of the early stages of the HP compressor (at approximately half the rotational rpm), resulting in parts of the airflow becoming choked and highly distorted. This often results in the combustion process being disturbed to the extent that combustion instead of occuring in the combustion chamber, occurs in the turbine itself. This of course results in massive overheating of the turbine blades and stators (and is what is suspected occured in the #2 engine on G-BOAA in 1991.
To prevent running in rotating stall, the Olympus automatic fuel start schedule would accelerate the engine quickly to around 67% N2 before dropping back to the normal idle figure of around 65% N2. (The stall clearance N2 figure was ambient temperature dependant, the higher the temperature the higher the N2 that was required and hence scheduled by the automatics).
What had happened on G-BOAA was an engine starting/accelerating problem, where the N2 ran at a sub-idle of around 40% N2 for several minutes. This was enough for the malignant effects of rotating stall to take hold, and the resulting turbine blade failure over the Atlantic the following day. In all fairness to everyone involved, none of us, including Rolls Royce realised just how potentially serious this phenonomen was, and salutary lessons were learned by one and all. (The following year Air France had a similar failure; their first and last also).
I flew out to Shannon on a BAC 1-11, that was sent to fly the Concorde passengers back to London. As I and my colleague were coming down the ventral door steps of the 1-11, a chirpy Aer Lingus engineer asks 'have you guys come to fix the broken engine?, there are bits of it lying in the jet pipe'. Now up to now, from the information we'd been given in London, we thought that we were going to be looking at either an intake or engine induced surge, a few systems checks and boroscope inspections and we'd all be on our way, so we naturally thought the Aer Lingus guy was joking. He was most certainly was not; as you looked into the jetpipe (through the secondary nozzle buckets) you could see a large quantity of metal debris, accompanied by a strong smell of burnt oil. I remember this day well, it was the day that the first Gulf war ended; how ironic.
The aircraft departed on three engines, flown by a management crew late the following day, my colleague and I returned to London by Aer Lingus one day later. (No passengers whatsoever are permitted on ferry flights, even expendable ones like me).

Dude

Landroger
Good to see you here again Roger, I'll try my best to give you my take on rotating stall. (I worked very closely with Rolls Royce in the Concorde days, and everything I know about the process is thanks to them). Turbine engine combustion is a precise and delicate affair, particularly during start, and too much or too little fuel can cause severe problems. With rotating stall, the rotating cells of stalled air. if they manage to take 'hold' can cyclically choke the flow into the latter compressor stages (it's the cyclic nature of the cells that is the real problem, hence the 'rotating' stall term). The cells as they 'hit' the compressor blades (the cells are rotating at half shaft speed in the opposite direction of shaft rotation) can cause blade vibration and can also cause minor surges within the engine. The combustion fire literally can burn in the turbine section, but any distortion to the combustion process will result in local overheating, due to poor air/fuel mixing etc. In some engine types, damage can be also be caused to the HP compressor blades (due to vibration) but with the Olympus the main danger was to the turbine blades and stators. It's difficult to relate to any common analogy for this lot I'm afraid Roger.
Rotating stall was avoided in the Olympus by starting the engine with the primary nozzle driven wide open, and controlling two parameters; those being the opening rate of the fuel valve and the rate of rise of exhaust gas temperature. (During the start sequence, once ignition had occured the EGT rise was held to 6 degrees per second, right up until rotating stall clearance at 65% temperature corrected N2 ). So the engine accelerates without let or hinderance right through the danger zone, but was prevented from dipping below 65% temperature corrected N2, where the danger zone starts again. (Absolute minimal idle for the Olympus 593 was set at 61% N2).
I sincerely hope this blurb helps Roger, if not then feel free to ask again or PM me.
Regards

