Posts about: "Airbus" [Posts: 64 Pages: 4]

A pot pourri of responses after my Christmas reading!

This actually is interesting in that the n umbers show one of the fundamental features that made the Ol 593 such a good choice. If you look closely at the TO and cruise values you will find that at TO the overall compressor pressure ratio is 13.5 the compressor exit temperature 460 degC and the turbine inlet temperaure is 1152 degC. In cruise the pressure ratio is 10.5, the compressor exit is 565 degC and the TET 1100 degC.

Somebody, I can't find the exact post, was asking whether the elevated cruise total temperatures affected engine life, and here we see why this is so. As Christian said in another posting, when you compress air it gets hotter - from 21 degC to 460 degC at take off and from 127 degC to 565 degC in cruise. A fundamental limit on engine operation is the turbine entry temperature. Not only does it affect the maximum TO thrust you can get but also the continued exposure to cruise TETs has a very big effect on engine fatigue life, and engine manufacturers have shown extremes of ingenuity when developing new materials and ways of cooling the blades to increase allowable TET.

The problem with supersonic operations is that you start from an elevated intake delivery temperature so that when the flow exits the compressor it is already very hot 565 instead of 460 to be exact. But the maximum temperature one can stand for fatigue reasons is limited, therefore the amount of fuel you can pour in must be limited also, and the thrust you can develop per pound of airflow is roughly proportional to the fuel input/temperature rise. To get any sensible cruise thrust then one must squeeze the cruise TET as high as you dare for fatigue reasons but also you need to keep the compression ratio down so that the temperature going into the combustion chambers is as low as you can get away with. This tend to drive engines designed for extended supersonic operations to having a low pressure ratio. This is against the trend in subsonic operations where compression ratios have been steadily increasing along with bypass ratios.


The net result then is that the engine must be designed with a low OPR and must operate with cruise TET much closer to its TO TET value than would be necessary, or indeed desirable, on a subsonic design.



Actually, here, as on some other apparent carry-overs, one should look at the equipment supplier rather than the aircraft manufacturer to trace continuity. Here we have Messier supplying Concorde's gear and Dowty (OK they are now part of Messier) supplying the A330. And having worked on both, I seem to remember that the means of doing the shortening are quite different.

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Originally Posted by Brit312 The Britannia and now you are talking about the love of my life and yes I do remember the story of the nose and visor selector, but we have forgotten the most obvious. Where do you think they got the idea for the control column from

Yes, they both came out of the Bristol drawing office. One minor anecdote: the 'ramshorn' stick was a novelty to the Concorde flight test crews but they got to like it, or at least put up with it. All went well until it came to the time when Dave Davies, the ARB Chief Test Pilot, came to put his rubber stamp on the aircraft.

Concorde's seats, just like those on your car, could be moved back and fore to get your legs on the pedals and up and down so you could see over the bonnet (sorry, instrument panel). The control column of course stayed in one place, so the relationship of the 'horns' to ones thighs varied with ones height. Andre Turcat was about 6ft 2in, Trubbie and the others of average height. The smallest regular pilot was Jean Franchi at, I suppose, about 5ft 7 or 5ft 8. No problems. But Dave Davies was short like me and he found that he could not get full back stick and full aileron because the ramshorn fouled his thighs.


Consternation! Completely unacceptable! I don't know what arguments they used to convince him it was all OK really, but it got through certification. I would certainly be interested to learn from the pilots in this group as to whether it was ever a problem.

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Originally Posted by exWok ........which was one reason it was so important to touch down with the wings level - even a very small angle of bank could result in bucket contact as they translated to the reverse position. It was a surprise coming to Concorde to find it was even more restrictive than the 747 in this respect

I can't resist this one!. Has anyone ever noticed/wondered about the tiny bit of the outer elevon that has been chopped off? That was my first real input into the design as a young erk looking at variability of touchdown conditions and coming to the conclusion that if the pilot got into trouble and was trying to pick up a trailing wing with too much AoA as well then he was likely to hit the ground with the downgoing elevon. I persuaded my boss that this was so and we made a small adjustment.
In self defence I am going to plead that this was well before the days of the Type 28 nozzle, so the issue of buckets contacting the ground first never came up!

