OS 55AX
 

I have an OS 55AX on a profile plane that dead sticked on me last weekend. Im in SC and its HOT so I figured it must be running rich. So today I tried tweaking the l/s and h/s needles. I have a 13x4 prop, it idles @ 2400 rpm and maxes at 10,400 rpm. There is a slight hesitation from idle to flat out. After 2 tanks of fuel I have a large wet spot from exhaust and the motor is still hot to the touch after 3-4 min. Does this sound right? close? back up and punt? thanks for any help..

RE: OS 55AX
 

Adjust your high speed needle for maximum RPM. Do this slowly, just a click or two at a time until you get it right on. Then back it out (richen it) 2-3 clicks or until it loses 200-300 RPM. Next, set your low speed needle. If it is lean, the engine will usually die when you advance the throttle. Usually these come little rich from the factory though and it will sort of sputter and hesitate as you accelerate. Slowly close the low speed needle 1/8 a turn at a time until you get a reliable idle and smooth transition.

Once you get the .55-AX set right it is very, very reliable. I have noticed that the high speed needle isn't quite as sensitive as some engines. Be sure to use a tachometer. I have pretty good ears and I can use them to tune an engine fairly good but they are still not as accurate as a tach.

RE: OS 55AX
 

I fly an OS .55 AX on a ModelTech SU-31 profile. The nature of the plane is that you spend a lot of time in a "nose up" attitude or high alpha if you prefer. This means your fuel is being drawn straight up (fighting gravity). This can cause a lean run if the engine is not getting enough fuel. Tank presure is a must to feed the need in these situations as well as a good mixure setting. Ensure you tune your engine so that it runs reliably in the high alpha atitude by holding the plane upright for 30 seconds or so while running at less than full throttle, about what you need to hover (less tank pressure). Good luck.

RE: OS 55AX
 

That's a good point. It might be a good idea to adjust the needles while holding the plane vertical.

RE: OS 55AX
 

oops, wrong thread

RE: OS 55AX
 

thanks guys.. this is an OMP Edge V3 Profile so the alpha attitude test is a great idea... what prop are you using on your profile w/the 55AX and do you happen to remember what your high and idle RPMs are?... I used a Great Planes tach. to get mine.. my idle is at about 2400 and will sit there all day it seems and the high is at 10,400. I think I should back off a click or two on the high..

RE: OS 55AX
 

I am using an APC 13x4 wide. While I have a tach I have never bothered to tach this engine/prop combo as it is more than enough to rocket out of a hover... The engine was still pretty new when I installed it on this plane and have noticed that as it continues to break in it is running much better.