The following is a recommendation on how to best build such wings.

1) Use only Epoxy resin, use a good thin resin which is a 2:1 mixing ratio (fool proof).

Epoxy is the best for strength, and can also be used very lightly. Latex based contact cements are also popular, and is lighter, but lower on strength and less versatile on high stress areas such as undercarriage mounts, nor is latex sufficiently rigid on thin areas such as trailing edges.

2) Prepare the foam cores.

a) Rub off all the foam 'spider' webs left on the core.

b) Prepare any servo cut-outs, undercarriage mountings etc at this time.

You may choose to glue the blocks at this stage or wait until the actual skinning process.

3) Prepare the wood skins. Balsa is superior to veneer or ply with the exception of dent resistance. Dent resistance is not a problem when the wings are 'glassed'.

a) Use only the lightest straight grain balsa. We suggest only the following weight.

1/16 x 4" x 48" / 1.5 x 100 x 1220 18 - 28 gm (2/3 - 1oz) per sheet

1/16 x 4" x 36" / 1.5 x 100 x 915 14 - 21 gm (1/2 - 3/4 oz) per sheet

Where possible use 4" wide sheets to reduce the number of glue lines.

b) Arrange the first sheets to have the grain parallel the leading edges. The diagrams (next page) shows two ways of arranging the wood sheets. The Mk 2 way is to join all sheets parallel to each other, then cut to shape with the leading edge having parallel grain (easier to curve) and the grain at an angle to the trailing edge (stiffer).

c) When matching the sheets, try to match the naturally curved edges to each other. If this is not possible, use a straight edge and a very sharp knife to trim all edges straight and square.

d) To join, use masking tape across the join to hold it together, then run another piece of masking tape along the join. It is not necessary to glue the sheets together.

e) After taping together and trimming to size, apply a thinned coat of dope to the side of the wood which will be adhered to the foam. Make sure some dope enters the taped join to seal and 'glue' the joints.

f) If taking the trailing edge to a fine edge (ie, pylon models), draw an overlap line on the edge ( ie, align 6 - 8mm from the wood edge). This is the line of the foam core.

4) Before mixing the epoxy, prepare all items needed for the job, and have a test run on the skins by putting them all together dry. It is very easy to tape the skins on the wrong side.

If you need extra strength, the use of lightweight (no heavier than 2.5 oz / sq. metre) glass fibre cloth or carbon cloth / tape between foam and balsa skins is recommended. See the diagrams below. If installing undercarriage mounting plates, make sure to use a patch of glass over this area.

Mix enough resin to do the job. We suggest mixing 6 gm of Resin/Hardener per every 100 square inches of surface to be covered, ie, double the wing area. This should be the correct amount to do the job.

Brush resin onto the doped wing skins, bottom skin first. Wet out any glass reinforcement on the balsa.

With the balsa skin placed on the bottom foam shell, position the foam core, aligning the trailing edge of the core with line drawn on the balsa skin.

Mix a thin Q-Cell (micro balloons) and resin paste to travel along the trailing overlap. This will fill any slight gaps and strengthen the trailing edge.

Add the top skin, aligning it with the trailing edge of the bottom skin. Position the top shell to complete the assembly.

Make sure the complete assembly is sitting on a flat surface. Place a sheet of glass/plywood or particle board over the top of the assembly. Add as much weight as practical to the board to compress the assembly, we use an 8" depth of bricks. Make sure your flat surface, remains flat under this weight.

Allow 24 hours before removing, trim all edges (except TE) with a very sharp knife. Add the LE and Tips as necessary. Sand to shape.

The result is a strong, rigid, accurate but light wing.

PLEASE NOTE: Some models use a different style of trailing edge to the above method, often by trimming the wood to match the foam, then adding another wooden trailing edge etc.

As used on some Bolly kits, Honeycomb wings, when properly built are very light and strong, with lighter tip weights for improved Aerobatics performance.

Highly recommended is the use of carbon fibre spars. With the introduction of snap roll manoeuvres to the Aerobatics schedule, wing breakage’s have been all too frequent. Generally the break occurs through the retract wheel well, and will occur with or without honeycomb.

The use of carbon fibre spars is highly recommended for all wings which will be subjected to high loads. The below system is without doubt the easiest and most satisfactory spar method for foam wings.

Procedure:

The most popular way of attaching foam wings to glass fuselages is via two (2) or more nylon 1/4 x 28 bolts. These bolts go through the wing and thread into a suitable plywood plate mounted in the fuselage.

The wing must have a suitable hardwood support for the bolts, be it a plywood plate on the outside, or a hardwood dowel set through the wing, (drill or file a hole through the wing, glue in the dowel and sand flush, top and bottom. This is later ‘glassed’ into place along with the centre section of the wing.

With the ply or dowels in place, the wing is attached to the fuselage, then drill (13/64) through the wing and fuselage mounting plate. The wing is removed and drilled hole is drilled out to 1/4" diameter. The mounting plate is threaded using a 1/4 x 20 tap available from any hardware store (1/4 x 20 is standard 1/4" ‘Whitworth’ bolt thread).

This system assures a perfect fit every time. To mount the wing to the fuselage we use the following system.

A) Cover the centre section of the wing side adjacent to the fuselage with 'invisible' tape by Scotch.

