Has anyone experimented with an OS 55AX for stunt.  I've had one tucked away for a couple of years and have installed it in a ARF SV11.  It's a bit on the heavy side but not so much to rule it out.  I know a couple of RC guys that are using them in Sportsman pattern and they have a reputation for being very smooth and powerful runners.  Yes I'm well aware that dosen't mean a thing when it comes to stunt...however it's a start.

I just wondered if anyone else has tried to do this with one?  I've installed a .280 venturi with an Aeroproducts (Randy Smith) Needle Valve Assembly.
On the bench it proves to the rumors of being smooth and powerful...turns a Bolly three blade 12.5 X 3.75 at 10,800 in a loafing very fast four cycle.
It will probably need som additional head shims as it doesn't return to a four stroke very quickly when forced to two cycle.

I haven't experimented very much with props etc., since I'm just trying to get it fully broken in to fly it first.
Should have the airplane ready to fly in a few days...it's been ridiculously windy here in Tucson for the past week...supposed to calm down this weekend.

Would entertain any suggestions for setup from those that know what they're doing!

Thanks,
Randy Cuberly

I got a OS 46 AX some time ago.  Converted the R/C carb to a S.T. unit.  First few flights it ran very well in a steady 2-cycle.  It consumed horrific amounts of fuel, so I put it away.  Took it out sometime later into another plane.  I put a restrictor in the venturi (piece of Al tubing that just fit).  Fuel consumption was more reasonable and power didn't seem to suffer.

The 46AX, being a B.B. engine and designed for R/C, is a bit heavier than the equivalent OS 46LA, but it runs well and has lots of power.

Floyd

Hi Floyd,
Do you remember what the restricted size actually turned out to be?
I have a 46AX  also but decided to try the 55AX because it fits the same exact bolt pattern as my RO Jett 61 and 65.  The 46 is a little lighter (as are the RO Jetts), but doesn't turn the prop that the 55 does.
This reall seems to be the most powerful engine in the 50 to 65 range I've played with yet.  Hope I can harness the torque curve.
I'm not at all sure it's going to make a serious stunt engine but it's always fun to experiment a little.

Randy Cuberly

Why would it not make a serious stunt engine?

Well, that's a good question...
It's a bit heavy at 14.7 oz without a muffler.  It has fairly high exhaust timing.  It has a slight tendency to run away on the bench, which could be caused by simply not being broken in enough but more likely it's too much compression, which can be cured (maybe).  It's not inexpensive and may simply be more trouble than it's worth.
All that said I believe it has some potential or I wouldn't be trying it.
For instance...back in the 1980's...I experimented with a then new Super Tigre called a Bull Ring 46.   After a lot of trials, making new parts (even rings) and a cylinder I finally did get it to run about as well as an OSFSR 46.  At that time I figure I had about 6 times as much money and time in it as a FSR.
It was fun but I wouldn't call it a serious stunt engine!!!!  Too much effort for results that were only as good as something that existed pretty much out of the box for a lot less investment.

Randy Cuberly

A lot more people are interested in the 55AX then you realize.

Even the new 65AX.

Well, I'd be interested in knowing who they are and what they are doing!  Which of course is why I started this thread.
I also have a 65AX but OS lists it's weight at 17.5 oz without a muffler.  Mine actually weighs 18.4 oz without a muffler.  With a .280 venturi and PA needle assembly it uses 8.5 oz of fuel to run for 5 minutes on the bench and has a strong tendency to run away.   I started getting disinterested when that happened.
The 55 on the other hand will run for over 6 minutes on 6oz of fuel on the bench...more interesting.
I should have the 55AX flying in the SV11 by next weekend with a little luck and a break from "Honey Do's".

I am definitely interested in hearing from anyone else who is interested and or starting to work with a 55...or a 65 for that matter.

I would mention that I'm not intending at this point to "rebuild" the thing to get it to run.  Lowering sleeves and making new heads is fun but I'm not really interested in doing that now!  However if someone else is doing those things I would be interested in hearing about it.

Randy Cuberly

Randy I see a definite pattern here. Both of your motors run away. I suspect you are not sharing the TV remote with them-sorry couldn't resist. Both of these motors have a very good reputation for not running away in RC use. But, both run away in your use. What are you not telling us,(or maybe it's something personal you don't want to share).

Well, I haven't decided wether or not you're just baiting me.
R/C use is a very different senario than serious stunt.  Different loading properties different power requirements and don't forget the ubiquitous carburetor that allows throttling the engine.   Throttling down definitely limits run away!  In some regards it's more demanding in terms of power and heat generation but serious stunt motors require a broader torque curve to accomodate the loading properties of very tight maneuvers and rapidly changing torque requirements to maintain a semblance of consistent speed.
When trying to run a "high Timed" motor in the meaty portion of the torque curve rather than in the peak or near peak horsepower curve the engine has a tendency to seek it's happy portion...as the rpm increases or heat in the cylinder builds the engine will go to its peak power range due to leaning of the mixture and if the port timing supports that it will tend to stay there.  The 55 AX, in stock configutation except for a venturi instead of carburetor, can be coaxed to do this on the bench by artificially leaning the mixture by pinching the fuel line...when the fuel line is released the engine will sometimes be very slow in returning to a richer setting.  The 65 will not return to the richer setting at all.
It's likely possible to improve this situation with the typical compression/venturi size/nitro manipulation but in some cases it doesn't work very consistently and you wind up with an engine that gives good runs about 2 times out of three.   Not acceptable for a serious stunt engine Needle sensitivity is also an issue that cannot be tolerated on a "serious" stunt engine, but the above described conditions usually mean needle sensitivity that is unacceptable.
I have and run several PA's and RO Jetts and aerotigre's as serious stunt engines.  They are very different in terms of type of power generation than almost all R/C engines with the possible acception of the OS LA46, which in fact is very different than most R/C engines in type of power generation.
That should be the pattern you see here.
It is fun to experiment but one must also be realistic in terms of expected outcome.
I don't really know what your experience level is so if I'm talking down to you...my apologies.  You did sort of "Ask for it" however.

