Concorde

[Up Front]

Thinking back to the Concorde disaster last year will bring to mind the mortality of human kind. Although a tragic waste of life, I can not help wondering how many more times it would have taken for a tyre to blow out before anyone realised there was a serious flight safety hazard. Tyres can explode on any kind of aircraft I know but not many aircraft have reheat as a means of getting of the ground and obviously this is an ignition source. The aircraft has been the focus of other tyre failures with consequential fuel leaks in the past yet with no real concern as to the possible,and now unfortunately actual, outcome.
This also brings me onto the subject of grounding the aircraft. Obviously something had to be done and the correct decision was taken yet how many other types of aircraft are flying around with "unsolved" accidents/incidents tarring their name. Mind springs to the 737 Uncommanded rudder deflection problems. Still not confirmed, only thought to be the slides in the rudder PCU. This aircraft suffered numerous incidents of this nature including some fatal accidents yet no grounding was carried out. Also the TWA 747 that exploded due to suspect wiring in the fuel tanks. Again only a theory but these aircraft are allowed to cruise around without even a thought of grounding. I realise the commercial implications of such actions yet it annoyed me the way the americans jumped up and down when Concorde crashed stating how unsafe it was and how it should be banned from american airspace. They have always been bitter towards Concorde because we beat them to it.
Like to hear peoples views on this subject and what they really think.
Anyway, glad to hear Concorde will soon be back and take her rightful place as the queen of the skies and once again be the most beautiful airliner flying. And she's British. (with a bit of French I know).

[Ultralights]

Agreed, I still dont believe the TWA 747 incident was an internal wiring problem, why has it never happened before? almost every airliner built has wiring inside its fuel tanks, i believe it was causedby Human Intervention, i guess now we will never know. Investigators knew at an early stage what cuased the Concorde demise.

[Leanan Sidhe]

Was it the Americans that threw a fit when the Condorde went down? It seemed to me that just about everybody in aviation, with the exception of the folks at Air France, got a little steamed by the catastrophic failures, given its suspected origin...
I still don't trust that they'll be able to compensate for those design vulnerabilities by April--let alone have it thoroughly tested and ready for the flightline.
People have let their sentimental attachment to the "first supersonic airliner" get the better of them. The P.R. circus pressure is pushing engineers to make alterations to an airframe that is especially sensitive to changes, owing to tremendous flex in topspeed flight, and it'll be a miracle if it doesn't backfire on them.
But hey, what the public clamours for--they'll get--whether it's good for them or not. :rolleyes:

[This message has been edited by Leanan Sidhe (edited 14 February 2001).]

[NIMBUS]

Up Front,
You're right. The Americans have always been bitter about the tremendous achievement of British know-how.
If Boeing et al had shown the same determination, they, too, would have an overpriced, fuel-guzzling, and basically unwanted aircraft.

Those Yanks will never learn! :rolleyes:

[Roger Turbojet]

Aaah please.....

someboddy bring me the puke bucket........ :rolleyes:

[WOK]

I have to say that my recollection is that most of the clamour to ground Concorde came from "mid-Europe".

The plan is not to resume services by April, but to start validation flying then. Services should restart in June barring unforeseen problems.

Contrary to the suggestions that this machine is being rushed into service on a tide of public sentiment, the current mods have been in development since VERY soon after the accident. I don't know where this concept that the liners will be a problem because of structural flexing has arisen: 1. The liners are flexible and flexibly mounted and 2. In my experience the whole shebang aft of tank 9 (the forwardmost tank, at the apex of the wing) is bar-tight in the cruise!

It's a shame that the 'fixes' for 737 rudder hardovers are not so closely and verifiably tailored to address the failure modes.

[Up Front]

Reference the last message. WOK you are totally correct with regards to the 737 'fixes'. Having worked in aircraft maintenance for a number of years and holding an approval on 737 I must admit the engineering solution to this problem to me falls short of that required. Scheduled function checks of the rudder system are carried out periodically yet this really is unconvincing considering that researchers have only been able to reproduce this failure on a very very small number of occasions. So I don't know what makes them think that it will show itself on a maintenance check. The PCU's are also sent away for a check of the secondary slide yet again this is only a check of the slide in its current state. Other aircraft do not suffer with this problem so what prevented a total redesign of the PCU. Maybe life does have a price!!!

[Leanan Sidhe]

As I understood it, BAe is hoping to launch flight testing in the U.K. by late February and looking at mid-March for testing in France.
Not for nothing but, design modifications had been under development--by the NASA & Dryden Reseach teams, using a specially equiped TU-144L as their flying lab--for years prior to the AF4590 crash.
Even though SST's are outfitted with a number of expansion joints and supports-- supersonic flight does intensify the various loads and exascerbate strain in the airframe--any modification is serious business.
I'm not sure what the forward trim and collector tanks (as previously mentioned) have to do with any modifications outside of the Kevlar bladder lining retro-fit kits... I had also heard that they're going to work in some protective enhancements of the undercarriage along critical electrical and hydraulic systems and try out a new type of tire that's supposed to disintegrate if it's punctured (or so I'm told).

