Airborne Magazine



by Matthew Downes

Plan No. 702

Wingspan: 1.4M
Length: 1.3M
Engine: .40 - .46 2 stroke
.48 - .52 4 stroke
Radio: 4 channel
Plan Detail

Plan No. 702
AU$33.00 plus P&H (AU$3.00 within Australia).  

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: 
PO Box 30 Tullamarine Vic, Australia, 3043

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.

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.

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.

Plan Detail

Plan No. 702
AU$33.00 plus P&H (AU$3.00 within Australia).  

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: PO Box 30 Tullamarine Vic, Australia, 3043
Airborne Plans Service: P.O. Box 30 Tullamarine Vic, Australia, 3043