Randy Cuberly

Obviously there were some jokes there but, I do see a consistant pattern of engine runaway. Just because it's RC does not mean the motor has to run away. Plenty of RC motors has been converted to ukie use with great results. Now, when you buy a purpose dedicated stunt motor, a lot of elements has been done for you. But I can tell you, cats have gotten even helicopter motors to stunt great.

That said,there is no easy way to say this, it requires expertise and experience. The less of it you have, the more difficulty you will experience. I personally had to develop expertise flying RC 4 stroke motors. That is a double whammy. It took time. But, I have developed a body of knowledge that gives me considerable confidence in setting up and flying these motors. These motors are far more different from our perspective then the OS Max AX series.

Windy Urtnowski has a video of him getting on top of the then new Rojetts. During the video, he frequently mentioned about developing a body of knowledge. His testing and ramp up were systematic. But, it took time!!

Randy, you are just going to have to be more persistent as to venturi size, compression ratio changes and tank configurations to get the results you want. You are simply going to have to develop more expertise.

I started flying CL in 1953.  I started flying stunt in 1957.  I've been working on engines both professionally and as a pastime for over 50 years.  I've built several engines from parts and pieces I made.  I have successfully converted R/C engines to CL for at least 30 years.  I was a professional motorcycle racer for nearly 10 years. 
I have a doctorate in Mechanical Engineering and have recently retired from Raytheon Missile Systems.  I have time, once again to play with model engines and I know how to approach it.  I understand fairly well the mechanics and dynamics of both two strokes and four strokes.
Maybe you're right I need more experience...then again maybe you're just a smart AXX.

Randy C.

Randy, the reason I am pressing this is because I think what you are doing is right. I think your headed in the right direction. Randy Powell also has done some work with the 55AX. I have seen plenty of them run in Los Angeles, CA and ALL of the RC guys love them. At $160.00, I think they are one of the best bangs for the buck out there.

In addition, all of the AX motors have a reputation for smoothness. OS really worked on counterbalancing on this line, (especially the 65). A new 46AX has just been announced in Japan. Smaller and lighter than the 55AX. I don't have a picture of this but once I had my Saito 72 COMPLETELY disassembled all over the living room floor. It runs the way I want.

My ST 51 didn't run the way I wanted it to. I didn't give up-it meant a talk with the local machinist-it runs they way I want.

Bob Reeves is one of the best examples IMHO of stunt flyers with motors. Check out his Saito Stunt carbs. He didn’t develop that overnight. He was persistent!!

Randy Smith has a got a Fox 35 to run successfully on pipe. You know he put some time into that ONE!!

I get my hands on a 55AX,trust me; it's going to run the way I want. So, I am not a smart AX, (I like that one) but man, when I tell you it’s going to run the way I want, I mean it.

P.S. I had more jokes about them running away-dating priviledges etc. but I guess I’d better cool it.

It's always possible to make an engine "run the way you want".  The question becomes whether it's worth the effort.  I have lots of really good running stunt  engines.  Some took tremendous effort to get that way.  Some were no effort at all.  I have a PA61 side exhaust that runs very much like a pipe setup on a tongue muffler and required very little effort to make that happen (an assortment of shims).
But then I've basically said this all before...I'll let you know when the engine "runs the way I want" and whether or not it's worth the effort. 
I may be a little more demanding about a serious stunt engine than you!   'Nuff said.

Randy Cuberly

Most RC sport engines have a peak torque around 10-11,000 rpm.  So pick a prop that will four cycle at those kind of speeds and it will do a nice 4-2 break.  You may have to open up the combustion chamber a bit too.    The question is whether or not you like how the plane flys on a 12/3 or an 11/3 3 blade.

Hi Phil,
Yeah that's the rub...3 pitch props can have some peculiar habits above 45 degrees or so.  The 55AX will definitely do a fast four cycle with a 12.5 X 4 APC at 11,700 RPM, and 10,800 with a 13 X 4 APC.  I ran it for about a quart of fuel on a 10 X 5 for initial break in before trying larger props.
I think you're dead right about needing to reduce the compression ratio...I'll try some shims first and if it looks promising I'll machine the combustion chamber to increase the volume.    To date I've only run it on 10 % nitro in high heat (100 degrees or more) and 2400 ft altitude.  I think I need to get a little more time on it before I try pushing it too much.
So far it's been an easy starter and runs very smooth and stays relatively cool through the run.

I was hoping to get it in the air this weekend but Honey Do's have probably curtailed that idea.

Thanks for your suggestion.

Randy Cuberly