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Building Tips and technical articles. => 1/2 A building. => Topic started by: John Crocker on June 23, 2007, 04:20:36 PM
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Got a prob guys. My Big mig .049 wont run more than half a tank before it cuts off. Running 35% Nitro Norvel 1/2 A fuel. Using a tank mount, and yes I did follow the break in to the T and did change the take up tube so it picks up on the lower outside. Have had the best luck taking off rich and it leans out on its own after about a 1/2 circle, but that only works 10% of the time.
This is really frustrating cause its an awesome engine. In combat with my buddy who uses a golden bee, I eat his lunch til the cut out.
Oh yeah, it seems to get worse after a full loop. Half loops, no problem, cut a full one after 10 or 11 laps and watch out, its cutting off.
Been thinking bout switching to a Sullivan 1 oz wing mounted clunk tank cause round here you cant find triangular tanks.
Any thoughts?
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Assuming it is a standard NORVEL tank mount, are you running a pressure line from the muffler to the fill tube on the tank? If not, give it a try.
If you are not running a muffler, make sure the fill tube on the tank is facing foreward.
If it still acts the same, check the metal pickup line in the tank for a crack or pinhole. Also replace the external plastic tube from the tank pickup to the engine.
My $.02 is spent. H^^
George
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yep, running the pressure line. Have already checked the pipe and have replaced the tubing. What I'm using is listed as "small" tubing. Don't know the dia.
Do most of you guys lean out the needle valve till you get the high pitched whine before launching (hand) like I always did with my Cox engines? Does not seem to work as well on the Norvel. It seems to run better if I launch it rich and leans out in the first turn
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All my Norvels unload considerably in the air; I do launch them fairly rich--as much as a breaking 2/4 cycle sometimes. But I never had much success with the Norvel tank mount, don't know why exactly--looks like it oughtta work OK, but never did for me. I use separate tanks exclusively now, and have for years. Homemade or bought, metal tank, plastic clunk, floppy balloon, all work well. Pressure is best of all any time you want an extremely consistent run even through hard maneuvers; a little extra trouble but worth the effort if you're flying combat. But you still need to launch rich.
--Ray
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Thanks Ray.
On the balloon tanks are you running tubing to the back of the balloon? Also, how are you securing the balloon to the tubing, and how are you securing the bladder to the plane?
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Not Ray, but I see the guys using plastic 35mm film canisters for the tank compartments. "Goop" will glue it.
IIRC, I saw Ray's set up for the balloon: A piece of tubing with regular fuel line attached that had some "notches" cut down it's length for a pickup, and wrapped (with thread??) once installed in the balloon. Make sense?
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Bill got it...here's a pictorial from awhile ago:
the "tie" is just a twist-tie as on a loaf of bread or something. The fuel line runs about 2/3 of the way back into the balloon.
Just keep in mind these are NOT pressure tanks, but "floppy balloon" tanks. The balloon is not stretched at all when full.
--Ray
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Nice photo layout. Couldn't have said it better! H^^
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Thank you sir. Simple things I can handle!
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Ray
A picture is worth a thousand words. So you just gave us seven thousand words of instruction. Also no spelling errors either.
Clancy
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John,
Additional thought: If it is unloading a lot, perhaps you are using too large a prop. For a Big Mig .061, many agree that a 6x2 or 5.7x3 works well. The Big Mig .049 is not just smaller, it also has less HP/cu in. You may be over-propping it. Some people were having fuel draw problems with NORVEL engines until someone noticed that they must be allowed to rev up to get enough ventouri velocity. This was on the AME more than the Big Mig (perhaps because most were flying the AME at the time).
While running on present setup, I would try a smaller prop and adjust needle with plane pointing ~45 degrees up (although pointing up may not help since you are running pressure).
Good luck with it.
George
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Running a Master Airscrew 6X3. Cant find anything smaller.
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I think George has a point, that's probably too much prop. 5x3 would be better. You can order them online. Or send me a couple of bucks and your address and I'll mail you one.
--Ray
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Really dont think its the prop (although I had a 5x4 Thimble Drome prop that screamed til I tent posted it n~)Funny thing is, it will run through a whole tank if I hold on to the plane, and will do it at the highest RPM (based on sound). Thats why I think it has got to be the tank.
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I agree, John, I think it is tank problems.
I would cut the prop down, probably to 5 1/2. The Norvels are strong, but they need to rev, and it seems they work best on slightly smaller props.
You can definitely cut the ends down on props. Do you have a way to balance them?
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don't have a "prop balancer", but can dang sure build one.
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don't have a "prop balancer", but can dang sure build one.
An unbalanced prop could very well be your problem. Shaking the airplane can cause the fuel to foam in the tank and do all sorts of crazy things. Holding on to the plane could allow your hand to absorb the vibration and mask the problem...go for the balancer.
I use a Top Flite magnetic balancer, which works well, but I think the type that uses big wheels (High Point?) would be a better investment in the long run. If you build your own, make sure it is sensitive enough. A "rough" balance on something as light as a 1/2A prop is not much good.
I got into the habit of balancing a prop as soon as I remove it from the package. That way I have no question as to which ones are balanced...they ALL are.
George
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I use the Top Flite magnetic balancer, but threw out the junk plastic coned pivot. I got the Great Planes (or maybe DuBro? I don't recall which) balancer and use that as the pivot instead.
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HI JOHN, the balloon tank will work grate on the big mig .049 , the first time we used this type tank was over 50 years ago. the tank came with the FIRE BABY and a O K CUB .049 and was just a bit thicker than some ballons you get now.
BOB
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Yup, that was my introduction to it too. Jim Walker RTF Firebaby, balloon tank inside the plastic canopy and an OK Cub with an aluminum propeller. All balsa, aluminum and screws--no glue that I recall. Practically indestructible. I (and a bunch of other kids) learned how to fly with that thing.
--Ray