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