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OK Cub .049 Empty OK Cub .049

Post  rdw777 Fri Jan 20, 2023 5:22 pm

I bought this one when they were advertising in the magazines in mid to late 90’s…. I have never ran it until today, Just kind of on a whim….. Took a while but I finally figured out it likes a really healthy prime…. After I got used to it , It cranks and runs fine…. Power is nothing like a Bee, But I was expecting that….. Best it would turn a Cox 6-3 was
10,300 rpm on Fitz 24%…. It did run fairly steady though and needled better that I expected after reading that their blunt tips made them finicky to adjust… Wasn’t that bad….Just not a lot of power…. Not disappointed, Still a neat little engine for what it is….I’ll find a job for it on something one of these days…. Thoughts from other Cub owners?…. OK Cub .049 3df71e10
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Post  rsv1cox Fri Jan 20, 2023 6:16 pm

I picked up a few on ebay.  Nice looking engine and an easy starter.  I probably ran Cox 25 or 35% but did not tach it.  I like the stampings and presentation.  For me the attached tank always presented a proble mounting in an airplane.  I always opted for the Cox radial mounts.

OK Cub .049 Ok_cub13
OK Cub .049 Ok_run13
OK Cub .049 Ok_cub14

Looks like you put a little shine on your's Robert?
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Post  rdw777 Fri Jan 20, 2023 6:46 pm

Thanks Bob, That is a nice looking group you have there Thumbs Up ….. Actually the finish is just how I received it…. Looks like case may went through a tumbler or something at the factory…. I’ve read these later ones were a little hit and miss in quality control so I’m  just  glad I got it to run at all….
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Post  706jim Fri Jan 20, 2023 8:42 pm

I had one of those 0.049A. Wore it out in one afternoon's flying (maybe 40 minutes?) all castor fuel snow on the ground so no dust or overheat. At the end of that day zero compression. Guess I got one with a soft cylinder?
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Post  Ken Cook Sat Jan 21, 2023 5:26 am

The aluminum extension tube in the venturi stack is killing performance. It's like trying to breath through a coffee stirrer.
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Post  getback Sat Jan 21, 2023 6:36 am

I got two like it when they were going out for the last time , decided to run one like to never got it started like you said needs to bee about flooded to start and run . Needled pretty good with not a lot of power , it started better after first run but still needs a spring if you ask me LOL Cleaned it put it back up for now !
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Post  rdw777 Sat Jan 21, 2023 5:18 pm

Jim, Not sure why yours failed, But after reading up on them from a few sites on the net including here, It seems a random very few do wear out in a very short time… Others seem to have a decent life span… I don’t have enough experience with them to really know…. I only ran a few tanks thru mine and compression seems the same as when I started…It’s interesting to note that the Bee’s mounting screw pattern is the same as the Cub….. I’m guessing that was by design…

I don’t doubt Ken that the tube on the venturi is restrictive…. It is however .080 in diameter, larger than a Bee backplate….I may not be able to use that comparison though due to different  induction methods….I read somewhere one time (can’t remember where) they were installed as sort of a patch to help poor fuel draw or starting or something of that nature …. It does look like some kind of after thought …. The one on mine cracked the case a little when it was installed…OK Cub .049 9ac35a10

Thanks for sharing your experience Eric…. Sounds alot like mine…. Does yours have the pressed in venturi tube?
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Post  Oldenginerod Sun Jan 22, 2023 2:10 am

The venturi extension places the air intake higher than the exhaust ports, so that it draws clean air, not spent exhaust gas. I think on the Comet models it helped to keep the intake outside of the cowling
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Post  balogh Sun Jan 22, 2023 3:14 am

I have never had a OK Cub, but my guess is the most power-robbing part - as in COX engines with normal conversion heads- is the conventional glow plug whose thread gaps add to the compression space of the cylinder and reduce the compression ratio. It would be interesting to see how this engine re-energizes with a high compression Tee Dee head or let alone, a Kamtechnik turbo head...I am not sure if the OK Cub cylinder top thread dimensions allow the use of these, though..
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Post  Oldenginerod Sun Jan 22, 2023 4:43 am

balogh wrote:I have never had a OK Cub, but my guess is the most power-robbing part - as in COX engines with normal conversion heads- is the conventional glow plug whose thread gaps add to the compression space of the cylinder and reduce the compression ratio. It would be interesting to see how this engine re-energizes with a high compression Tee Dee head or let alone, a Kamtechnik turbo head...I am not sure if the OK Cub cylinder top thread dimensions allow the use of these, though..
Some of the later Cub .049s had a glow head that was interchangeable with a Cox one. The previous model Cub which used a standard glow plug had the same set-up as the earlier Cox heads, having the head seal at the top of the threads rather than the bottom. I'd suggest they would have had a huge improvement in performance using the later glow head.
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Post  getback Sun Jan 22, 2023 6:16 am

OK Cub .049 16743810
I couldn't find the one I was running this was the other but I feel sure it's the same bought 2 at 1 time
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OK Cub .049 Empty OK Cub A and R

