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Engine basics => Engine set up tips => Topic started by: Bob Zambelli on May 22, 2007, 05:25:16 AM
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Came across this the other day.
I've seen two-needle setups on Fox & K&B but never Cox.
Info?????????????????????????
Bob Z.
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Cox did some experimentation no doubt. Much of it the average modeler may never see or hear of. Especially the failed axperiments. However, many modelers have done their own modifications for various reasons.
I wonder why two needles? Is there also a fuel nipple under the other needle that cannot be seen in this pic? I am thinking there is but it still is puzzling.
It will be interesting to find out more about this one.
Robert
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Hi, Robert - yes, there is a fuel nipple for each needle valve.
The actual NV body does not look like a homebuilt gadget.
Back in the early days of engine speed control, engines were equipped with two needle valves, set for two different engines speeds. A diverter valve, controlled by radio or third line would direct fuel for either high or low speed.
Bob Z.
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I recall seeing the two NVA set up advertised. I think it is a factory product. As said, for two speed RC operation.
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As for not looking hand made, some who have modified are skilled machinests and their work would reflect that. Some of course are not and are merely tinkerers or simply lacking the access to good machines.
As for the two speed operation, that sounds logical but by simply having to needle settings would not be enough to make a big difference. You would need to also alter the amount of air intake and additionally, if possible to increase/decrease the venturi opening. Much like when you kick in a secondary set (of bbls) on an automobile.
Is there any way of switching from one NV to the other? I suppose a valve could switch from one common tank to divert from one nipple to another...
Ideas?
Robert
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I think that was the way it worked. One needle set regular and the other set rich and a valve to switch back and forth. In the 50's a fair number of engines could be had with two NVA's installed. Torpedos and Cameron 19 are two that I recall. I have a Cameron 19 case set up for two NVA's.
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what size is that engine?? ;D
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Cox made special engines for some people to try out at special contest like the world champs especially in free flight. I hear tell of a drum valve cox in the the late 60s for World free flight contest for one of our local flyers. There was a five way fly off for first and I think he missed one max.
Willis
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Bill - it's an .049.
Bob Z.
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Back in the golden oldie days, before glow,(BG) many of the spark ign. engines offered dual points to retard the spark for throttling. Jim Walker used these in his Fireball's with a relay to switch between the two. These were also used in early R/C planes. When glow came along they went to two needle valves to control speed somewhat. Fox 59's of early vintage have a second spot, not drilled out, for the second needle. I believe the Foxes also had the switching valve mounted on the back plate of the motor.
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As for not looking hand made, some who have modified are skilled machinests and their work would reflect that. Some of course are not and are merely tinkerers or simply lacking the access to good machines.
As for the two speed operation, that sounds logical but by simply having to needle settings would not be enough to make a big difference. You would need to also alter the amount of air intake and additionally, if possible to increase/decrease the venturi opening. Much like when you kick in a secondary set (of bbls) on an automobile.
Is there any way of switching from one NV to the other? I suppose a valve could switch from one common tank to divert from one nipple to another...
Ideas?
Actually, it was initially quite simple. I had a Fox .19 (circa about 1954-56) with two needle valves for primitive throttle control in the early R/C days. You adjusted the high speed run for one needle valve and the low speed run for BOTH needle valves (a kind of R/C 4-cycle; very rich!!!). It was a real balancing act. High speed was not very good but low speed was not bad. It didn't work well but, remember, it those days we were thrilled to have ANY KIND of throttle control. The "controller valve" was similar to a fuel line pinch off common in those days in racing or free flight. By the time someone had "engineered" a rotating valve to easily switch from high to low and back again, someone else had engineered a workable carb and the two needle valve system went into R/C history! I doubt that the two needle throttle control was available on engines for more than a year or so. You can often see that middle 1950's Fox .19 I had on EBay with a single needle and a blank space in the venturi for adding a needle. Incidentally, that was an excellent .19. I still have a single needle version I bought at the PX at Lackland in 1956.
regards,
bill marvel
Robert
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The engine is a Space Hopper, and the needle assembly was a production C*x product intended for RC throttling. Rather than switching from one needle to the other, one needle was set for full speed, the other was switched on or off to add extra fuel to richen the mix. Much simpler than trying to valve two needles back and forth.
The Space Hopper was the last high performance Reedie until we got to the Killer Bee. I have one with the KB crank and Tee Dee top end. It is a screamer!
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Cool! Thanks, Larry!
Robert
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Back in my FF days I bought several of these with the duel needle valve setup and converted them back to single needle valve with bored out intake. Ran them on preasure. They were totaly useless for RC and they sold them at 50% off. The single needle body only cost $.25 back then. I liked them beter than the TD.
Ed