Posts about: "Hydraulic" [Posts: 49 Pages: 3]

Point taken GF, but it was discovered during development flying that that the Olympus 593 could be relit, given sufficient IAS, at almost any altitude within the normal flight envelope. The variable inlet would even be automatically scheduled, as a funcion of N1, in order to improve relight performance at lower Mach numbers. I certainly agree that you would decelerate and lose altitude fairly quickly under these conditions, however a multiple flame out was never experienced during the entire 34 years of Concorde flight testing and airline operation. There was, as a matter of interest an un-commanded deployment of a Concorde RAT AT MACH 2!! (The first indications of the event were when the cabin crew complained about 'a loud propeller sound under the rear cabin floor'. A quick scan of the F/E's panel revealed the truth of the matter). The aircraft landed at JFK without incident, and the RAT itself, apart from a very small leak on one of the hydraulic pumps, was more or less un-phased by the event. Although it sounds horrific, a prop rotating in a Mach 2 airstream, the IAS it 'felt' would be no more than 530 KTS at any time. The RAT was of course replaced before the aircraft flew back to LHR.
Not quite sure about your reference to the RAT on an F16 being Hydrazine powered; a Ram Air Turbine is just that, using the freely rotatting propellor to power hydraulics, electrics or both. Or do you mean the the F16 has an emergency power unit? Either way, it's fascinating stuff.
Yes, I do remember that the Germans used Hydrazine as a fuel during WW2: The father of one of our Concorde pilots was on an air raid to destroy one o the production plants there, this aviation business is such a small world.

Galaxy Flyer
Thanks very much for your comments. It's true, that while supersonic, a windmilling Olympus engine would have sufficient N2 to keep all servics on line. (The hydraulic systems on Concorde also operated at 4000 PSI). The RAT itself was 'said' to be good down to approach speeds, fortunately we never had to find out if that was true. (Although the thing was tested routinely using a hydraulic rig to drive it and check the variable pitch speed control). Thr RAT was in fact located and stowed in the fwd part of the R/H inboard elevon Powered Flying Control Unit Fairing. It was an absolute work of art by Dowty, to make the device fit into such a small space.
Yep, an ash cloud would be particularly bad news, particularly at FL600
Stlton
You are most welcome, thank you for posting this topic also. These forums are a wonderful way for all of us out there in the aviation world to share and learn interesting information from each other.
TURIN
I remember reading By the Rivers of Babylon many MANY years ago. The terrorists, I seem to remember, had a bomb fitted inside Tank 11 (the rear trim tank) during construction 'before it was welded shut'. Not sure if the author had researched how aircraft were built, but still I guess it sold a copy or two. (Well at least you and I read it).

Hi Christiaan, yes THAT was the MEPU (Good photo of G-BBDG by the way). As far as fitting an APU in the tail cone, I still personally think that UNLESS you are prepared to pass a sizable pneumatic duct through a fuel tank , (Remember that tank 11 occupied the entire rear fuselage between the rear cargo aft wall and the front of the tail cone). then I don't think that this was really on. (It's quite possible of course that I'm missing something here, it comes with age ).
As far as the MEPU goes, all it really did was drive 2 hydraulic pumps; the Green System then powering the 40 KVA emergency generator; unless you are going to use the APU for engine starting and ground air conditioning, then I honestly don't think that there would be much point. It's interesting also to note that the MPU, being a rocket motor, needed no air intake, and as it was not driving any huge loads, the exhaust duct dould be quite narrow.

Biggles78
I must admit, it seems excessive carrying 10,000kg in a trim tank, but this fuel system really was a study in elegance. Every single drop of fuel carried was usable by the engines, and the Mach Trimming was so good that you could fine-tune the process so as to achieve the minimum drag configuration for the aircraft of 1/2 degree down elevon in supersonic cruise. One rather amusing point about the fuel Mach trimming; the airworthiness authorities insisted that the aircraft also had a conventional Mach trimmer built into the electric pitch trim system. As the aircraft was mostly flown on autopliot, assuming the fuel trimming was being done correctly (it always was), the auto-trim would wind off this Mach trimming as it was applied, the net result of course being no change to the pitch demand. This really was a totally superfluous addition to the electric trim system. (If for any reason the aircraft HAD been hand flown during acceleration, the pilot would have to nudge the trim button nose down all the time as the A/C accelerated, in order to to oppose the nose up electric trim input).
The fuel, apart from 'lighting the fires' and trimming the aircraft was also used as a cooling medium for engine and IDG oil, as well as for the hydraulic system also. Where it was used to massive effect, was as a cooling medium for the air conditioning system. Here, at Mach 2 conditions, we needed air to exit the 'packs' (on Concorde these were called 'groups') at around -25 deg's C. By the time this air had travelled through the wing ducting it had risen to a sweltering 0 deg's C, at which temperature it entered the cabin. The astonishing thing is, that the air used for this, HP compressor delivery air, P3, was at around 550 deg's C as it left the engine. The ram air itself, used to cool the Primary and Secondary heat exchangers, had a total temperature anything up to 127 deg's C, and to complete this story, the fuel itself had an average temperature of around 60 deg's C. And surprisingly enough, it was a more or less conventional air conditioning system, using air/air intercoolers, an air cycle machine, with just the addition of the fuel exchanger (between the outlet of the secondary heat exchanger and the ACM turbine) to make it any different in concept to most other air cond' systems.

