I started a previous thread on this subject but thought I would start a new one to document the results of my experimentation (if you can call it that), with the OS 55 AX modified for stunt.

The modifications are simple and consist only of an extra head gasket (.008 thick), a venturi from a OS 46 SXS (.283 diameter), a Randy Smith Aeroproducts Needle valve assembly, and two layers of panty hose material (because it really needs about a .270 diameter venturi at this altitude).
It had a slight "charge" to it on down lines that tank adjustment wouldn't cure until the panty hose material was added and that totally eliminated it.
Smaller venturiis are on order.  (My lathe is still non-functional after my move).
Muffler is RSM tongue for OS46 SX with a OS pressure tap I added.  Pressure was added to eliminate richening going into wind.  Pressure is to uniflo tube.

As mentioned in the earlier thread the engine is mounted in a Brodak SV11 ARF With an all up weight of 61 oz.  Incidentally after some head scratching trimming this has proved to be a very good flying airplane.
Propeller that worked best so far is a 13-4.5 Bolly two blade...but a 13-4 APC worked almost as well.
Fuel is Powermaster 10-22 half and half.
Ground setting with either prop is 9400-9500 RPM and that gives 5.2-5.3 second laps on 67 ft .018 lines (center to center).
Plug is Thunderbolt R/C long.  Tank is Brodak 6 oz wide wedge uniflo with Figg style vents.
This engine is an easy starter...usually on first flip after a couple of chokes.

All flight testing was done in Tucson AZ at 2200 ft altitude and 100+ degree temperatures (not so different than the midwest this year), huh!!

This thing is very powerful and easy to handle.  Needle adjustment is non-critical and fuel consumption is 5.7 oz to fly the pattern with about 10 laps left over.  

The run is fast 4 cycle with just an occasional beep at the top of some maneuvers and on overheads.
The power and stunt run is on a par with any of the dedicated stunt engines.  (No...I'm not kidding)!

The only down side is the 14.5 oz weight of the engine but in this airplane is not a problem.  (Yes it took 1 oz of tail weight to overcome it)

For anyone looking for a really good stunt engine for a largish airplane that doesn't want to spring for a PA or RO Jett, I can heartily reccommend this engine and setup.  Price is about $160 at Tower.
I'm building a dedicated airplane for it.

Don't tell OS...they'll probably stop making it...

Randy Cuberly

PS:  This is a good one, and will fit in PA or RO Jett mounting...

Randy Cuberly.

If you do a search on this forum you will see that Randy Powell looked into the 55AX quite some time ago.  OS also has the NEW version of the 46AX out which has the same head shape of all the other AX's. The 65AX is coming on strong in Classic RC Pattern.

Hi Randy,
wouldn't the quoted weight of 14 .25 oz come down a bit by dumping the RC carby and that air craft hanger sized muffler?

Should come to down to less than 13 oz methinks.

HI Randy,

A great running stunt engine that doesn't need reworking is a good thing to bring to our attention.  Who would have believed that the OS .46LA would become such a widely used engine when they came out?

For many of us that are "just shy" (LOL!!!) of the (unofficial) *Masters Class*, a good running engine will make a large difference in flying better.

Thanks!
Bill

For anyone looking for a really good stunt engine for a largish airplane that doesn't want to spring for a PA or RO Jett, I can heartily reccommend this engine and setup.  Price is about $160 at Tower.
I'm building a dedicated airplane for it.
Randy Cuberly

Hey Randy: 
Thanks for the report, this engine sounds very interesting.  Might have to have one of these..
What do you have in mind far as a dedicated plane for it ?    Will you shorten the nose because of the higher weight ?

Hey Randy: 
Thanks for the report, this engine sounds very interesting.  Might have to have one of these..
What do you have in mind far as a dedicated plane for it ?    Will you shorten the nose because of the higher weight ?

I'm going to build a Jim Armour "Epic" for this engine.  The Epic was originally designed for an ST60 and is very large at about 740 Sq in.  Jim was a good friend and and a true Gentleman.   I've intended to build one of these gorgeous things since I flew his in the late 1980's (I think).  He won the Concours at the Nat's with it in the late 80's or early 90's (My memory has faded a bit) and it was published in FM.
Sort of Cobra looking.  I have a beautiful sheeted foam wing for it from the master Mr. Hunt!  It is the primary reason for my quest to find a really good side exhaust engine.
I Have a PA61 side exhaust engine that I had originally intended to use (yes it runs great), but decided to try something different since they are getting difficult to obtain and I hate building an airplane for an engine that doesn't have a quickly obtainable replacement.  Besides it currently resides in another airplane (KA10).

I may have to shorten the nose a bit but likely not very much.  Most current designs in the 650 sq in range would likely need to have the nose shortened a bit or one could stretch the tail a bit or simply build a slightly heavier, stiffer stab and rear fuselage section.
The available power in this engine will allow a little (only a little) extra weight to be carried.

I think Jim's original Epic weighed 66 oz and flew very well.

Randy Cuberly

There is no point. Could be on Stuka Stunt. Randy stated that he purchased the 55AX and I return posted him about his results. This was a long time ago. I am going to purchase the 55AX and the 65AX -I know about the weight. I looked into the 55AX a long time ago down in Los Angeles.

