Now that the OS Engines 0.46 AX has been released for a while it's time to see how the new design is holding up. The AX series is the follow on to the successful FX series engines. The most noticeable difference between the FX and AX series is the square muffler. While the AX shares a lot with the older FX series like dual ball bearings, mounting pattern and long crankshaft the folks at OS have added some improvements to the AX. These improvements include a finer taper on the needle valve for precise adjustment, redesigned ports for easier operation and a redesigned needle valve bracket that works in both the horizontal and vertical positions.

SPECIFICATIONS:
Stock Number: OSMG0547
Displacement: 0.455 cu in (7.5 cc)
Bore: 0.866 in (22.0 mm)
Stroke: 0.772 in (19.6 mm)
Practical rpm: 2,000-17,000
Output: 1.65 hp @ 16,000 rpm
Weight w/muffler: 17.2 oz (489 g)
Includes: #A3 glow plug, E-3010 muffler
Requires: glow fuel, prop
Recommended Props: 10.5x6, 11x6-8, 12x6-7
Price: $104.99

• Airframe
• Propeller
• Engine Mount
• Fuel Tank
• Spinner or Propnut (optional)
• Fuel
• Field Gear (Glow lighter, starter)
  

Assembling and installing the OS 0.46 AX is similar to any other 2 stroke engine. The engine comes wrapped in plastic and the only assembly required is to mount the engine to the engine mount, install the throttle linkage, fuel tank, muffler, propeller and spinner.

OS has made mounting this engine in place of a 0.46 FX easy since the mounting pattern is the same. Chances are if you are installing this on an airframe that you have already flown, it will bolt on without modification. The weights of the AX and FX engines are identical. If your just doing a motor swap, you don't have to worry about the Center of Gravity (C.G.) changing.

When installing the throttle you can adjust the position of the throttle linkage to suit your setup. You should be able to shut the carburetor all the way, since this is how you will kill the engine. The engine should be able to idle with the throttle on the transmitter closed, and the idle trim somewhere between centered and full up. Typically you would set the idle with the throttle trim and then be able to close the throttle trim all the way to kill the engine. Many of the newer radios have an Idle Cutoff feature that will do the same thing if you hold the button for a few seconds. You should be able to reach full throttle on the carburetor in either case.

When installing the fuel tank OS recommends that the tank is at or above the carburetor level. A normal hard tank with muffler pressure will work fine with this engine for most applications.

Installing the muffler is as easy as bolting it on. An old tip that is still recommended is to remove the small nut at the end of the muffler and apply a drop of red threadlocker and re-install the nut. This will keep the nut from falling off in flight. OS has included hex head screws to hold the muffler on which is far better than the phillips head screws found on other engines. The hex head screws are less prone to stripping if you use the correct size wrench.

The rear half of the muffler can be rotated to any angle to position the outlet. The outlet port has a lip machined into the end. The lip will give a small clamp or zip tie something to hold on too. This is handy if you are going to attach some tubing or an exhaust deflector to the outlet to keep your model clean.

Before flight OS recommends that the engine have a short break in period. I completed these on the airplane with the help of a friend. The instructions tell you to run a tank of fuel through it by running the engine at full throttle and richening the mixture so the engine starts to 4-stroke. It is easy to hear when this is happening as the RPM decreases and the muffler is spitting fuel. Then you need to lean the engine out to peak. This process is repeated for a full tank of fuel.

Propeller Static Thust (Lbs) 10x5 APC 7.25 10x6 ASC 6.50 10x6 Master Airscrew 6.50 10x7 ASC 6.06 11x5 ASC 7.19 11x6 ASC 6.31 12x4 ASC 7.56

These measurements were taken on a warm day with the temperature at 84.5 degrees and the local atmospheric pressure at 29.75 inches of mercury. Magnum 15% Fuel with Synthetic Castor oil was used for all tests. The best thurst was measured with the 12x4 ASC propeller at 7.56 lbs continuous and slightly more at peak (see pictures). The 10x7 ASC propeller gave the least thrust at 6.06 lbs. The idle RPM was measured near 2500 rpm and the peak RPM on any of the propellers was measured around 15,000 RPM. The kind of flying that you intend to do will determine which propeller you should select. Try a 12x4 or 12x5 for hovering and 3-D aerobatics. If you are flying a sport plane then a 10x6 or 11x5 may work better for you. If you find you have too much thrust at idle, then you may have to give up some top end thrust to bring down landing speeds. Several pilots at the local flying field recommended a 11x7 for the best all around performance for sport flying and best static thrust. It is reccomended that you find what works best for your plane and your style of flying. There is no one propeller that will work best in all situations. 0.46 AX ABL Parts Listing from OS Website 0.46 AX ABL Exploded View from OS Website

The OS 0.46 AX starts easy. Plug in your glow lighter and a quick hit with the starter and this engines comes to life. Adjust the needle valve just like any other 2 stroke glow engine of this size and chances are you will not need to adjust it very much.

After starting the engine and adjusting the needle valve it was time to taxi out and takeoff. The low to high power transition is noticeably better thanks to the redesigned ports and low speed needle valve.

On climbout it was apparent that the AX had more power than the FX. Our club holds pylon races weekly during the summer and it is clear that the AX has more power than the older FX series. All the winners have AX engines on the nose.

Driving around the pattern, it was hard to tell if the AX is truely quieter than the FX.

Aerobatics are no problem for this powerplant. The engine did not surge or sputter during any of the normal manuvers including rolls, loops and inverted flight. Some pilots have reported surging and almost always it was cured by replacing the clunk in the tank with a bubbleless clunk that won't allow bubbles in the fuel line.

Watch the video review and see the OS 0.46 AX in action! CLICK the images above to select the video size to watch.

The OS 0.46 AX has several improvments over the older 0.46 FX engine. The idle and power transitions are noticeably smoother. Every time I run this engine I am suprised at how slow it idles, which is very nice if you fly an airplane that floats on landing or from pavement. Normally as engines get more powerful so does the weight, OS has done a good job of increasing the power and not the weight. OS has also added a seperate high speed needle valve bracket. With the old FX engine, if you broke the needle valve bracket in a crash you had to replace the whole rear cover. With the new bracket this is much less expensive.

Overall the 0.46 AX engine benifits from several upgrades from the FX engine and continues OS's reputation of making high quality and dependable engines.