Engine time now (my favourite), and this month we will take a long hard look at the Mackay AW 30 - a 30 cc petrol unit. Now I know what you are thinking, petrol, huge - heavy - clumsy - crude etc. - am I right? Well you could not be more wrong, for this one is a real model aero device, neat and compact, light small and designed for the job.

First impressions are favourable indeed with quality castings, very elegant and sophisticated design features and an attention to detail evident in quality engineering products. This 180 sized engine is a rear induction rear exhaust unit, using the tried and tested Walboro pumper diaphragm carburettor that a billion industrial units fit and forget the world over. The propeller driver is a multi bolt anodised unit, and further enhances the engines appearance. There are arguments for and against multi fixings on propellers and I won't enter into the debate here. The spark plug is a miniature NGK, much smaller than the ones fitted to the chain saw converts using standard plugs. A suitable plug spanner is included in the box. Spark ignition is facilitated by a purpose built capacitor discharge system (CDI unit) that is neat and small. It operates on a total loss system, so you will need a battery for this, but this system is way smaller and lighter than a magneto and a couple of quick charge nicads are all you need for a days flying.

The Mackay instructions are clear and concise and incorporate a wealth of practical information that will enable the purchaser to get to grips with the AW 30 and enjoy the best from it. These attractive engines are designed and produced by active model flyers and the information provided bears that claim out, as does the general appearance of the engine itself. I particularly liked the radial mount castings that are supplied, which give the user a choice of mountings. This alone can save a lot of hassle with some airframe installations.

For this 30cc engine a 16 to 24 oz tank is recommended which, given the frugality of a petrol engine over glow, will give plenty of duration for sure. New users of petrol engines more familiar with glows need to pay special attention to the instructions regarding fuel lines and filters, for these are subtly different in their needs to a glow installation, but the information provided is clear enough. Usual advice here - RFM (read the FLAMING manual!).

I was going to run the engine and give you a feel for its handling and performance - but I was without a battery and socket to match the supplied fitment to the CDI unit unfortunately. No matter, you will have that to look forward to! These Mackay units are tested as part of the normal final inspection process and the performance figures provided by the suppliers are a good indication of what can be expected. For sure these will improve when the engine is well run in, but an idle of around 1800 r.p.m. and getting on for 5300 r.p.m. on full throttle is the minimum performance you can expect to achieve on a 20 X12 propeller and that certainly equates to a healthy draught indeed! For those of you interested in moving up to larger models, but are less than impressed by the thought of carrying half a strimmer on the front of your aeroplane - take a look at the Mackays - they are rather nice. I am going to put this one in a CAP 21 from Modeltech, replacing the 180 glow that presently hauls the beast. It will be interesting to compare the performance. The Mackay engines are available through Stuart Mackay Models, Tel. 01379 644777.

The Mackay 30cc

Last month we looked at the Mackay 30cc Petrol engine, this time round we will continue with our evaluation of this lovely power plant and see how it handles and performs.

With its compact CDI (capacitor discharge ignition) system, which operates on a 'total loss energy system, i.e. it employs a battery, which requires periodically charging, rather than a magneto system that self regenerates, starting was always going to be easy and so it proved. Magnetos are heavy, need considerable impetus before they provide a decent spark and in my humble opinion, are not as elegant as an electronic ignition system like the Mackay. The penalty of having to carry another battery for ignition purposes is hardly worth worrying about as itís just another nicad to charge before flying, and at the size and weight of the type of model that this lusty device is intended to haul, of small consequence.

Petrol engines used to be large, crude, heavy, vibratory, invariably converted from industrial usage and therefore not ideal for the job. They often had exhaust and inlet tracts that were inconveniently positioned, and in my opinion, were less than satisfactory compared with a 'proper' model engine. In the last ten years or so real inroads into petrol power have been made and engines such as this Mackay are a prime example of how far we have come. I am not denigrating the chainsaw converts out of hand and for the really big models, engines from 'Quadra or Zenoah' have proved splendid, but this Mackay bridges the gap between the big glows and the much bigger petrolís. This engine is hardly any different in size and mass to something like an Enya or Moki 180 glow and the power is pretty well up there too. I liked it a lot.

Fuel used was the recommended 50:1 Petroil mix using a commercially available fully synthetic motorcycle product, available from any filling station. UNLEADED petrol should always be used, in a two stroke, as there is less chance of spark plug fouling and as it's cheaper anyway - it's a win win situation. Propellers in the 18- 20 inch range are catered for with the Makay, and pitches in the 8-10 inch region will prove useful. It is important to appreciate that compared with a relatively small glow engine, big petrols do not rotate at the high r.p.m.s that the screamers enjoy, so to harness the torque and generate useful airspeeds, coarser pitch propellers are employed comparatively.

'Running in' with this engine is not really much of a consideration, just treat it with mechanical sympathy and empathy for the first few hours of its life and you will be rewarded for sure with a long lasting product. I do not advocate bench running, preferring to put my engines straight into a model where they will enjoy the benefits of a constant cooling airflow and a variable load - perfect 'running in' conditions in fact.

The performance of the Mackay was impressive and for those of you not used to operating this kind of engine, you will for sure be impressed by the healthy draught and useful torque at moderate r.p.m.s. Petrol engines do seem to produce oodles of effort free urge.

I have a slightly bent CAP 21 from Modeltech, previously hauled by a 180 glow, which will be an ideal flying test bed for this lovely engine. Direct comparison with its previous performance will tell the real story and when the model is back in one piece I shall fly the Mackay and further report on its performance. I am looking forward to using this engine in its intended environment, it's a beauty. ___________________________________________________________________________ I'd like to take this opportunity to thank Peter Dawson from Traplet/RCMW for giving his permission to reprint Steve's articles on this website.