RE: Help! Overheating/Lean ST G90

RE: Help! Overheating/Lean ST G90
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RE: Help! Overheating/Lean ST G90 - 7/12/2006 6:17:07 AM

Flyboy Dave

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....good idea !

I agree totally with your signature line.

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RE: Help! Overheating/Lean ST G90 - 7/12/2006 1:35:01 PM

speedster 1919

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From: Martinsville, IN, USA
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The key here was the first flight was good. It's all about muffler pressure. Don't even think about running a gasket. Your tank is very level with carb. (good) I like the gray RTV (can't see it) clean both surfaces with alcohol and apply RTV and let set and cure for a day , so you don't blow out rtv sealant. I see you used red ,but the 4 1/2 turns tell me you didn't get a seal or your LS is still out of whack. The 6 or 7 turns is to compensate for fuel delivery problem on low RPM and High RPM.

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RE: Help! Overheating/Lean ST G90 - 7/12/2006 2:51:13 PM

doubledee

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Looking at the photo of your cowling I really do wonder if those air vents are big enough. The general rule of thumb is 2 to 1 as a start point. In other words, you should have twice the size heated air exhaust as you have cooling air inlet, but the inlet side must be large enough to allow adequate cool air in.
It is a beautiful set up but I still think you need more/larger holes. Just my thoughts.
Regards,
doubledee

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Post #: 28

RE: Help! Overheating/Lean ST G90 - 7/12/2006 2:53:18 PM

KojakDave

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From: Lakeland, FL, USA
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quote:

ORIGINAL: speedster 1919

I see you used red ,but the 4 1/2 turns tell me you didn't get a seal or your LS is still out of whack. The 6 or 7 turns is to compensate for fuel delivery problem on low RPM and High RPM.

I may have had an out of whack LS. I did the toothpick in the carb/blow in the fuel inlet trick last night and adjusted the low speed a little richer. I will run it again today or tomorrow and will also borrow an IR thermometer to measure head and muffler temps. It is possible that I didn't get a good seal because this is the first time I've used sealant and probably tightened the muffler too much while it was still curing.

Dave

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RE: Help! Overheating/Lean ST G90 - 7/12/2006 3:07:12 PM

KojakDave

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quote:

ORIGINAL: doubledee

Looking at the photo of your cowling I really do wonder if those air vents are big enough. The general rule of thumb is 2 to 1 as a start point. In other words, you should have twice the size heated air exhaust as you have cooling air inlet, but the inlet side must be large enough to allow adequate cool air in.
It is a beautiful set up but I still think you need more/larger holes. Just my thoughts.
Regards,
doubledee

Something that's not easily visible in the photos is the fact that I mounted the cowl so that there is an air space between the cowl and the fuselage around the entire inner diameter of the cowl...not much, but enough to help pull some air through.

I know that in-cowl cooling is important, but I'm trying to reach a happy medium between cooling and aesthetics. Not enough and your engine overheats, cut away too much and it's so crappy looking you might as well not even have a cowl. Part of the problem here is that the standard engine mount orientation is such that even with a Pitts-style muffler the exhaust does not come out directly underneath the cowl. If you're looking at the nose of the plane the exhaust exits the cowl at approximately 4 to 5 o'clock and is very visible. Normally I cut a large opening around the exhaust exits, but that's not possible in this case without munging up the whole cowl.

I've thought about building an air dam at the front of the cowl to help limit the amount of air coming in where it's not doing any good, but I'm not sure if that would keep air from getting to the muffler, which in turn would cause heat to travel to the rest of the engine.

Also, the cowl on this plane has so much open space in it that a lot of folks aren't even cutting holes in it for ventilation, but I'd rather be a little on the safe side.

Dave

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RE: Help! Overheating/Lean ST G90 - 7/12/2006 5:57:00 PM

Bax

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Air in must pass THROUGH the fins on the engine. Just because you have a large air inlet and an large air outlet doesn't mean that air is cooling the engine. If you can see the outlet from the inlet, then the air is following that same path. Also, just because you have holes on the bottom of the cowl, don't assume air actually exits from them. They may be in a high-pressure zone. To get air to exit a cowling, the air must exit into a low-pressure area with respect to the air inlet. That's why cowl flap point aft. That's why many cowls have gaps between the cowl and the fuselage at the aft perimeter.

Many times, with cowled engines, baffles are needed to insure proper airflow throught the cylinder and cylinder head fins. Overheated engines inside cowlings is actually quite common, but the solutions are usually fairly simple. The above discussion does not include problems that may be associated with the fuel system.

