OS 55ax
 

apc 12.25x3.75 13200
apc 13x4w------11400
factory muffler
ys 20/20 fuel

RE: OS 55ax
 

After 1/2 gallon of break in time on the OS 55 AX I have some numbers:

On 15%, Just off peak, slightly rich. 50* air temp.
11x6 Scimitar = 13,000 rpm
12.25X3.75 APC = 12,100 rpm
13X6 APC = 9,850 rpm
13x4 cleaned up wood Pro Zinger = 10,400 rpm

Very easy starting, Strong even transition. No hesitation when stabbing the throttle after a long idle. Nice smooth low idle.

RE: OS 55ax
 

Wow, that's some major variance on the one prop you both tried, the APC 12.25 x 3.75. I understand that atmospheric conditions can have a dramatic effect, but absent any details about the wether during testing, it's hard to conclude what's causing the difference. I can't imagine that the extra 5% nitro allowed for an additional 1,100 rpm. Do either of you have any details about the wether during your testing?

RE: OS 55ax
 

I'd agree. 12100 on the 12.25x3.75 isn't that great. That's what my 46FX does.

RE: OS 55ax
 

apc 13x4w 11900
ultra thrust sport long
ys 20/20

about 50* air temp

RE: OS 55ax
 

More on the OS 55 AX. All props are APC. 15% nitro.
9x9 @14,300
9x9 @ 15,400 baffle removed on this and following.
9x10 @ 14,980
11x6 @ 13,280
11x5 @ 13,800
12.25x3.75 @ 13,090

There could be hope for this engine with an Ultrathrust or Jett muffler. Over 1000 rpm jump by just taking out the baffle with a 9x9.

RE: OS 55ax
 

Not very impressive numbers for the 55AX-I get 13,500-14000 with 46AX using 15%, #3 plug, and 11/6 APC. (baffle removed)

RE: OS 55ax
 

Power Master 20/20

55* air temp
APC props, Perry VP30 pump with bypass system and short/standard Ultratrust muffler

13x4 13,600
13x4W 12,350
12.25x3.75 14,950

It has less trouble spinning bigger props. Throttle response is still fine with the 13x4W.

My 'old' 50SX did 15,200 on the 12.25x3.75 and CP 30% heli fuel. It's RIP now after 6 months with the piston in pieces.

So the 55AX performs as expected with I think a little more torque than the 50SX and it's much better constructed.

My 46AX does 15,800 on an APC 9x8, 30% and Macs pre-tuned pipe.

edit: It only ran 6 tanks.

RE: OS 55ax
 

Well I have about half a gallon through the engine and it's runniung soaking rich in the mid range. It looks like the spray bar of the carb is 1/16 too short. How much space do you guys have when it's all the way open?

RE: OS 55ax
 

OS .55ax no baffle
12.25 x 3.75 APC
YS 20/20
3rd tank of gas
13000-13100 rpm
12900 backed off
perfect transition
40 or so degree day

Dave

As it should be the low end was a little rich and the top end was set rather rich from the factory. I never checked the manuel, just bolted it down and ran it. Dang nice running engine. The idle is great already and it doesn't seam to load up even though it is still a bit rich. I say that because I tried to load it up by giving it a minute or so at idle and then jammed the throttle and couldn't get it to stumble. Nice carb. I think as most will agree, the carb is what makes an engine.

RE: OS 55ax
 

Same set up as above except with the one piece mac's muffler/pipe.

same #'s as 12.25 x 3.75 = 13k
12 x 4 APC = 14.1k

Some square tipped wood prop that I cleaned up, 12 x 4 = 12.9k - 13k

All around a great running engine.

Now going to mount it and hopfully fly on Sunday with the 12 x 4 APC, which is my choice since I love the quick response.

See ya,
Dave

RE: OS 55ax
 

Ok get this, I just swapped out my Magnum 52 2-stroke and ran it EXACTLY the same as the 55 and it gets 200 - 300rpm MORE than my 55 with the 46ax carb and remote needle on the magnum. I am talking same fuel, prop, and muffler!!! Wow, I never would of guessed it was so strong and so cheap. Now I had a ton of trouble and frankly gave up on it when it was stock and thought it was junk but NOW I am sold on it. I paid 80 bucks for it a couple of years ago and in defense of the 55 it does have a coule of gallons throught it but dang it is strong. I guess I am dissapointed in the 55 after this and think I may give up on my thinking that the 55 is something special, when in fact is isn't, just more expensive.

Somebody tell me i am nuts, please
Dave

Magum 52 2-stroke
YS 20/20
Mac's pipe/muffler - one piece
APC 12 x 4
14.3k rpm
Dave

RE: OS 55ax
 

Dave,

Try an APC 12x6 or 11x7 on both engines. Let's see if the AX .55 has more torque at 11,500 - 12,000 than the Magnum .52.

Other reports have hinted that the .55 AX is better suited to running at closer to 12K than 14K or so.

RE: OS 55ax
 

Sorry but those are not props i have any use for. I may try a 13 x 4 though.

Dave

RE: OS 55ax
 

Would someone who owns this engine please post some tach readings with an 11x7, 11x7.5 and an 11x8?

