We had the same problem (tightening up of pitch controls) when we did our
Mod No 46 (pitch torque tube end cap replacement).
To remove the tube we had to break away the flox bedding of the supporting
brackets and re bed them in. This resulted in end pressure on the torque
tube and some resulting stiffness.
The only real solution is to re bed the end brackets (CS09) and temporarily
insert an extra washer between the brackets and the tube while the flox is
going off (one each end). Once the flox has set, remove the extra washers
and reassemble. You should have a much freer pitch control system after
though you may need to use an extra thin washer to get the spacing exactly
right.
The other problem area we experienced is to make sure the fuselage dosent
twist when you put the lid on. You need to align it with clecos before you
even consider mixing up the redux. Make sure the tailplane (or rather the
tailplane torque tube) is still parralell to the wings (Or whichever datum
you are using ) . It is very easy to put a twist in the tailplane so you
need to check this before you start glueing.
CHECK< CHECK< CHECK that the pitch control system is completely free before
gluing on the lid. Dismantling the tailplane torque tube assembly after the
lid has been installed is a very slow and painful process (I speak from
experience !)
The other tip we found was that thin oils are better for lubricating the
control bearings and rod ends than grease (by all means use a thin film of
grease when you assemble things). You get a much freer system this way but
the downside is you have to lubricate often. We have drilled small holes in
the tufnol bearings (in the cockpit module) and use a syringe and long rigid
tube (same as the rudder cables are sleeved in) to drip oil to the bearings.
It is quite easy to access the rear tufnol bearings through the "wing
holes" - just needs a bit of practice.
It is certainly true that when you are building, the controls seem stiffen
up over time. We started off with what we considered a very free system and
found years later that everything had tightened up. As long as you are
careful at each stage it is probably better to get the plane built and worry
about the stiffness when everything is finished. You are going to have to do
this on your final inspection anyway, so why duplicate the effort.
One thing that is interesting to note is that the wings are aligned with the
cockpit module and if it is bonded in slightly skew, then the wings will be
out of alignment with the fuselage. It is fairly easy though to correct this
misalignment when installing the lift pin sockets.
It is probably worth doing a temporary installation of the cockpit module
and supporting everything carefully, rigging the wings (support these too !)
and checking two things.
Firstly that the distance on both sides measured from the wingtips (trailing
edge) to the tailplane torque tube is the same on both sides (use a long
piece of string). You will need to move the wings about to achieve this.
Secondly, once you have done this check that the spacing between the sides
of the fuselage and the W22 and W23 (lift/ drag pin mounting plates) is
roughly the same on both sides. Note the distance between the front plates
and the fuselage will be less than the spacing between rear plates and fus'.
If the difference between port and starboard side gaps here are more than
about 5mm then it is possible the cockpit module is slightly skewed and may
need a bit of "jiggling" (or something similar) to get everything into line.
Once you are satisfied everything lines up then cleco everything in place to
ensure alignment when you start glueing the module in.
We discovered this problem after bonding in the cockpit module and had to do
some fairly major adjustments when we installed the wing lift pin sockets.
Please note we are talking about a CLASSIC Installation here. The XS setup
is likely to be a bit different.
Carl P
From: "Fergus Kyle" <VE3LVO@rac.ca>
Subject: Those tight pitch controls
> Cheers,
> If the title grabs your attention, you remember text on
"tightened"
> pitch controls, or you have not yet placed your cockpit module in the
> 'canoe' - this may be for you..
> There were a number of messages concerning the pitch losing its
> 'loose' quality after a while. I am ready to install the cockpit (an XS in
a
> Classic Mk.1) and have the module standing on its nose where I can install
> further fuel fittings. In the process, I noticed that the aileron travel
was
> markedly tighter than I remembered it, and so applied some of that
"Harrison
> juice" ( Brasso) to the four Tufnol bearing surfaces and ran my
stick-shaker
> (a slow 12Vdc Motor driving a stud through a seven-inch circle, and
inserted
> into the stick tops) to exercise the Brasso. Lo or behol', the bank
control
> path loosened up magically, but the pitch channel remained frictionful.
> I had philosophised that it was the "canoe" imposing its shape
upon
> the cockpit which diverted the control paths enough to force the four
> tufnols out of common plane, and so had sworn to use some bright builder's
> plan to insert the cockpit into the canoe with the former carrying "yokes"
> (oaken bucket style) which are then winched down into the canoe while the
> latter is held perfectly horizontal - on the grounds that the canoe would
> then peripherally take on the cockpit shape rather than the other way
around
> (all variables being monitorred of course).
> Then entered a visitor with swift mechanical mind. He soon noted
the
> relative friction in the pitch mode. We were fiddling with the module when
> the pitch I was exercising suddenly eased up! I marvelled at this till he
> said "I just pulled this bracket outboard", and showed me the top of CS09!
> Remember the end brackets on the pitch torque tube and their "cuddle
> plates"?
> Egad! The simplest pressure outward on the peak of CS09
relieved
> the pitch system instantly. Then it dawned - the slightest pressure on the
> shape of the cockpit bottom cheeks would add pressure inward to the
> CS09............
> That's where I think our common complaint originates - forcing
> the CS09s inward at the bearing toughens the pitch control run a great
deal.
> So, I am going to see if it can't fix a pry between these
CS09s
> such that they are held open only enough to ensure relieved pitch controls
> while the 420 hardens in the canoe. Naturally, sweet logic dictates
guarding
> against any excess force which might cause excessive wear.
> Any other suggestions greatfully received. Flamers even.
> Ferg A064
>
>
|