OS55AX mixture setting advice sought

[Graham Bowers]

I have 4 bench runs plus about 10 flights on a 55AX I bought new, and have followed the "break in" instructions to the best of my ability. Running it on Southern Modelcraft 10% Nitro and APC 12x6. Model is a Balsacraft Xtreme at about 5 and a half pounds. I'm using it as a sport plane to practice precision aerobatics,** so modulating the throttle accordingly. **Not quite so precise just yet ;-)

 

The instructions then say to lean it out, but not too lean. Not really helpful to me. Reading around suggests leaning it to peak RPM and then screwing the needle out a bit. Some say 2 or 3 clicks. Others say different things. 

 

What are thoughts on how much slower than peak to run it please, clicks or RPM? I have a hand held tachometer. I imagine  this will change as it gets a couple of gallons through it, however some sort of steer would be useful please?

[Flying Squirrel]

There's some good info on this thread that may help?

 

 

[Jon H]

There is a load on that other thread, some of which will not apply but there is a bunch of stuff there. 

 

The only thing i would say is to forget the tacho and put it back in the box. Tach's are very useful tools for checking engine performance but they are useless for tuning. peak RPM will vary day to day with temperature, air density etc. Also a cold engine will run faster than a hot one so if you check it 1 minute after starting, tune it up with 20-30 seconds at high power, the rpm will drop due to the engine warming up. You then say 'where did my revs go' and sit there flat out staring at the tach trying to screw all the revs back out of the needle. All the while the engine gets hotter and hotter, and slower and slower. Tach's also do not react fast enough to be of much use. Certainly they are slower than your ears when it comes to detecting a change. 

 

The biggest issue i think people have with engines is using their ears to identify issues. We are all used to looking for problems with our eyes, so a tacho seems a good idea, but often the 'secret' language of engines is all in the sound. You just have to learn the language and that takes a little practice. 

 

 

[J D 8]

  Before the days of electronics/computers in cars it was your ears that told you it was running right and nose for mixture. Eye was for looking at the spark plugs to determine if the deposits from combustion were the right colour. 

[Graham Bowers]

Thanks for replies folks. It all makes perfect sense now.

[Jon H]

46 minutes ago, Graham Bowers said:

It all makes perfect sense now.

 

 

I guess the big takeaway is not to be frightened of the engine and not to be frightened of breaking it. There are many stories about how one lean run will nuke your engine and life as we know it will come to an end. To a degree this was true on old engines as overheating a steel liner/iron piston setup during run in could cause damage if done repeatedly, but its unlikely to to do any harm today. Equally engines with ferrous liner/piston setups needed to get hot for the iron to work harden so running mega rich was not a solution either. This could explain all the horror stories as engines were either run over rich or screamed, and then over heated which didnt help either. 

 

Modern engines with ali pistons and some sort of plated liner are intended to be pushed pretty hard from the get go and if you over shoot slightly and it suffers a lean cut (this will happen instantly) then no real harm done provided you are using a good fuel with a good oil in it. and its quality over quantity when it comes to oil in fuel. 

 

As detailed in the other thread, an over heated engine is not a lean engine. A well tuned engine can over heat if badly cooled and its overheating which is the real enemy. How hot is too hot? Difficult, but a general and admittedly vague guide i use is that you should be able to touch but not hold the engine. If you touch it and get an instant burn (like a 4 stroke exhaust!) thats bad. If you can hold it for a short time before its too much you are probably ok. In general terms, i guess 80-120'c depending on the engine? But there is so many variables its hard to pin down a number and i absolutely would not bother with temperature probes or anything like that. 

 

 

 

 

[Graham Bowers]

Thanks Jon, I didn't want to damage it through my own ignorance, however am comfortable with making the necessary adjustments now.

[Jon H]

What i would suggest is to fire it up, get to full power slightly rich and just keep leaning it off until it stops. You only need to do it once, but keep going at the rate of one needle click a second and just listen to it. It will get faster, faster, faster, no change, no change, maybe sound a little harsh with a crackle sound, revs drop, dead. 

 

Open the needle and go again but this time you have that sound change profile in your head and you stop short of the crackle and certainly short of the rev drop. 

 

I know its a 4 stroke, but this video shows me tuning up a 150 laser and the principal is exactly the same. You can hear the rev drop clearly as i pass the peak and how the engine responds when i dial it back. setting a needle is that fast, no need to take any longer. I also faff about with the slow run after that but you can ignore that part. Start at about 1 minute 18 seconds to skip all the starting and warmup. 

 

 

[Graham Bowers]

Great, thanks. Seeing (and hearing) is believing 😉

 

Flying tomorrow so that's what I'll be doing.

[Jason Channing]

Wow what a great way to promote safety showing a really damaged prop, Im sure excuses and reasons will follow🤣 

Edited April 4, 2023 by Jason Channing

[Graham Bowers]

29 minutes ago, Jason Channing said:

Wow what a great way to promote safety showing a really damaged prop, Im sure excuses and reasons will follow🤣 

Don't feed the troll 😉

Edited April 4, 2023 by Graham Bowers
Different viewpoint

[John Stainforth]

3 hours ago, Jon - Laser Engines said:

What i would suggest is to fire it up, get to full power slightly rich and just keep leaning it off until it stops. You only need to do it once, but keep going at the rate of one needle click a second and just listen to it. It will get faster, faster, faster, no change, no change, maybe sound a little harsh with a crackle sound, revs drop, dead. 