That's a respectable degree of alteration... If they can pull it off, Bravo, but the timeline makes the cynic in me a little nervous.


[This message has been edited by Leanan Sidhe (edited 14 February 2001).]

[WOK]

The armouring of electrical supplies to brake cooling fans is a possibility ,but is a relatively minor mod. (esp in engineering terms).

The possibility of redesigned tyres was mooted but is not definitely ascribed to, and if it were to go ahead is some way down the line (years). The efforts to regain a CofA are not predicated on new tyres.

The only structural relevance of the liners is the fixing points - these are located to be of negligible significance. It is true that loads are higher on an SST in CRZ than a blunty, but the airframe is much stronger in this respect. Flexure on the Conc is greatest on take off and at it's least in the crz.

[Leanan Sidhe]

Agreed, WOK, the alterations are of minor technical complexity. The more imperative factor (put simply) involves the subtle interplay of the added weight (fixed to the frame) of these modifications--and how that weight in its respective positions will change the way that stress loads move (via resonant vibrations) through the airframe.
Those strains evidence themselves only after many cycles in operation. The frame may survive mathmatical projections and destuctive load-testing, but that doesn't necessarily mean you're ready to stamp it with the seal of approval.

[This message has been edited by Leanan Sidhe (edited 16 February 2001).]

[WOK]

That's why the design work has been done by EADS whose progenitor designed this part of the airframe in the first place.

There are several stages of stress-jacking involved in the fitting of these liners - that process hasn't been derived at random.

The work involved has less significance structurally than the profusion of aerials (TCAS, SATCOMM etc)most subsonic a/c have grown in recent years.

[Leanan Sidhe]

Okay pal,
Have it your way.

[Tobbes]

Sorry if this has been asked before, but what's the impact on the useable fuel capacity of fitting these liners to the wingtanks?

If significant, what impact will it have on range?

Thanks

Tobbes

[Leanan Sidhe]

Tobbes,
This gives a pretty good idea of what's going on with the Concorde (with a thorough section on the tank mods):

http://www.concordesst.com/returntoflight/mods.html

------------------
Okayerjusmakinthi****upasyougoarntyou?!

[jonno]

I agree with the comments regarding the unresolved position of a number of airline disasters, makes you wonder, doesn't it!

In regard to the Concorde crash, as I understand it, the most critical time for the undercarriage/wheel combination is the actual rotation to flight attitude, putting a very high downward vector when the elevons rise on command.
Surely the answer is to relieve this very high load, which is at least partially to blame, is to fit Cannards.
Used primarily for this 'lifting of the nose for rotate', they can be used for all 'low speed' flight, and then parked at neutral during cruise, and used again for the approach and landing.
Seems it would make them much more resposive at lower speeds/altitudes, but not detract from their normal flight profile.
Been done before on other aircraft, for similar reasons, to good effect.
comments! - seems to simple!

[Flight Safety]

I'm concerned that the current modifications to the Concorde to get it back into the air, may not be adequate to prevent the problem that caused the crash back in July. I think the Kevlar liners will do more than an adequate job of reducing the rate of fuel leakage in the event of a fuel tank puncture. However the cause of the July crash was a fuel tank "rupture". This "rupture" mechanism is described fairly well in the following text from the BEA interim report on the crash dated 12/15/2000.

16.7 Tank 5 Rupture Mechanism

The rupture mode originally mentioned to explain the hole in tank 5 was a direct penetration, from the exterior towards the interior of the tank. However, the first observations of the piece of tank found on the runway seem to indicate that the rupture occurred from the interior to the exterior. To explain the mechanisms of the rupture, a numeric simulation was developed by EADS based on the so-called « finite elements » method. This method involves decomposing the structure into small volumes on which an approximation of the laws of mechanics shows the behaviour of the solid and the fluid in question. Tank 5 was modelled with around 70,000 finite elements for the tank and around ten times that number to model the fuel it contained. The results of the tests carried out by the CEAT in 1980 on an empty tank were used to perform a first validation of this model. In almost all cases, the model and the test gave the same result ; where they differed, the deformations calculated during the simulation were always higher than those noted during tests.

According to the first results of the simulation performed with the conditions of the 25 July 2000 flight, the rupture of the tank could thus be explained by the conjunction of two phenomena induced by the shock, without penetration, from a large piece of tyre on the tank :

· a solid mechanics phenomenon inducing a wave of deformation on the wall of the tank,
· a fluid mechanics phenomenon, with propagation of a wave in the kerosene leading to a sort of action-reaction of the over-pressure effects on the lower wing skin.

In this report (which I have in pdf format), there's a diagram showing a sine wave shaped shock wave propagating through the wing tank skin as it flexes (but the skin is also anchored by the ribs), and a shock wave labeled "excessive hydraulic pressure" showing the behavior of the fuel as an incompressable liquid acting as a source of pressure on the wing tank skin. The report authors believe the two effects combined caused a "rupture" (what I would call a "major skin tearing event") of the fuel tank skin, which produced the massive fuel loss that resulted in the very large fire.

