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Old 18th Aug 2010, 21:35
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There's an interesting piece here...

Concorde: story of a supersonic pioneer By Kenneth Owen, Science Museum (Great Britain)

Dr Hooker's argument that it makes more sense leaving the dead weight of an APU on the ground rather than carry it around at supersonic speed makes sense. (I presume this is the late Sir Stanley Hooker)

"It surprises me to hear you people asking for equipment to be carried around at supersonic speed when it could be left on the ground. It cannot be economical to carry this stuff around at Mach 2.2 just to save a little labour cost at the airport. On the possibility of aircraft damage, you must organise yourselves so that you do not damage the aeroplane. [Damage by engine starter vehicles to aircraft, and the labour costs involved had been mentioned by Eastern Airlines]. The problems you are imposing involve us in developing entirely new equipment at vast cost. The equipment will be baked consistently at 150 deg C. The problems of certification must be worked out for this equipment and may alter the case considerably."
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Old 18th Aug 2010, 22:19
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TURIN,
Thnks for the headup... I still have to get that book into my little library.

I've seen that quote before.
Dr. Hooker was right of course.

I think we'll never know what Iran Air's reasoning was......
Even with the vastly inferior infrastructucture in the Middle East at the time, it would seem to me it would have been much cheaper to station enough GPUs and ASUs at their various destinations (only two aircraft, after all), rather than go for an airline-specific APU fit.
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Old 19th Aug 2010, 00:22
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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.
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Old 19th Aug 2010, 04:10
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Damn, guess I am really that stupid. (Let's just keep that between you, Christiaan and myself ).

M2, the figures you give are incredible (I like stats) so I shall ask for more. Anytime you get tired of answering please just say enough.

How much fuel was used in the taxi. T/O roll. To TOC. Usage in cruise. From TOD?
How long did it take to get to TOC and was it done in one hit or were there stages when fuel burn allowed the climb to resume? What was the ground distance covered to get to TOC? How far out was TOD and what was ROD during the approach?

The amusing trim piece I found quite funny. That requirement must have been designed by several different Government committees; net result, nothing changes.

Had a question on the nose. You mentioned somewhere about a decompression when the nose was lowered to the 5° stage. This indicates that the nose had more than the Up and Down positions that I always thought. Were there multiple nose positions and when would they have been used. (Obviously nose full down was for T/O and Landing)

Last one for this post. What was the CoG range? I remember when I started flying and finally twigged to what it was all about that the PA28 had something like a 5" from the forward to aft limit and was massively surprised by the small "balance point". Trim tanks on 1 aeroplane I flew would have been most welcome.

I know I have asked a lot so please answer at your convenience.

