I ran my first tank of fuel through my new OS 55AX, mounted in my Phoenix Super Decathlon, today

Having experience from the 46AX (my first engine) I primed the engine with two flips of the prop, and she started up on the first flip with the glow plug installed, using a chicken stick. I performed OS' routine of running rich for one minute, then cycling between super rich and rich for 10 seconds at a time. Boy is this engine QUIET! It has a nice deep, 'throaty' sound to it, not typical of most of the 2 strokes I've heard thus far. I am simply amazed and baffled at how easy OS series of AX engines are to start and tune, and at how forgiving they are. I was not as nice to my 46AX as it was my first engine. I definitely ran it lean the first time I started it, but no damage done; my 46AX is the best running and most reliable engine at my field, probably until my 55AX is fully in service.

So my plan with the new engine is to run it for the first flight as rich as I can get it while being certain it's not too rich that it will quit in flight. I will run it this way for a few flights, then lean in out a touch, and progressively lean it out until I get a gallon or two of fuel through it. I guess this is where I could use some advice as to how long it should take to get the engine fully leaned out, and how many tanks between adjustments (2?). I bought a tach for this one as I want to do it right, though shouldn't need the tach for a few tanks as I'll be running pretty rich.

As with my 46AX, I am using fuel with a blend of synthetic and castor oil. I personally like the added protection of the castor during the break-in period, and am not so concerned with using castor once the engine has been run in. This is my own personal belief, and I understand there are many different theories on what type of oil to use.

Again, the AX series from OS is the best engine I've seen. I have an electric starter and have not once found the need to bring it out of my trunk. The combination of performance, reliability, and ease of use is simply unmatched.

I am PRAYING for no rain tomorrow so hopefully I can maiden my BEAUTIFUL Phoenix Super Decathlon and write about how much I love the plane, too

I've probably told this story a hundred times but the .55-AX impresses me so much I'll tell it again... I got my WM Rambler 45 finished up late on a Friday night with a brand new, never ran .55-AX. I fired it up that night for a few seconds then shut it off since it was late. The next morning I went to the field, fired the engine up, set the high speed needle and took off. It never coughed, sputtered or quit. After a couple flights I leaned both needles a little and it has been flawless ever since. In fact, it still has the original glow plug.

If you think it sounds cool with the stock silencer, try a Pitts muffler on it. It gives it a deep sound sort of like a small 2-stroke gas engine, kind of similar to a good running chain saw or my old string trimmer with "custom exhaust". It's very cool.

If you decide to step up to bigger planes in the future, try the .75-AX. "Stump puller" is an understatement for that engine.

I also have an OS .81-FSa sitting in the box and I am contemplating what plane to try it in. I can't wait to fire it up.

Your 55AX will be good to go after the first run-in, if you followed the directions. I tuned mine in as if it were already broken in, running it to peak RPM and then backing off slightly. I would adjust accordingly until the peak RPM started getting easier to reach with each tank full. Well, now it starts on the first crank just about every time and I'm not having to make any adjustments. It'll start and run at a very low idle, lower than my 46AX I do believe. Then transitioning is perfect, no fussing with the carb there either. Both it, and my 46AX are just warm to the touch after each flight, no overheating that I've ever noticed. The only time I ever had a deadstick with these engines was when I had fuel tank problems. Now the LA series: Mine have been a bit more finicky and they also idle faster. Their power band is narrow in comparison. All of my AXs have been money well spent and cheaper in the long run as opposed to the LAs.

NorfolkSouthern

gaRCfield,
You will probably get a few different answers to your question. So here is my motto: before all else fails, follow the manufactures recommendations, but that's just me. I have 3 OS 2 strokes, one is the 55AX (on my GP Venus 40) with the bisson pitts style muffler, and like ChuckW says, it does sound very cool. The only problem I have had is trying to run a 12" prop. It just does not like it! This motor was in my Pulse when it went in almost nose first into the dry lake bed (kid's, don't try that at home!). Shattered the aluminum spinner, couldn't find all the prop pieces, and NO damage to the engine. Just inspected it, cleaned it up real good, and it fired right up.

