I have had the new YS115S on backorder for some time. Has anyone used the new OS 110FS-a in a plane yet ? I do not want to get into a YS vs. OS, which is better, etc. I use a YS110S now, plenty of power, and realize it will have more then the OS in same class. With my limited pattern experience, I would proboably not know the difference in Sportsman.

I am going to put another Focus Sport together, thinking of this new pumped OS.

Thanks,

Vince
Hobe Sound, FL

Good question Crankpin. I also am considering a Focus Sport build and wondering about power choices. I am almost convinced to go with an OS120AX. I realize that I would have to modify the engine and install a Perry pump or put the fuel tank behind the firewall and live with trim changes. I flew afriends Venus II with a 120 AX and was amased at the throttle response, power, and torque. It seems like a much better 2 stroke than most that are available.

Hey Vince,
I have, but haven't run it yet - sorry, not much help there!! When I was researching the OS 110 here on RCU I did find a comment (somewhere) that a fellow flier replaced the
YS 110 in his aerobatic (may have been a 3D airplane) and felt the power was almost the same as the YS. As for the 120AX, I ran one in an Explorer VR-90 about 3 years ago (for 200 flights) and was very impressed with the engine. Ran an APC 15x10 from the beginning and had plenty of power and pretty good throttle response (not as good as a 4-stroke). Also, good fuel economy and I only the changed the original plug once after 140 flights (though the idle had been getting crappy for about 10 flights - I'm just cheap). The downsides: no pump, and the muffler bolt failed after about 150 flights. I also 'strength' tested the engine when I made a vertical landing [X(] with a Chip Hyde Dream after just 3 flights [:@] - I forgot to put the screw back in the elevator servo output arm (I knew it as soon as I lost elevator control - killed the power and watched the 'event'). Fortunately, the ground was pretty soft and the engine didn't suffer any damage.
Lastly, the tank placement issue for an unpumped engine (also know as the cave-man set-up as it was referred to in another thread here about the OS 160FX I think). First, the CG shift may not be noticable as the tank size isn't that big. It also depends on where the CG is located (I did not have any trim changes with the Explorer) - the more rearward the cg (within the range) the more sensitive the airplane becomes to CG changes. You can also use the 2 tank approach - 1 main tank on the CG and one, small 'header' tank (no more than 2 ounces) at the firewall. I used this set-up on an Arch Nemesis powered with an unpumped ST 2300 and it worked very well. I'm not sure if it would work with a 4-stroke.
Just a few things to think about!
-Will B.

Is there any reason that you can't install a Perry pump on the 120AX? I thought you could use a Perry pump on any engine by removing one backplate bolt and clear drilling the bolt hole through to the cranckcase.

I was just looking at weights of the engines - the OS 110 pumped 4 stroke is nearly 8oz lighter than the 120AX with muffler, that is, if you can trust OS's specs on Tower's site. 8oz savings in the nose plus balancing weight in the tail is a pretty serious savings on a 110 size airplane.

The 120AX is an awesome engine. The big difference in performance between that engine and the YS 110 is the throttle response; with the OS you need to give throttle well in advance of a maneuver and spool the engine up for power into a climb. With the YS, add throttle when you need it, almost instantaneous.

I ran a 15x10 on the YS and a 16x8 in the 120AX - the 15x10 just lagged in throttle response way too much with the 120AX (for me anyway).

All of this was in a Venus II. If you are working with a lighter airframe, I imagine the OS 110 4 stroke would have ample power. Furthermore, you get the reliability of an OS engine, which I was told and have learned, is priceless. You can't beat an easy, reliable engine that gives you nothing but stick time.

I ran the 120AX with a Perry Pump. I had problems, most likely due to garbage in the carb and only a season of tuning experience. The carb on the 120AX is not designed for that kind of fuel pressure and it is more sensitive to tuning. I had a dead stick in my best round at a contest and decided that was enough for me, and switched to the YS. Of course I had problems with that, too, and now am going to fly electric. I think with a pumped OS 4 stroke, I would still be flying the Venus and very happy with it, that is, if it had enough power.

Another thing is that you can still run 30% nitro in an OS engine for some extra power. The YS engines are supercharged, so they are more powerful, however some of that extra power theoretically has to be due to the higher nitro content and thus increased fuel consumption. Most people (like the guys not flying pattern) are running 10-15% nitro in OS engines so it's even more difficult to make a comparison.