Common power sources are Nitro (nitromethane-methanol internal combustion), electric batteries, gas turbines, petrol and gasoline.
Mechanical layouts include CCPM in all power sources, fixed-pitch electric rotors and coaxial electric rotors.
Practical electric helicopters are a recent development but have rapidly developed and become more common, overtaken nitro helicopters in common use. Gas-turbine helicopters are also increasing in popularity, although the high cost puts them out of reach of most people.
Nitro
Nitro helicopters come in different sizes: 15, 30, 50, 60 and 90 size. These numbers originated from the size of nitro engine used in the different models (0.30 cu in, 0.50 cu in and so on). The bigger and more powerful the engine, the larger the main rotor blade that it can turn and hence the bigger the aircraft overall. Typical flight times for nitro helicopters is 7-14 minutes depending on the engine size and tuning.
Electric
Recent advancements in battery technology are making electric flying more feasible in terms of flying time. Lithium Polymer (LiPo) batteries are able to provide the high current required for high performance aerobatics while still remaining very light. Typical flight times are 4-12 minutes depending on the flying style and battery capacity.
In the past electric helicopters were used mainly indoors due to the small size and lack of fumes. Larger electric helicopters suitable for outdoor flight and advanced aerobatics have become a reality over the last few years and have become very popular. Their quietness has made them very popular for flying sites close to residential areas and in places such as Germany where there are strict noise restrictions. Nitro helicopters have also been converted to electric power by commercial and home made kits.
The smallest remote-controlled production model helicopter made (Guinness World Records 2006) is the Picooz Extreme MX-1 sold at many toy stores (although this is infrared controlled, not radio), electronics stores and internet stores, costing about $30 (£28). The next smallest is the standard Picooz helicopter.
Several models are in contention for the title of the smallest non-production remote-controlled helicopter, including the Pixelito family of micro helicopters, the Proxflyer family, and the Micro flying robot.
A recent innovation is that of coaxial electric helicopters. The system's inherent stability has, in recent years, made it a good candidate for the design of small models for beginner and/or indoor use. Models of this type, as in the case of a full-scale helicopter, eliminate rotational torque and extremely quick control response, both of which are very pronounced in a CCPM model.
While a coaxial model is very stable and can be flown indoors even in tight quarters, such a helicopter has limited forward speed, especially outdoors. Most models are fixed-pitch, i.e. the collective pitch of the blades can not be controlled, plus the cyclic control is only applied to the lower rotor. Compensating for even the slightest breeze causes the model to climb rather than to fly forward even with full application of cyclic (nick). More advanced coaxial constructions with two swashplates and/or pitch control - common for the big coaxial helicopters like Kamovs - have been realized as models in individual projects but have not seen the mass market as of 2009.
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