B) When satisfied with the alignment of the wing (by measuring from each wing tip to a point on the fin or tailplane), carefully cyno the tape (and hence the wing) to the fuselage.

C) After drilling the holes, a sharp knock with your hand to the wing will release the cyno from the tape.

After a foam core wing is sheeted and mounting blocks etc installed, the ailerons need to be made from the sheeted wing. (Some kits do this by adding a large trailing edge / aileron stock)

A) After sheeting and sanding to shape, mark out the position of the ailerons with a fine tip ink pen, top and bottom of the wing. Then mark the wing & aileron for the area to be removed and replaced by the balsa edging.

B) Carefully cut through the wing skins from top and bottom until all the way through. Carefully sand the edges to 'clean up' the area.

C) Glue the balsa facings to the edges of the aileron and the wing. Sand to shape and hinge as per normal.

Many kits require torque rods to actuate the ailerons. Make sure the rods are stiff enough and use a plastic sleeve as a bearing material.

D) Mark out the position of the tube onto the wing.

E) Cut through a wing skin (usually the bottom) and remove the wood and most of the foam to enable the rod to fit.

F) When happy with the operation of the aileron, tack glue the rod each end of the tube.

G) Fill the gap in with wood or a epoxy resin / Q Cells mixture and sand smooth.

Be careful not to glue the rod and sleeve together. Put a drop of oil between the rod & sleeve before bending the rod to size and when epoxying the gap, use a piece of plasticine at each end of the tube to prevent resin entry.

It must be noted that some builders find it acceptable to simply cut the ailerons from the wing and other than a light ply facing at the ends, use the wing / ailerons ‘as is’. The hinging edges are not faced with wood. This system is very simple and light, but can only be used when the hinge is film or tape.

A fully sheeted wing can be finished in any way chosen, the most popular is the iron on plastic film, or tissue followed by painting.

For the very best of finishes, a ‘glassed’ wing using a lightweight glass cloth and resin, primed and painted is an excellent way to go. As this method is not well known, the text below outlines the procedures for ‘glassing’, using .5 or .75oz glass cloth and epoxy or polyester resin on balsa surfaces.

Polyester has a slight advantage in speed and sanding (K&B Finishing Resin is highly recommend), but the disadvantages of higher shrinkage, attacks foam and is prone to being slightly brittle (in comparison to Epoxy).

The Bolly epoxy resin is the best resin for the job we have found..... reliable cure, easy to apply and relatively easy to sand.

Prepare the surface by sanding to final shape and applying thinned dope, allow 1 hour and lightly sand.

Plan the method of covering, remembering it's usually not possible to cover a complete wing or tail at once, but the complete wing, etc must be completed as quickly as possible.

Never glass only the top or bottom of a surface without completing the other side immediately. As soon as the first side can be handled, complete the other side, or shrinkage of the resin may warp the surface.

The usual procedure is to glass one panel, top and bottom, at a time, using the other side to hold the job.

Glass the top first, allowing approximately 15mm to be wrapped around the leading edge and tips. Wrapping a sharp TE usually unsuccessful ... allow a small overhang at the trailing edge, which can be trimmed after both sides have cured Next the bottom is done without wrapping.

Once the first panel is able to be handled, cover the remaining side.

Allow not less than 24 hours before sanding, the longer the better. If the surface is mildly tacky, dust with talcum powder.

Start wing with 180 grit Aluminium Oxide sandpaper, finish with 240 or 320 grit , unless re-coating to achieve a mirror finish, initial sanding can be 120 grit.

A satisfactory finish can be achieved by using a strong pigment for the finish, but more often the glassing is used for a base to paint.

TIP Use an overlap method in the centre of the wing, ie, the left panel is covered with the glass overlapping to the right panel several inches, and visa-versa. This gives a double layer in the centre for extra strength. On smaller or lightly loaded wings, this is enough ‘glassing’ to join the wing halves.

There are many ways of applying the glass to the wing, The most common is to brush or roll on the resin. Care must be used to prevent tearing of the glass grain.

A good procedure is to apply the resin reasonably heavy, followed by a soaking up of excess resin with tissue or toilet paper to achieve a 'dry finish'. Follow this (after curing) by a quick sanding and a second thin coat of resin only, or alternatively finish by using a dope and talc mixture (sanding between coats).

When done properly, glassing is not heavy, the following is an example of building a 300 square inch Flash Cat wing.

Complete doped wing before glassing 148 gm

Glassed - 1 heavy resin coating 200 gm

Wing after sanding (2 hrs) 182 gm

Wing after painting, (2 colour auto paint) 190gm

All 1 piece wings need to have the wing centre joint glassed.

Take care when joining the two (2) panels together as it is a vital operation (ie, don't set one wing at a different angle to the other). If in doubt use an incidence meter set at 50% span of both panels.

Use a slow epoxy to join the two wing panels. Sand the area smooth.

Use a light weight cloth to glass the centre, top and bottom. We suggest a layer 50 to 100mm wide, (depending on model), or cloth no heavier than 2oz. We use two staggered layers of .75 to 2oz cloth depending on the wing size. Additional cloth can be used in high stress areas such as mounting bolt locations.

Please note, small or lightly loaded models will only require minimal glassing.