As with any project peruse the plan carefully to get
a good feel for what the different parts are for and how they will
ultimately be used. There are subtle angles and set backs that need
to be noted. Compare the material list with the plan, again to see
what will need be used and where.
The first step is to purchase your material from a reliable supplier;
any of those advertising in this magazine will supply good quality
gear.
Preparing Templates
To start the cut out process photocopy the various shapes on the plan
preferably on A3 size to use as transfers. Place the transfers ink
side to the balsa and wipe a rag or sponge damp with turpentine over
the back of the paper, make sure to hold the paper still and don’t
overdo the turps or the ink will run. You may have other methods of
achieving the desired result but I have found this to be very satisfactory.
Make sure you identify each part.
Easing Into Construction
From 1200mm by 9.5mm sheet, strip 5 pieces 18mm wide for leading and
trailing edges, 5 pieces 6.5mm wide for webbing of ailerons stab and
tailplane. Two pieces 12.5mm wide are also needed to use as fuselage
webbing.
To Prepare Wing Ribs
Rough cut template ribs (leaving excess material to trim accurately
later) from the previously marked balsa, drill a 2.5mm hole through
the front and back lightening holes. Place the rough-cut ribs over
a full sheet of balsa allowing room to cut between. Put a drop of
cyano through the previously drilled 2.5mm holes, this will now have
the template rib attached to the balsa sheet for cut out. Cut around
rough-cut templates. Sand the paired ribs to accurate shape. Stack
the pairs of ribs with the transfer side up and put an identifying
mark (marker pen) across what will be the top of the ribs. This will
identify rib tops during construction, especially needed if ribs are
not symmetrical. Complete the preparation of ribs while they are tacked
in pairs, cutting W1, W3 and W4 in half along the dotted lines (refer
to plan), these ribs are butted against the dihedral brace at a later
date. Cut out the non-tacked lightening holes and then the tacked
lightening holes to access individual ribs, ensure they are clearly
identified. From now on ignore the transfer lines on the ribs, as
they are mirror images of the plan due to photocopying.
Building The Wing
You have obviously got a large enough straight building board a supply
of tee pins and your choice of adhesives, a good square and clamps
are always handy to facilitate a warp free job. I also have lead weights
about 45mm in diameter by 25mm deep, these are handy building aids.
As with any job cover the part of the plan you are using with a cling
wrap for protection from adhesives. The lead weights are handy to
stop the plan moving.
Build an outer section (I built the port side first) of the wing W4
to W8 over the plan including the leading and trailing edges and the
1/16inch ply dihedral brace B4. Take care the brace is fitted accurately
as this sets the angle of the Gull configuration. Note W4 is cut and
glued to either side of the dihedral brace. Leave this section pinned
to the building board.
Build the inner sections (this requires a lot of measuring and comparing
for symmetry so take plenty of time, however it is not difficult if
you understand the required outcome).
Cut spars to accurate length over the plan. Glue end on to the outer
spars and against the protruding dihedral brace B4 accurately, flush
top and bottom, check for parallel alignment, this is where clamps
are handy. Slide W2 in and glue to spar at the end of B4, use the
D2 gauge along the spar to check W2 angle. Fit W3 to the centreline
of B4, use D1 gauge along the spar to check the angle of W3. Remove
from the plan. Build the second half of the wing to the same stage
as above.
To Join The Halves
Position the wing halves over the plan with a 40mm block under each
tip at the main spar W8 junction. I used heavy blocks front and back
(brick wrapped in cloth) to keep wings in position while gluing. Measure
from the building board to centre of the leading and trailing edges
to ensure a horizontal chord line and eliminate twists. Very slight
variations can be removed during sheeting. B2 balsa block slides between
the spars and W2s. B1 is fitted to the back of B2 between W2s. Note
on the plan that the spars run at an angle in relation to the centre
dihedral block B2. When satisfied glue in position.
Position accurately and glue both W1s.
Cut and fit centre section leading and trailing edges remembering
to use B5s at the end of W3 and B3 at the end of W1s. This brace will
be slightly bent fore and aft to accommodate the trailing edge forward
angle.
The Fiddly Bits
This takes more to describe than to do. Glue tip pieces T1 and T2
together, fit tips taking note of the vee groove to fit over the inner
side of the leading edge spar.
The following pieces are fitted to support the ends of wing section
sheeting.
Fit and glue W3A and W3B to the top outer face of W3, and W3A and
W3C to the outer bottom face of W3. Fit and glue W2A to the outside
of W2 in front of the main spar, this double thickness rib supports
both the ends of the hatch cover and the wing sheeting.
Servo Hatches:- You will have noted in studying the plan that servos
are located in the wing and attached to the hatch lids. Fit and fix
the required gussets in the hatch corners. Ensure that fixing points
are strong. Also remember that the hatch covers need to be flush with
the finished surface of the wing.
Sheeting the Wing
Ensure the wing is free of warps. I did this by screwing right angle
brackets to the building board and clamping the leading and trailing
edges to these with the chord line, horizontal as before.
Fit T4, 5 and 6 to the top of the tip leaving 1.5mm above the rib
W8 to allow for rib caps.
Prepare accurately and glue the leading edge sheeting from W8 to the
inner edge of packer W3A. Prepare accurately and glue leading edge
sheeting from W3 to centreline of wing leaving the servo hatch area
uncovered. Do not cover W2 in the hatch area as this supports the
hatch cover.
Finishing the Top
Is the gusset at the junction of W8 and the trailing edge in place?
Prepare and fit the 1.5mm trailing edge sheet in similar fashion to
the leading edge.
Sheet the centre section between W2 and W2, yes it has to be joined
along the centreline!
