For making foam core wings, and working with Glass fuselages, using a good epoxy resin is the key to success. Use only a thin, easy to mix resin with a good working time and a reliable cold weather cure.

The Bolly Epoxy Resin is an easy to use, reliable low viscosity (thin) resin, that is very easy to sand.

When using any epoxy resins, please do so in a well ventilated space, avoid contact with the skin and avoid breathing the vapours or the dust from sanding.

The secret to using epoxies, is to take care to apply a thin, even layer/s. Using a pigment in the resin is the best way of recognising the depth of resin being used. Almost any non oil based pigment or dye will be OK - but don't use any more than is needed to lightly tint the resin.

In cold weather it is best to pre-warm the resin by standing the bottles in a bowl of warm (not hot) water. The reverse applies in hot weather.

Epoxy resin cures by chemical reaction. The speed of the reaction is dependent on heat. Too cold and it will stop, too hot and the resin will boil. A temperature of 25oC is considered ideal. In hot weather mix in a shallow dish, the reverse applies in winter.

Allow at least 24 hours, before using a product that has been epoxied (curing time). The longer the better. After 24 hours the epoxy is at about 96% of cure, the last 4% will take a week or more.

All resins will shrink with curing, (Polyester resin can shrink 10 times more than epoxy), for this reason never glass only one side of a flexible object, or it will be distorted by the shrinkage. The best procedure where it is impossible to do both sides at once is; resin/glass one side, allow to cure to a tack free state (6-12 hours), then do the second side.

Most epoxies are hydroscopic, ie, they will absorb moisture. This generally, is only a problem in cold, wet weather. The cured surface will have a slightly tacky surface. A liberal sprinkle of talcum powder will usually solve the problem. It is a good idea to make a ‘Hot Box’ from a large cardboard carton or similar, with a low wattage globe to provide heat for use in winter.

Stored epoxy can often change to a whitish honey type consistency. Don't worry, the resin can be reverted back to normal by gentle warming; ie, place bottle in hot water, etc.

Bolly Epoxy Resin is a 2:1 mix; ie, 2 parts Resin to 1 part hardener, by volume or weight. It is highly recommended that a set of scales be purchased. Small electronic scales for about A$50 are a good investment for any modeller.

Unless you have an accurate measuring system avoid mixing very small quantities. We suggest 20gms as a minimum mix.

Epoxy resin is compatible with most other resins including polyester resin. Always thoroughly sand the resin layer that you intent to epoxy over, as many resins will give rise to a wax layer to assist curing - this must be removed. Note: Polyester resin will not usually go over epoxy.

Building model aircraft is generally a common sense procedure. Attention to detail is important for a successful and long lived model. The first thing to do is to sit down with all of the components and plan the procedure for building. Most modellers start with the wing, as this is the core of the model, and is used to determine the correct fits and alignment of the fuselage and tail components etc.

An incidence meter is a very handy item to check the alignment of wings, tails and thrust lines. A correctly aligned model has a good chance of success, a badly aligned model, whilst it may be flyable, is generally unpredictable and not much fun to fly. For all models except dedicated pattern type models, the wing should have at least 1 degree of positive incidence compared to the tailplane.

A common error when building models is the lack of down or right thrust. Almost all models will benefit from both. Pylon models need approximately 1 degree of both, pattern maybe as much as 3 degrees, usually 2 degrees and sports models at 1 - 2 degrees.

The heart of all models. It is vital the wing be built straight. The leading edge should not be too sharp as this makes for a sensitive wing. Blunt thick trailing edges have the effect of de-sensitising the ailerons at the expense of precise feel, the opposite is so for sharp trailing edges. It is important the wing be set square to the fuselage. Measure from each tip to a point on the centre of the fuselage at the rear.

Like all components it should straight and square. Special attention should be given to the installation of the firewall and servo mountings. Make sure the engine bay is well fuel proofed and that there is a drain hole if the worst happens and the tank leaks or has a fuel tube come adrift or break etc.

The important factor apart from the obvious need for a warp free tail, is that the elevators move freely and an equal amount each side (for split elevators using a Y shaped pushrod). It helps if the elevator servo is mounted to drive the pushrod down the middle of the fuselage.

If using a tailwheel driven from the bottom of the rudder, a less easily damaged system can be fashioned by attaching the tailwheel driving arm to the rudder via a rubber band and hooks. If the wheel has a sideways knock it will not break the rudder.

Bad hinges crash models. For models under about 10 pound weight the thin 1 piece mylar style hinge (i.e. Sig Easy Hinges) are good.

