Senior Member
Hi guys
I have a WH baby extra; OS AX 1.20 up front with 16x8 APC. The plane flies great, but I have a problem with cooling, and don't know if I need more inlet air, or more outlet area, or outlets in a different place. After I land, the engine smokes very lightly for about 15 seconds. It is not the cowl, not tubing, and not debris that is smoking. Obviously something is too hot. Never had this problem with my other cowled aircraft.
The mixtures seem about right - I am 3-4 clicks rich of peak (150-200 rpm down from peak), and the pinch test still gives me a burst of speed, so I think the hi speed needle is ok. It idles well, and takes throttle without stumbling or cut out, so I think the lo speed needle is about right also.
I know the rule-of-thumb ratio of 3:1 exit area to inlet area. The intakes are about 3 square inches surrounding the spinner, but part of that area is blocked by the spinner. I have about 17 square inches of outlet area, along the bottom of the cowl, so I am better than 5:1.
The OS AX 1.20 muffler can be mounted transversely, so it would almost fit into the cowl, but I opened the cowl forward of the muffler, to about 1 inch forward of the cowl ring.
So... the question is, should I cut a few slots in the top and front of the cowl for more cooling air inlet over the head, or do I somehow need more outlet area. Is there any reliable method to tell which is the problem?
Thanks in advance
I have a WH baby extra; OS AX 1.20 up front with 16x8 APC. The plane flies great, but I have a problem with cooling, and don't know if I need more inlet air, or more outlet area, or outlets in a different place. After I land, the engine smokes very lightly for about 15 seconds. It is not the cowl, not tubing, and not debris that is smoking. Obviously something is too hot. Never had this problem with my other cowled aircraft.
The mixtures seem about right - I am 3-4 clicks rich of peak (150-200 rpm down from peak), and the pinch test still gives me a burst of speed, so I think the hi speed needle is ok. It idles well, and takes throttle without stumbling or cut out, so I think the lo speed needle is about right also.
I know the rule-of-thumb ratio of 3:1 exit area to inlet area. The intakes are about 3 square inches surrounding the spinner, but part of that area is blocked by the spinner. I have about 17 square inches of outlet area, along the bottom of the cowl, so I am better than 5:1.
The OS AX 1.20 muffler can be mounted transversely, so it would almost fit into the cowl, but I opened the cowl forward of the muffler, to about 1 inch forward of the cowl ring.
So... the question is, should I cut a few slots in the top and front of the cowl for more cooling air inlet over the head, or do I somehow need more outlet area. Is there any reliable method to tell which is the problem?
Thanks in advance
Senior Member
That's a good question. I've used a glow engine on this plane with not trouble, but I only flew it a few times and it was a Thunder Tiger 1.20 so my experience may not be relevant.
I think the first thing I'd do is try to determine if the engine is actually overheating, that would involve some sort of cylinder head temperature recorder or at a minimum an infrared heat gun. It's possible you are just getting some oil on the fins that's smoking.
Assuming it's really overheating, maybe somebody else on here can help. I haven't flown glow in many years and I've never had a 1.20 AX.
TF
I think the first thing I'd do is try to determine if the engine is actually overheating, that would involve some sort of cylinder head temperature recorder or at a minimum an infrared heat gun. It's possible you are just getting some oil on the fins that's smoking.
Assuming it's really overheating, maybe somebody else on here can help. I haven't flown glow in many years and I've never had a 1.20 AX.
TF
Senior Member
Tom
Thanks again for your suggestion. Problem solved - i had a small split in my exhaust pressure line leading to WAY LEAN conditions for the engine. Turned out not to be cowl related at all.
Was flying the plane again today with new pressure line with no problem.
It is a very lovely airframe. It flies beautifullly. Thanks for having it on the market!
Bill
http://www.rcuniverse.com/forum/m_9675411/tm.htm
Thanks again for your suggestion. Problem solved - i had a small split in my exhaust pressure line leading to WAY LEAN conditions for the engine. Turned out not to be cowl related at all.
Was flying the plane again today with new pressure line with no problem.
It is a very lovely airframe. It flies beautifullly. Thanks for having it on the market!
Bill
http://www.rcuniverse.com/forum/m_9675411/tm.htm
