Guys,

I wanted to share my experiences with different fuel viscosities. I undertook some fuel testing a couple of years ago to compare a leading 30% nitro heli fuel (denoted Fuel A in the graphs) with a prototype fuel of similar constituency (Fuel B). There were several aims with one aim being to test the engine performance as a function of variation of fuel viscosity and another to reduce the smoke production during F3A flights. All tests were done on the same day so weather conditions could be comparable. Needle settings were optimised during each test. A single schedule of PO9 was flown and the model landed. Each time crankcase, cylinder head and exhaust gas temperatures were recorded.

The results were surprising in many ways but the relevant bit here was that more oil lead to higher temperatures and lower engine speeds. At the worst case 23 % KL200 oil (standard Klotz super techniplate: denoted normal viscosity oil in graphs) reduced engine speeds by up to 200 rpm compared with the 20% KL198 (denoted low viscosity oil in graphs) mixture with engine temperatures rising by 22 degrees C at the cylinder head.

I guess any thermodynamic system will have an optimum lubrication vs fuel mixture but the evidence here clearly suggests that anything more than 20% oil in a DZ170 leads to poorer performance and higher temperatures, with the incumbant effect on engine longevity.

Best wishes

Keith