Biggles78,
To complement M2dude's notes re nose and visor:

There were basically four 'positions':
Nose and visor up (supersonic),
Nose up, visor down only (subsonic climd and descent),
Nose down 5\xb0, visor down (take-off and initial climb),
Nose down 12.5\xb0, visor down (approach and landing).

Normally nose and visor are raised and lowered by the green hydraulic system (as is done until today on F-BTSD at Le Bourget).

In 'standby' mode, the visor was lowered by the yellow hydraulic system.
Then the nose uplocks were released by the yellow system, and the nose would free-fall to the 5\xb0 position.
Another switch allowed to hydraulically release the 5\xb0 downlocks, and the nose would free-fall again, now to the 12.5\xb0 psition.
In this 'standby' mode, the nose and visor could not be raised again.

In the best "belt, braces AND a piece of string" tradition of Concorde, if both the 'normal' and 'standby' system failed, there was a big handle on the F/O side of the central pedestal.
This released the nose uplocks manually, the nose would start to free-fall, automatically unlocking the visor, and both would then free-fall down: the nose only to the 5\xb0 position.

To complete the story... there is a 5th position: nose 17.5\xb0 down!
This was the 'nose fully down' position as designed originally and installed on 001 and 002.
It met with sharp criticism from the test pilots, because of the lack of a forward visual reference with the nose fully down. "It's like looking over the edge of a cliff", was the unanimous comment of the pilots.
So a couple of mechanical stops were added that limited the 'nose down' angle to 12.5\xb0.
But the basic design of the nose was not changed otherwise, so even on the production aircraft the nose could be lowered to 17.5\xb0, but only in the hangar, by removing the mechanical stops. It may have been done a few times, for better access to the visor and nose mechanism.

Minor anecdote... the nose and visor were up during supersonic flight, of course, but also when the aircraft were on the ground and parked outside, simply to keep the rain and dirt out.
But... the prototypes had a metal visor, with two tiny windows, and it was inconveniently dark on the ground in the cockpit with the visor up . So on the ground we always kept the visor down, unless the aircraft was parked outside for any length of time.

Thanks for your answer CJ. There must have been some flexibilty built in around the window openings other wise the window openings near the fixed point would show less movement than the ones at the other end which would show 3 to 4 inches difference between the inside panel and the actual window. I guess all the hydraulic and fuel lines must have had some "slack" to allow for expansion.

I would say not: there wouldn't have been any space in the wheel well.
The gears retracted inwards, and when up, the bogies were right next to each other on each side of the keel. As a matter of fact, the main gear legs had to be "shortened" while they retracted, otherwise they wouldn't even have fitted...
No, because the inside trim wall panels were relatively short (say about 10 ft, don't remember exactly) and each moved with their bit of fuselage (think roof tiles). Same applied to the floor panels, which also were in fairly short sections. The movement was of course hidden by the carpets.
Yes indeed. Flexible sections all over the place.

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
Sorry Biggles78, I'd forgotten to answer your CofG query, so here we go: CofG was a really critical parameter on Concorde, being a delta, with no tailplane made it more so at take off speeds, and as we've previously said, was how we trimmed the aircraft for supersonic flight. CG was expressed as a percentage of the aerodynamic chord line. To get indication of CG you needed to know the mass of fuel in each tank; easy, from the FQI system. You needed to know the moment arm of each tank, (fixed of course). You then needed the zero fuel weight (ZFW) and zero fuel CG (ZFCG); these were manually input into the CG computers by the F/E, from load control data. The final parameter you needed was total fuel weight, again easy from the FQI system.
The 'normal' T/O CG was 53.5%, but in order to increase fuel weight (and hence range) an extra 'bump' was enabled to allow a max T/O CG of 54%. (CG was indicated on a linear gauge, with forward and aft limit 'bugs' either side of the needle. These bugs would move as a function of Mach and at the lower end of the speed range, A/C weight also). As the A/C accelerated, the limit bugs would move rearwards (with of course the rearward shifting centre of pressure) and so the fuel would be moved from the two front trim tanks 9 & 10 to the rear tank. 11. Once tank 11 reached it's preset limit (around 10 tonnes), the remainder of the 'front' fuel would automatically over-spill into tanks 5 & 7. (Once the fuel panel was set up, the whole process was controlled with a single switch). At Mach 2, the CG would be around 59%, the whole rearwards shift being in the order of 6'. As we said before, the 'final' CG could be tweaked to give us a 1/2 degree down elevon, for minimum drag.
I really hope this helps Biggles78.

