Well broken in and flown OS .55AX on bench.
Weather, low 80's, very humid, just after 3 days of rain in NW Florida.
Fuel: Omega 10% Castor blend
Tach: Thunder Tiger mini-digital
Props: All APC
Muffler: Stock with baffle and Jett-Stream ordered for the 55AX
10-6 Stock: 15,700 Jett: 16,500 Gain: 800
11-5 Stock: 14,000 Jett: 15,000 Gain: 1,000
11-6 Stock: 12,800 Jett: 14,500 Gain: 1,700
11-7 Stock: 12,200 Jett: 13,700 Gain: 1,500

Comments:
1. Looks like the 55 isn't going to be a really high rpm engine
2. The Jett-Stream is supposed to be designed for the 11-6 and it gained a bunch on that prop.
3. I was surprised that the 11-7 gained that much.
4. Looks like high 12's to low 13's is the sweet spot on the ground.
5. I should probably go back and do some 12" props. A 12-5 might be right in the sweet spot

I have 2 OS 55 AX Engines. Broke them in By book but one runs hotter and not as reliable as other. Any ideas or suggestions. richgrow

I took some more readings with the Jett-Stream only and some 12" props.

Temperature: low 80s
Humidity: medium
Fuel: Omega 10% nitro, castor blend
Props: All APC
Muffler: Jett-Stream

12-4: 15,000
12.25-3.75: 14,500
12-5: 14,600

The 12-4 looks a little small.
The Jett-Stream looks like a good thing for the 3D people who like the 12.25-3.75 wide blade.
I didn't have an APC 12-6, but I'll bet it would be good, too. Probably be the best sport prop.

Hello again Ed !

Real good numbers
Your engine likes the 10%. I'll have to try that using my Ultrathust muffler.
The 11-7 is the sport prop of choice for 40 sized planes IMHO. You may be right with the 12-6 for 50-60 sized planes. I've had the best results wth the Master Airscrew's S-2 series 11-7 rather than the APC... that surprised me.
Betcha the 3D guys would like the 13x4w prop too, this thing like big lumber

I like the 11-7 best myself. I haven't tried the 12-6, but thought it might be good with the Jett muffler.

I think I'll pick up a Jett Muffler and do a head to head test. Get a 12-6 too, but it will take a while as I have a lot of irons in the fire right now.




Karl Jensen, KK6AE 73

APC 12*7 11900
Zinger 11*8 13800
15 perent nitro

Used this engine in a modeltech p-51. Besides the plane weighing in at almost 7 pounds for a 46 plane it flys it well.

New OS 55 AX, 45 minutes run time. 10.5x7 Zinger break in prop, 10% Cool Power fuel, 3,500' altitude, 70 degrees F. Stock muffler w/baffle in place. 13,500 RPM.

Switched to 11-7 APC sport prop. 13,000 RPM.

Typical top quality OS product. Fires right up, excellent idle right off the bat. I bet there is a lot more power to be found here with tuned muffler/pipe, nitro, etc.

This engine replaced an OS 46 AX in a Graupner Skylark (50 size sport pattern plane) that weighs about 5.5 lbs empty. Significant performance gain! I will post more numbers as time permits.

Happy flying,
Robert

Stock pipe n plug
Cool power 10%
APC 12x7
10,200 peak rpm

That's the perfect prop for a Fox Eagle IV .74.

I've seen a lot of changes over the years, but seeing forty sized crankcase engines (regardless of displacement) swinging such large props still amazes me.

No, I'm not being critical of anyone choosing to use these props since it is obvious that the engines are handling it well.

In the meantime, I'll still being using 11x6 to 10x7 props on such engines. Old habits are hard to break - plus I love the sound of a screaming two-stroke. Up until they escort me off the field. <G>


Ed Cregger

It does handle the 12x7 just fine, but I'm thinking the 12x6 is a better fit for this engine. This engine is in a pattern plane and I'm going for more of a "4 stroke" power band, which is why I'm running the bigger props.

P.S. - O.S. recommends a 13x6 on the high end, this has got to bog the engine down. My tower .75 only turns like 12,000 on a 13x6 (when I can get it to run).

I cant believe 15% nitro bumps rpm by 1900, maybe I'm doing something wrong.

Hey - WM T-34 O.S 55 AX Macks Tuned exhaust 4.750 header length
10/8 apc 15,500 to 15,700 on the ground .
10/9 apc 15,200 to 15,000 on the ground
but both fully unloaded in the air , the engine sounds the same peaking
next week we will try a 10/10 but I belive that 10/9 is max

Tower Hobbies muffler
10% CP
OS #8
APC 13x4W 11,200 rpm
APC 12.25 x 3.75 13,500 rpm

Prop: MAS K series 13X5; temp: 65F; a little under a gallon thru it; 15/18 Byron fuel; stock muff; 10,900 rpm
Will try 14X4 MAS K. Don't know when.

Hi

I am going to run the 55ax in the new Sundowner 50 was going to try a 10x10 prop. Think this would make a good combo for speed?

thanks

hey there Brew--- I have pushed 55's to there limit and there is no way you are going to get a decent R.P.M with a 10 X10 , if your lucky 10,500 to 11,500 . A 10 x9 is the max for that engine and I have tried alot of differnt exhaust systems and fuel combos to back up my position .

A Jett .90 uses a 10x10 for high performance/high rpm operation. I don't think the OS.55AX (though I own two of them) is up to the task.


Ed Cregger

---------------


And what happens when you pull the nose up in an extended straight up ascent? That's what I'm talking about...<G>


Ed Cregger

See my post #22 of this thead. 10X10 @ 14,400 W/tuned pipe. With a pitts or stock muffler however all bets are off. 12000???

Try a Master Airscrew 11X7 ( S-2 style ! ) to start with, fits right in between a APC 11-6 and APC 11-7 for prop load.

Good luck



Hey Joe, My P-51 is ready. Test flight on Wendsday PM if the weather holds. Has a mistery prop on it[>:]

Joe, you may have "fell off the pipe" make the header longer and try the 10X10 again.

jeffk464,

10,200 with an APC 12x7 seems low.

I get 10,400 rpms with that prop from the FSa .56 4-stroke and everyone else's figures seem to suggest the .55AX should trump the 4-stroke by a considerable margin.

I have lost 2 muffler halfs on the 55ax power box. I have tried red lock tight on the nut on one but it did not work. Any other suggestions to keep the pipe together? I was thinking of using JB weld on the next one.

I use RTV silicon sealant on the mating surfaces and bolt threads.

The brand i have is Permatex and is rated for high temps.

Give it at least 24 hours to cure and it works well. I've never had a a muffler come loose when using it on both 2 and 4 strokes including heli and gas motors

Two piece mufflers are one of my pet peeves, engine mfg's should be ashamed. JB weld or orange high temp silicone works sometimes. Can you fit an Ultrathrust or Jett tuned muffler on it, perhaps with an extension?