OS-120AX cookbook
 

I'm hoping this thread will help answer some questions about the OS-120AX that I am having.

I've got it in an 8lb 2oz, 110 sized pattern plane, stock muffler, 420cc tank (14oz), OS-F plug, 3-line system (Vent, carb clunk line, fill clunk line), 15x10 APC and for break-in, PowerMaster 10% with 29% Caster... will switch to 15% with 16-18% Synthetic after this gallon.

The tank is fairly close to inline with the carb, maybe 1/2" higher. On neg/inverted pushes the motor seems to starve until I close the throttle a little. On pos/upright pulls it seems ok, maybe a slight richening. There is a nice smoke trail as after my first flight I wasn't rich enough and the flight ended a bit early. I'm sure it will run a bit easier after it's broken in, but has anyone tried a foam clunk like the YS's use?

Any other tips? It has enough power with this set-up to go through the F-09 sequence, but about half way through it starts this 'cutting out' deal. It's just annoying to have to power back as you're climbing to keep it running.

Also, what differences has anyone noticed flying the 15x10 to 16x8 in testing?

Thanks,
Jason

RE: OS-120AX cookbook
 

I have one and havent had any issues as of yet, tons of power and never quit or cut out, you might try an OS FS plug that might fix your problem Jason

RE: OS-120AX cookbook
 

Jason
I had one in an Epsilon a couple of years back, with stock muffler, OS-F and 15/15 fuel. Initially I ran it with APC16x8, but then I felt the mid-range to be 'weird'. I switched to 16x10 and it behaved much better for me. I never had any lean-run issues, I suspect that your issues is related to your run-in fuel that is really not necessary on new OS's as they dont need much running in. With 'proper' fuel you can run it more rich without burblig, and you will most likely avoid the starving in flight.
Best luck
Ola

RE: OS-120AX cookbook
 

29% Castor! That will be your problem for sure Jason. Your model must be covered in so much castor after each flight. Yuk! Follow what the instructions say for fuel and you should be right. In other words RTFM (Read the friggin manual).

I run 18% synthetic in all my engines... Only got one now :-) going all electric with my models. No mess, no deadsticks, no mixture issues and no dramas....

Cheers
Jason.

RE: OS-120AX cookbook
 

I stuck my amp meter on it and it didn't tell me anything... I guess I'm going by old school memories on not breaking motors in on synthetic fuels. And with my exhaust diverter, it only takes 20 min to clean the airplane...lol.

RE: OS-120AX cookbook
 

Jason, is the engine mounted on a 90, inverted or what? I ran one in a showtime 90 with no problems of any kind. Run just standard 15% sport fuel in it and go to the #8 OS plug. I know we run the OS F plug in the 1.60's and the plug may not be the problem, but I alway ran the #8 and I know that works. I liked the APC 16x8 prop on mine the best I even tried the 17x6 with good results. Also take the baffle out of the muffler and it will let the engine breath better. I'm really suprised that you are having trouble with this engine, it's been one of the easiest to tune and very reliable.

Chris and I are going to be practicing this week before Districts and you are welcome to bring to our field and we will figure it out. Just a thought.

Larry

RE: OS-120AX cookbook
 

I'm sure my fuel has a lot to do with it, that's why I'm not too worried. And I know these are the easiest motors to run... but I have been an electric guy for a few years now (although my .55 is bulletproof). Here's a couple pics of the install. I'll have it with me in Jax too.

RE: OS-120AX cookbook
 

What plane is it in, Jas ? Looks interesting.

Doesn't look like something you would normally fly . . You having a bit of R&R ?? . .

Cheers, JB

RE: OS-120AX cookbook
 

Its the 2nd proto Eon 110 I'm testing. I liked the Era (.50 sized) but as of right now, this one flies even better. No elv mix and 2% aileron mix.

RE: OS-120AX cookbook
 

Hi Jason,
I put one in an Explorer 90 ARF a few years ago. APC 15x10, 10%nitro all synthetic fuel, OS #8 then Tower (OS #8 knock-off) glo-plug, tank c/l slightly below carb c/l, inverted engine. Ran great for 180 flights (oh yeah, 2 line system); kept it rich enough for slight mid-range burble - tons of power for the airplane. The original OS #8 plug that came with the engine lasted about 135 flights. I really like the new AX design.
Where'd you get Fox Missile Mist fuel? That's the only fuel I can recall made with 29% castor oil. I, personally, dislike castor oil both orally and in fuel: creates varnish on the piston and sleeve which causes the engine to run hotter and the ring to stick to the piston - just run it rich with synthetic oil (my 2 cents ;) )
Good Luck - the 120AX is a very friendly, powerful engine!
-Will Bartlett

RE: OS-120AX cookbook
 

Hi Jason
Another possible solution to the problem of the engine going lean on negative pushes is to add a second vent to tank that is the reverse of the standard overflow vent. This second vent can also be used to fill/empty the tank. This is similar to what is used in UC models. It seems to prevent a change in the fuel feed caused by a single vent being restricted by being immersed in fuel. I used it in several models in the past to cure the problem you described.
BTW, current thinking by some engine gurus is that engines should be run at or very near their normal needle settings during breakin period. Normal wear required for breakin cannot occur with too much oil/fuel in the engine.

