ORIGINAL: MTK
Brett,
Exactly right, one needs to burn a lot more fuel to get equivalent output when using alky based fuels. That doesn't matter as much in my view...what matters is the associated cost. Why burn twice the fuel for a given amount of power? If there was some kind of magical improvement in the operation, then okay, maybe I see it and I include the 4 stroke in there. The big negatives to 4 strokes to me is their shake and their fuel. They do give more mid throttle torque, but so what? If I need more output I just advance the throttle a little more. The SAP 180 probably doesn't have the pure output of the YS 170 but isn't far off.
On the SAP, I am getting rid of all my glow stuff and converting over. The field manners of this engine are so good that it simply makes best sense for me to do that. Now that I've experimented enough with pipe, prop, carb and fuel settings and have arrived at a good recipe, it's time to burn fuel.
This is exactly my line of thought on the issue. I LOVE engines and think the YS is pure mechanical joy when they run right. However I can guarantee my engines will die in the air if I get them a touch too lean (which is difficult to determine, btw). The cost of the fuel is hard to bear, especially as we are running out of local hobby stores that can/will stock the required fuel. The remaining stores usually have car fuel by the quart, and maybe a gallon or two of 10% Omega or Cool Power, and that is about it.
I was seriously considering converting my YS to spark on glow with a cheap RCEXL ignition and 1/4-32 plug, just to have the tighter control of the ignition point, better starting characteristics, and eliminate the preignition kickback at full throttle, but gave up a few years ago when I moved across the country. I love the handling characteristics and CHEAP flights of my IMAC planes on gas engines.
I recognize the Syssa engine won't quite keep up with the YS 1.70 which is fine with me, as my current plane flies very well with the YS 1.40 (with an APC 15x10) currently installed. The SAP-180 will be a huge increase in power over that. I will likely look for a (used) somewhat larger and draggier airframe when I get a SAP-180, and the Focus II seems to be nearly perfect for it and isn't really prohibitively expensive (it is about the same cost as a decent 50cc IMAC plane).