I'm just not sure that the kevlar liners are going to solve the problem of preventing a major skin tearing event (or rupture) that results from a large object impacting on the wing tank skin when the tank if full of incompressable fuel. I just don't see how the liners are going to stop a major skin tear from developing. They might signifacantly slow down a fuel leak from a smaller tear, but a larger tear, particularly if it occurs at one of the ribs, could still be real trouble.

------------------
Safe flying to you...


[This message has been edited by Flight Safety (edited 21 February 2001).]

[Leanan Sidhe]

Ha, "Prophets of Doom"?!

No, no, never that... Prohpet of caution perhaps--doom? Never.

I have no doubt that engineers and techs are hard at work, doing everything they possibly can to ensure the successful modification of this a/c.
My concern has always been with how much authority the ENGINEERS have been given to determine the amount of time they'd need to satisfy themselves that these alterations are safe and sound--rather than having to bow to the pressure of the it's-a-"Pretty Concorde"-pride-thing faction.
Don't oversimplify perfectly reasonable concerns just so you can give yourself an excuse to break out the pom-poms and beat your little chest buddy. This isn't a pride thing, it isn't a joke...
If these mods are being rushed (and I believe, devoutly, that they are) the consequences to the reputation of your "beautiful aircraft" are going to be devastating. Nothing spells "Ooops!" like turning your commercial flightcrew into test pilots while your half-assed modifications crack-up your aircraft at supersonic speeds, with 100 passengers along for the ride.

------------------
Okayerjusmakinthi****upasyougoarntyou?!

[This message has been edited by Leanan Sidhe (edited 21 February 2001).]

[This message has been edited by Leanan Sidhe (edited 22 February 2001).]

[Leanan Sidhe]

Solari,
The red flags started to go up when they began to lay down timelines for a "return to service" of these a/c prior to any comprehensive understanding of the accident, any concrete determination of what would need to be modified on these 25 year old aircraft, or how they would go about engineering those alterations.
The timeline for mods had obviously been determined by BA & AF's need to get their supersonic flagships back in the air in order to restore their profit schedules. The economic incentives to push modifications and get these a/c back into service, before the losses sustained while they're grounded preclude their viability in the fleet, are all too clear.

So here we are today--the timeline hasn't changed--and I can't help but find that a wee bit unsettling. Now, that doesn't mean that anything deliberately untoward is going on--but it isn't doing too much to allay my cynicism about what their priorities lie.
Whether or not the Civil Aviation Authority signs off on the modifications and reinstates Concorde's certificate of airworthiness is something, as yet, to be seen.


------------------
[email protected]

[Roc]

Upfront,

an aside, Who do you think makes up the largest percentage of Concorde passengers? probably Americans, and where does she fly to? America! Before I began reading Pprune I always had warm feelings for all Europeans, and I always assumed you guys liked America, but after spending a few months here on Ppune, I'm amazed at the Anti-Americanism I find on many threads...sad.

[virgin]

Leanan
Wyh can't you accept that the 'timelines' are forecasts/estimates made by those enhineers who know the aircraft? They will be adapted as required, and pushed back if necessary.
You say "Whether or not the Civil Aviation Authority signs off on the modifications and reinstates Concorde's certificate of airworthiness is something, as yet, to be seen."
Correct!
That is the point.

Roc
I agree there's a problem, but it's by no means one-way traffic. Sadly, it happens in both directions - and I speak as someone who loves America, and enjoys the company of Americans.
But you can't really blame people for being deeply suspicious of American attitudes to Concorde. Have you forgotten the disgraceful self-interested stance the US took towards Concorde at its inception?

[Leanan Sidhe]

virgin,
You--somehow :rolleyes: --managed to miss my entire point! The engineers didn't dictate the timeline--that's the feckin' point!!

[GJB]

Leanan - I think that you are reckless in suggesting BA want their Concordes back in the air to 'restore their profit schedules.'

I agree that there must be a deadline, beyond which it will not be commercially viable, to return the Concorde fleet to normal operations. But to suggest that this deadline is purely profit driven is absurd. Concorde services only contribute approximately 5% towards BA's annual profits.

I believe that their commitment to restore normal Concorde ops, is due to the demand from passengers who previously used the service. These customers have expressed that they want the service restored. I would suggest that BA's commitment is to serving their customers needs, not just their profits.

[virgin]

Leanan
You--somehow :rolleyes: --managed to miss two entire points! BA wouldn't risk further damage to their reputation. And anyway the CAA makes the final decision --those were the feckin' points

(Roughly translated from the English version which was: I understood your point, but I disagree with you. Did you understand mine? :) )


[This message has been edited by virgin (edited 24 February 2001).]

[WOK]

Just because you're not paranoid, it doesn't mean they're not really out to get you.

Jeez.