Guy Croft wrote:If it was my task I would more-or-less copy the Zenoah! As all experienced engineers know it is always easier to refine a contemporary design and maybe improve it - than to start from scratch.
Inevitably any deviation from that basic layout will be a cost add-on. They pared the design to the limit quite obviously on weight and cost grounds and quite right too.
The only thing I would add is I would personally never develop an aero unit like this as a 2 stroke, far too 'thirsty' and prone to misfire, never mind 'ticklish' to tune (via exhaust) to get the powerband_u_want. But it's your project, not mine!
Thanks for your input Guy. The cylinder head I'm using resembles a scaled down Zenoah. It has to be smaller though because the 23cc Zenoah weighs too much and the 26 and 29 cc versions that weigh the same as the 23cc are much bigger than needed. A Zenoah style twin 52cc or 58cc in one of these helicopters would be like putting a Rolls Royce Merlin in a Cessna. The 20cc I'm using has nice big transfer ports with the flow web, nice big cooling fins and a suitable over square configuration. The porting closely resembles the Zenoah but is maybe proportionally bigger.
I'm not sure which motor you mean when you talk about misfiring ? All petrol 2 strokes ? Zenoah ? Boxer petrol 2 stroke ?
The alternative highly tuned Methanol/Nitro burning glow plug engines are more than twice as thirsty and more cantankerous to tune than 2 stroke petrol ('Gasser') engines. By comparison the 26cc single cylinder (badly vibrating) Zenoah that most of us have replaced the Methanol (commonly called 'Nitro') engines with are easy to tune and perform fine evern if run safely rich. The same can't be said for Nitro engines. Then there's the prohibitive cost of Methanol/Nitro fuel.