Guys, back to the Airbus thing; My friend ChristiaanJ gave some really accurate insights, (he always does) but there is another legacy that carries on the this day; some of the audio warning tones were COPIED from Concorde into Airbus. (For example, the A/P disconnect audio is identical). I think this is great, and gives 'our' aircraft a lasting everyday legacy.

As far as the fly by wire goes, Concorde had a relatively simple analog system, with little or no envelope protection (Except at extreme angles if attack). As has been previously poted before, production series test aircraft 201, F-WTSB, pioneered the use of a sidestick within a new digital fly by wire Controlled Conviguration Vehicle sytem, with envelope protection and attitude rate feedback. (This evolved into the superb system known and loved by the Airbus community). It is a really bizaar twist of fate that the Concorde FBW system has more mechanical similarities to the system used in the B777 than Airbus. (Mechanically similar at the front end, with an electric backdrive system moving the column in A/P mode; Concorde being backdriven by a hydraulic relay jack).
As a final piece of irony; the Primary Flight Control Computers on the B777 are designed and built by GEC Marconi Avionics in Rochester Kent, now BAe Systems. This is the same plant where Elliot (becoming Marconi and finally GEC Marconi Avionics) developed and built the UK half of the AFCS computers. Isn't this aviation world strange?
Galaxy Flyer
Your inputs here are great, and I'm sure appreciated by all. (I assume from your name that you were a C5A pilot. While I was in the RAF on C-130's, our Lockheed rep' used to supply us all with company magazines, that were full of stuff on this new (it was then) giant of the sky. I fell in love with it there and then).
Anyway, back to Conc': The decel' positions were carefully worked out and adhered to; the aim was to be subsonic to within (I think) 50 nm of the east coast. I'll wait for one of my Concorde pilot friends to confirm that here, but i think I'm correct. I do have a fond memory of one flight out of JFK; we were temporarily 'held' by Boston ATC to Mach 1.6 (and at around FL440) because of an Air France Concorde heading for JFK. We saw this guy above us, at around FL580 on a near reciprical , doing Mach 2, screaming straight over the top of us. We were excited by this amazing spectacle, and so were the AF crew over the VHF ('you never boomed us, did we boom you?'). But the most excited person of all was this guy in Boston ATC. ('I've never seen anything like it guys, your two blips whistled over each other on my my screen like crazy').
Stliton
As far as the F/D noise levels were concerned, once the nose and visor were raised, it was as if someone had switched off the noise . The main source of noise up there was just the equipment cooling, and that was not bad either. It was, in my view, little noisier up than most subsonics. (But not the 744, where you are so far away from all the racket ).
Ozgrade3
You're making us blush here; thanks for your comments, I think we are just trying to share some of our experiences (and 'bit's we've picked up over the years).
From my perspective, I did write some stuff used by our pilots, AF even got a copy or two I think.

Nick Thomas

... My other query concerns the FE. I understand that he set take off power etc...

Actually the F/E didn’t set T/O power, but did set most of the other power settings.

Broadly speaking, taxy-out to gear up, and gear down to engine shut down, the handling pilot operated the throttles. At other times, it was (almost) always the F/E.

Bear in mind that several of the routine engine power changes were effected through controls other than the throttles. For instance, selection of the re-heats, engine control schedules, engine ratings and intake lanes were all switch selections.


... I also understand that he also checked the pilots inputs into the INS system...

Correct, using INS3.


...So was he/she also a qualified pilot?..

No, they were professional flight engineers, who held a Flight Engineers Licence; they were not pilots biding their time before moving to the right hand seat.

I believe one or two may have held a PPL, but that was purely incidental, not a requirement.

All of the Concorde FEs had spent years on the VC10, B707, DC10, L10-11 or B747 fleets before coming to Concorde.


Biggles78

...Am I right or even slightly so in thinking that cruise climb and cruise descent was the flight...

Cruise climb, yes. Cruise descent, no.


...and there was minimal actual level cruise in the "pond" crossing?..

Correct, any level flight in the “cruise”, was just coincidence, probably caused by the outside air temperature increasing very gradually. Typically, she drifted up at around 30 to 50 fpm, but, if encountering warmer air, she would start to drift back down, in order to maintain M2.0.


... As you have said, fuel flow was reduced the higher you got. I think it was 5T per powerplant at FL500 down to 4.1T at FL600...

Rather optimistic figures for FL500 I’d have said! 6,000kg/hr/engine would have been nearer the mark!


...I am curious to see how much less fuel would have been used at the higher FLs considering it was reduced by 900Kg/hr for just 10K feet...

The reason the fuel flows dropped so much at the higher altitudes was that the aircraft had to be a lot lighter before she would get up there. It was her lighter weight that was the primary reason for the reduced fuel flows, not the higher altitude.

Forgive me if I’ve misunderstood you, but in her cruise climb, Concorde was flown at her optimum speed (M2.00) with (constant) optimum power set (max cruise power) and so (assuming a constant OAT above the tropopause) the only thing which affected her cruising altitude was her weight.

So, in theory at least, in cruise climb, she was always at her optimum altitude.