I'm curious to see how this engine compares to older pattern sixties of the '70s.

(BTW, what type of aircraft uses those really low-pitch props?)

Thanks,
David

RE: OS 55ax
 

If you want speed (pylon), what's the best prop for this engine?

Thanks.

RE: OS 55ax
 

I just broke in my 55ax yesterday....

PowerMaster 15% nitro 18%oil castor/synthetic
Tower 46 muffler
APC 12.25x3.75
14,100-14,200 RPMs

It only has roughly 50-55 onces of fule through it, and I followed DarZeelon's break in thread.

http://www.rcuniverse.com/forum/m_18...tm.htm#1850473

Needless to say I am VERY impressed by these numbers, especially seeing as how it still has a bit of running in to do. I think that it should pull my Funtana X50 very nicely. I had it on a test stand that is in turn mounted to a pretty large wood hobby box and it was trying to scoot the box across the parking lot! I had to hold it down while doing the leaning in/backing off part of the break in. Once I tuned it to hold max RPM's it really wanted to creep along!

Once it has some time on it I will go to a 20-25% nitro fuel and see what it gets.

RE: OS 55ax
 

I did manage to put the Ultrathrust on my OS 55 and got a nice surprise. On my Goldberg tiger II (40 size) I run a 10x7, 3 blade Master Airscrew for clearance, climb rate and braking. The 55 with stock muffler and baffle was 11,700 and with the Ultrathrust it jumped to 14,000 backed off 300 rpm rich. This is about 2 Hp at only 14k.
I would not hesitate to recommend this combo for performance sport. Low noise, hover with fast climb out, cool running, fuel efficient and great speed. Now let’s see how the engine holds up. 15/20 Power Master Heli fuel rules!

Note, you may have to turn your engine sideways to get the carb lowered to the center line of the fuel tank for best performance start to finnish. Avoid lean runs!

I've see a OS 55 with a red Jett muffler on a World Models T-34 spinning a 10X8 APC @ 15k on 15% Power Master. A real fast ship!

RE: OS 55ax
 

Tried a 11X 7 Master Airscrew Scimitar and it pulls real hard! The OS 55 AX with Ultra Thrust was turning 13,850 rich.
The engine unloads higher and the plane is faster than it was with the Master Airscrew 3 blade 10X7.
90 degrees OS #8 plug Power Master 15% Heli fuel.
I think the key to this engine is to loose the stock exhaust and find a prop that loads it at 14,000(+-200) on the ground(12X5,11X7and10X10).

RE: OS 55ax
 

apc 11x7
magnum 30% heli
sea level 90 degrees
macs tuned pipe and header cut down
15,600

RE: OS 55ax
 

Wow, That's about 2.8 hp and 10.8 Lbs of thrust! What # pipe and what was the header # and cut lenght, bbagle?
That's working real hard, I wonder what the engine life will be.
I was sure the engine would'nt like 30%, but this is the second time I've heard of someone using it and it's making power.

RE: OS 55ax
 

Broke-in another OS 55AX on the stock muffler than installed a Mac's header. I tried four Mac's pipes, a 7.5cc & 8.5cc Muffled and 7.5 & 8.5 Quiet pipes. I began switching them in and out and cutting down the header. One constantly performed better than the others and that was suprisingly the 8.5 Quiet pipe which had the best transition and RPM. The header cut length ended up 5" flange face to cut measured down the tubes center line length. The one exception was the 11x8 prop that peaked with the header at 5 3/8".
Fuel Power Master 15% heli, OS #8 glow plug, air temp 89*.

Master Airscrew Scimitar 11X7 14,400
APC 11X7 13,900
APC 11X8 13,250
APC 10X10 14,200

Last test just for the heck of it, Master Airscrew Scimitar 11X7 14,900 on 30% Power Master Heil, OS A5 glow plug. A 500 RPM gain is not worth it.

RE: OS 55ax
 

Thanks for the test results freakingfast! Those are very impressive numbers. It looks like this engine is an excellent replacement for '70s pattern sixties. I suspected that the AX .55 might be a good current alternative to the Webras and ST's used in classic pattern designs while weighing about the same. You might want to post your numbers in the Classic Pattern forum. There are lots of people who don't care to lengthen the tail of their model and fly with an OS .91 Surpass (the SPA norm). In fact, today's sixties only weigh about an ounce or two less than the 4-strokes. I can see this engine in a very light Mach I or Banshee, for example.

David

RE: OS 55ax
 

So is the stock muffler better than running a Macs pipe? I prefer the look of the Macs but if it runs better stock, so be it... I may buy one of these for my Phoenix Sukhoi.

RE: OS 55ax
 

I think on this engine the Mac's BLACK muffler may perform a bit worse than stock. But it won't fall apart and it's lighter. The Mac's tuned pipes are the way to go for perfomance, not the Mac's Black muffer.

If you wan't to run somthing that's more compact with performance, run the Ultrathrust from Performance Specialties. You should use thier muffler extention if you need one to clear the fuselage.
Expect about 700 RPM less than a well tuned pipe. They also have a longer version tuned muffler for lower RPM/Larger props.