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As far as your point about the prototype engines; they were way down on thrust anyway, (even without the 'help' of the silencers), produced more black smoke than a 1930's coal fired power station.

To the point where an American Airline maintainance engineer, watching a prototype taking off and with full benefit of being located strategically for maximum sideline noise, remarked on what he described as 'visible acoustic radiation'

On another occasion, it was reputed that Stanley Hooker, watching a TO in the company of HRH the Duke of Edinburgh, remarked that "You know Sir that that noise represents less energy than it takes to boil an egg". to which he got the reply "Then I must congratulate you Sir Stanley, on producing so much noise for the expenditure of so little energy".

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Originally Posted by CJ One example : in theory the aircraft did weigh 1.2 % less, so the lift was 1.2 % less and the drag was 1.2 % less, so the fuel consumption was less too, so did Concorde have another 50-odd miles range thrown in 'free' by flying higher and faster than it's low-down subsonic brethren?

There was an effect and in consequence the aircraft performance brochures were formally calculated for north/south flight. Pity really, it would sometimes have been nice to be able to fly guarantee performance demonstrations in the most favourable direction

That's enough for today!

CliveL

Spot on, Clive.

I've said something similar (while at the same time being full of admiration and effusive praise for M2Dude). It's worth bearing in mind that at the time (2003 or thereabouts), AI were fighting a battle to keep the A380 project viable (like Boeing with the 747, they'd effectively "bet the company" on the project's success) - and sadly, in terms of business realpolitik Concorde was costing them money, being just a small-run legacy airframe capable of operating profitably for a single customer. Things weren't going to get any better, and as such AI's decision was as understandable as it was regrettable.

I have far less sympathy for BA, who acted with what seemed to me indecent haste to permanently mothball the airframes (the press at the time speculating that Branson would try to get his hands on at least one of them), and while the UK Concorde community have a right to feel aggrieved at the way things panned out - the fact that what was left of BAe effectively bowed out of the Airbus consortium, the better to focus on military hardware with the Americans, meant that we'd thrown away any chance of having a say in what happened to Concorde in the end.

EDITED TO ADD : In reference to Bellerophon's post below - this was *not* intended to take the technical discussion off-course. I was simply trying to thank Clive for summing up how I felt about the whole situation far better than I ever could. Sincere apologies if this was misconstrued as such.

May I ask you guys another question relating to the book I mentioned earlier, in the same book it shows a Concorde with a Airbus sidestick control. I wondered if anymore information is known on this modification I suspect t must have been quite an systems integration exercise.

ITman, nice question.
I haven't seen any of the detailed (block) diagrams, so I'm not sure at all how the sidestick was "hooked into" the AFCS.

Don't forget Concorde already used "electrical flying control signalling" (aka "Fly-By-Wire")., so system integration would have been easier than on some other aircraft.

For those unfamiliar with the story... F-WTSB, very late in its career, was used for some flight trials with a sidestick controller fitted to the left-hand position (the right-hand seat controls still being the normal ones,and with the right-hand seat occupied by a 'safety' pilot).
The flight test data were later "fed" into the A-320 programme.

How much of the "rate" control and other A-320 control logic was already implemented in the test system is unknown, AFAIK ....
Would be interesting to know some more about it, I agree!

CJ

I personally doubt very much if the Emergency Pilot would be the 'way in' for the sidestick input. EFC ROLL commands were inputed from the SFC computer to the Autostab computers as 'stab demands' and therefore drove the MIDDLE and OUTER elevons only for roll. To make matters worse, if your test flight was really 'exciting' and you found yourself at any time at Vmo + 20 KTS, roll control would be through the middle elevons ONLY. I'm with CliveL in that the most likely scenario would be for the demand would feed via a D/A converter somehow. (It would be great to find out though).
I would have thought that the whole venture was a proof of concept by SFENA for future implementation in the Airbus family. This excersise would have been both costly and highly complex at system level, any other reason would really have been quite daft.

Best Regards
Dude

Not the first time that's mentioned.
Do you (or does anybody ele) have a schematic of the Vulcan system?
It should be on my CD of the Vulcan manual, but unfortunately my CD drive is on strike.....

MFgeo , I think we're talking Europe here... the Avro Arrow was Canadian,so I would think it unlikely the flight test results would have been available to Airbus.