Bigger models should use a more solid style hinge. We find the Sig ‘Poly Hinge’ which is installed with epoxy impregnated pores to be excellent.

The above diagram is our preferred hinging method. It is very easy to determine the hinge line, as it is a constant depth from the top, just under the wing skin. Make a small template to mark the required depth. Please Note: The above hinging method can’t be used on thin surfaces using the torque rod method of actuating the control surface.

The golden rule of hinges is to NEVER use less than 3 hinges on any surface, sometimes up to 5 will be needed. Make sure the hinges are square and are pinned. The easy way to pin, is to measure the depth of the surface, cut a pin to that length or slightly less and push in place. An advantage of the Sig Poly hinge (not to be confused with the Easy Hinge), is that the pores in the hinge trap epoxy and make for a certain bonding, and reduces the need for pinning the hinge.

If using mechanical retracts, it is vital that the system work without ‘snapping’ or placing a load on the servo at each extreme. Mounting plates in the wing etc should be supported on light ply sub ribs.

For fixed gear, the use of nylon bolts will help protect the mountings from tearing out in a heavy landing.

Use as big a wheel as practical for use on rough or lush grass flying fields. Rearward position wheels are prone to nosing over, but if this problem can be avoided, makes for excellent landings. Forward position wheels are great for preventing nosing over, but are prone to bouncing if the landing isn’t perfect. Make sure the wheels are free to rotate, and if possible have a touch of camber and toe in built into the undercarriage

Use a good alloy mount for high performance engines.

The use of rubber type ‘soft’ mounts are good for noise reduction and more importantly help prevent the transmission of damaging vibrations through the airframe.

There are many types of ‘soft’ mounts available, few of which are cheap. The most common method is to mount the engine in a normal radial mount, then mount the assembly to the firewall via suitable ‘soft’ mounting rubbers.

For large models (above 25cc) the ‘Scale Aviation’ ‘engine vibration isolators’ are good.

For smaller models the cushion mount (often called Lord mounts, or ISO - Mounts), as available from Sullivan and Gator brands etc are excellent to use. These manufacturers supply an alloy plate which is mounted to the backplate of the engine, using the engine backplate screws.

Our personal favourites are the ‘MK’ brand (and the numerous copies) beam mounts. This style of mount are becoming more common for Aerobatics style models. The installation requires a horizontal ply plate into which the mount is screwed.

Take care to wrap the tank with a vibration absorbing material to prevent fuel frothing (and wearing a hole in the tank). For high vibration models such as FAI pylon racers, the use of bladder tanks is almost mandatory for good fuel supply. Commercial bladder tanks are available but can be difficult to find.

Tanks should be well secured, a full 16oz tank is heavy, and combined with the G-forces a model can generate, the tank will moving unless restrained.

Fuel lines should be in good condition and not be able to kink.

Use a good fuel filter, we highly recommend the Sullivan brand ‘crap trap’.

Many a model has crashed due to bad radio installation. Attention to detail is paramount.

All linkages should be rigid and free to move, and all clevices made secure by sleeving with a short length of fuel tubing or similar. The servos should not be strained at the limit of travel.

All servo leads must be tucked away neatly so as to not foul on servo arms, pushrods etc.

The receiver MUST be well packed with sponge rubber or similar.

The battery pack should be in good condition and secured properly in sponge rubber or similar. Heavy battery packs can easily come loose and pull out the lead or snag other components. Almost all receivers and servos are made to use 6 volts (as in 4 @ 1.5 volt alkaline batteries), but most modellers use 4 @ 1.2 volt ni-cads. Using a 5 cell ni-cad pack (making 6 volts) is recommended for any model application using more than the standard 4 channels and 4 servos.

Before the first test flight check the model for....

A) The C of G, Never test fly a rearward C of G model. The C of G will vary between model types. A Pattern model is usually 34-37% (of average chord). A racing model is usually 20-22% (of average chord). Most sports models are 25-30%.

B) No warps in the wing, tailplane or elevators. It is especially vital that elevators be warp free and that split elevators have equal movement. If split elevators have a different degree of movement or are not level in neutral, it will induce a rolling action.

Make sure all servo’s are properly screwed in and the output arm screws are in place. Check that all controls operate properly, and that the hinges are secure.

Before flying make sure the engine will idle and throttle up properly. The last thing you want is a dead engine on take off or to land ‘dead stick’ on the maiden flight. Tune the engine for a click or so rich in case of a tank or fuel feed problem.

If possible fly with the help of another modeller, who may pick an obvious problem you have overlooked, (we have all done it). It is also safer flying with help to hold the model etc. Upon landing check that vibration has not loosed any screws, and that the tank hasn’t leaked.