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Building Tips and technical articles. => 1/2 A building. => Topic started by: Robert W on October 28, 2008, 11:56:07 AM
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I did a quick search and may have missed this, but I am looking for what is a good ID size for the venturi on the TD049 that will give good performace on suction from a uniflow tank. The math I use for the larger engines would require an opening smaller then what is on the reed valve motors, so I do not trust the math for this size.
I am trying to get some of my 1/2A planes running better.
Thanks
Robert
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Robert
Way back when we were doing Tee Dee 1/2 A stunters the early Tee Dee venturi with the .125 (app) hole worked the best... FWIW
thanks
Jim
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Why suction? The side nipple pressure works really well. Take a 2x56 "T" nut and turn the flange down to make a nipple out of it. Screw it onto the side nipple on the carb housing with a bit of epoxy or Goop adhesive to assure a seal. Drill the pressure tap per Cox's instructions and plumb to the tank. I get incredibly good, reliable runs with this setup. You can even drill out the venturi a bit if you need even more power and can handle the fuel load required in your plane.
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Thanks for the information, I measured the one I have been using with a drill bit and it is around 0.108". I will keep experimenting till I get good runs.
Regards
Robert
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Why suction? The side nipple pressure works really well. Take a 2x56 "T" nut and turn the flange down to make a nipple out of it. Screw it onto the side nipple on the carb housing with a bit of epoxy or Goop adhesive to assure a seal. Drill the pressure tap per Cox's instructions and plumb to the tank. I get incredibly good, reliable runs with this setup. You can even drill out the venturi a bit if you need even more power and can handle the fuel load required in your plane.
I have a Madallion .049 that I run on pressure. I have trouble keeping the fuel line on the pressure tap. Is the above a fix? do you have pictures? #^
As a side comment I have found pressure hard to hand start but an electric starter works fine. H^^
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I flew 1/2A stunt with TD on a pacifier tank or with crankcase pressure off the backplate. Do not flip a TD. Headprime, turn the prop backwards to vertical, attach glow plug and hit the prop forward with your gloved finger. With practice it works almost every time.
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To John Rist: see above for the best way to keep the hose on the nipple. There are a couple of other ways as well. One way is to super-glue the hose on. Another is to gently scribe anullar lines around the nipple with a #11 blade. This adds friction to prevent slippage. The 2x56 nut filed down to become a real hose nipple is far and away the best.
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To John Rist: see above for the best way to keep the hose on the nipple. There are a couple of other ways as well. One way is to super-glue the hose on. Another is to gently scribe anullar lines around the nipple with a #11 blade. This adds friction to prevent slippage. The 2x56 nut filed down to become a real hose nipple is far and away the best.
I am fairly new to U-Control BBs. It never ceases to amaze me what can be learned on one. Thanks all!! y1
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Here is a photo of the nipple modification I use on the Tee Dee and Medallion. You screw a 2x56 "T" nut onto a bolt and chuck it into your power drill. Use a file to cut the flange down until it is a nice hose nipple shape. It will then screw onto the plastic nipple on the carb housing of either engine, and if you use a bit of Goop, epoxy, or JB weld, will seal perfectly. Drill out the tap per factory instructions, and you have a very reliable pressure tank drive system.
I like the ultra fine control that the Kirn or Klaus needle system provide, but it is quite workable with the stock needle. I seem to need about 1 ounce of fuel to do the classic pattern on 42.5' lines with a bit of margin left over. I do tend to set it screaming all the way, keeping attention on not going over-lean on the verticals and overheads. If you want something closer to a 4-2-4 break, you will need a bigger tank. Currently, I like the APC 6x2 prop to give me lap times in the high 4-second region.