Cut and fit 9.5 by 1.5mm rib caps to exposed ribs. Turn the wing over
and repeat the process as used on the top, including holding and fixing
in position to eliminate warps. When dry remove and sand to profile.
Note the rather blunt leading edge. This is characteristic of fun
flys and should be adhered to, to enhance performance.
The Fuselage
This is a piece of cake to build. Decide on your engine before starting
as the bearer assembly may have to be altered to accommodate your
choice. I built the frame over the plan. The bearer assembly was built
with epoxy for strength and remember the solid balsa between the bearers.
The stab was fitted and glued (I’d built the control surfaces
earlier) at this stage to ensure accurate and straight positioning.
To sheet the fuse, laminate 3 sheets (for one side) of 100 x 1.5mm
together edge to edge with cyano and sand lightly. Rough cut to shape.and
glue in place with aliphatic resin. To minimise the likelihood of
warping I quickly sheeted both sides and weighted them so that they
went off together. The cutout for the wing and tail plane were also
done at this stage. Trim to the frame and sand lightly.
Making It Look Like a ‘Plane
Hold the fuse perpendicular to the building board and insert the wing
through the slot, position so that the tips are equidistant from the
fuse. Check also that the distance from the outer end of the trailing
edge to a common point on the fuse at the tail is equal both sides
to ensure the wing is square to the fuse. Some packing or trimming
may be needed. When satisfied, fix in position using epoxy. Prepare
and fit triangle stock fairing to the wing / fuse junction as per
the plan, soft section is recommended and some further softening with
water or cloudy ammonia will help. I actually carved mine from 12mm
block but it is a slow process.
Control Surfaces
As I said previously I constructed them early on in the job. Build
them over the plan with the usual good warp free and gluing practices.
Shape to the profiles shown on the plan.
Covering
I used Profilm with good results (dark blue), and covered the wing
in sections. Concave areas like the join of the inner and outer wing
sections have a tendency to lift when shrinking. Tips are easy to
get wrinkle free, as the area is large and the use of plenty of heat
to pre shrink / stretch helps considerably. I used to tack the film
to the tip and the try to shrink the rest, often with very wrinkled
results. As they say you’re never too old to learn. Obviously
cover the fuselage taking particular care to fuel proof around the
engine mount area.
Hatches and Servos
Construct, fit, cover and trial screw the servo hatch lids in place,
The inner edge should fit under the wing fairing.
Mounting the servos is very easy. The location of the servos is as
per the plan. Use 6.5mm square spruce for the rails, which are epoxied
to the inside of the hatch covers. These run fore and aft and are
obviously fitted to take the chosen servos. Two servos (rudder and
throttle) are fixed to the starboard hatch and one (elevator) to the
port hatch lid. I varied from the plan with the elevator servo running
at right angles to the fuse for a better fit. A pull - pull configuration
for the rudder was used, one pull wire passing through the fuse about
150mm back from the main spar on a 45 degree angle. This arrangement
gives a lot more control in high G manoeuvres. Aileron servos are
mounted in the under wing hatches in the same way as the top ones.
Trial position the servos and drill a 13mm hole through the hatch
covers to expose the servo heads outside. The rest is simple, fix
the servos, attach the hatch covers and fit the push rods. The battery
pack is located in the front of the wing as per the plan as is the
receiver. The undercarriage is constructed and fitted as per plan.
Installing Power Plant & Fuel Tank
The engine you selected and prepared the mount for earlier needs to
have 3 degree right thrust. This can be achieved by making ply wedges
or using steel washers. In my case approximately 3mm thick ply at
the front running to zero just beyond the back edge of the engine
mount was used. The fuel tank was mounted to the starboard side of
the fuse located as per the plan. I preformed a U of wire the base
20 mm shorter than the length of the tank with the sides long enough
to pass through the fuselage / engine mount timber and to form a hook
on each end. These hooks take rubber bands across the tank similar
to holding the wing on a trainer, self tapers have a habit of vibrating
loose. Keep a check on the strength of the rubber bands if you use
this method.
The Fun Begins
Test flight day, Sunday ‘arvo at the Hamilton aero club. A rare
sunny day with light wind. All the usual checks were done to make
sure that we had a flawless first flight. Photos taken, engine started,
taxi to the runway, a final control check. Open throttle and the Coarse-Air
is airborne in about 10 metres. Just the slightest up trim to the
elevator, beautiful! A few circuits and a roll, aileron only. Loop,
so easy, tight or loose. Lets try out the profile fuselage which some
thought was a bit flimsy, with a knife edge pass, looked superb, no
drama here. All this powered by an OS 46 FX turning an APC 11 x 4
prop. Gain altitude to try a stall, damn, only a porpoise. Landing
was a dream, line up reduce power and float in better than a trainer.
Next flight, knife edge loops and sick manoeuvres like you’ve
never dreamt of! This really is a “fun fly”.
At the time of writing the Coarse-Air has had 20 odd flights and is
performing beautifully, it can be what ever you want, docile at low
power for a novice or sick as hell when fired up.
In Conclusion
A great profile fun fly replica of the real thing, flies like a bird.
The plan is detailed and accurate, the C of G position was as shown
without any addition of weight. Congratulations to the designer George
Buzuleac. Thanks to Airbourne magazine for the chance to build and
review the plane and thanks to the Hamilton club members for their
support.
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With one wing panel finished, itis easy to see the construction
method giving this wing it's unique shape. Ailerons are yet to be
fitted.
All major components made, awaiting sheeting is the fuseage.
The servos and receiver all fit inside the wings and have flush
mounting plates that screw down.
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