The G\’s got a Q&A about what it all means. Here\’s the real worry:
Aviation experts believe that as well as the engine losing its protective cowling, sections of turbine blade sheared off. A photograph taken by a passenger from inside the plane shows a small hole in the left wing, possibly caused by flying debris.
Good discussion here.
Turbine blades shearing off is really something that shouldn\’t happen. They\’re an extremely strong alloy (single crystal nickel rhenium alloys, jet engines being the major consumer of the metal rhenium….why, yes, I have occasionally provided ammonium perrhenate, the precursor material for rhenium metal, to the Rolls Royce supply chain) and they are, as you might expect in a jet engine, spinning at extremely high speed.
If they start to shear off while doing so they\’ll make one hell of a mess of the wing: which, as you may or may not know, is where the fuel tanks are. One or two maybe causes what we\’ve seen. But one going unbalances the engine, making more shearing off more likely of others, leading, possibly, to a catastrophic failure.
Yes, I too think that firing hot sharp metal through fuel tanks is probably not a good idea.
I\’m sure there will be a lot of people at Rolls Royce crossing fingers and hoping that this is an exceptional event, not some problem inherent in these rather new engines.
But now to the chicken gun! In order to test that a bird strike does not cause such a catastrophic failure, traditionally new jet engine designs have had a chicken fired at them from a cannon. The engine is spun up to full power (ie, take off levels) and then said chicken fired from said cannon right at it, straight into the spinning blades.
If it munches the chicken and carries on, all well and good. If it explodes in a shower of turbine blades, well, back to the drawing board you go.
British Rail, when designing the 125s, decided that there were sufficient cuttings etc, where there might be low flying birds, that they\’d better test the new trains with the chicken gun. So, it was flown over from the States (Lockheed owned it I think? Maybe Northrop?) and set up. They procured a chicken (no, of course not, already dead one, from the supermarket) and fired.
Straight through the armoured window, the steel back of the drivers\’ seat and embedded itself in the back wall of the cabin.
This wasn\’t, to be polite about it, quite what the BR engineers were expecting. So, big report written up, detailing everything they had done, distance, gunpowder charge, tensile strength of window and so on, sent off to Lockheed (or Northrop?).
And back came the response:
In order to use the \”chicken gun\” please note these operational steps.
1) First, defrost your chicken.