Greetings !
We spent last weekend trying to reduce the friction in our control linkages.
The roll was fairly simple but the pitch took much more work.
First we disconnected the long tube connecting rear from front of aircraft
and it became clear that there was a problem both with the pitch torque tube
and the tail tube end bearings. We had to remove the end support brackets
and rebond them as they were compressing the torque tube and bearings. Like
you we think this problem crept in when we did the end cap mods. It seems to
be quite difficult to fit the brackets without pinching the tube. It is
necessary to tighten up the bracket support bolts otherwise the brackets
drop causing problems with the pitch push rods. The trick would seem to be
to temporarily insert an extra spacer washer (eur 001) between the bellcrank
bearings and the end caps until the flox bedding (under the brackets) has
hardened. Then you need to remove washers as necessary until there is no
pressure whatsoever applied to the tube (it should fall away from the
brackets if left unsupported). We found that even the slightest amount of
pressure against the sides of the bearings caused an increase in friction.
When we had finished the control sticks behaved like pendulums returning to
the centre when displaced from centre (in pitch only).
Unfortunately when we looked at the tail end the torque tube was really
stiff, the control linkage having masked the severity of the problem. We
tried forcing oil into the bushes but although it was apparent that we had
succeeded in thoroughly lubricating the bushes, there was little improvement
in the situation. It was at that point that we had to consider the
unthinkable (ie- dismantling the torque tube assembly in situ - we are
talking about a fully built fuselage with TOP ON !). Surprisingly although I
have no skin left on my hands we managed to disconnect and remove the TP12
drive plates. When we had dismantled everything we eventually identified the
problem. The starboard TP12 drive plate tube (which slides inside the TP11
bush) was not circular but oval and did not fit into the bearing properly.
What was originally a machined piece of tube had presumably distorted when
welded to the end plate and this was not picked up in quality control (or
unfortunately by me !!!). The tube was about 0.5 millimetre wider than it
was high and only contacting the bearing at the sides.
The ideal solution would have been to ask Europa to replace the component
but this would have meant re drilling the torque tube in situ which would
have been an almost impossible job (its funny though, you get used to
achieving the impossible when it becomes a necessity !) .
Next best would have been to find a lathe and try and re machine the tube.
Not having a lathe to hand we resorted to using fine emery paper (and wet &
dry) and a lot of elbow grease. About two hours later we now have a part
that fits and moves freely. Incidentally I suspect some wise guy will tell
me the bushes were bonded in crooked (as we thought initially). We
eliminated this as a possibility by temporarily switching the TP12 plates -
the port TP12 plate moved freely when inserted into the stb bush but not
vice versa. If the bushes had been at fault (ie misaligned) the problem
would not have moved from one side to the other when the plates wre switched
(note, the tailplane torque tube remained in situ during this process). We
also checked the distortion with a vernier caliper ( we didn't have a
micrometer to hand).
We cant help feeling that we should have noticed these problems at the
beginning but one often assumes some things dont need to be checked by the
builder and also its difficult to know what degree of tolerance the factory
is working to. The trouble is you dont know what you are looking for till
you have built at least one Europa !!! It is all too easy to build a system
that fits perfectly but is so tight as to be unusable - a bit like the early
rod ends which seemed stiff but otherwise OK till you had six connected end
to end (the aileron linkages have a total of 12 - six on each side).
So what is the moral of this story - check and double check everything. Also
its worth noting that no amount of lubricant will help if the engineering is
wrong. If it dosent fit properly, chances are it wont work properly. We
could have left "well alone" in the hope that the parts would eventually bed
in but I suspect we would have experienced an eternity of uncomfortable
flying before any worthwhile improvement.
I hope this salutory tale might save other builders from the grief and
frustration we went through. Though hopefully ours was the only faulty TP12
that evaded the quality control net.
Happy building
Carl
G- LABS
PS - Thanks to all of those that offered advice and possible solutions to
our problem including Andy Draper at Europa.
----- Original Message -----
From: Tennant <Tennant@t-online.de>
Subject: Re: Navaid Wing Leveller
> Hi Carl.
>
> My roll control was free of friction in the begining but after I made the
mod.
> with the end caps on the torque tube I got some friction which I cannot
get rid
> of!
>
> I think you will know if there is friction in your system.
>
> Happy building!
>
> Barry
>
>
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