BAX 95AX question
One, what is the max Nitro percentage the 95AX will tolerate comfortably?
Two, what plug have you guys found to be best?
Three, I have read the comments about the knocking sound the 75AX and 95AX make and my question here is, Are you guys really convinced it's not pre-ignition/detonation?
To expand on my questions Bax, I've been in this hobby for around 48 years. I've been involved with building race engines of all types for more than 40 years. Having said that, let me say this engine is the most strange I've come across in all my years of glow engine modeling. I have telemetry on the plane so I can see in real time the engine temp and rpm etc. It runs very cool compared to others and no amount of leaning will get it to run even near 200 degrees F. Yes mine makes significant noise at some power settings. In the air it sounds horrible as if "Knocking" or maybe detonating. I can't see any indications, such as the glow plug element being distorted, that it is detonating but it sure sounds that way.
My reason for this thread is it dies a lot in flight. Most of the time it is on throttle retard from full to around half and it just quits without warning. It's now been in two different planes with two different fuel systems so that's ruled out and plus it doesn't sound like a fuel issue anyway when it quits. In gasoline terms it sounds like you just shut the ignition off inflight. Hence my question about the plug range. It currently has a genuine OS #8 and changing the plug to another #8 makes no difference. I've run it leaner and richer on both the idle and main circuit and either way on either needle makes the problem worse especially if it's rich enough to four stroke. At that point it's guaranteed to die inflight making me think the plug might need to be just a bit hotter. Again, it does not like to be even the tiniest bit rich. I've also thought about blocking some of the cooling fins on the head as this thing will never exceed 170F in flight even so lean it will barely stay running. As far as the quitting in flight issue leaner is better if that helps, but even that is not a sure cure.
I am not concerned about the knocking noise as the engine is very smooth turning over with no discernible slack in the rod bearings. I added it because the more it is doing it (the knocking sound) the more likely it is that it will die. Problem is that the knocking doesn't seem connected to needle setting but rather the weather conditions, hence my concern about pre-ignition and the max level of nitro tolerance. High pressure very dry days are the worst. It will do it with 10% but seems worse on 15% so do you recommend trying an additional head shim? I hate to tear into this thing as it's quite new, without hearing from you, so if you can, please point me in the directions you see as best.
I would prefer to stay with 15% fuel as this is what I use in everything else. My Tower 46, all of my SuperTigre's, other OS's, etc, etc all love the 15%. Your advice is appreciated Bill and thanks in advance for any help you can offer me.
Edited to add: Bill it has a 14X6 prop on it, do you think it might help to put a 13X6 on it? I didn't try that because of how cool it's running and unloading it with the smaller prop would seem like it would make that worse.