Dude

Mr Vortex
First of all, 'welcome aboard'; I'll do my best to answer your queries.
The area of the primary nozzle Aj, was varied for 2 'primary' purposes :
a) To act as a military type 'reheat' or 'afterburning' nozzle; opening up to control the rise in jet pipe pressure P7, as reheat is in operated.
b) To match the INLET TOTAL TEMPERATURE RELATED (T1) speed of the LP compressor N1 to the HP compressor N2 against a series of schedules, ensuring easch spool is as close as safely possible to its respective surge boundary, (with a constant TET, see below) and therefore at peak efficiency.
Now, in doing this a complex set of variables were in place. As the nozzle is opened there is a REDUCED pressure and temperature drop across the LP turbine. This has the effect of enabling a HIGHER N1,as less work is being done by the turbine. Also the change (in this case a decrease) in the temperature drop across the turbine will obviously affect the turbine entry temperature, TET. A closing down of the nozzle would obviously have the opposite effect, with a DECREASE in N1 and an INCREASE in TET.
In practice at a given T1 there was always an ideal N1 versus N2 on the control schedule (known as the E Schedule), the TET staying more or less constant from TAKE-OFF to SUPERSONIC CRUISE!!
As far as noise abatement went; when reheat was cancelled and power reduced after take-off, an E Schedule known as E Flyover was automatically invoked. This had the effect of driving the primary nozzle nearly wide open, reducing both the velocity of the jet efflux and in essence the noise below the aircraft.
The real beauty of this primary nozzle system was that it really did not care if the engine was operating dry or with afterburning ('it' did not even know). P7 was controlled against a varying compressor outlet pressure, the variable being controlled by a needle valve operated by the electronic engine controller. (If this is unclear I can post a diagram here that shows this control in action).

As soon as I receive back the majority of my technical notes that I have out on long-term loan (I've requested their return) I will post a schematic here. But for now; The tanks were vented to atmosphere via tandem vent galleries, the two vents openings being on the left hand side of the tail-cone. At an absolute static pressure of 2.2 PSIA (around 44,000') twin electrically operated vent valves, also in the tail-cone, would automatically close; the tanks now being pressurised via a small NACA duct on the right side of the fin. A tank pressure of around 1.5 PSIG was maintained by the action of a small pneumatic valve at the rear of the aircraft. There was massive protection built in to guard against over-pressure (eg. if a tank over-filled in cruise).

I hope this answers some of your queries
Best Regards

Dude

The "venom" is in the tail of your question.....
Best glide angle for Concorde is in the order of 1:10, so with an multiple failure at 40,000ft (7.5 miles) your "nearest airport" would have to be well within a distance of 75 miles.
(BTW, I think somebody earlier already mentioned that a large part of the actual descent from top-of-descent was with the engines barely above idle, so that it was much like a glide. It was during the final hold, approach and landing, that it was preferable to have a few engines left.....)

Four-engine surges have happened a few times during flight testing, but I don't think there ever has been a four-engine flameout.

Re the SAAB Draken, I would think a dead-stick landing would be possible, but only IF you could arrive 'overhead' at about 10,000ft and IF you were well aware of the horrendous sink rate 'on the back of the drag curve' once you committed to the final approach and landing.
Even the F-104G, not known for its gliding qualities, could be and has been landed dead-stick - there is a section on the subject in the flight manual. On the 104, things were further complicated by the fact that without an engine you also lost the "blown flaps", so your landing speed was a lot higher.

In Western Europe, with its densely populated areas on the one hand, and a lot of airbases on the other hand, there were certainly cases where you thought twice before 'punching out'.

CJ

galaxy flyer
Well the RAT was 'advertised' to be able to maintain 4000 (ish) PSI on Green and Yellow systems down to around 200 KTS, so IN THEORY you'd be ok (ish), refering to Brit312's post. Incidently, one of the prime reasons that the engines were housed in twin nacelle pairs, rather than the original TU144 'monobloc' style was to eliminate the chance of a severe ripple surges flaming out all four engines. (But as the thing had half of the engine air passing over the massive stowed main undercarriage, they had other problems to worry about anyway).
I have to echo your point GF about carrying on asking questions, even if they may seem dumb at the time. It's all about how we all had to learn in the first place; Personally I'm happy to answer any questions at all here (the questions may not be stupid, but some of my answers........... ).
Regards to all

Dude

Hi all,

I've just wonder that does the Concorde use a surge tank or
some a kind of a NACA duct like on B737 for pressurize the fuel in a tank?

Also, in Concorde F/E panel around the fuel control panel there're switch call
trim pipe drain switch. Which I tried to read and figure it out but finally I don't
know what it actually do and in which circumstance do we need to use it.

Thanks for yours reply.

Best Regards

Vortex