Mesa, are you saying 12" is too big or too small? Ive got a 13x5 on mine, sounds ok so far.

just saw the manual says break-in is for 10 flights = )

My 55AX works just fine with a 12-6 prop, and one of the recommendations in the owner's manual is for a 13-7. You should be good to go with your setup. I'm thinking, that 13-6 might add quite a bit of torque, so you'll want to manage that throttle while taking off. A 12-6 would offer better ground clearance, while power should still be more than adequate for that Decathlon. This engine will pull stumps just about as good as any old John Deere tractor. Trust me.

NorfolkSouthern

When the engine was on the Pulse, I wanted speed, so I had a 11x6 APC. Turned about 12,300 on the ground, and ran perfect. Tried the same set up on the Venus, and the plane was a little bit too fast for me at full throttle, and took forever too slow down enough to land. I tried a 12 x 7 APC and a 12 x 7 wooden Zinger to see if I could get it to slow down a little. Also bought a 13" prop, but didn't try it. With the 12" prop, the engine was real picky on transition to full throttle. Sometimes it would just die, and other times it would hesitate, gurgle, and keep going. Tried adjusting low end needle and I could get it to run just OK. But, when it was in the air, the mid range was pretty crappy. It would spit and sputter, but keep running. I tried to fine tune it (I will admit that I am no expert, but I understand how it works), but I couldn't get it to run any better. Switched back to an 11 x 7 and an 11 x 6 and it runs perfect. I have read a few other guys have had the same problem. It might just be my tuning abilities are lacking, so for now, I will just fly it at 2/3 throttle for awhile. If you guys can help, I'm open to suggestions. The engine has about 20-25 tanks of gas through it, running PowerMaster 15% nitro, 18% oil. Maybe it's just not broken in all the way?

gaRCfield,
Sorry to jump on your thread. Hopefully you won't have any problems.

gaRCfield,

I'm jealous of you're 55AX. All I have so far is a measly 46AX, which I still haven't broken in I'm also praying for good weather Friday!

Best of luck on your maiden flight with it. Your weather is looking good, especially after 11am. http://www.usairnet.com/cgi-bin/laun...=KBTV&state=VT

Measly 46AX? Don't underestimate that engine!

For what it's worth, when I broke in my 55AX, 75AX and both 46AX's I ran one tank-full on the ground and then slightly rich for two or three flights. Then I tweeked the needle and they've been running like champs ever since.

I did the same thing for my students 55 as Mike did, I ran one tank on the ground then A couple of slightly rich flights then gave it A full on tune up.
As to props I can't remember what we ended up with. I have A big tub full of different size props, mostly APCs. I broke it in with whatever OS said but then started looking for the prop that flew the plane the way the pilot liked. When we found that prop we headed over and bought some more just for that engine/plane.
Outstanding engine, I put the AX line right up there in my top two two strokes.

46AX is far from measly!

Thanks for the tips guys. I wasn't sure if it would be ready for a pattern meet next weekend, but with the amount I fly (granted decent weather conditions) it should be no problem

I am sure you will love the .55 AX

I have the 55 in my H9 Arrow and it is perfect. I have run over 3-gallons though it and it has not dead-sticked on my once!

Mine is not transistioning from low-speed to high-speed very well, so I still have a bit of tunning up to do.

My arrow seems to do very well with an 11X6 prop, although I have to be careful about flutter on the ailerons. I tried an 11X5 and it seemed not to have quite as much top speed as the 11X6. I tried a 12X7 and that seemed to be too much. I did not have a tach, but it seemed the revs were down and in a dive you could hear it rev up.

So?

I would expect an engine to speed up in a dive due to the engine not having to work as hard. I also don't like to over-rev engines. A good practical RPM for a 2-stroke is 11,000 - 11,500 RPM

And the OS 55AX manual even recommends a 12x7 to 12x8 or 13x6 to 13-7 prop.

By using an 11x6, you just might burn that thing up. Hell, I use an 11x7 on a 46!