 

Open the needle and go again but this time you have that sound change profile in your head and you stop short of the crackle and certainly short of the rev drop. 

 

I know its a 4 stroke, but this video shows me tuning up a 150 laser and the principal is exactly the same. You can hear the rev drop clearly as i pass the peak and how the engine responds when i dial it back. setting a needle is that fast, no need to take any longer. I also faff about with the slow run after that but you can ignore that part. Start at about 1 minute 18 seconds to skip all the starting and warmup. 

 

Jon, great video, but I waited in great anticipation of seeing you throwing the tacho away. Somehow I missed that!

 

[Jason Channing]

59 minutes ago, Graham Bowers said:

Don't feed the troll 😉

That's not trolling. it goes against everything that is taught about using a damaged propeller. Tell me how that is trolling!  Its not even a small chip its chunks missing. If you cant see the chunks missing then you should go to specsavers 🤣😆🍋

[Jon H]

2 hours ago, Graham Bowers said:

Don't feed the troll

 

Aww he will be so sad if we dont play with him. he just wants to be included the conversation but has nothing constructive to add. And look, cant you see the delight in his comments, the joy? he really thinks he is on to something and yes..wait! he has finally scored a point against the great Jon of Laser who made a mistake with his chonky prop....except, he hasnt. Jason, its a test prop and it never leaves the ground. Of course, you know that and just wanted the point to make yourself look big and me look silly by explaining the obvious but for the others that were interested in the actual facts of the matter, there it is. it is pretty chewed up, but then you would be too after more than...good lord i dont know...10 years? and probably over 3000 starts? Most if which are by hand. I would replace it, but they are discontinued and as its structurally fine, meh. All my test data is with this prop too and im not going to do it all again. Would i fly it or recommend anyone does so with a similar prop? absolutely not, is it fine for testing? yes. Its even balanced 🙂

 

 

 

[john stones 1 - Moderator]

I've been an I.C flyer a long time, so I read most posts on the subject, a prop in that condition would never go on an engine of mine, test bench only is irrelevant, reason for not using isn't coz it'll be less efficient in flight, it's that it may break and cause injury, poor video and poor response for me Jon.

[Graham Bowers]

8 hours ago, Jason Channing said:

That's not trolling. it goes against everything that is taught about using a damaged propeller. Tell me how that is trolling!  Its not even a small chip its chunks missing. If you cant see the chunks missing then you should go to specsavers 🤣😆🍋

There are often more to communications than first meet the eye.

 

I took in to account the fact that the video was clearly made at work so the context of the activity comes under the safety legislation that covers activity at work, which mandates risk assessment. We knew nothing about the reasons for using that prop or the controls in place to ensure it's structural integrity and / or containing any failure.

 

I also took in to account the tone of your response, that seemed to be intended to provoke a reaction.

 

My eyesight is fine, thanks for your concern.

[Jon H]

8 hours ago, john stones 1 - Moderator said:

I've been an I.C flyer a long time, so I read most posts on the subject, a prop in that condition would never go on an engine of mine, test bench only is irrelevant, reason for not using isn't coz it'll be less efficient in flight, it's that it may break and cause injury, poor video and poor response for me Jon.

 

Hi John. You are absolutely right, the rules about damaged props are integrity based and not efficiency based. if i had any concerns about the integrity of the prop i wouldnt use it as i have had a blade failure before in the air (wooden prop, i think the spinner retaining bolt failed and took the prop with it) and it was not something i fancy experiencing from 2 feet away. The damage on the trailing edge was caused by pre ignition on hand start under specific conditions. as the blade flicks round it whacks the starter stick and chips the blade trailing edge, while also doing no favours to my wrist. There is no damage to the hub or any part of the blade that would reduce its overall integrity so it is still safe to use given my use case and environment. 

 

I do pay attention to propeller integrity and when i started testing the FT310's i looked up the limiting speed for the 18x8 master classic i intended to use for running the engines up as i suspected it would be close. Limiting RPM is 9167 according to their formula. RPM seen on the engine during test 9100 with peaks of 9200 on some engines. Sailing pretty close to the wind on that one if the RPM limit is absolute. If they assume 9167 on the ground it will be safe to 10000 in the air but this is not disclosed. Graupner Gsonic props have very low limiting RPMs and its easy to exceed those limits. 

 

I appreciate the concern John, but i am on top of it. 

 

 

 

 

 

[Frank Skilbeck]

Graham the OS55AX is a cracking engine I've got one in my Astro Hogg, just follow the instructions, lean it out then come back a couple of clicks, I initially ran mine on 5% (Southern Model crafts) but was given a couple of gallons of straight ( Southern models synthetic) and it runs great on that after a slight retune.

 

I hardly ever use an electric starter on mine just prime it and a few lazy reverse flicks and it's away on the first flight of the day and then 1 or 2 reverse flicks after that.

 

I'm running a 13 x 6.5" prop on mine so probably not getting max performance but it's more than ample for the Astro Hog