Any variation from that optimum altitude, such as a premature climb to higher altitudes, would have cost fuel, not saved it.


... How much of the descent was carried out while supersonic...

At the decel point, the cruise climb ceased and she was flown level at constant altitude. The F/E partially throttled back the engines and she stayed in level flight until her speed reduced to 350kts IAS, typically M1.5.

This took about 50nm, and most of the passengers would have sworn that they were already descending.

She then descended at 350kts IAS, meaning the Mach number would reduce constantly. On a straight in approach to JFK, with no subsonic cruise section, she would become subsonic descending through (around) FL350.

For a straight in approach, in zero wind, on a standard day, from FL600 to touchdown, typical figures would be something like a track distance of around 200nm, flying time of 22 minutes and 3,500kg of fuel.

Into LHR, she had to be subsonic much further away from her destination, and then had a subsonic cruise section on airways, so a slightly different procedure was used, and approaching FL410 she was slowed still further, becoming subsonic around FL400.


Anonymous

In response to your PM, earlier posters were correct in what they posted, however the manual reversion they refer to is a reversion from electrical to mechanical signalling to the flying controls.

There was no way to operate the flying controls manually in the absence of hydraulic power.

Galaxy Flyer
We never had a case of lost pressurisation, ever. The cabin windows had dual laminated panes; an inner pressure pane and an outer thermal pane. We had dual systems that kept the cabin at a max diff' of 10.7 PSI, the engine bleeds pushing about 200lb of air per minute into the cabin. This allowed you to fly the cabin at an altitude of around a 6000' maximum only, right up to TOD. If you HAD to fly subsonically, the ideal was Mach 0.95 at FL290. (Subsonically the aircraft had similar range to normal, but took well over twice as long of course). If however you had to shut down an engine, your range deteriorated quite dramatically, and a diversion was usually sought.

It's great that Bellerophon is posting here again; we need a steely eyed Concorde pilot's input here (not just the boffins/nutters and nerds [that's me ]. To touch more on a couple of his valid points;
Fuel burn: The aircraft would naturally require less fuel as she became lighter and as a consequence gently climbed to maintain cruise Mach number, this is what the engine control system was doing all the time, even though the throttles were wide open it was 'tweaking'.. BUT, the decreasing IAS as you climbed, due of course to the reducing density, just like any other aircraft meant that drag was reducing too, so it was a combination of both of these factors, reducing weight and reducing drag.
Flying controls: It was a slightly weird but wonderful arrangement; pilots inputs would move a servo valve in the hydraulic relay jack, the jack would move in response and drive both a resolver AND mechanical linkages. The resolver ourput was sumed with the flying control position resolvers, and the error signal was fed into an autostab' computer, where it was summed with stabilisation demands (primarily axis rate and acceleration). The autostab computer would the directly drive the surface, and the reducing error signal would reduce the demand etc. While all this was going on, the mechanical linkages would slavishly follow, but as long as you were in FBW (what we used to call 'signalling') mode, these mechanical inputs were de-clutched at the PFCU, so did nothing at all. Only if there was an EXTREMELY unlikely failure of BOTH FBW channels would these inputs be clutched in and the flying control group (rudders, inner elevons or outer and mid' elevons) would then be in Mechanical signalling. The system redundancy was checked after engine start on every flight. But to reinforce what Bellerophon stated, there was no mechanical reversion here; without hydraulics you had nothing. Another aside here; the designers, being paranoid like all good designers (no offence Christiaan ) were worried what would happen if the controls would somehow jam up. A jammed mechanical flying control input run itself would have no effect on FBW operation whatsoever, due to spring boxes being fitted to the runs. A 'Mech Jam' light would be set, together with a separate red light and audio warning, but this was all. But to completely protect against the aircraft was fitted with a Safety Flight Computer (SFC) system. The idea was, if a control axis (pitch or roll only) jammed up, the captain could press down on a switch light set between the two halves of his control wheel, (at the centre of the 'W') and the Emergency Flight Controls would activate. Strain gauges at the front of the control wheel, two sets on each control column for pitch and roll axis, would input into an SFC that would covert the control force into an elevon demand. These commands were then fed into the autostab' computers, and hence directly into the controls. (A little like L-1011 CWS in a way). There was a little test button that was used to test this system, again after engine start. So although the controls were jammed, the aircraft could still be flown. (Never used in anger I'm pleased to report).
But there was a problem; if this system was inadvertantly used, the results could have been catastrophic, as the system was extremely sensitive indeed, and full elevon movement could be enabled with only moderate effort. Because of this hairy prospect some safeguards were obviously put in place. The first safeguard was an interlock in the autostab' engage logic; If the switchlight had been inadvertently selected beforehand (the light was green by the way) you would not be able to engage pitch or roll autostab's (both channels too) so you would not be going flying until that was fixed. The second safeguard was a little more subtle; A plastic, frangible cover was fitted over the switchlight, unless the captain pressed reasonably hard the cover would prevent the switchlight from being pressed. At least that was the theory, in practice this little bit of plastic could be a pain in the ass . It was carefully fashioned, and I seem to remember BAe charging the airlines a few hundred pounds each for these things. If some wally fitted the cover upside down (and unless you were careful it was easy to do) THE THING WOULD NOT BREAK!! I remember at Fairford in 1976, G-BOAD was on pre-delivery flight testing, and the late great test pilot John Cochrane was doing a test of the system. The cover on this occasion HAD been fitted upside down, and of course he could not plunge his thumb through it and engage the EFC button. After trying everything, in the end he removed a shoe, took out his pen, and smashed the plastic cover until it broke. (It's OK, the autopilot was engaged at the time). Unfortunately, his combined shoe/pen emergency device also wrecked the switchlight as well, so the system still could not engage. (There was only a switchlight on the captain's side). After he landed and he confronted us all with his dilemma, he was shaking; not with rage but with laughter. (This was the great John Cochrane, sometimes the dour Scotsman but he was always able to see the lighter side). After that event, careful instructions were issued regarding the fit of the cover, and it was modified and made a little more frangible.