John Wisniewski
Scottsdale, Az

RE: OS-120AX cookbook
 

Jason,

I've been running my 1.20AX on Omega 10% with an OS #8 plug and a 17X6 prop bolted up to a Venus II. No problems at all, generally starting with a single flip of a chicken stick. Plenty of power with unlimited vertical, the bigger prop helps to slow the downlines. Turns around 8800 rpm static.

RE: OS-120AX cookbook
 

29% castor is probably the issue,I've had 3 of these engines(OS 120 AX) and I run 15% synthetic cool power and they run great...29% castor! You must have smoke and oil slicks all over the field! Did you see airplanes behind you sliding around...lol

[sm=lol.gif]

RE: OS-120AX cookbook
 

A friend had a similar problem on a Venus II with the OS120AX. Problem was most prevalent in large outside loops. After much fiddling and not wanting to add a pump, etc, we lowered his fuel tank about 1/2 an inch and the problem went away. The tank height was just high enouph to create a slight fuel starvation when doing outside maneuvers. More fuel pressure from the muffler might help but you will end up leaning the high end to compensate and may end up with the same situation when doing negative G maneuvers.

The break in fuel may also be a contributing factor but that will be easy to test out with regular fuel.

Woodie

RE: OS-120AX cookbook
 

I flew one more tank and then left the 29% (didn't say CL anywhere on the can) fuel at the field. I ran 2 tanks of 15/16 and it worked much better... but still some hesitation. Is 16% oil enough? I felt like the YS guys using no smoke fuel (of course mine ran the whole flight... sorry couldn't resist). The worst part of all this... SLIME!!!! How can you guys do this... YUCK...lol.

So what RPM's are you guys running this beast at with what prop?
Needle setting?
Stock muffler and muffler pressure (baffle or not)?

I know there's a whole bunch of Venus 2 pilots out there with this motor... spill the beans please (here if you don't mind, that Venus 2 thread is 52 pages long).

RE: OS-120AX cookbook
 

I have close to 150 flghts on my VII, with on OS 120 using 15% cool power, 16x10, 16x8 prop, stock muffler w/o any issues, plenty of power with uplines.

RE: OS-120AX cookbook
 

Turning my 1.20 AX around 8800rpm with a 17 X 6 prop w/ a Bisson Pitts style muffler on the Venus II. Running Omega 10% nitro w/castor/synthetic blend no problems.

RE: OS-120AX cookbook
 

Jason,

If you are having transition problems, don't hesitate to play with the low end. I had to adjust mine a little bit. Once I got it right though it just purrs. I have mine in the front of a GP Chipmunk that my dad and brother are now beating on. I flew the 15X10 and the 16X8. I liked the 15X10 just because it made it a little faster.

Give me a call if get to the field and its still acting up.

Arch

RE: OS-120AX cookbook
 

I run 15% heli fuel, 15x10 apc with the baffle removed. The 15x10 gives better upline speed than the lower pitch props to me.

RE: OS-120AX cookbook
 

How many are running the muffler with no baffle? Difference in performance?

RE: OS-120AX cookbook
 

Jason,

I ran the muffler without a baffle a couple of times. 200 RPM difference, but hated the noise. Been flying pattern too long I guess.

Arch

RE: OS-120AX cookbook
 

You know, coming back from four strokes and electrics in your case, to a two stroke. Yeap.<div>I've tried fiddling around with an OS 91 that I retro fitted to a small pattern plane after it's 91FZ went sick. What can I say? Fiddling with props, baffles, pumps and god know what else trying to get some decent action from the girl. Drove me mad. I've had it with two strokes, all this court ship period, the shopping, the dinners, working you way through the bases until the shop eventually opens... and it wasn't anywhere near as good as you expected! Least with a YS, it's skirt up, knickers down action straight out of the box. If you know what I mean.</div>

RE: OS-120AX cookbook
 

I've had 3 OS 120 AX, 1 of which is in a Venus II with standard muffler, no pump, standard fuel tank position, works great, cool power 15%. I can put it on it's tail and it will hit airliners...no problems in outside loops either.