Many thanks.
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Old 19th Aug 2010, 11:16
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Stupid, you? no way!! (Besides, I'm Mr Stupid of the aviation world, that's my title ). The thing is, out here in the world of flying machines, there are almost an infinite number of questions (and hopefully answers too). This applies to just about all aircraft from the Wright Flyer up!!.
Keep asking away, there are so many of us Concorde 'nuts' out here who are more than happy to help out/bore the socks off you.
Fuel burns: The problem was that when flying slow/taxying, Concorde was an extreme gas guzzler, even when idling each engine burnt around 1.1 tonnes/hour (so every 15 minutes after push back meant over a tonne gone). A typical taxi fuel would be around 1.4/1.5 tonnes, depending on the runway in use on the day. I'd have to leave it to some of my pilot/F/E friends to remember some of the specific fuel burns after take off etc, but I can at least give you some interesting consumption figures:
At the beginning of the take off roll, each engine would be burning around 21 tonnes/hour. (Made up of around 12 T/Hr dry fuel (Fe) and 9T/Hr afterburner (reheat to us Brits) fuel (Fr). As Fr was scheduled against Fe, as a function of inlet total temp (T1) by the time V2 was reached (around 220 KTS) the rising T1 has pushed the total fuel flow (Ft) up to a staggering 25 tonnes/hour/engine. As i've pointed out before in previous topics, although the afterburner only gave us a 17% improvement in take off thrust, it was responsible for around an 80% hike in fuel burn. (Hence that is whay it was only used sparingly). However when reheat was used for transonic acceleration, it used a dramatically reduced schedule (roughly a 60% rise in fuel flow) , so it was not quite as scary. The afterburner would be lit at the commencement of the acceleration (0.96 Mach) and cancelled completely at 1.7 Mach. After this time the aircraft would accelerate on dry power only up to mach 2 and beyond. (The cooler the temperature the quicker the time to Mach 2). On an ISA+ day, it sometimes felt that the aircraft was flying through cold porridge, and could take quite a while to get to Mach 2 after reaheat cancellation, where as on a nice ISA - day, she would go like a bat out of hell, and the AFCS would have to jump in to prevent overspeeds.
Before I hit some more numbers, let me say that with Concorde, TOC = TOD!! After reheat cancellation at Mach 1.7, the aircraft would be at FL 430. The aircraft would climb at an IAS of 530 KTS until Mach 2 was reached at fractionally over FL500. From then on the aircraft would cruise/climb as fuel was burnt, up to a maximum of FL600. On warmish days (eg. the North Atlantic) TOD would typically be around FL570-580. On a cool day (the lowes temperatures would of course be reached in the more tropical regions; the LGR-BGI sector encountered this), FL 600 would be reached easily and she would love to climb some more. BUT, the aircaft was only certificated to 60,000' with passengers onboard, for decompression emergency descent time reasons, and so we were stuck with it. The pity is of course, the fuel burn would have been improved, but we never were able to take advantage of this. On test flights however, the aircraft would routinely zoom climb to FL 630. On her maiden flight, aircaft 208 (G-BOAB) reached an altitude of 65000'; the highest recorded Concorde altitude was on one of the French development aircraft, which achieved 68,000'. On a technical point, the analog ADC's were 'only' calibrated to 65,000'.
Anyway, back to some figues; at Mach 2, 50,000', the typical fuel burn per engine would be around 5 tonnes/hour, falling to around 4.2 tonnes/hour at 60,000'.

THE NOSE You are quite correct in your assumption, there were two positions of droop: 5 deg's for taxi/take-off and low speed flight and 12.5 deg's for landing. The glazed visor retracted into the nose and could ONLY be raised once the nose was fully up, and had to be stowed before the nose could move down. There were 2 emergency nose lowering sysyems; one using stby (Yellow) hydraulics and a free-fall system. Free-fall would drop the nose all the way to 12.5 deg's, the visor free falling into the nose also.

Last edited by M2dude; 19th Aug 2010 at 12:40. Reason: mistooks
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Old 19th Aug 2010, 13:21
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Mate, if you could have seen my jaw drop when I read the T/O burn you would probably hurt yourself laughing to much. That is just incredible but the cruise flow seems like stuff all especially considering the speed. The idle flow was also a bit of a jaw dropper.

Was surprised, yet again, that Mach 2 was achieved without reheat. They really were/are an amazing powerplant.

On my list of regrets, not getting a flight on Concorde would be in the top 5. If they hadn't grounded them what sort of life did the airframes have left in them?
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Old 19th Aug 2010, 13:24
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Expansion

As I understand it due to friction heat caused by flying at mach 2 Concorde would expand by approx 6 inches. Some of this expansion could be seen between the FE panel and flight deck partition. Obivously the interior would be at a comfortable temp of say 21c; thus the exterior would expand but the interior linings etc would not. So finally to my question- How was this differential expansion delt with? I have really enjoyed reading the clear answers posted answering many interesting Concorde questions.

Last edited by Nick Thomas; 19th Aug 2010 at 13:26. Reason: Clarity
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Old 19th Aug 2010, 14:37
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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°, visor down (take-off and initial climb),
Nose down 12.5°, 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° position.
Another switch allowed to hydraulically release the 5° downlocks, and the nose would free-fall again, now to the 12.5° 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° position.