Biggles78
The tailwheel design really was the one exception in poor design terms, but I'm sure that if the aircraft was doing what she should be doing right now, (you know routinely flying across the Atlantic and beyond, instead of languishing in museums), modifications would have finally put this particular malady to bed). In design terms, the rest of the aircraft was nothing short of a flying work of art, a masterpiece. Having said that though, personally I would rather that four rather than three hydraulic systems had been used. Originally there were four systems in the design, but the RED system was deleted, as it was felt to be superfluous. My own view is that this particular decision was total poppycock. Oh, and Green, Blue and Yellow hydraulic systems was something else that Airbus copied from Concorde.... although we ourselves pinched that idea off of the Comet ).
As far as the hydraulic expansion joints go, I will scour around and see if I can find a diagram for you. Try and picture two titanium (or stainless) tubes, on inside the other, with a sealed chamber being formed at the join. Inside this chamber were multiple lands fitted with special viton GLT seals. They did work incredibly well, although occasionally one of the seals gave out, and things got wet, VERY WET.
As far as the 4000 PSI hydraulic system, as EXWOK quite rightly pointed out, the loading on the flying control surfaces were immense throughout the whole flight envelope. (Picture alone just the T/O from JFK RWY 31L, where the aircraft is tightly turning and the gear retracting, all at the same time). As well as the flying controls and landing gear, you also had the droop nose to consider, four variable engine intakes as well as a couple of hydraulically operated fuel pumps. Oh, and in emergencies, a hydraulically driven 40 KVA generator too. The reason that 4000 PSI was chosen was that if a large amount of hydraulic 'work' was to be done, the only way to keep the size of jacks and actuators to a reasonable size/weight was to increase the system pressure by 25% from the normal 3000 PSI. (On the A380 they've gone a step further and gone for 5000 PSI, saving them over a tonne on the weight of the aircraft).
Concorde used a special hydraulic fluid, Chevron M2V. This is a mineral based fluid, as opposed to the ester based Skydrol, used by the subsonics. The reason that we went for a different fluid was a simple one; Skydrol is rubbish at the high temperatures that Concorde operated at, no good at all in fact, so we needed something better and in M2V we found the PERFECT fluid. As an aside, unlike Skydrol, that attacks paintwork, certain rubber seals, skin, EYES etc., M2V is completely harmless, wash your hair in it. (I did, several times when we had leaks. Thinking about it, maybe THAT is why my hair is such a diminished asset

EXWOK
It's so great having another of my pilot friends diving in to this post, welcome welcome
I remember the Mech' Signalling part of the air tests, my lunch has just finished coming back up thank you. (for interest chaps and chapesses, with mechanical signalling, using just the conventional control runs under the floor, there was no auto-stabilisation).

The artificialfeel system worked incredibly well I thought, I always found it curious that the peak load law in the computer was at the transonic rather that the supersonic speed range. It was explained to me long ago that this was because the controls really are at their most sensitive here, but at high Mach numbers are partially 'stalled out', due to shockwave movements along the surfaces, and were therefore less effective. (For this reason I was told, the inner elevons were so critical for supersonic control, being the most effective of all elevons at high speed).

To all , I forgot to mention in my previous post regarding the engine failure in G-BOAF in 1980; I remember an FAA surveyor, who was taking a look at the carnage within the engine bay, saying that in his opinion, no other aircraft in the world could have survived the intensity of the titanium fire that ensued. Analysis showed that the fire was successfully extinguished, possibly at the first shot of the fire bottle. This was a testament to the way that the Concorde engine bay could be completely 'locked down' when the fire handle was pulled, as well as to the way that the whole engine installation was technically encased in armour plate. To put all this in context, acording to Rolls Royce a titanium fire, once it takes hold, can destroy the compressor of a jet engine in four seconds.


