RC Helicopter Engines
Note that engines of the 60's and 70's were primarily designed for aeroplane use (though a number of models could be supplied in 'marine' form) and had to be adapted for helicopter use. This was generally achieved by fitting additional heat sink to the cylinder head as in the early days, heat generation and dissipation was the main problem. It was to be many years after the introduction of radio control helicopters before engines were designed to have a suitable layout and also a power curve that would suit this specialised requirement. Although the section is called RC helicopter engines it will include 'aero' type engines that were to be commonly used in helicopters; given that even up to the 90's many helicopters manufacturers (Morley and Vario to name but two) specifically brought out designs for the 'aero' configuration.
Note that this section has two methods of review; you can either read through the individual 'decades' or by the major engine manufacturer however, where I only have a couple of items for a specific engine manufacturer, they will only appear in the relevant decade section.
The convention for model glow engines is to 'size' them according to their cubic inch capacity as per the old 'imperial' convention. Though not always followed, engines of the same size will generally fit the same mountings though may have slight variation in overall length etc. Additionally engines tend to be grouped into mounting sizes so that say a '30' size helicopter would be able to take a OS32 or an Irvine 36 or a Super Tigre 34; you get the picture.....
Sections will cover decades in basic detail with manufacturers providing specific helicopter engines covered in more detail.
Engines Pre 1970
Up until the mid sixties, the two stroke for use in motor vehicles of any kind was considered a 'bread and butter' engine that provided 'cheap and cheerful' transport for the masses. It was therefore not particularly developed for high powers or efficiencies; that is until the Japanese bike boom of the mid to late sixties when the two stroke became the rip roaring, howling, speed machine that the two stroke had the potential to be.
Model engines mirrored this basic layout and thus were not particularly powerful, especially in the small sizes. They generally had what is called 'loop' scavenging where the mixture was drawn into the cylinder on one side, was 'deflected' by a raised tag on top the the piston to go up the side of the cylinder. It would then go over the top and push the old mixture out of the exhaust port on the other side of the cylinder i.e. in a loop. To get a reasonable compression the cylinder head had a 'cut-out' to take the tag on top of the piston and therefore there was a lot of turbulence caused by these protrusions and cut-outs so the efficiency was poor.
Development in the 'real' world though would also follow in the 'model' world and so these deficiencies would be designed out. New ways of scavenging by cylinder port configuration (getting air in and exhaust gases out) would allow removal of the tags and cut-outs thus providing smooth internal surfaces for gas flow and increased efficiency and power. Carburettor design would adapt to give more effective fuel air mixing plus greater control of mixing throughout the control range and in particular Exhaust systems would be developed (originally not fitted in the 60's) which would actually enhance the power and/or silence the engine without reducing the power. That is all to come so moving back in time again.........
Sixty size engines were generally used in competitions and scale planes as they allowed models of a reasonable size to built and effectively powered; thus they received the most attention and development. In post 70 years this was to change as development progressed and it became viable to make small powerful engines. You will note though that as per everything in life the principle of more is better and thus as an example the OS 25 grew into a 28 then up to a 32 and by 2010 it would be a high power 37.
So, lets start in 68-69 as this is the era the helicopter story comes of age, note that many reviews do not measure power but only quote the Rpm of different propeller sizes which was the standard reference at the time when considering them for aeroplane applications.
ST G60F - 1968
Merco 61 series III - Engine review - 1969. A good British engine and was as powerful if not more so than some other manufacturers; this engine had a well developed carb which gave good throttle control over the whole speed range.
Webra 61 RC - 1969
Throttles - Engines for helicopters require to have a good throttle response, especially fixed pitch models where this has a direct impact on the lift and more importantly the speed of change in lift, generated by the main rotor. This article covers the development of 'throttles' for radio control engines including the use of carburettors and also exhaust valves etc.
Comparing the tests that include power curves and you can see that model engines tended to produce their maximum Torque at about 50% of the Maximum power Rpm; a very useful feature which is why large propellers could be operated without stalling an engine.
Tuned pipe info - 1988 article covering tuned pipes and setting up
Komatsu Zenoah Co - G230PU - Petrol engine instructions and part list
Reference notes below only
Enya 25XH / SS30BB Heli / 49XH / 60 H XH
Kalt GS 22
Bluebird 46 for MFA Sport 500
Rossi 61H front exhaust rear intake especially for Heim mechanics
Schlüter/Webra SHC 10 ring - 60 size ringed modified plus ABC version
Webra 61 RCH