Over the years there have been many materials used for model propellers. Some good and some bad, some cheap and some expensive, some are dangerous and some are safe. As with most things in life, you generally get what you pay for.

The best materials for propellers are glass or carbon reinforced epoxy, where the strands run from tip to tip for maximum strength. The extra strength of these materials allows for a better designed propeller.

Whilst it may seem that metal would be the perfect material, they are prone to metal fatigue and if bent will stay bent and not return to their original shape. These factors produce a high risk situation. Metal is just too dangerous and for this reason they are quite rightly banned from use.

Carbon Fibre is a wondrous material, it is light and strong (when used in conjunction with a good resin system). It is very important that any carbon (or glass) prop by made using the correct resin ... usually a high quality epoxy resin.... hence the description of CRE.

Carbon Fibre propellers will flex less under load, maintaining their efficiency, producing an increase in RPM and / or decrease in noise. Some modellers believe a glass prop is quieter than carbon due to it’s ‘softer’ sound .... this may be true to the ear, but generally the carbon is quieter on the noise meter.

The greater strength of Carbon Fibre also allows the user to thin down (file or sand) the propeller. A thinner propeller will almost always perform better. Carbon is the easiest of all materials to work with.

The disadvantages of carbon are it’s expense and sometimes brittle nature (this is only a problem with small, thin racing propellers). Many carbon props are made with a core of glass fibre in the middle with the carbon on the outside faces (much in the same way of a balsa covered foam wing), this offers advantages in cost and reduction of the brittle nature of carbon.

When moulding carbon (or glass) propellers, the aim is to pack in the highest concentration of carbon to resin as possible. For this reason the mould is overfilled resulting in the excess escaping the mould in the form of what is known as ‘flashing’. The down side to this method is that it becomes impossible to produce a perfectly balanced or finished propeller. All carbon props are black.

As a matter of interest, Aramid fibres (kevlar) is far too flexible to make good rigid propellers.

Glass reinforced epoxy props are similar to carbon, they differ in being slightly heavier and not quite as strong but less brittle. They are also cheaper in material cost. It must be said however that most of the expense of a GRE or CRE prop is in the labour, it can take from 15 to 115 minutes to make a prop, depending on the size. Glass props can be any colour (pigment in the resin).

Generally a Glass Fibre prop will be able to deliver the performance required except at high RPM where Carbon Fibre props should be used. Glass props can be slightly quieter than carbon, if sufficiently rigid in the glass form .... carbon props often have a slightly metallic ‘ring’ to them.

Fibre contents for CRE or GRE props is usually between 55% and 65%, the more the better.

The most common of props until the advent of good plastics and fibres. Generally made of good strong maples etc, the wood prop has the advantage of light weight and suitability for any size of prop.

The disadvantages of wood are it’s ease of breakage and are sometimes prone to warping. The light weight of most woods can be a problem when operating 4 stroke engines, which prefer a heavier propeller for smooth running.

Modern laminated woods are almost as good as fibre filled epoxy props, being almost as strong and possibly quieter, but with the disadvantage of being machined to shape which prevents the optimisation of the design. They are also very expensive.

Along with the advent of plastics came the nylon prop. These props are made by pressure injecting molten nylon into a mould, which when cooled, is opened to reveal a finished prop. The advantages of these props are that due to the fact they take less than a minute to make and are all the same.

The disadvantages of nylon are it’s lack of strength , weight and flexibility. For these reasons the performance of a nylon prop is less than better materials. When used for larger props the weight of the prop combined with the low strength will actually stretch the prop to the point of breakage. It is possible for a 15" prop to stretch 1/4" in operation.

Never use a nylon prop on a high performance engine.

The modern ‘plastic’ prop uses a nylon filled with very short lengths of glass fibres. The length of fibres varies from manufacturer to manufacturer, ranging from very short, to claims of being reasonably long (we have analysed several props claiming to be long strand, but have only found short strands), but nowhere near being the full length continuous strands of a ‘glass’ or ‘carbon’ prop.

These props are a big improvement on straight nylon, but still suffer from the same problems, but to a lesser degree. The downside to the manufacture of these props, is that the more glass fibres in the nylon the more brittle and breakable the product becomes. Common glass fibre contents vary from an industry ‘normal’ of 30% up to about 50% for high glass content props.

For the average modeller, glass filled nylon props are the ‘normal’ prop. They are cheap, and the better brands perform very well. It must be said however some brands generally the older designs) are not very good in design or quality.

All nylon based props should be accurate and close to perfect balance.

Use extreme care when using these props on high performance engines, they are simply unable to cope at extreme performance levels. This is especially so with large 4 strokes, or bad engine mounting. A glass filled nylon prop may survive above 50,000 rpm on an electric engine, but fail at 15,000 in a high vibration environment such as a 2 or 4 stoke model engine.

There are many different carbons, glass’s, resins, woods and nylon type products available. The above can only be regarded as a summary of the different ‘styles’ of materials. There are some GRE props which are badly made and dangerous etc.... just as there are some outstanding glass filled nylon props available.