Dude

Notfred
Love the lightning story, hadn't heard that one before.
That would have been production series test aircraft G-BBDG, A/C 202 before a purpose built hangar (more shed really) was built to house her, with fin and U/C removed. This aircraft has now been beautifully restored at Brooklands museum.
You are quite correct about the pushback, not having an APU (THAT story again ) meant that a one engine in each nacelle pair had to be started on the gate, and the other in each nacelle started after push. Having a symetrical pair started enabled all 3 hydraulic systems, and hence most of the critical systems to be checked puring pushback.
Brake temperatures always had to be monitored; they really could get very hot. If a wheel was still too warm after T/O, then the gear would be left down just a little longer to aid cooling. (Each brake also had an electric cooling fan).
Idle thrust was always a problem in that it was too high; there was a 'lo idle' setting, but depending on the temperature of the day the difference was not that big. You could not just reduce idle some more because of a malady known as rotating stall. This can plague any engine, but the Olympus 593 was particularly susceptible. At very low idle speeds, pockets of air 'rotate' around the first few compressor stages and can completely alter the airflows through the engine. It is important that the engine is always accelerated quickly through this zone on start-up, because serious damage can occur if the engine runs for any period of time in the rotating stall region. If the engine DOES operate in this zone, then the combustion process can even occur in the last few stages of the HP compressor, causing extreme damage. This damage, although malignant, can result in blade failure and the subsequent damage to the combustion chamber and turbine areas. This can occur within a few flights of the event, so just cranking down the idle was never an option.

As a BA apprentice in the early eighties I spent 12 months in the old 'wing hangar' (TBB) cutting my teeth, as it were, on the future of aviation. (The newly introduced B757 was also housed there so I was partly right). I was still growing-9 stone wet through and I had to run around in the rain to get wet-so if there was work to be done in the "Bent Nail's" fuel tanks then I was volunteered. Pouring tins and tins of Thiokols best sealant along leaking joints was a favoured pastime, so it begs the question were the leaks ever plugged?

I have a load of photos of G-BOAG just before it was reintroduced (rebuilt?) into service after being a Christmas tree for years. I think it was taken out of service after the wrong hydraulic fluid was uplifted but I may be wrong there. Never seen so many robbery labels before or since. If I ever get my scanner I'll post 'em up one day.

Fascinating thread gents, keep it going.

I had the pleasure of one trip as SLF on Concorde LHR - JFK (1978/9? grey cells depleting) which involved a return to LHR after dumping fuel due to hydraulic failure of two systems. No complaints from me, two take offs and landings for the price of one plus two hours of additional catering at LHR while the aircraft was fixed. Big run on asprins by the time we approached JFK!
However on the second departure the AC also suffered loss of hydraulic systems and I understood that it arrived at JFK on one system. After a storm delay at JFK I departed on AA listening to the ATC on the IFE with the Concorde following. Yet again the Concorde requested fuel dump and return due to hydraulic failures. The previous days I believe the Concorde had also experienced hydraulic failures and at one point BA cancelled some flights. AF were not experiencing the same problems and I read several years later that the problem was attributed to minute quantities of water being introduced into the system by a repenishing tanker being parked outside, wheras AF stored their tanker inside. The water then generated steam when the system ran with consequent seal failures.

Is the above cause correct, or was there more to the story?

Apart from all the normal Concorde observations, I also noticed that when trolling around over Bristol dumping fuel at a relatively high AoA the rear outboard surfaces, I was seated at the rear, vibrated at an alarming aplititude and frequency. Would this be caused by aerodynamic buffet or rapid auto pilot control inputs?

Thanks in anticipation.

