OS .15 Steel Fin?
 

I just picked up a couple of older OS engines, one of them was titled "OS .15 Steel Fin." On its left side is printed "MAX-III OS 15." It has a carb with a link from the throttle arm to a moving baffle, no muffler.

I would like to run this engine on a Dynaflite Butterfly. I'm hoping that some of you guys have some more information about this engine, experience, or running recommendations like what kind of fuel I should use and prop suggestions.

Also, since there is no muffler and no pressure tap, what do I do with the tank pressure line? Will it run reliably without pressure on the tank?

RE: OS .15 Steel Fin?
 

I would suggest finding a muffler.. Tatone used to make one that I think fit it...and there are probably others.. if you find one, tap it for pressure. The motor will probably run fair without pressure ...being it was never set up for pressure... but without the muffler, would be too noisy.... I had/may have one of those...but may not be able to find it. Their a great durable motor...and runs well on 10-15%

RE: OS .15 Steel Fin?
 

Hello Lomcevak, I still have my .19 which has steel fins on the cylinder. Maybe you have just the .15 version. We ran these engines on 75% methanol and 25% castor, no nitro. Throttling was just fine, with the baffle or with a muffler, but a glow plug with an idle bar helped. The muffler was made by OS and had no pressure tap, just a bushing for priming the engine with a long needle on a syringe. The carburetor had enough suction to do without tank pressure if only the tank was at about the same level as the carb.

RE: OS .15 Steel Fin?
 

some of the older engines had a pressure tap that was either in the back cover plate or one of the screws that hold the cover on had a replacement screw that had a fitting with a holeto provide crankcase pressure to the tank. 

RE: OS .15 Steel Fin?
 

8x4 or 7x5 is the general range of props that will work.

RE: OS .15 Steel Fin?
 

I had .35 CL versions. The best thing I can say is castor oil. No synthetic. They run fine. If you dont try to get a muffler, you need to keep the baffle. It helps keep the plug warm at part throttle.

RE: OS .15 Steel Fin?
 

Try and find an OS 702 muffler. It'll fit the 15 very well. It also has a pressure tap.

RE: OS .15 Steel Fin?
 

Strange, my OS-702 muffler (about 1968) has no pressure tap, just the bushing for priming. The tap in the back cover plate requires a check valve, the tap in the case below the carb doesn't, but both are for real pressure tanks and a regulator (like [link=http://www.rcuniverse.com/forum/fb.asp?m=8550127]this one[/link]) would be needed. At least I thought so. [link=http://www.osengines.com/history/ostimeline03.html]http://www.osengines.com/history/ostimeline03.html[/link]

RE: OS .15 Steel Fin?
 

I feel it is a mistake to remove the baffle of an articulated baffle throttle engine and try to make it function with some muffler. Remember also to start using muffler pressure with the carburator intended for 100% suction supply (venturi's for suction supply carbs are considerably smaller than those intended for combined suction/muffler pressure supply.

If noise is not a problem I would urge you to use the engine unmodified.

Here is my little OS pet .10 articulated baffle throttle engine that has worked great in my Aero 9 remake for some years now.

John

RE: OS .15 Steel Fin?
 

When you installed a muffler, you removed the baffle. The engines would usually run quite nicely that way. The purpose of the baffle was to increase back-pressure to help keep the glow plug hot at low throttle settings. The muffler would usually have enough back-pressure to keep plugs warm, too. Idle rarely suffered when a muffler was installed.

RE: OS .15 Steel Fin?
 

Thanks for the replies, fellas.

I have both a .15 and a .19 and have not attempted to run either of them. It appears that the baffle is fully closed over the exhaust port while the thottle is still about 1/4 open. Is this correct?

RE: OS .15 Steel Fin?
 

Yes this is typical of this type, also note that most (not all) baffles do have a small hole or holes in them to allow some gas passage when fully closed.

If noise is not a major problem at your flying site I would urge you to run them as intended. Its great fun and also a bit unique. You see when compared to a modern engine of similar displacement when at idle it will make far less noise than the modern counterpart. However when at full throttle it will make more noise than the modern engine. This can be great fun with the buds if they have never experianced this type of engine.

If you do use them as intended simply run the tank vent line up and facing forward or with a angle cut facing forward.

I still operate two articulated baffle throttle engines: the OS .099 Pet in the photo I posted above and an old Super Tiger .23. I love the way they operate, run and sound especially at idle (this particularly so in the old timers since they spend most of their time at idle.

John;)

RE: OS .15 Steel Fin?
 

LD here is a vidio of the little OS flying and it may give you an idea of the sounds although this engine is roughly half the displacement of yours. Note the very distinct sound changes with throttle changes to the point where the engine cannot be heard at all in flight:

http://www.youtube.com/watch?v=GW3CU...Y-99tsiYKMw%3D

John

RE: OS .15 Steel Fin?
 

Very nice video, neat little plane and engine. :)

RE: OS .15 Steel Fin?
 

Thank you LD

John