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Building Tips and technical articles. => 1/2 A building. => Topic started by: frank mccune on January 28, 2021, 10:51:15 AM
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Hello All:
I was gifted two of these engines and am curious as to what airplane I should build for them.
How well do they run for u control?
Comments/suggestions
Tia,
Frank
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The OK Cub .049A I had years I flew most of the 1/2A kits available back in the late 50's and early 60's. I even out flew a Golden Bee a club mate had on a combat wing by Consolidated. When they came out with an ad for the .049A a couple of years ago I bought two. Put them on a block of wood and tried to run them. Even had some 20% nitro fuel I tried on them. They would run the prime out and quit. Checked the fuel lines and needle valve for leaks. Finally got disgusted and put them away in the shop. I still have my original in the shop some where. Hope you have better luck with yours. D>K
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Hello All:
I was gifted two of these engines and am curious as to what airplane I should build for them.
How well do they run for u control?
Comments/suggestions
Tia,
Frank
If you can get them to start. I never got mine to run past the prime.
Ken
I see I am not the only one!
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My first useable engine was a Cub and it ran just fine. I have had a few since and they all run. I even hopped one up to at least Cox Medallion standard or better. Had it on a 1/2 A Spacer at Taft and coming back from a flight a fellow modeler was flabbergasted and said “That’s a Cub?”
They can run just fine and can be hopped up with a few simple mods and really hot fuel. The compression is low, the fits tend to be loose, so they can handle the Nitro just fine. A hot battery for starting is a good thing. The best mod is to substitute the needle assembly from a Cox rtf backplate for the Cub one. (more later) Orient the exit hole about 15 deg below horizontal for optImum fuel draw.
There is a weird ledge in the port in the crankshaft that obstructs flow. I grind that smooth. I also clean up and smooth the entry to the bypass ports. If truly inspired, the crankshaft balance can be improved. With all this done you can amaze your friends with what a Cub can be.
An ideal model for a stock Cub is the 1/2A Snapper. Full pattern capable on very light lines. Not quite so good would be the Brodak 1/2A kits unless you lightened them up a lot! Perhaps a Goldberg Jumpin Bean is in the ballpark.
If all you want is to go round and round, of course all the ScientIfic and Blackhawk replicas would be fine.
The Cub needle really sucks. It pretty much works by a blunt end shutting off the fuel hole. Almost an all or nothing approach making perfect adjustment impossible. Not the standard smooth taper giving easy control of the metering. Chamfering the top of the venturi would be a good thing too.
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Thanks Larry, may have to find mine and see what can be done. D>K
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I was never a OK Cub fan. Then a co-worker (a good friend) gifted me a couple of engines and tin box of spare parts and whatnot from his childhood. Said he was trying to get the house organized. So I proceeded to clean them all up and put some of the missing parts back on. They were looking pretty solid, so I told him how they came out. He said he regretted giving them away so I immediately offered to give them back. I walked back to my office and grabbed 'em right then. I had hopes that the elaborate plot would get us another retread modeler and club member. Still hoping, but guess now I really need to twist his arm. Would love to see them mounted to one of his original-type models. Probably a Zig-Zag or somesuch.... although if you are going to go Musciano, ya really ort ta go with the Cyclone.
I'm not sure it is legal in the USA to hop up a Cub. I think that would fall under "indefensible acts" or something like that. But Larry does like to live dangerously....
The Divot
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Our OK Cubs run well
https://youtu.be/VUeZQqyW-NI
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Cub Controller by Walt Musciano :)
https://outerzone.co.uk/plan_details.asp?ID=5562
Designed for the cub way back when!
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I love it Dane, loud little suckers. I have a .074 in my Dakota free flight and it has a note to it. If you ever had the pleasure to hear the OK .19 run, you will be surprised how loud that is.
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I’ve been curious about the Sig Mini Zilch. See: https://sigmfg.com/collections/control-line-kits/products/sig-berkeley-mini-zilch
Cute little plane, Maybe the Cub would be an appropriate engine?
NormF
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I think the plane would be too small. It was designed for the old .020 K&B
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I think the plane would be too small. It was designed for the old .020 K&B
The Cub will work OK. I flew one of the prototypes with a Babe Bee with no problems.
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The Cub needle really sucks. It pretty much works by a blunt end shutting off the fuel hole. Almost an all or nothing approach making perfect adjustment impossible. Not the standard smooth taper giving easy control of the metering. Chamfering the top of the venturi would be a good thing too.
Yup, I have that problem on both of mine, the A & B. There is a bad leak around the threads of the needle. They use an odd split collar around the needle, which makes sealing with a short piece of silicon fuel line nearly impossible. The needle is very twitchy, hard to get a good consistent run.
Thanks, I think your idea of a Cox NVA from an RTF back is a good approach to try. I did that with a Testor McCoy .049 Rotomatic to fix its botched NVA (bought used off an Internet auction).
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My main complaint with the Cub .049A was the plastic tank. Mine appeared to be shrunk and distorted. The leaks around the mount screws flooded the engine while starting. Had to use an external tank and got some good runs that way.
Bill
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I love it Dane, loud little suckers. I have a .074 in my Dakota free flight and it has a note to it. If you ever had the pleasure to hear the OK .19 run, you will be surprised how loud that is.
I have lots and lots of 1/2a Cubs, up to the .099 but I don't have a .19! Now I gotta find one. Lol
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Cub Controller by Walt Musciano :)
https://outerzone.co.uk/plan_details.asp?ID=5562
Designed for the cub way back when!
I've never seen this model, but I just downloaded the plans. I gotta have one!!
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The Cub needle really sucks. It pretty much works by a blunt end shutting off the fuel hole. Almost an all or nothing approach making perfect adjustment impossible. Not the standard smooth taper giving easy control of the metering. Chamfering the top of the venturi would be a good thing too.
So all I did was remove the needle and then got some pliers and slightly crushed the part the needle screws into. Just enough to make the needle hard to turn. Makes it easier to creep up on the sweet spot because it’s harder to turn too far. Also because of the slight bind, once it’s there it stays. Over doing this can ruin the part. If that happens, follow Larry’s advice and use a Cox needle assembly.
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I had a Cob .049A on a Scientific "hollow log" back in the '50s. Put on very large elevators and had fun doing the "Sabre Dance" with it. The engine wasn't a "one flip starter" but ran really well.
My experience with several .049 to .099 Cubs in the '50s was (1) the good ones were usually very reliable and strong, and (2) the poor ones weren't worth wasting time on - but they were usually few and far between. I rather suspect more recent products were of lesser quality.
Dennis
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My main complaint with the Cub .049A was the plastic tank. Mine appeared to be shrunk and distorted. The leaks around the mount screws flooded the engine while starting. Had to use an external tank and got some good runs that way.
Bill
One danger with the plastic tanks is that after a few overtightenings of the tank screws, the tank compresses, requiring the screws to be tightened in further than they are supposed to be. The upper screw is supposed to be into a blind hole, so either the screw bottoms out and can't be tightened enough to stop the tank leaking, or when you mention flooding, someone has overtightened the upper screw and punched a hole into the crankcase allowing fuel to be sucked directly into the crankcase past the screw threads. This can be corrected by sealing the threads of the upper screw if it hasn't damaged the case too badly. Maybe shorten the screw before it punches through.
Rod.