Hi canuck slf, Your incident was not the hydraulic contamination one, I'll describe that one in a minute or so below.
As far as your adventure goes, in the early days of Concorde operation there was an on-going issue of hydraulic seal failures. This led to the sort of thing that you described, where a major seal failure would occur, resulting in the loss of a main system. The standby Yellow system would be switched in to replace the failed one, and depending on the nature of the initial failure, could leak out of the same failed seal. (There were a couple of 'common areas', they were the intake spill door jack, and the Powered Flying Control Units; failures here could result in a double system fail). Your incident was almost certainly due to one of these cases. In the early 1990's the original Neoprene hydraulic seals were replaced with a new Viton GLT seal; this material had far superior age shrinking characteristics to Neoprene, and more or less cured the problem overnight. Eventually all the seals in each aircraft were replaced, and apart from a very few isolated cases, dual system losses were eliminated forever. Air France suffered a similar proportion of failures, however as their flying hours were a fraction of BA's, the effects were not as immediately apparent.
As far as far as the hydraulic contamination story goes, this happened in 1980 but involved one aircraft only, G-BOAG, but in it's original registration of G-BFKW. (having previously been on loan from British Aerospace, where it flew originally as a 'white tail' under this registration). The fragile nature of Concorde hydraulic fluid was not fully understood at this time, and as you say, a hydraulic drum dispenser had inadvertently been left exposed to the atmosphere, and had subsequently suffered water contamination, and this contaminated fluid had found it's way into G-BOAG. Now this hydraulic fluid, CHEVRON M2V has only two vices: One is that is extremely expensive, and the second is that it is highly susceptible to water contamination, EXTEMELY SO. If my memory serves me correctly, the maximum allowable level of water in the fluid is about 8ppm. (parts per million) and the fluid that was analysed after G-BOAG's problems was at about 30 ppm. The water deposits in the fluid gave the equivalent effect of 'rusting up' of critical hydraulic components. I was investigating an air intake control defect the previous day to the incident, but like everybody else had no idea that the real issue here was one of major systems contamination. We were all convinced that we had nailed the problem, only to find that the aircraft turned back on it's subsequent LHR-JFK sector with more serious problems, not only affecting the air intakes, but the artificial feel system also. It was now that we realised that there had to be a hydraulics problem here, and after fluid analysis, the awful truth was discovered. After this event, and the fragilities of M2V fluid were better understood, a strict regime of housekeeping was put in place in terms of fluid storage, and no such incidents with BA ever occurring again. The aircraft itself did not fly again for nine months, all components that were affected were removed from the aircraft and completely stripped and overhauled. Also all of the system hydraulic lines had to be completely purged, until there were no further traces of any contamination. After the aircraft was finally rectified, she successfully again returned to service with her new 'BA' registration of G-BOAG. However the following year, during a C Check, it was decided that due to spares shortages, and the closure of the LHR-BAH-SIN route, there just was not being enough work for seven aircraft, and therefore G-BOAG would be withdrawn from service. (In terms of spares, BA at the time for instance only had six sets of aircraft galleys, as aircraft went in for C checks the galley was 'robbed' to service the aircraft coming out of it's own C check). The aircraft was parked in a remote hangar, and was only visited when a component had to be 'robbed' for another Concorde, and the aircraft soon fell into disrepair, was filthy externally and became a really sad sight. Many people (not myself I might add) were adamant that G-BOAG would never fly again. However, in 1984 things had really started to improve for Concorde, with the charter business increasing and the LHR-JFK route in particular becoming a staggering success. It was decided that OAG would be returned to an airworthy condition. In 1985, with a fresh new interior, and with the new BA colour scheme, she was finally returned to service; and remained as one of the mainstays of the fleet right up to the end of Concorde services in October 2003. She now resides at the Boeing Museum of Flight in Seattle. (I have particularly fond memories of G-BOAG; in a previous post I mentioned flying through an electrical storm in late 1991 over Saudi Arabia, while returning from BKK-BAH to LHR. What I forgot to mention was the spectacle of DOZENS of fierce fires burning on the ground, towards our starboard horizon. These were Sadams oil fires, still burning in Kuwait. It made a sombre contrast to the amazing electrical spectacle right in front of us).

As far as low speed flying control activity was concerned, this was a combination of the fairly flexible outer wing sections, being buffeted by low speed turbulence (the wing tip tanks 5A & 7A also being empty), as well as some autostab inputs. This was perfectly normal, and part of the design our aircraft. However the development aircraft had even more flexible outer wing sections, which used to almost straighten up in high speed flight. However due to fatigue concerns, external lateral stiffeners were added to the underside of the wings during production of the airline aircraft. (these can be easily seen from underneath the wings, just outboard of the nacelles). Unfortunately these external stiffeners also resulted in over a one tonne fuel penalty to the production aircraft, due to increased weight, as well as higher drag in a critical part of the wing aerodynamic surface.

Dude

BRIT312
This story is totally hilarious, can't quite get this visual out of my head. ('100 KTS, POWER SET' sounds so boring in comparison). I never had the good fortune to meet any of the Braniff guys; sounds like there was certainly a character or two there. It really is a pity that their operation never really got a chance to expand into the proposed Pacific Rim service, who knows, it might really have done something.
It's generally known that the BA aircraft were temporarily re-registered to facilitate Braniff's operation out of IAD to DFW; G-BOAA, B, D & E were re-registered from G-BOAA and so on, to G-N94AA etc. Being an older registration, G-BOAC was re-registered as G-N81AC. At IAD, the 'G' part of the registration was covered over, leaving a now perfect 'American' tail number. Only five aircraft were involved in the operation (at the time BA operated just six aircraft, G-BOAF was still at the manufacturers at Filton, and G-BFKW (later to become G-BOAG) was on loan from British Aerospace. In order for the necessary FAA certification, required for operation by a US airline, a modification package were required by the FAA. Some of these modifications seemed a little 'picky' and irrelevant at the time (they still do). However some modifications were certainly not in this category, and quite honestly should have been 'picked up' by the CAA & DGAC during original certification of the aircraft. As an example, if the flying controls had been operating on GREEN or BLUE hydraulics only (due to an indicated spool valve jam) and that particular hydraulic system was subsequently lost, there was originally no automatic switching to select the standby YELLOW system into the flying controls; the controls would have been completely unpowered until a manual selection was made by the pilot. . One of the 'FAA Mods' was to facilitate just that, so if this (extremely unlikely I grant you) scenario had occurred, then YELLOW would automatically been selected into the controls, and at no time would the controls have been in an unpowered state.
The Braniff operation ended in May 1980, due to heavy losses on the subsonic only route, and it's a rather sad irony that aircraft G-BOAF had been modified and reregistered at Filton, from it's original registration of G-BFKX to G-N94AF. Unfortunately the aircraft was delivered to BA in June 1980, one month too late to participate, and prior to delivery it's registration was converted to it's 'normal' British registration; all other aircraft also reverted to original registrations also.
ChristiaanJ
Not really, being the sad b****d that I am, I still remember the Concorde flare law of: h+5h. = 0, so it was fairly easy to work out the programmed descent rates. (I did have to check the final 1.7'/second figure though). The rest I'm afraid is straight out of this sad old memory of mine.
Bellerophon
A brilliant description of the mechanics of final approach. It's so easy for us mere mortals to forget just what an involved and skilled process it was, to fly, and in particular land our totally amazing aircraft.

