In the hope of making life slightly easier for some of you contemplating
this mod this is how I did it on GK Whip.
Before starting the layups access is obviously required into the fuselage
behind the rear bulkhead. The upper part of the plywood sternpost, from 12
inches above the bottom to just below the foam section of the fin, was
removed. This is just wide enough to slip an arm in. (Gynaecology, here we
come!?) A splash moulding was then laid up on the inside, right hand side
just below the tailplane, 4 plies of BID in a 10 in diameter circle. This
was to be the flange for the inspection hole. After cure the hole itself
was marked out, 6 holes drilled for the attachment screws plus a couple for
small Clecos for location. The splash was then cracked off, (we did
remember to wax the fuselage first,) and the hole itself cut carefully with
a Stanley knife. Gentle taps on the blade with a small hammer produce a
nice accurate cut. The foam was routed out of the edges of the =93biscuit=94
and the hole. A piece of wire bent L shaped in a high speed drill is ideal
for this. All edges were flox filled. The splash was saved to be floxed in
place at the end of the whole job. ( Better access through the hole without
the flange. )
The multi layer reinforcements were then completed as per the Europa layup
schedule. Each 3 ply BID layer was laid up on cling film on the bench, then
transfered to the fuselage and carefully stippled and cajoled in place with
a brush and sticky fingers. Another brush taped to a stick proved
invaluable. A 40 watt bulb hung inside the fuselage also helped, both in
illumination and speeding the cure.
The 1/8=94 steel plate for the front attachment point of the spring was found
to be too soft and bent slightly when the single bolt was tightened. 1/4 in
hard steel, widened in line with the bolt hole was used instead because it
was felt that the tortional shocks from the tailwheel might cause further
bending leading to slackening of the bolt.
Finally the flange for the inspection hole was floxed in place, anchor nuts
fitted and the =93biscuit=94 turned into an inspection hole cover. The edges of
the screw holes were routed, floxed and countersunk. The cutout in the
sternpost was repaired after all the mechanical details had been completed.
Tailwheel Steering Connection.
The original tailwheel pivot was modified, a second wider steering arm
being bolted on top of the old one to provide attachment for the cables
which ran through the bulkhead, through stainless tube fairleads in the
sternpost and down to the tailwheel. The cable run is almost straight but
because of the slanted steering arm pivot shaft, moves vertically as the
arm turns. This could be avoided by remounting the pivot casting with the
shaft vertical or even slanted slightly back. The springs were fitted in
the run between the rear bulkhead and the sternpost. Turnbuckles were
fitted into the cables close to the tailwheel allowing easy adjustment of
tension.
Because of the possibility of either cable slipping over the tail spring it
was felt essential to have positive limits to tailwheel turning range. This
was achieved neatly by using a quadrant, basically a 6=94 pulley, with a 120
degree cutout at the front, bolted on top of the tailwheel fork assembly
and replacing the steering horns. The cables were attached at the back. The
original Europa differential causes the cables to be tight at mid range, ie
straight ahead, and slack at the limits. Initially G-KWIP was set up with
even tension across the whole steering arc. There was some noticeable
friction which prevented the rudder self centring completely in flight.
This did give a measure of adjustable Rudder Trim but it was decided to
forgo this luxury in favour of less sensitivity to steering on hard runways
and the differential was altered, (by moving the quadrant forward) to give
slack (just) cables at mid range and tight at the limits. Eventually we
will probably revert to a fixed steering arm in place opf the quadrant when
the geometry has been finalised.
We have been pleased with the results so far, on both hard runways and soft
wet grass. After we have had a chance to fly with stronger crosswinds and
satisfy ourselves there are no unforeseen problems waiting to surface, we
will consider offering full instructions and the extra parts needed for
this modification.
Graham
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