The formula we used was very simple. Amsoil saber 2% and jp-8 fuel.
The engine modification we made was to replace the carb and inlet on the OS.91FS with a set from an OS.52OS. All that is required is to enlarge the mounting bolt holes, I do not remember the # drill I used, just large enough to allow the stock bolts to be used. Do yourself a favor and use the gasket here. We also removed the head shim and lapped the head to the cylinder. I use toothpaste.
For starting we used an inline tank with 50:1 regular gas and Amsoil Saber. This allowed the combustion area to become warm enough to sustain ignition.
Wee also have a C&H Ignition installed and used either a NGK or a Rimfire spark plug. I found no differance in performance or lonjevity between the plugs.
Once fully warmed up there was no noticable smoke coming from the exhaust at any throttle position. I have in fact held a white piece of cloth directly behind the muffler, but not touching and only had a lite brown/ tan bit of residue after 15-20 seconds.
Transition is responsive once the needles have been dialed in.
After long periods, 15+ minutes, of 2-3,000 opperation there is some coughing untill the engine reaches full rpm. While observing this transition in the dark I noticed red sparks fly out the exhaust. We determined the plug was fowling with carbon as well as arround the exhaust valve.
I am still working on developing a spark ignited diesel. By using a spark ignition there is a slight weight penalty and a power drain. I feel as these are easly offset by the ease of use and the engine will last much longer without raising the compression beyond the design limits of the engine.
I have over 100 hours on th OS, less with the Saito ( A bushed rod in the Saito would help dramatically).
As you can tell we were not flying standard RC aircraft. The plane is a SilverFox made by Advanced Ceramics Research.
Since the time of the OS ACR has gone to the Honda GX25 with many conversions and come up with a very user friendly and reliable engine. One of the major problems with the OS is trying to teach people to tune a needle.
If you have any questions or coments you can contact me directly @ [email protected]
Please do not send pictures as I have dial up and very little patience.
Steve Mills