To complete the story... there is a 5th position: nose 17.5° 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°.
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°, 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.
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Old 20th Aug 2010, 00:05
  #29 (permalink)  
 
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Originally Posted by Nick Thomas View Post
As I understand it due to friction heat caused by flying at mach 2 Concorde would expand by approx 6 inches. Some of this expansion could be seen between the FE panel and flight deck partition. Obivously the interior would be at a comfortable temp of say 21c; thus the exterior would expand but the interior linings etc would not. So finally to my question- How was this differential expansion dealt with? I have really enjoyed reading the clear answers posted answering many interesting Concorde questions.
"...due to friction heat caused by flying at mach 2 ..."
"Friction" is the "easy explanation", but not really true.
It was due to the air being compressed, being "pushed sideways" by the aircraft trying to make its way through the air at Mach 2, if you like
Same as what happens in a bicycle pump, that get hot as you compress the air. The analogy is somewhat oversimplified, but the phenomenon is the same.
The hottest spots were actually the nose and the wing leading edge, not because of friction, but because that's where the air was locally brought to a total standstill, hence compressed the most. Temperature there could rise to +127°C, from the -50°C and less of the air at 50,000ft just ahead.

"How was this differential expansion dealt with?"
Mostly by attaching things like equipment racks (think of the hat) and floors, and other bits and pieces, to the outer fuselage structure only at one end, and making sure they could move relative to the outer structure when it expanded.
Hope that explains it?
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Old 20th Aug 2010, 00:22
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Originally Posted by M2dude View Post
...on this APU issue...we are talking here about a duct with sufficient size that can provide enough mass flow to turn over an Olympus engine to at least between 10 and 20% N2. You are looking at an least 10" diameter duct
Not really..
We are looking at two 4 inch diameter ducts, the same that are still used to this day on aircraft such as the B777.
One for the air start turbine, which was driven at about 45 psi nominal by the same kind of ASUs (Air Start Units) as are still in use today.
The other for the aircon... not to be confused with the huge near-ambient pressure hoses that were connected directly to the cabin, rather than to the aircon packs.
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Old 20th Aug 2010, 01:31
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Absolutely fascinating, the fuel burns are way beyond what I expected.




One of my favourite sentences is that TOC=TOD !



It all makes sense though.




Not to beat a dead horse, but, on the choice of location for APU, the 727 had a problem with this but for different reasons. Because of the location of the engines that were all mounted at the rear, the Aircraft was quite tail heavy and adding more weight with an APU in the tail section was not desirable.



The solution found that I have not seen in any other Aircraft was to mount it in the wheel well transversely across the keel beam with the exhaust out and over the right wing. Quite unusual but it worked fine with the restriction that it could only be operated on the ground.



