Hi! Ian,
You quote :-"This was something of a surprise as, to the best of my
knowledge, we had not had an accident with the nose wheel"
Do you mean your bird specifically or in the fleet generally?
Where were you when I tried to give a "heads up" to trike operators two
years ago about my incident of nose wheel/yoke departure? Everyone I
highlighted this self same issue to seemed once again to put it down to
"Bob Harrison Syndrome." The factory did load tests and gave assurances
as to the adequacy of the arrangement so how come we are needing to
revisit the matter? My claim was that simple load tests do not represent
real time operation and because of the prising action of the friction
assembly the stresses can far outweigh the dead weight factors.
I don't need "brownie points" but I do have a conscience for other
flyers lives.
Now to return to the main points of engineering:-
I think you may well find that aft of your yoke spindle hole the metal
is beginning to be compressively distressed if the spindle has been
bent.
Your roll pin seems to indicate that movement has taken place so there
will also be compressive distress in front of the spindle hole at its
lower forward reaches. (BTW the application of Loctite was part of the
original assembly procedure anyway.)
The solution you proffer is to put an additional 1" of spindle into the
Yoke as I did but may I suggest that you also insert a second roll pin
1" below the original and still use Loctite but also applied from the
bottom of the hole.
As to the cause of the failure and pot holes etc. the possibility of a
"wheel barrow" landing also adds loads from forward of the spindle
centre line and I posted a message only last week on the Matronics Forum
in a debate about Bungee/Springs and suspension only supposed to be by
flexing of the nose leg. These forces "out of vertical plumb" also go to
cause the prising/opening action of the friction device against the
castellated adjustment nut holding the whole assembly together.
Much more attention is needed to be applied to inspection and the
loading applied by the castellated nut. I had re-set my friction loading
only 10 days prior to the incident but unbeknown to me the assembly was
being pulled apart by the adjustment loading.
BTW let me know the mod. number for the longer spindle when you have it
!
Ignore all this at your peril.
Regards
Bob Harrison G-PTAG
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