CJ

Thanks for that much better picture Bellerephon.

I have a bit more information now, although my French is very rusty so I may not have it all correct - CJ can probably correct me if necessary.

They did 8 flights over 10 hrs, preceded by about 30 simulator 'flights'. Most of the flight testing was looking at low speed behaviour, since that was where they expected to see most gains on Concorde, and where the most problems might be expected, but they did go up to 2.04M. The primary advantage was seen to be the possibility of using very aft CGs for takeoff to reduce trim drag - they flight tested as far back as 56% at around 0.4M (no consideration of limits from U/C location of course for this sort of testing). In addition they were predicting a weight saving of around half a tonne.

The simulator work sorted out the basic laws, where they tested a pure pitch rate feedback and a C* law with load factor and pitch rate terms. The pilots preferred the latter (which became in time the basis for the A320 laws).
The simulator was also used to establish the best ergonomics (movement and force harmonisation) of the sidestick.

The 'blue' electrical signalling system for elevons was replaced by the digital control and sidestick arrangement, keeping the 'green' signalling as a safety backup. Normal rudder control system was retained, as well as the mechanical backup.

In the general arrangement of the digital control system one can see clearly the genesis of the A320 design - two computers with the software written by separate teams etc.

Pilot reaction seems to have been very favourable, the aircraft being somewhat easier to fly than the basic Concorde (which was already pretty good ....).
In particular the paper suggests that the precision with which the aircraft could be positioned was much improved.
Stick force per 'g' was pretty much the same throughout the speed range at about 7daN/g, whereas on Concorde it varies from 20 to 40 daN/g - but on a sidestick rather than a control column of course.

One problem that did show up, although not peculiar to Concorde, was the sensitivity of these systems to structural response, particularly during ground roll.

Not contained in the report, but in a side letter from Dudley, is a remark that the guy most responsible for the development of the Concorde basic system and later in charge of the Airbus system thought that these Concorde experiments were the key to the success of the A320.

'Nuff said!

CliveL

Did the Sidestick controller have the same authority as the Conventional Control yoke or were there 'hard limits' a la Airbus 320 and on ?

I think the estimate is that the supersonic passenger requirement today could be satisfied by ten airframes. Hardly an attractive economic proposition for a manufacturer. If it were otherwise, Boeing and Airbus would be addressing that market with a state-of-the-art SST.

I think we could all speculate until the cows come home just how many SSTs could be built. To put my own two penny worth in here, personally I tend to agree with Steve that to justify the huge capital investment required, a hypersonic aircraft with just about antipodal range would be required. Here in the UK, the Reaction Engines Lapcat A2 project seems to be the way to go. Fueled with liquid hydrogen, making London to Sydney in just around 3 hours carrying THREE HUNDRED passenger. All this using four Scimatar hybrid engines. Contrast this proposal with the clumsy Airbus ZEHST effort that has to use THREE different types of engine for the flight cycle, carries only 100 passengers and won't be around (acording to them) for FORTY YEARS!!. Both imagination and practicalilty seem to be totally absent here.
It seems that the technology required for an HST already exists in the UK (the Scimitar engine is a deritive of the engine originally designed for HOTOL, thanks to the genius of Alan Bond and Bob Parkinson) but we need partners for obvious economic reasons, (probably not European), the will, and most of all, as I mentioned before, the vision to do great things again. In my humble opinion Lapcat A2 should be the true successor to Concorde. If only......

Best regards
Dude

Interesting... but unlikely.

The first question : why? The old analogue systems still worked well.

Second question : who? There were only 14 aircraft in service... who would paid the immense bill for redesign and recertification?

A third question : we know one of the major factors in the 'end of service' decisions were related to the rapidly increasing maintenance costs (as billed by Airbus). A complete upgrade of the avionics (digital, glass cockpit, etc.) would not necessarily have resulted in less maintenance costs.... it would still have been for only 14 aircraft.

In the end, the only real and 'visible' avionics upgrade was the installation of TCAS, and that was only because it was made mandatory.

CJ

Sorry all, this is now forty years back, literally....
So no, I don't have all the block diagrams and circuit diagrams in my head any more... I'll have to look through what I still have in the way of documentation.
i'll try to give some quick answers.