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RE: Help! Overheating/Lean ST G90 - 7/15/2006 4:44:31 AM

KojakDave

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I ran another tank of fuel through her today and she is doing great...dialed out to about 3 to 3.5 turns, lots of smoke, passing the pinch test and pitch test at all throttle settings. As soon as I feel she's getting broken in (nearly a gallon through her now) I will start leaning her out a little. I know a lot of people complain about the transition on SuperTigres, but this engine is awesome. Very smooth transition, good idle, excellent power at WOT. Even when I was running lean it was smooth, but now I don't have to worry about burning it up. Thanks again to everybody who helped me out. I'm gonna take her up again this weekend and I can't wait to see how she does.

Dave

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RE: Help! Overheating/Lean ST G90 - 7/15/2006 12:57:01 PM

Ed Cregger N2ECW

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How old are you, Dave? I'm 60.

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RE: Help! Overheating/Lean ST G90 - 7/15/2006 1:51:17 PM

PropSpinner

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From: Pickerington, OH, USA
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I found this thread interesting. I have a ST61ABC that has the exact same problem. Ran fine first few flights then when I started demanding more performance it started flaming out. I didn't want to plug one of the exhaust pipes so I decided to buy a Perry pump to resolve the problem. I have never tested the new set-up. Got distracted by other planes.....attention deficit I guess. I should have just plugged the exhaust and I would still be flying my Stinger.

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RE: Help! Overheating/Lean ST G90 - 7/15/2006 6:39:55 PM

KojakDave

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From: Lakeland, FL, USA
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quote:

ORIGINAL: Artisan

How old are you, Dave? I'm 60.

I'm 34. I just started this hobby a couple of years ago and nearly everyone I've met has been wonderful about sharing their opinions and experience. I actually started flying models so I would have something fun to do with my son (he's almost 2 now) that would get us out in the sun and fresh air. Now it's an addiction, lol. I love my job, but it's very stressful and tiring at times, so it's nice to just go out, unwind, and toss the planes about for a little relaxation time.

Dave

< Message edited by db4962 -- 7/15/2006 6:40:54 PM >

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RE: Help! Overheating/Lean ST G90 - 7/16/2006 7:40:11 AM

Ernie Misner

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Artisan, I will be 61 Sept. 5th. Will I beat you?

Ernie

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RE: Help! Overheating/Lean ST G90 - 7/16/2006 3:19:47 PM

doubledee

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Some days I feel 40 and some days I feel 80. I'm older than all you young whippersnappers. Regards,
doubledee

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RE: Help! Overheating/Lean ST G90 - 7/16/2006 3:37:20 PM

speedster 1919

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Great DB It sounds perfect now so don't touch it. Super Tigres are one of the few engines that will keep running on the lean side.

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RE: Help! Overheating/Lean ST G90 - 7/16/2006 7:43:44 PM

KojakDave

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From: Lakeland, FL, USA
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What a day...I took her out to the field today and things just did not go right. The first flight she was definitely too rich. She didn't have enough power and it looked almost like I was skywriting, there was that much smoke coming out. Brought her in and adjusted her a little leaner, then took her back up. It just so happens I almost crashed her because somebody was running a 1/3 size Telemaster/Cessna hybrid on the ground and I couldn't hear the engine quit. I had fueled her back up, but because she was running so rich she went through the fuel like crazy and emptied the tank!! Then the problems started. I again leaned her out a little. On the ground she was awesome, excellent idle, great transition, and still a little rich on the top end (it is still being broken in, I'd rather run a little rich than burn her up). But when I took off this time, she deadsticked after just a minute. Hmmm, brought her in, got her running on the ground, decided to let her run for a while, do a few transitions, etc....sounded great. Started idling, got her out on the runway and I had a nose-over. Oops, pilot error. Walked out, started her there, let her run for a sec, throttled up, and she died. I decided that the Gods were not smiling, packed her up, and am now ready to see what the problem is where I can curse in the privacy of my own home. One of the maestros at the field (I think old-timers sounds disrespectful) said that an Enya #3 glowplug might help. I'm running the SuperTigre glow plug that came with the engine. Anybody have any input on this? I don't think I leaned her out too much because she's still smoking and passes the pitch test (you know, throttle up and somebody points her nose up, if she revs up a little she's good, if she dies off she's too lean). As far as overheating I checked the engine after her first full flight and she was not what I would consider too hot, I could touch my finger to the cylinder head for a second without getting blisters

Thanks for any help,

Dave

< Message edited by db4962 -- 7/18/2006 3:53:03 PM >

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RE: Help! Overheating/Lean ST G90 - 7/16/2006 8:13:06 PM

pilotpete2

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Dave,
Sounds just my G51 when I had the low speed needle a tad to lean, drove me nuts till I sorted it out (with me that's a very short drive

)
Pete

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