I have been curious about this engine ever since I first saw them hit the market, probably well over a year ago. My first thought was that after discontinuing the LA.40 and .46, why come out with a higher end ball bearing .35? I don't think it has any basis in any helicopter version as far as I know. I have emailed with Randy Smith a time or two about them when I first saw that he offered a version set up for C/L stunt, but had really never seen one. The local hobby shop has pretty much stopped carrying any kind of I/C engine because they just do not sell any of any kind. I had seen one come up on eBay only a time or two and they sold quickly. It just seemed really unusual in that they were in such short supply.
I ran across one on eBay again at what seemed like a good deal and picked it up. When it got to me, I checked it out and on first impression, the designers at OS added a lot of modern styling to it and to it's accompanying muffler. Lots of cooling fins, squarish shaped cylinder, crank case and muffler. In looking for and collecting OS.32's they evolved into the same type of styling with the .32SX and can't say I'm a big fan of it. That translates into being heavy. I compared weight to an OS.32 and it's a bit over 1 ounce heavier due to what looks like bigger bearings and over all bigger cases, but the mounting dimensions are the same as the .32. I decided to break it in and then try it out on my Primary Force that I have been running a .32 in for several years. The mounts are the same, but the case is deeper so I had to shim out the mounts with some 1/8" aluminum, and with a tongue muffler, I was able to leave off the nose weight I had in it to balance correctly.
I contacted Jim Lee for a venturi for it, and decided to go for .260" throat and a standard OS needle valve. I broke it in on a test stand as per the instructions with a 9-4 prop and after a few 2 ounce tank fulls, it started to start and handle easily. I made a few more runs with a 10-4 just to see how that went and all was OK. I bolted it to the P-Force using the same tank as I have been flying it with and the APC 10-4. The first few flights were pretty erratic with the engine never really settling down. It didn't run that way on the test stand at all, so started to looking at the installation. At the same time, I have been working with a flying buddy who was having some run issues with a OS. LA46 on a large profile model and was having trouble getting consistent runs. It was one of those situation where we tried everything twice, even taking his engine off and trying it in another model where I was using a LA.46 and it ran fine. So the trouble must be in the model itself. While looking at my P-force a week ago, I realized that we were both having the same problem, and I was thinking that in both models, the tank had to mounted pretty close to the engine. His engine is pretty low time, but as I looked at the cylinder, it was starting to bake on some castor on just the very back of the cylinder. Just behind the cylinder at that portion of the tank is where the feed line exits the tank, but low on the face so it can clear the engine for better fuel line routing. The tank he is using is one I made that is a copy of the tank I use on my P-Force, and commercially available tank called a "snub nose" for just such situations, I guess. I just made his a bit longer for more fuel. On my P-Force, the back side of the .35AX is longer and is close to the tank also at about the same place. I came to the conclusion that even though they are both profiles, and everything is out in the breeze, the engines might not be cooling properly, or at least heating up the from of the tanks so that it changes the fuel viscosity as the run goes along. It doesn't have to boil the fuel, just get significantly warmer. I had remembered reading stuff Brett Buck had written here about fuel viscosity and that was in my thinking also.
To address the problem, I had e quick and dirty heat shield/deflector for my P-Force out of soda can stock. A simple V shaped piece with long enough legs to go over and under the tank. I glued a bamboo skewer at the bend and poked a couple of holes in it to wire it to the engine at the center line of the cylinder. I figured the air goes through the fins, hits the shield and has to flow over and under the engine. I tried it out this past Thursday and the engine ran pretty sweet! nice steady needle where ever I put it. I had the APC 10-4 prop on it and it isn't quite enough for this older, oil soaked veteran so i went back to the Zinger Pro 11-4 that I had been running on the .32. The next flight went well and I just need to fine tune the tank position a bit ( don't know why but the .35 needs it just a bit lower than the .32) and I'll put a few more flights on this set up tomorrow hopefully to get some more experience with it before putting the .32 back in the P-Force. We shut down for the afternoon to head to my house to make up a heat shield deflector for his model, and I hope that clears up the problems with his airplane.
This whole long story was just to tell my limited experience with this new engine and to see if there is anyone else playing around with these at all. It still seems strange to me that OS would come out with this size engine at this point in time and maybe some one has more information about it. Jim Lee thought it was a helicopter engine, but the head isn't nearly as large as the .32 F and .32SX copter engines are. And OS surely doesn't appear to be flooding the market with them. I don't think it will be a world beater or anything like that but is another offering for the sport flyer market or someone looking for a power house ball bearing engine for a Classic or Super Seventies model, and the AeroTiger .36 isn't available any longer. Pop in here if anyone else has been flying them at all.
Type at you later,
Dan McEntee
Topic: OS .35AX (Read 2546 times)