OS 46AX engine test
 

Ya'll's thoughts? I think it's a bit on the rich side but it's running pretty good. It does have an alarming tendency to start backwards but if I trim the idle low enough it will bounce itself over in the correct direction and stabilize after a few moments. I also want to add one head shim, as I'm running 15% nitro and I think I can hear it objecting to the compression ratio and nitro percentage around 3/8ths throttle. See 2:00 into the video, it captured it pretty clearly. But other than that I'm quite happy, and it will certainly fly the way it is.

I do not know what RPM it's turning. I lack a tach. My ear wants to tell me it's running between 12,500 and 14,000 at WOT, but being as this is the first aircraft engine I've owned there's no telling how far off I am.

RE: OS 46AX engine test
 

why size prop are you running? the engine seems slightly overloaded (isnt wanting to unload)

RE: OS 46AX engine test
 

It's the stock 11x5 two blade that comes with the airframe.

RE: OS 46AX engine test
 

Starting backwards can be linked to a leaking back plate, and so can weak performance.

RE: OS 46AX engine test
 

I have no way to judge the performance at the moment. No tach, no scale, and I can't put it up in the air and see how it flies because I don't have a suitable receiver. We'll have to see on that. I've never had the backplate off, but I don't know if the previous owner did or not. Might be worth a check if it shows up weak.

RE: OS 46AX engine test
 

I just matched it to my synthesizer and it is about an A or G on the scale.  According to my calculations that is about 12,500 rpm.  (A) would be 13,200 rpm.  My ear is only slightly tone deaf.  It may unload in the air a bit.

RE: OS 46AX engine test
 

I've had 4 OS .46AXs and still have 2 of them. Outstanding engines.

It sounds to me like it is too wet when you start it. I hand start all my 2-strokes and have never needed a starter on the AXs. Choke your engine as you normally do and turn the prop so the piston it up against compression where you normally would flip start it. Hook up the glow ignitor and take the spinner with your right fingers and snap it backwards. The piston will go down, then back up and hit compression as if to start backwards. Since the cylinder is a little wet from the prime, it will fire prematurely and start forwards. If you don't have a spinner, spap the prop backwards. I use a glove. In no case should you pull the prop through compression and top dead center. To do so will cause it to fire backwards and attempt to get your finger.

Set the high end needle to peak and back off 4 clicks or more. Idle down and time 30 seconds, then pop the throttle to full power.
1. If the engine rumbles and blows smoke, it is too rich.
a. Close the low end down 1/8 turn and try again.
b. Keep doing this until you can go from idle to full power without and stumbling.
c. At the end of your adjustment you may need to turn the low end adjustment only 1/16 turn.
d. It is better to be slightly rich than to be a little lean on the low end.
e. As fuel burns down in your tank, the engine will lean out slightly and you don't want it to overheat and kill a glow plug.

2. If the engine coughs and spits, it is too lean.
a. Open the low end adjustment 1/8 turn and try again
b. Keep doing this until you can go from idle to full power without and stumbling.
c. At the end of your adjustment you may need to turn the low end adjustment only 1/16 turn.
d. It is better to be slightly rich than to be a little lean on the low end.

3. This takes a while so don't be rushed.
4. I use 10% Omega, castor blend for my OS engines. It is my opinion that the ABN, nickel plated OS sleeves need some castor oil for long life.
5. I like the OS A3 plug. It is now called the OS #6.
6. An 11-5 is my preferred prop for sport flying on my OS .46AXs. It revs up good and pulls well.

RE: OS 46AX engine test
 

I just recorded the peak rev sound at about the 1:20 mark then trimmed it to a period of 0.1 secs so I could count the individual firing impulses. There were 22 in that time which works out to be 13,200 revs.

RE: OS 46AX engine test
 

You're a piece of work......:D

RE: OS 46AX engine test
 

Hrm...I'll try bouncing it off compression next time. It's proven to be able to do so, when it starts backwards I trim the idle down to an unstable but still running point and it will bounce itself over in the correct direction fairly quick. I will admit I probably have it set a bit rich. Habit from the cars where if you peak them out they overheat in half a tank I guess.


Oh, and it does, indeed, have a spinner.


I'll print this out next time I head out. I've had really good luck with the OS #8s myself, and I am using 15% Odonnel aircraft fuel. 18% total oil content, and judging by the slime on the side of the fuse and right gear when I shut down, quite a bit is castor.


....Damn. I have but two things to say.


1: You have some really good equipment and a well trained ear to be able to determine the RPM I'm getting from the audio my cell phone recorded.

2: My ear isn't as off as I thought it was, that falls right in the middle of the range I guessed it to be in.

Just out of curiosity about what kind of RPM should I be getting on 15% fuel and an 11x5 prop?

RE: OS 46AX engine test
 

Hi!
A 11x6 or 12x4 (RAM, Graupner Cam-prop/ Sonic or APC) is the prop size to use if you fly at sea level and using it in a trainer aircraft!

RE: OS 46AX engine test
 

I lack the ground clearance for a 12x4. The tips would be so close to the ground that I'd need a paved runway to take off AND I'd have to grease every landing lest I bump the tips into the tarmac. Even a mildly rough landing would compress the springy front gear enough to give a nice prop strike.

If I change props it's going to be to a 10x5 three blade, for two reasons. One: I like the looks of three blades better, and two: It will give me better ground clearance without sacrificing any performance. The 11x5 came with the plane, it will be used until I'm good at flying. Or until I break it on a rough landing, whichever comes first.

Thrust calcs put me at a flying speed of about 65MPH, seven pounds of thrust and 1.1HP, more than adequate to learn to fly with.

Also, I'm ~850 feet above sea level.

RE: OS 46AX engine test
 

Three bladed props are a good choice for trainers. Another benefit you will get is some braking action.