>This mail has been composed after consultation with a number of builders
>who have been waiting in vain for some days to see reactions to the "Main
>Gear" letter, mod no. ??. Is it shock, resignation, or apathy ? The
>mods.in this area have been getting more severe each time at significant
>expense to the factory and the builders in terms of both effort and cash.
>In the beginning the bungy block, (a re-usable energy absorber) seemed
>like a good idea until it turned out that in returning the energy, it
>bounced the aircraft (quickie-wise) back into the air. Is this why it has
>never be used before ? Although I have driven an American car with piston
>mounted bumpers, modern car protection is based on crumple zones as near
>the accident as possible, not on springy systems. Introduction of stops
>increases the load transfer when they are reached, and a hydraulic damper
>(returning the energy progressively) was apparenty is not sufficiently
>large in the space available to do the job. The various mods to the frame
>and its stops have resulted in isolated case(s) of buckling which means
>we have an inbuilt crumple zone which might be a bit too weak.
>Unfortunately in the absence of recorded data from these instances, the
>actual load to which it has been subjected is not known. Quite rightly
>the factory set out to remove this doubt with drop tests, which seem to
>have shown that it has to be a very abnormal load to damage the frame,
>but nevertheless have offered more strengthing to prevent it. But is this
>the correct thing to do ? Leaving aside the difficulty and/or expense and
>delay of doing the latest mod. to complete or near-completer aircraft, it
>will certainly increase the possibility of passing more load beyond the
>frame into the tunnel/fuselage. The tests carried out with the frame
>only, cannot tell us where the buck(le) stops now. So please can the
>factory repeat this test with at least a dummy tunnel and bulkhead in
>place if not a real fuselage, before we do this mod. only to find that
>the next time the fuselage collapses. If a problem is then found, a
>number of suggestions are available, such as removing the block assembly
>and replacing it with two or more hydraulic dampers as used by many
>conventional undercarriages, motor cycle forks etc.
>
>gemin
>
>
The fact that making the landing gear frame stronger means that the
fuselage will see higher stresses has not been ignored here at Europa. The
frame will fail before the structure, but not in the manner as before. It
appears that variables in overcentre geometry of LG08 and the shock
absorber, torque effects of the LG03 bearings on the lower pivot tube due to
differences in bearing tightness from aircraft to aircraft, and the shock
absorber limit stop, were all factors as to why some aircraft suffered
damage and others didn't.
Catering for these variables without going overboard on strength has
resulted in the Mod now required to the L.G. frame.
The failure mode has changed, as one would expect, but to a more easily
identifiable part of the mechanism, which is also easier to replace than the
entire frame.
You will note, from the Mod sheet which will accompany the parts you will
receive shortly, that the stops will be removed from the shock abosrber, and
a shim of rubber inserted instead.
Regards
Andy
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