Its all academic now but, just out of curiosity could this have worked on the Concorde ?
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Old 20th Aug 2010, 01:49
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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.
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Old 20th Aug 2010, 11:44
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Originally Posted by stilton
Its all academic now but, just out of curiosity could this have worked on the Concorde ?
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...
Originally Posted by Nick Thomas View Post
...some flexibilty built in around the window openings... 3 to 4 inches difference between the inside panel and the actual window.
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.
I guess all the hydraulic and fuel lines must have had some "slack" to allow for expansion.
Yes indeed. Flexible sections all over the place.
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Old 20th Aug 2010, 12:06
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Biggles78
Mate, if you could have seen my jaw drop when I read the T/O burn you would probably hurt yourself laughing to much. That is just incredible but the cruise flow seems like stuff all especially considering the speed. The idle flow was also a bit of a jaw dropper.
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.
Was surprised, yet again, that Mach 2 was achieved without reheat. They really were/are an amazing powerplant.
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
On my list of regrets, not getting a flight on Concorde would be in the top 5. If they hadn't grounded them what sort of life did the airframes have left in them?
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 Aérospatiale 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
Not to beat a dead horse, but, on the choice of location for APU, the 727 had a problem with this but for different reasons. Because of the location of the engines that were all mounted at the rear, the Aircraft was quite tail heavy and adding more weight with an APU in the tail section was not desirable.The solution found that I have not seen in any other Aircraft was to mount it in the wheel well transversely across the keel beam with the exhaust out and over the right wing. Quite unusual but it worked fine with the restriction that it could only be operated on the ground.
Its all academic now but, just out of curiosity could this have worked on the Concorde
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.
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Old 20th Aug 2010, 13:56
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Once again thanks M2dude and ChristiaanJ for such interesting answers. Whilst Concorde was not a commerical success it was certainly a technical "tour de force". Would it be too much of an exaggeration to say that Concorde provided the sound technical foundations on which Airbus have now so successfully built?
Am I right in saying that Concorde was the first fly by wire commerical plane?
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Old 20th Aug 2010, 15:36
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Hi Nick, thanks again for your comments. As far as not being a commercial success, for the airline this side of the Channel it was a HUGE commercial success (but of course I accept that in manufacturing terms this was far from the case. The project suffered from very poor financial control). Concorde was the first commercial FBW aircraft as you rightly surmised.
A huge amount of Airbus work was 'burried' in the Concorde project; at Filton a large amount of Airbus components came through that were almost identical to those on Concorde. (witness the STRIKING similarity between the A300 main gear and that of Concorde). Apologies if this post is a little tardy, it's done from my IPhone).
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Old 20th Aug 2010, 17:58
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Thanks M2dude.
I agree that Concorde was a commerical success especially for BA. Unfortunatly due to outside factors ie cost of fuel etc; it never had a chance to sell in sufficent numbers.
I wonder if it had been an american product if it would have sold more? Ideal speculation maybe!
What is certain is that everyone involved in designing,maintaining and operating her has every reason to be proud of their contribution to aviation.
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Old 20th Aug 2010, 22:55
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Originally Posted by Nick Thomas View Post
Once again thanks M2dude and ChristiaanJ for such interesting answers.
No thanks needed.. I like plunging back into the history, especially when people are interested, and I have a sneaky suspicion that M2dude does too!
Would it be too much of an exaggeration to say that Concorde provided the sound technical foundations on which Airbus have now so successfully built?
As M2dude says... to some extent, yes!

As an example in my particular field, you have to be an expert to distinguish the Concorde ADI (Attitude Director Indicator) and HSI (Horizontal Situation Indicator) - the two big central instruments on the pilot's and copilot's panel - from those on the first Airbus, the A300, or the early A310s. Apart from a couple of lights and buttons, they were the same, and the innards were pretty well identical.

And a lot of the technology in the AFCS (Automtic Flight Control System, i.e., the autopilots, etc.) was also virtually indistinguishable (the circuitry was obviously different... an A300 did not do Mach2).

But even more than the technical foundations, Concorde also laid the foundations for an effective and successful international cooperation in aircraft design, development and production.
We learned a tremendous amount from Concorde... Airbus might still have happened without Concorde, but it certainly would have happened years later.

Am I right in saying that Concorde was the first fly by wire commerical plane?
Yes, you're right.
The one difference with "modern" FBW commercial planes (such as the A320) is that Concorde still did have a mechanical back-up for when all else failed.
At the time, there was still a doubt about all these new-fangled elektriks replacing good old rods and cables, so when you look under the floor in a Concorde, the rods and cables are still there.
But apart from tests and training for emergencies, essentially they were never used.
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Old 20th Aug 2010, 23:21
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Originally Posted by M2dude View Post
ChristiaanJ
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.
I think we already do agree about the story that Iran Air was going to have an APU, that Rotring had already been put to Mylar to sort out the how and where, and that some traces are likely to be left in 214 and 216.

So I happily agree to disagree on the rest... between the two of us, each looking at our own clues, and with the help of anybody else who has more info, we might still find the answer!

One thought I had... with an APU in the forward baggage hold, you'd also have to take the air intake and exhaust through the pressure hull, and provide sound and thermal insulation for the entire APU itself.
From a design point of view, I'd have gone for the same location of the earlier pseudo-APU (the MEPU), and then solved the remaining problems from that starting point.
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Old 21st Aug 2010, 03:07
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Oh what I would give for M2dude and Christiaan to write technical book on the Concord for pilots to read.....oh and not to forget the stories of operations.

M2dude your info is far from boring.........i call it enthralling. Pure Gold.

As in the great line from a movie ...."more plese"
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