The RC field in Los Angeles is across the parking lot from the control line field. One gentleman was using the 55 AX in a pusher jet style RC plane. 11-7 APC reverse -high nitro. The engine was rear mounted. We talked at length about the 55AX. I watched many runs with it. He thought the engine was a winner, and that he specifically stated that, “it had true 60 power”. 

He advised to hold off purchasing it until, they were sure the OS Max “liner peeling” problem was solved. He let me start it using my hand, (he used electric). I asked him to time me for 60 seconds. It cranked right up immediately.

This issue with you and I started with you stating that you were having trouble with the 55AX, and me stating that I will get the motor to run the way I want. Nothing has changed. I will still get the motor to run the way I want. My Saito 72 was one of the most difficult motors I ever encountered to get to run the way I want. I runs the way I want, all the time-no exceptions,(if you are diligent and watch for certain things). The motor runs on custom blend fuel that I developed-in addition to other modifications-that’s what it took.

I am glad that you are having good results with the 55AX. I think it is a good motor. My setup and yours will have nothing in common. But, I am sure that I will have equally just as good results with the motor.

You need to go back and read the thread again.  I never stated I was having "trouble" with the engine.  I simply said that on the bench it had shown some tendency to to return very slowly to a four cycle when forced to two cycle.  This could point to a tendency to "run away"...
I also said it was completely stock and not fully broken in.
It does not show any tendency to run away but did need an extra shim and a smaller venturi than was on it at that ime to give a good reliable stunt run.
I was merely inquiring wether anyone else had a known setup for this engine not asking for advice on how to tune it.

Your "bravado" was not any help.  Try the simple setup I listed you might be surprised...

Randy C.

Hi Randy.  Thanks again for your insights into this engine.  I bought it on Ebay without knowing anything about it.  All the ad said was NIB.  I thought "what the heck, its an OS and around the size I need." so I put in a $25 bid and won! LOL  Totally surprised!  I have been a wee bit apprehensive about useing it, because I never saw anyone else mention it, till you did.  Now I'm good to go!  Thanks very much.

I never knew that the Brodak, full fuse Spitfire was a Windy Urtnowski design!  Now I am impressed!  I am a total Spitfire freak, ever since I was a kid, sitting through all three showings of "The Battle of Britain" at our local theatre in Whitehorse.  Boy did I catch heck when I got home, because no one knew where I was!   I eventually was able to sit again though!

Now that I know I have a good plane (the kit is typical Brodak excellent quality) and motor combo, I'll have to build her this winter.  I'll do a build thread on the forum so I caqn get all the help I can! LOL

Thanks again.

I just went and pulled the plans out of the box.  Its a 54" wing span and is designed by Pat Johnson.  But you know what?  I am just as happy that Pat designed it.  He is definitely no slouch in the toy airplane design department!  I got weak in the knees again looking at the plans.  I have got to save a bit of coin so I can order the wheels, tank, spinner, etc.  Small things, but lots of money for the likes of me! LOL

Wished I could afford the match....I'd burn mine too! hahahaha

Hi Randy.  Do you think its too much even if I use a flatter pitch prop or maybe some headshims?  Or do you think that would make it run poorly.  If you really think it will cause some trouble, I guess I can always trade it for a .46.  That would only cost a few bucks in postage.

Now here's an odd thing (not unusual for me!) I just went into my little shop and discovered that that beautiful 55AX is actually a 46AX!  Oh man, my brain just aint what it used to be! LOL  Now that I have given you guys the real size, do you think it will be good or bad?  Its a very pretty motor, not that that means anything, but still....  I just weighed it on my super duper digital food scale and it weighs 12.30 oz. without a muffler.  Is that good or bad for the Spitfire?  Should I be thinking of trading her for an la46?

Now here's an odd thing (not unusual for me!) I just went into my little shop and discovered that that beautiful 55AX is actually a 46AX!  Oh man, my brain just aint what it used to be! LOL  Now that I have given you guys the real size, do you think it will be good or bad?  Its a very pretty motor, not that that means anything, but still....  I just weighed it on my super duper digital food scale and it weighs 12.30 oz. without a muffler.  Is that good or bad for the Spitfire?  Should I be thinking of trading her for an la46?

Glenn,
Even the 46 AX is too heavy for the "Johnson" Spitfire.  It probably could be made to work by shortening the nose and setting the tank back into the wing or building a custom tank with a higher profile...but, it would be far better to go with the LA46.  Besides ther's no garantee that the 46AX will give a stunt run like the 55 without some experimentation.  The LA46 will give a good run pretty much out of the box.  I like to change the remote needle valve to a ST or Aeroproducts needle valve because they are more reliable and tend to give a stedier run.  But basically the LA is a great stunt engine with an inexpensive 11.5 X 4 APC prop and 10-22 (half and half) fuel for this size airplane.
If you want to use the 46 AX I would consider getting a kit for an airplane in the 650 to 700 sq in range.
Brodak and RSM both make a lot of kits in this size range.

Randy Cuberly