We gotta problem here !!!
> >How do you know when you have a totally friction free system. Our roll
> >linkage seems to be fairly free moving though the pitch seems to be a bit
> >stiff (as yet we havent fitted the tailplanes and drilled out the
> >counterweights).
>
> Carl, greetings
> >Both pitch and roll should be friction free. That means if you knock the
> >stick gently it will continue to move in the direction of the knock
> >without stopping immediately. Obviously some friction is inevitable but
if
> >there is significant friction in the pitch direction it will be very
> >difficult to balance the tailplane accurately. If the balance weight is
> >light the plane will tend to oscillate in pitch. (No, not flutter.)
Having spent an evening trying to free up our control system on the fuselage
only (ie wings not attached), we had some success with the roll but
definitely have a headache in the pitch system. When we built the control
system, we fitted grease nipples to the tufnol bearings but now feel that
grease is not the right lubricant (too much drag). We have tried a mixture
of engine oil and graphite grease and this has freed up the system up no
end. It is possible to use an old fashioned pump type oil can with a short
length of PVC tubing over the nipple end and then you can force oil into the
bearings. Having flushed out the grease and also checked out and lubricated
the ball ends everything seems much looser. Despite this we have not got to
the stage where the stick can be pushed and it will continue moving (unless
you give it a hard shove !) but the forces needed to break away the friction
feel small. We went out today and purchased a small fishermans spring
balance and the force required to displace the PTT switch at top of stick
was about 2-3 ozs (60-70 grams). The pitch system is a different matter.
>
>
> Some of the early supplied ball joints were much too stiff, they were
close
> tolerance type. The ball joint should drop under its own weight, or very
> nearly so, when held by the center boss. The other cause of excess
> friction in roll is to tight fitting of the flanges on the torque tube.
> Those of us who went for a perfect fit with no play had trouble.
We are fairly sure the least of our worries are with the ball ends. We did
get ours from the early tight batch and had to spin them up on a drill to
loosen them. Most of them passed the drop test after this treatment - you
run the balls up on a drill mandrel till the whole thing gets hot (using a
little lubricant) and then immerse the ball end in cold water to reset the
teflon liners. Sounds drastic but it works (Andys suggestion, but given
without official Europa approval).
I guess we should have asked Europa to replace them but they seem fine.
Having disconnected the pitch (connecting rod/ tube) there seem to be
problems both in the torque tube (probably flanges too tight) and in the
bronze bushes., though we think the nylon sleeves that keep the tailplane
tube centred have been fitted too tightly against the bronze bushes and are
pressing against the sides of them. Its going to be a devil of a job to
rectify this. At the moment the tailplane tube (without the planes fitted)
can be moved to any position and require some force to move the
counterweight arm up or down (obviously without weights fitted). The strange
thing is that before this discussion we didnt really think the forces needed
to move the stick back and forward were particularly high compared to other
aircrafr we had flown.
Discounting the fact that balancing the tailplane could be a problem we
wondered whether having a slightly stiff pitch system might not have some
advantages in that small amounts of retrimming in flight would become
unnecessary. The counterbalance could easily be set up using a spring
balance and measuring the forces required to move it up and down. When these
forces became equal one would assume that the tailplanes were in balance.
>
> Pitch stiffness is usually misalignment of the bronze bushes caused by
> distortion of the fuselage moulding after bonding the bushes in.
If our problem turns out to be a bearing misalignment problem is there
anything we can do (other than commit hari kari !) Better hari kari now than
kamikazee later !
It would be really useful if we could get a real idea of what the stick
forces should actually be - measured in grams or ounces. At the moment it
seems likely that our stick forces in pitch are going to be in excess of 1
lb (or 500grams !). We really need some figures for comparison.
>
Carl
G-LABS
PS - any suggestions on the best lubricant to use on the bearings/ rod ends
etc.
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