Reading the various postings on the internet regarding the main gear frame,
there seems to be quite a bit of confusion as to the whys and wherefores.
It would seem timely to clarify the situation.
Approximately three months ago we were contacted by a couple of builders who
said that they had either had a total or partial collapse of their main gear
frames. They assured us that this was not the result of a heavy landing but
what could be considered normal operations. We were a little surprised at
this as YURO had completed over 1500 landings, two other company aircraft
G-ELSA and G-ODTI had similarly operated without any problems and there were
also over 20 builders' aircraft flying without any reported incidents;
however, we took these reports at face value and instigated a series of
tests. A rig was constructed which simulated the fuselage and engine weight
and a series of drop tests were done on several frames to destruction. We
found that a drop exceeding 10 feet per second was required to simulate the
type of failures that we had seen. However, it is very difficult to
simulate the exact dynamics of a landing aircraft on a test rig and even
though we simulated a side load by dropping the gear on to a sloping side
plate to impart a side load, we cannot be sure that this reproduced
faithfully what may have been experienced in the field. We came to the
conclusion that, if indeed our builders had not had a heavy landing, then
there was clearly something at work that we could not fully simulate on our
drop test rig, and if our builders were to be believed, and we did believe
them, then we would need to increase the strength of the main gear. The
failure was caused by the bottom member starting to bend; this was largely
due to the forces on the swinging arm being taken in single shear. We
brought out a modification which consisted of two U bolts that not only
increased the strength but reduced the bending of the bottom member by
putting the load into double shear. This was hastily sent out to all our
flyers and I took several of these to the Europa weekend at Tetbury. The
vast majority of the builders present did not like the idea of some sort of
bolt-on fix and, to be honest, it is not our preferred style of engineering.
Indeed we intended to update all new frames to a spec using welded members.
The builders present at Tetbury thought that they would be disadvantaged by
fitting a bolt on fix. Basically, I heard them loud and clear and agreed to
give all the builders the benefit of what would be a later design. This,
of course, would involve some work for our builders and we wanted to carry
out further tests to really make sure that we had fixed this once and for
all. We spent another week and a half welding in place various tubular
members of various thicknesses testing each one to destruction. We started
with an overkill situation and on testing we considered that this would be
too strong. At this point I ought to just clarify what the goals for the
strength of this part are: that the pilot of a Europa should be able to land
quite robustly on his farm strip without fear of any undercarriage failure
but, in the case of a genuine crash (no option but the ploughed field ahead)
the best and safest thing to happen is that the tubular structure
progressively collapses absorbing energy, allowing the aircraft to sink onto
its belly and thus be in a stable position to slide over the field. What we
do not want in this scenario is a gear that is so strong that, should the
main wheel fall into a ditch, the aircraft is catapulted head over heels or
that the entire main gear/engine assembly is ripped out of the aircraft
necessitating major repairs or worse still entering the cockpit area and
injuring the pilot/passenger.
What we have put out as mod 37 is in our considered view the best way
forward. We brought G-ODTI into the shop and found that it was a very
straightforward operation to complete in situ and several of our builders
have now similarly completed the mod without problems. You need the
services of a competent professional "tig" welder. One of our builders,
Graham Singleton, preferred to remove the frame for welding and, by applying
a heat gun to the frame to soften the adhesive, found that it could be
removed without damage. Carl Pattinson and others have also done this
successfully.
If we were starting to see a problem with the main gear as more and more
aircraft enter service then, as a company we needed to take this seriously
for all our sakes. We have done just that, and I know that it is
frustrating particularly for our builders who are flying or were just about
to, but we have no alternative but to put safety first.
Sincerely
Ivan
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