Post  bsadonkill Fri Jul 14, 2023 6:21 am

I bought a .049R brand new for 20 dollars back around 2011. I bought a COX style glow head for it, plus I modified a COX style snap spring for it. The .049R is easy to start, especially with the snap spring. It seems a little slower than a Baby Bee, but I don't have a tach to check it. The .049A I bought in 2013 part of a limited production. It came with a replaceable glow plug style head, and a G-3 plug. I modified a COX snap spring for it also. The .049A is the one running with the eye dropper for a fuel tank. I have not used these engines in anything to date. I plan to use the .049A in Joe Wagner's Sioux model. I just need more practice starting and running it.OK Cub .049 116
OK Cub .049 215
 OK Cub .049 312
OK Cub .049 411
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Post  getback Fri Jul 14, 2023 6:50 am

I see you have the .049R hooked to a thrust gage how is that working for you ? I think EXModels sees them . Nice looking engines , like your mod for the starter spring , they need one Very Happy This Site Rocks!
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Post  bsadonkill Fri Jul 14, 2023 9:17 am

As far as the .049 engine mount thrust gage goes.  Well, if you look at the top you can see that the T-pin indicator fell out of it. Also, the graduates on the scale have no measurements. Plus, the sliding engine mounting is somewhat loose in it's holder. It shakes pretty bad if the engine is running rough. Overall, I think it's kind of cheap.
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Post  getback Fri Jul 14, 2023 9:51 am

bsadonkill wrote:As far as the .049 engine mount thrust gage goes.  Well, if you look at the top you can see that the T-pin indicator fell out of it. Also, the graduates on the scale have no measurements. Plus, the sliding engine mounting is somewhat loose in it's holder. It shakes pretty bad if the engine is running rough. Overall, I think it's kind of cheap.
Thanks kind of thought so but confirms <> WE had discussion some time back about this https://www.coxengineforum.com/t5779-engine-thrust-meter 2013 Very Happy
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Post  rdw777 Fri Jul 14, 2023 1:46 pm

Good to see another Cub running…. I like to bench run them just for fun…Maybe fly’em one of these days…. Sioux is a pretty plane…. Please post your build if you decide to go for it Very Happy
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Post  Ken Cook Sat Jul 15, 2023 6:07 am

I have the Sioux and the Dakota. I fly the Dakota with the OK engine installed in the inverted position. The Sioux has a horseshoe backplate with a Babe Bee cylinder.Both engines are using eyedroppers for fuel. The OK is a bit more problematic to get started because the needle valve is such a piece of crap. The height of the eyedropper impacts starting. If the eyedropper is mounted slightly high the fuel wants to run into the case which can flood it. A bit low and now the needle requires opening but the major disadvantage is the very end of the run. You don't want the engine to lean up abruptly especially the Sioux. It will almost try and loop but it stalls. This now takes it completely out of it's normal trajectory. I find a happy medium and I try to run the engine even with substantial downthrust a bit on the rich side. I don't have the room for a all out engine run for more than 10 seconds.
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OK Cub .049 Empty OK Cub A and R

Post  bsadonkill Sat Jul 15, 2023 7:07 am

Here is a picture of a Sioux with a Black Widow and a Cox International non tank backing plate. I had to use some bass wood squares to space the engine out a bit. This was due to the air inlet tube used on that style backing plate. It seemed to work alright as long as it was pulling hard enough to the left. This model was covered with Poly Span and clear dope, it was not very colorful. I know the needle valve setting is very touchy on the OK Cub A. I have also noticed the fuel line run is critical when it comes to running the fuel all the way out. OK Cub .049 117
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Post  Ken Cook Sat Jul 15, 2023 10:11 am

I put a MECOA diesel conversion head on my Cox .049 for the Sioux. I almost lost the plane that day. It went way out of sight. The bigger problem I have is when the engine quits, it stays up there forever and for some reason, it never spirals down in a circle for me. Murphy's law always has it going away from me. I found it better than a mile away in a soybean field. My buddy Frank had a drone with a camera and he flew it out over the field. He could see the red wings and we trampled through 4" high soybeans to get it.
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Post  GallopingGhostler Sat Jul 15, 2023 12:39 pm

Just curious Ken, but would the economy of the diesel (uses less fuel with longer run time) plus extra power (torque) be a bit more engine than the 38" (965 mm) 1949 Sioux nominally requires? Didn't Joe originally design it with a less powerful OK Cub .049 in mind?

I could imagine seeing it taking to the sky like a homesick duck with that diesel almost like a competition free flight. Your description of its flight seems to mimic that.

With that diesel, I could see it turn into a nice rudder only R/C plane.

Always wanted to build the Sioux, but wasn't until fairly recent the plane became available on Outerzone, long after the kits disappeared.
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Post  Ken Cook Sat Jul 15, 2023 4:19 pm

George the BMJR version is beautiful. Here is the first flight of my Sioux with a Davis Diesel head conversion. I'm not a big fan of the Teflon disc but they do work and I had this one working terrific. My engine also has the Davis Diesel shaft. My prop was a wooden Rev Up 7x3. https://www.youtube.com/watch?v=0p4KMvOXYCI
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Post  Ken Cook Sat Jul 15, 2023 5:30 pm

My flights after this were using the MECOA diesel head. That particular head offered easier starting and reliability but I still like the Davis head. After some out of sight flights, I went back to glow. I just found it easier to control the length of flights and power. Using the same prop, the .049 on glow works quite well. George you mention the Plasticote 7x2, that is a great prop for this kind of flying.
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