Da-20 monkey ,
Yes, Concorde had "artifcial damping", or "autostabilsation" as we called it, on all three axes (pitch, roll and yaw), even if it could be flown without it.
On the prototypes there were three separate computers (one per axis).
On the preprod and production aircraft the A/S function was 'compressed' into a single unit (I still have one).

CliveL has given the basic answer.
Don't confuse the Concorde FBW (which we referred to as "electrical signalling") with the current "Airbus" digital FBW.

One, rather than in previous-generation aircraft, the pilot no longer pushed and pulled on cables and rods to move the control surfaces. Instead, when he moved the controls, those movements were translated into electrical signals that were sent to the electro-hydraulic control surface actuators (even if in the Concorde days there still was a mechanical back-up).

Two, the entire system was "analogue". A concept difficult to explain in these days, where nearly everything is digital.....
Very briefly, you can convert 'physical' data, like control positions, or altitude, or pitch or roll rate, or Mach number, into 'analogue' electrical signals. You can then perform all kinds of 'computations' on those signals, like filtering them, or add or subtract them, or even multiply them, using electronic circuits based on 'operational amplifiers'.

In digital systems you go one step further.... you convert all those data into digital values, and use a digital computer to perform all your calculations, in accordance with the 'system software', then convert all the results back into physical data, such as control surface commands.

In analogue systems there is no "software". The entire system is defined by 'control laws ' (not the same thing at all as in the Airbus FBW aircraft) that are fixed in terms of 'transfer functions' of the various control loops.
Those in turn are determined by the values of the components in the various electronic circuits (resistors and capacitors mostly). So in those golden days.... we didn't re-write and re-program software.... we changed resistor and capacitors, and re-wired logic circuits.

I admit, you almost have to have been there to understand it....

I'm not sure whether it's worth starting an entire new thread on 'analogue computing' (maybe there's something on wikipedia, I haven't looked)....

CJ

Analogue computers are still very active on the Airbus A300-B4 100/200 srs.
A lot of the Concorde technology was transferred to the Mark 1 Airbus, and it still works very well. We are Cat IIIa certified and I have never had a failure when it was needed.
Yes we get a lot of drop out of things, but usually they work after a reset.

Following on from what EXWOK was saying, you've got to remember that the spec was hammered out in the late '60s - so it's not surprising that the flight deck could *appear* antiquated by 1980's standards. But in this case, as alluded to, appearances are deceptive. While the gauges and switches are very definitely of that vintage, the systems behind them were very much bleeding-edge technology (by aviation standards) in a contemporary sense. Even when Concorde entered production, the most complex digital displays available to aviation were of the 7-segment LED type (as used in the Apollo Guidance Computer), and they were both wildly expensive and of limited use. The flight and engine controls were in fact a pioneering kind of analogue FBW - way in advance of any other type, even those making their debut at the start of the '80s (though FADEC was becoming more widespread by then - with the advent of the B757 and 767).

Ergonomically speaking, both engineers and pilots of the era write of Concorde's flight deck being the best possible balance of form and function available at the time - sure it looks cluttered to the modern eye, but everything was placed in a logical manner and the sheer number of systems used in the aircraft made the accessibility of all that information a basic requirement. It's worth bearing in mind that even those not particularly well-disposed to Airbus will grudgingly admit that the flight deck ergonomics on those types are extremely good - and a lot of the lessons learned were from cramming all that information into Concorde's limited space.

As for the cabin, again appearances are deceptive - I have sat in one of those seats and they are extremely comfortable for the size. Also one must bear in mind that unlike the subsonic Atlantic crossings, these were happening in about 3 hours - so no need to be particularly wide or convert into a bed like we see in Business and First today - not to mention less chance of a queue for the WC!

I have to thank EXWOK for explaining the windows - but I'll add the more prosaic reason that you don't need a particularly large window to see the curvature of the Earth in all its splendour - which is for the most part all you'd be seeing during the flight!

[EDIT : I should also confirm that EXWOK is also correct in stating that BA had Concorde turning a profit from the early-'80s onward, and it took a combination of a financial downturn and the fallout from the terrorist attacks of September 2001 to end the service.