You might want to add some fuel in with your OIL...:DLOL

RE: OS-120AX cookbook
 

Hahahahahahahahahahahah . . . that's hilarious :D

Cheers, JB

RE: OS-120AX cookbook
 

Well I think I almost have run all the 29% oil out as it's really starting to groove. 15/16 PowerMaster and now a 16x8 APC. Not sure of the RPM's but the speed is still there but the downlines are a little slower (makes P and F a bit easier too). One more tweak on the low end (thought it was too lean, but now it's back to rich) and it should be all smooth for the contest in the morning. Hope I can wake at 5am... Night all.

RE: OS-120AX cookbook
 

Hi guys.

Just want to share my experience with this engine.

engine: OS120AX
configuration: inverted
tank: tettra 500 at the CG @ 1/2 inch above the carb, 2 lines only
fuel: cosmo 20% nitro - 18% oil synthetic
pump: none
prop: APC 16 x 8

comments:

Back pressure was more than enough. Had to lean out low end by 3/4 turn. Can be used to practice P-11 schedule.
It starts like any other OS engine does, easily.

More stick time than wrench time.

More power and Big Thanks to JeffRCU for the help.

RE: OS-120AX cookbook
 

I appreciate the thanks, but it was Arch (rcpattern) who gave me the advice originally.

RE: OS-120AX cookbook
 

Then I'd have to tank Arch (rcpattern) too.

Thanks guys!

RE: OS-120AX cookbook
 

29% castor?!?!? "ONLY" 20 min to clean?!?!

I'm pretty sure that a 18% - 20% castor + 5% nitro + Perry pump will solve you all problems... in plus you'll be able to place the fuel tank near the CG.

Good luck!!!

G.

PS: may be someone posted you about the same solution... I did not read all the thread.

RE: OS-120AX cookbook
 

I just propped down to a 16x6 on my 1.20 and love it. I started with 15x10 but didn't like the spool up time it took for good verticals, went to a 16x8 and it got a little better. For grins, I wondered what would happen with even less prop - much improved throttle response, still good speed with the higher RPM.

I run pretty much stock, tank a few inches behind firewall, 10-15% nitro with 18% oil.

Any issues I ever had with the engine were from some kind of film on the carb when it was new. I really struggled with the motor quitting during simple maneuvers when it was on a Perry Pump. Pulled the pump and still had problems - seemed to tune fine and run great on the ground, but would just cut out as I'd throttle up for a Cuban. Finally soaked and scrubbed the carb in alcohol and everthing is fine.

RE: OS-120AX cookbook
 

This thread has been inactive for 2 years, so maybe all have gone electric. Still, I have a question. Has anyone set up the OS 120 AX with header and tuned pipe? If so, please provide specifics of set up and performance differences. Thanks.

John

RE: OS-120AX cookbook
 

In pattern, mostly electric now.

The AX works very well with tuned exhaust. The Jett tuned muffler gave about an extra 800 rpm over the stock muffler with an APC 16x8. The Jett has no adjustment so you have to stay within it's tuning range, around 9500+. Pretty loud exhaust. The carbon pipe boosted anywhere from 750 to 1000 depending on prop and nitro content. I did not try it but I would bet APC 15x10 or 16x10 would work well for pattern use with a pipe.
Header length? If you have to ask..... It's best to learn how to tune it. This is another attraction of electric, it's just simpler.

The pics show a Mueller header which is no longer available. Just Engines will custom make headers.

Whatever exhaust works on the AX will also work on the DLE 20 with a flange change. The DLE probably outsells the AX by 10:1 these days. About the same power and weight. Pump carb is a plus over glow.

RE: OS-120AX cookbook
 

Macs products also makes a wrap around header. It is a two piece design: adapter for the engine exhaust and a separate wrap-around pipe. It is a 'floating' type design meaning there is a rubber 'o' ring at the exhaust flange which the tubing fits over. Eliminates the header breakage issue when used with a soft mount. here's the link:
http://www.macspro.com/cpftuhp.asp

RE: OS-120AX cookbook
 

Aerobear

Thank you for the response. I will look at the Jett muffler. No argument on the advantages of electric. Whose CF pipe is that? I have used the Aeroslave pipe on my 160s, so have some tuning experience.

John

RE: OS-120AX cookbook
 

Flywilly,

Thanks for the link. Think I will look at pipes and mufflers and pick one.

John

RE: OS-120AX cookbook
 

It's the [link=http://www.escomposites.com/2%20cycle.htm]ES2C120AX[/link] pipe from ES Composites. About 150g with header and coupler.

The Jett muffler requires an adapter to mate up to the AX. About 210g total. I made my own but Jett could probably supply what you need if you go that route.

Your Aeroslave pipe may work OK on the AX if you still have it.

RE: OS-120AX cookbook
 

The 20 cc gas engine and the 20cc glow engine can indeed take the same pipe. The only difference will come in with header length. Where the glow will require a tuning length of 22-24" from plug to baffle, the gas will require around 25-27"