I use a 12x5 on a 46AX. I also was used to using a lower prop and used to the high rpm's, but learned quickly that I don't need to be spinning at 13000+ rpm, now I like the sound of the lower rpm, and my plane is flying better and the engine seems happier/not over revved.

The 55 should be swinging 12,13 and maybe even 14" props.

I'm flying a 11x6 on a baffle-less .46ax in my Mustang. 13K and change static, ready for flight (500 off peak) unloads to over 17K in the air! 60 flights or so so far, most WOT from start to finish (she's a "speed plane").

The .46 is no wimp, and is very capable of high speed operation, something the larger AX series is less well suited to, including the 55. These 55 and larger AX engines are tuned for big prop torque, but the 46 (and hopefully the new 36 (i think it's a 36...)) are revvers!

J

The 11X6 seems to pull it much faster while going level and climbing while the 12X7 only performed well while diving, so the overall performance is much better with 11X6. I have also been using 0% and 10% nitro fuel, so that and my tunining issue might have me down on power a bit.

I think I really need to try and 11X7 and a 12X6, maybe they would do even better than the 11X6 and the 12X7?

AstroDad,
Yours sounds like it's running about like mine. Please let me know if you get it to run good with a 12x6 or 12x7, I would like to know if it is just a matter of proper tuning.

This kinda reminds me of a conversation I had back in the early 90's. We had a new guy in our club who owned a company that made Ducted-Fan airplanes (Or just the fan units, I don't remember - he didn't stick around very long). Ducted fans require an engine to spin in the 15 - 16,000 RPM range.

Anyway, he was trying to get our club members interested in flying ducted fan airplanes. He started making his sales pitch to me one day and I asked him, "How many engines did you burn out last year?"

"Three", was his reply.

I just smiled and said, "It was nice talking to you", and I walked away.

so you think my .55 is likely spinning the 11X6 at 15-16K RPM and I am likely to burn it up?

You're probably not spinning THAT fast, but the point is, the engine LIKES spinning at 11,000 - 11,500. Prop it accordingly

Good point. The .55 seems to have a different power curve than the .46. It makes its peak power earlier or at least it seems that way. I've had the best luck with a 12x7 and 11x8, both APC. I've also used a 13x4 on a fun fly plane that worked well.

The 11x6 is more suitable for the .46 in my opinion.

OS advertizes the max power at 16,000 RPM with a practical range up to 17,000 RPM. I would be really quite dissapointed if their definition of "practical range" means you can rev that high, but will not last half the season if you do so.

I had to jump in here, you are probably running that for RPMs, which is OK but i don't beleive the engine was intended for it. Developed for Sport flying, 3D and basic flying. I Was out flying both the 46AX and the 55AX on identical planes. I always favored the 12.25x3.75 props on fun fly's, 4*40's using the 46AX-Perfect. The 55AX also fly's well with this prop (screams) but is happiest with a 13x4. Lower RPMs, monster torque and good spool up so i may try something larger. The engine just seems to want to lug the bigger props to run good, cool and happy. Just my opinion of coarse. Plane below is around 4lbs and is amazing with the 55. I have another one with the 46.

The practical range claimed really isn't practical. It's like "miles per gallon" numbers for a car; they use numbers that inflate the product's performance as much as possible. If you're pulling a static RPM of 16,000 expect very short engine life. Remember, the prop unloads in the air. This means the RPM's in flight will be higher than your static reading.

Well, I guess I am going back to the drawing board and try to get mine to run with a larger prop. I sure don't want to burn my engine up, but I also want to get good performance out of it. I probably have done a little TOO much reading on RCU and started to believe want I wanted to believe. Check out this thread: http://www.rcuniverse.com/forum/m_67...13/key_/tm.htm
It's long, but has info in it regarding the 55, look at post 314 and 325. Now, I realize that these guys are trying to get max performance out of their engines, but I can't imagine that they would allow them to burn up on purpose. Anyway, I'll probably not comment on here again, simply because I am not a seasoned vet of this hobby, and I might give out some bad info. But as I stated earlier, I'm probably just doing too much research, just reading too much. Good luck.