While Concorde herself never recouped the development money granted by the governments of the UK and France, the infrastructure and R&D her development put in place paved the way for the Airbus project which, as we know, ended up becoming a leading player in airliner design and manufacture in the West. ]

Dozy

Yeah, well when we put a digital computer to generate the AICS laws that was NEW man!



Again, no digital multifunction displays on offer in those days

Errrr no, I don't think so. Concorde's flight deck was done at Filton and we had no involvement in the Airbus designs in that area.


Exwok's remark is not quite right IIRC. Certainly the window size was dictated by pressurisation failure, but one couldn't maintain cabin pressure with two windows failed - the design case was to get to a breathable altitude before you killed too many passengers! Also, there is very little to see when you have a delta wing under you.

Ummm - most participants reckoned that the Concorde infrastructure showed the way not to do it, and besides the early Airbuses were developed in parallel with the later stages of Concorde development. You have a point where R&D is concerned though - several technologies developed for Concorde found their way onto the subsonic fleet, not the least being the probability approach to system certification.

Hey Clive - nice to see you!

I was thinking more "indirectly" - in general UK/Euro flight deck layouts were more in line with improving ergonomics than those on the other side of the pond for a long time. Later work may not have been done at Filton as Concorde's was, but the Airbus folk would have been foolish in the extreme not to use the fundamental principles as a basis for that work!

Hence the catch-all term "paved the way" - whereby lessons in how not to do it are as useful as those which were a positive example!

Well, the 2707 project never advanced to the point where such practicalities were considered - but it's certainly the case that part of the Concorde "B" spec was intended to do away with reheat (afterburner) entirely, and be much more fuel-efficient as a result.

Not necessarily - supersonic travel as a "premium" product was always intended to co-exist with subsonic offerings, much as it ended up doing. There's a revisionist narrative that has the USA betting on mass transit with the 747 versus Europe betting on supersonic transit with Concorde - but all the contemporary material I've read indicates no such thing. Even setting aside the protests within the US against the Concorde, the simple fact is that SST was never going to be a viable domestic solution, so that limited the market for the 2707. Whereas a transatlantic SST was very much a viable proposition due to the transoceanic nature of the journey. It could be argued that even with the oil crisis and the subsequent drop in orders, the UK and French governments gave up on the Concorde project too soon.

If that were genuinely the case, then there would have been no Airbus project or consortium. As Clive correctly points out, the A300 project started taking shape while Concorde was undergoing her proving flights. While there's no doubt that the Concorde project was completed for political reasons most of all, the idea that she was a forlorn hope before she went into service is grossly unfair.

Yet, as alluded to before, the R&D gains and technological knowledge coming from the project helped to lay the foundations of a pan-European aircraft maker which would eventually go toe-to-toe with the best the USA had to offer. The sidestick technology which led to an unprecedented level of commonality between short-haul and long-haul types was first tested on a Concorde airframe (Google "concorde minimanche"). Added to which is the fact that in Concorde, for all the project's problems, an airliner was produced which - on a technological level at least - left every competitor in the world in the dust. That is something that can never be taken away.

I know Concorde engines were FADEC. Were the Thrust levers gated like on Airbus? I noticesd cocncorde pilots shovved the levers forward for take off thrust..not the gentle easing forward like most other turbojets..why was there this need?Did they take too much time to spool up?

The engine was electrically signalled, but it wasn't FADEC; the control system(s) were analogue.
I suspect the zero bypass Ol 593 would take less time to spool up than todays high bypass engines.

Thankyou.

Thankyou all, EXWOK, Bellerophon, CliveL, ChristiaanJ, M2Dude, Brit312 and landlady for providing these wonderful stories directly from "the horse's mouth". I love it. Please, since landlady is already publishing her piece of history, maybe you others could at least join forces and use this excellent, brilliant and awesome thread as inspiration?

I have read this thread for breakfast every day the past week and finally catched up and never got this sorted out.... HOW is it possible that Airbus now "operates" (weeeell, you know what I mean...) Concorde?

I have tried to follow all clues, looking up companies on Wikipedia and who was subcontractor to whom, but it's just a big mess and I need help to sort it out. Is there anyone who might help shed some light onto this?

Sorry if my post is long, but this is such an amazing aircraft and since I come from Sweden where all we have is a tiny (but hugely effective!!) SAAB Gripen I am in awe to you who have created a milestone in aviation.