Building Tips and technical articles. > 1/2 A building.
Norvel .061 Big Mig for Semi-Serious St
Dan McEntee:
--- Quote from: 944_Jim on June 28, 2024, 06:41:09 PM ---Mr. Dan,
I ran into an issue with a Cox .051 and high compression head. Sometimes it ran fine...other times an absolute dog. And this was on days where I could spend a few hours trying to fly on "same fuel," so it wasn't a "different weather, different day" kind of thing.
FredV4 and I talked this one through for a few days (over weeks of trying). He kept asking how I knew I wasn't over-compressed since all the variables were carefully tracked. One day I opened the top of the cylinder and chucked a few head gaskets in there.
It was a night and day difference! Now the engine merrily hauled the plane around, up, down and inverted.
Try the engine with a standard Cox glowhead. Yeah, it will look funny with a puny head. But it will keep heat in the top end, and may alleviate the issues. If nothing else, this one is a cheap test.
--- End quote ---
I have made some strides and have been getting some good runs, one right after another. First, I tried test runs in the driveway with the assortment of heads/glow plugs that I have, and decided to run the Galbreath Nelson head. I have the habit of mounting profile tanks with rubber bands, especially when trimming a new airplane, so if I need to change tanks for any reason, it's much easier, and easier to move the tank up and down. I finally settled on a location, and then I mounted the tank on brackets but still have some foam under the tank, one of the perfect 2 ounce #8 tanks I modified. The last flying session I had, I was getting really nice runs, upright and inverted, insides and outsides, and the engine just sounded "happy". I'm still on 15% nitro fuel, basically a SIG Champion mix, and dropped down to a 5-3 prop I made from a 5.7-3 that I cut down and balanced. All this made a big difference. I ordered up some of the recommended 5.5-2.5 APC props plus some of their 5-3 and was hoping they would be here by now but the local USPS distribution center has been sitting on them for a couple of days!!! And they are only 3 miles from my house!!. The tank I modified is too big. It has a 1 3/4 ounce capacity but runs forever on that much. I can short tank it down to to 1 1/2 ounces and it still runs over 8 minutes. I'm afraid to short tank it any more for fear of it causing problems picking up fuel on start up and take off, and at the end of the pattern in the clover, so I made a new tank that holds 1 1/2 ounces, so I can try short tanking it to 1 1/4 ounces. More test flights tomorrow morning. I am at the point that if the engine likes this new tank, I can really start trimming the airplane and testing props. It flies a decent pattern now, with the triangle being a bit mushy. I've worked on the controls some more and I think that should improve.
I went with a 2 ounce tank to start with, not really having any experience with trying to get a whole pattern in on a 1/2A model. I'm on 44 foot lines (eye to eye) using 20 pound Spectra, and trying for 4.3 to 4.5 second lap times. I don't think you can slow one of these things down to 5 seconds, unless it's super light. The Doodlebug weighs 12 ounces and has 200 plus sq. in. of area. It generally feels pretty good, but I'm finally getting it into my head that I have more to learn about props for these. I have a Brodak ARF Baby Clown with a Medallion .049 on it, and it swings the Cox 5-3 prop with ease, like it's got more torque. The Norvel acts like it' was over propped with one of these, and I may try cutting one down to 4.5. I don't have a way to measure pitch on these, my Prather gauge just won't work, but would like to try that prop at 2 or 2.5" pitch. I 'll get into testing props more in the near future.
Doers the fuel load I'm needing jive with what you guys are using to do the complete AMA pattern. i will be happy is I can get a consistent 7 minute run, maybe a bit less. Might play around with heads and gaskets some more also once I get to enjoy really flying it. It's been a challenge an fun so far. I got a stack of kits, foam wings, and lots of plans for these little boogers!!
Type at you later,
Dan McEntee
Motorman:
It would be better to fully round off the tips of the Cox 5-3 than to cut it shorter.
Chuck Matheny:
Hello Dan.
I used to have the same problem mostly with the first generation AMEs.
It was Larry Driskill who figured out that the crankshaft fit was a little bit too tight and this caused a "run away" overheating of the whole engine.
Enough to swell the piston and get it to seize in the most extreme cases.
IIRC he would chuck the crank into a drill motor and give it a quick polish with fine sandpaper. I think the key words here are FINE PAPER and QUICK POLISH.
He only worked on the middle part of the crank journal, leaving the extreme ends of the load bearing surface as is.
Afterwards, be willing to bench run it and nurse the engine through a few tanks of fuel until you see the damn thing behaving as it should.
Muffler pressure ought to give you pretty steady runs with a triangle shaped [wedge] tank with just the single vent for the incoming muffler pressure.
By the time this "service bulletin" came out about polishing the crank journal I had already sworn off Norvels...but now that I know about this remedy I might try a Big Mig or AME again.
Dan McEntee:
Hi Chuck;
Thanks for the information. I have had to set that project aside for a bit but may just tear that engine down and check it out. Doesn't seem that tight when flipping it through cold after choking it to start. The last couple of session I seemed to hit a good combo with going back to stock glow plug and the APC 5.5 X 2.5 that had been recommended to me. I guess if there is any heating an d friction I will see it in the cranks journal?? Maybe by this coming weekend I can get to that. i want to swap it out for a Wasp .061 that I converted to a TD venturi and see how that engine performs compared to the Norvel. I have read several good reports on those.
Thanks again and Type at you later,
Dan McEntee
944_Jim:
--- Quote from: Dan McEntee on September 08, 2024, 09:04:01 PM --- Maybe by this coming weekend I can get to that. i want to swap it out for a Wasp .061 that I converted to a TD venturi and see how that engine performs compared to the Norvel.
Thanks again and Type at you later,
Dan McEntee
--- End quote ---
Mr. Dan,
I'd love to see pics and read details please.
Jim in NE MS...a southern hockey fan!
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