Very Preliminary OS 35 AX test

[Mike Bufkin]

Just got it yesterday,and put 3- 6 oz.tanks of Sig 10% with 20% oil through it.

It seems to be very well made,and looks very nice.

After priming it started right up,and settled into a nice wet 2.
My break in prop is an APC 10 X 4,I wanted high rpm's with a fairly light load.

At about 2/3 throttle it was spinning the APC @ 12,500 !!! and the powerbox muffler sounds awesome !!

I don't know what the 2/3 throttle translates to as far as venturi size,but I'm betting Randy can figure it out.

This is perhaps one of the smoothest running engines I have(and,I have a bunch)ever seen.
My test stand is c clamped to a work mate and I could leave small tools laying right beside it ant they didn't vibrate off.

It reminds me of an electric motor as smooth as it is,except,it sounds,and smells right
That's all for now,if work allows,I'll run it some more today.
Mike

[Tim Wescott]

Without knowing the ID of the throttle barrel, it's not really possible to say what the throttle vs, venturi size is.  You gonna make (or have made) a venturi, or just try wiring the throttle in place?

If you have a pair of calipers, measure the diameter of the throat in the carb barrel, and the diameter of the throat in the carb body.  Then someone who's facile with math can turn that into a throttle setting for you.

[Dan McEntee]

  What Tim said should get you what a true venturi diameter would be, not a restricted type ventui. With the throttle open, the LA.40 I have in my Dusty scale/stunt profile used way more fuel that it does in stunt trim with a standard venturi and spray bar assembly in place.  I would just start out with whatever the OS FP, 40, LA.40 or used and should be a good starting point. It would be interesting to know if the venturi from those will interchange. I don't know if I have ever looked at one and will have to see if the hobby shop has any of those AX models in stock.
  Type at you later,
  Dan McEntee

[Mike Bufkin]

Yes,
I've heard that Randy Smith has a couple of them on the way,so I'll defer to him for providing venturi'.

I did pull a stock venturi,and NVA from an OS 46LA and the OD on the venturi was way too small.
The NVA was just slightly too fat.

I just tested it with a Jeff Traxler 3 blade 10 X 5 and without much effort got 10,600.

I think it's going to be very BBTU except a little larger.

My Fox 35 tounge muffler is a perfect fit also.

So far,I really like this engine.
Mike

[Brett Buck]

I think it's going to be very BBTU except a little larger.

    I think that is the way to approach it, but I strongly suspect you will find it so much more powerful than a "stunt 35" that you will want to put it in a regular-sized airplane as opposed to "35-sized". I ran the OS-35FP in my ST46 airplane with decent performance for the time, and this engine is likely to be much more powerful.

   BTW, the hallmark characteristic of the BBTU is that it is an ironic description (since there is absolutely no "tune-up" involved in any way) so don't be too quick to toss that muffler.

    I would look at props like the APC 11.75-4.25 or similar. It doesn't surprise me at all that it will spin an APC 10-4 at 12,500 RPM at partial throttle, or a 10-5 3-blade much faster than required,  The "new" 25LA can easily spin an APC 10-4 at 12500, in fact, I think Bob's your Uncle was trying that a few weeks ago. It doesn't work very well in flight with a 2" wide tank but it certainly has sufficient power.

    If I was going to run the engine, I would start with 40VF-sized venturis - a range from .260-275 in .005 increments, with a PA or similar needle, and start with the .265.

     Brett

[Tim Wescott]

What Brett said, except that I'd also look at 11-4 and maybe even 3.5 or 3 pitch props if there are such things available.  My biggest concern about trying any of the AX motors is that they might have a "happy speed" that's just too fast for stunt -- but I've been pretty happy with a Magnum 36 XLS with an 11-4 prop, and I suspect it's similar to the 35AX.

[BYU]

Well as my name has been mentioned I guess I should fess up that I have also tried out and used the 35AX on a profile plane. It is a very powerful little engine but does weigh as much as an LA 46. After running in I used the Enya plastic Venturis (perfect fit) and Enya pro needle valves run through the crankcase where the carb screws used to go. In side mount configuration it had a bad habit of burping on insides which I didn’t much appreciate. Not being an expert in these things (as many often point out) I decided to go back to using tried and tested motors. I believe someone like Randy or Brett could, with enough experience of the motor work out its exact fit for prop and venturi. My best guess having run one for a few weeks, is :- use it in inverted or upright config and play with props a lot. I used 10.5x5 11x4 (many types) and 12 x4’s. It will spin the APC 12.25 x 3.75 prop with more rpm than an LA 46 and not skip a beat  .  . . . Ooh and it starts 1st flip every time. I liked the engine and a Randy custom version would likely be about as good as it gets.

Err and one more thing . .  . don't put it in a 25-35 size plane (ask me how I know) .