Dude

Makes me wonder... In the event of a complete loss of thrust at Mach 2 (say fuel contamination) would the deceleration be significant ? If so I guess the fuel redistribution / pumping to maintain acceptable CG would become interesting...

Concorde did actually have a four engine failure drill, which covered it's complete speed rsnge including Mach 2.0. There was one assumption made in this drill and that the engines would continue to windmill which would allow them to give you full hydraulic pressure

As you could imagine, If all 4 engines cut at Mach 2.0 the F/E would be quite busy and so the the non flying pilot would use his fuel transfer switch to start the fuel moving forward. This was a pretty basic selection where fuel would be pumped out of Tank 11 using all 4 pumps [2 electrical and 2 hydraulic driven] and into the very forward tank which was no 9.

As a rule of thumb transferring 1000kgs from tank 11 to tank 9 moved the Cof G forward by 1%. Now with all 4 pumps in tank 11 running the tansfer forward was so quick that the pilot had to keep switching the transfer off and then on to stop the Cof G moving forward too quickly. It was usually to everybody's relief when the F/E could find the time to take over the fuel transfer as he had the selections to allow him to be more selective as to where the fuel went and so slow the rate down
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This was quite a neat system, as the gear was retracted, a SHORTENING LOCK valve was signalled, allowing a relatively tiny jack to pull the entire shock absorber body into the body of the oleo progressively as the gear retracted. So the shock

Forther to M2dude's explanation Concorde's main landing gear consisted of 3 seperate metal castings . there was the normal two for the oleo and these two were fitted inside the outer casting, which was the one you could see.
As the gear retracted a mechanical linkage , which was driven by the gear's retraction movement, would lift the oleo assembly up into the outer casing, so shortening the length of the leg . If I remember the shortening jack was just to assist in breking the geometric lock of the linkage
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The other difference between AF and BA aircraft was the DC electrical system

AF had Nickel cadmium batteries with an automatic charging system

BA had the good old lead acid battery sysytem, well except for AG where the DC system was one of the systems they never changed when AG was incorporated into the BA fleet

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.

As M2dude says, there were about three separate ways of extending the nose gear, making the event extremely unlikely, and indeed it never happened in service.
It's a halfway interesting "what if" question...
Bearing in mind the c.g. is already almost over the main wheels... could it have been done by moving the c.g. as far back as possible, keeping the droop nose at 0\xb0, and after touchdown keeping the nose off the ground for as long as possible?
The radome would have shattered, but the droop nose structure would have acted like a skid.
Just as well nobody ever needed to try it.

There is only one well-known case of a landing gear problem.

Visualise a moment the main landing gear. The main leg 'l' is held down in the vertical position by a large hydraulic "stay" '\' .
___
\l

(I know that, to most people, it looks at first like the retraction cylinder, but it isn't. The retraction cylinder is much shorter, and inside the wheel bay.)

Now the story... It happened during what was going to be the last-but-one flight of the British prototype, 002, during a demonstration flight at Weston-super-Mare.
After a slow pass with the gear down, the co-pilot flying the aircraft put it into a steep turn, retracting the gear at the same time.

The next moment, there was a very loud bang, and one of the main gear lights did not go "green".

Somebody from the crew went to the back cabin, where there is a small porthole to look into the wheel well. When asked what he could see, the answer was "nothing..." ; both the main stay and the retraction cylinder had parted company with the aircraft, and the gear leg was dangling free.

The pilot, John Cochrane, took over the controls, and brought the aircraft back to Fairford. With his guardian angel doing overtime, he managed to put down the aircraft and keep it straight during the roll-out, without the gear collapsing.

I didn't see the landing, but I saw 002 in the hangar the next day. By that time a steel bar had been fitted to keep the leg upright, but the damage was still impressive.
Later on, a spare stay was fitted, but 002s flight test career was over. She stayed in storage at Fairford for some time, and was then flown to the Fleet Air Arm Museum in Yeovilton, where she still can be seen to this day.
Wisely, for the few minutes flight, they did not retract the gear....

CJ