OK Cub 049R Question

I find the rear intake conversion on this Cub engine interesting. I believe the rear intake was intended for the Cub .049 A or B engine in 1960. In his book, "They Should Have Kept The Bear" by Ted Brebeck 1995, this engine is mentioned. I quote Ted's words. The OK Cub .049 RE 1960. Experimental reed valve intake at rear. Aluminum carb intake at rear, advertised, but not put into production in any quanity. In one of Ted's news catalog's from March 2008, he sold a conversation kit to make a .049 A or B engine into a reed valve/ rear intake engine. In the conversation kit that I purchased from Ted, it came with the new rear carb reed and needle assembly. Also included was a new blank crank shaft with no window that would replace the regular crank shaft. This complete rear conversion kit cost just $19.95 in 2008. To my knowledge it wasn't offered for the .059 reed engines, just the standard .049 engines. I have never mounted and run the conversion that I have, although I would like to see just how the engine would run with the rear intake as such. The Cub engines are really limited in their stock configuration to not much more than the 15,000 to 16,000 rpm at best. So other than the novelty of the rear intake, it was just an idea of, what if? Eddy

George, I know you and I have mentioned the OK .059 from time to time. I was fortunate to receive mine from Larry Scarinzi. Larry actually sold it to my son. He didn't want to do that but my son kept asking him for it. This is somewhat comical, Larry being a flat out combat guy with a attachment to a very low powered engine. Larry just said it was one engine that he could continuously rely on to fly free flight with. I have a 7x4 yellow Tornado on the engine. I've never really wound this engine up, I just run it as Larry did. Ted Brebeck prior to his retirement gifted me a new tank for the engine. I've become quite the OK fan these days. I really disliked them for years but as I dug deeper into them, they have quite a history and a following. I keep a small collection of runners of a variety of different sizes and offerings. I don't own a rear intake version as Matt shows. George you really need to run your engine, you might just be impressed with it. Ken

Appreciate the feedback guys! Definitely a bit strange compared to some other ones I've come across and can see if both ways either factory or aftermarket although if the latter it was done nicely.

I'll pull it apart and see what the internals look like as well. Will also measure the piston to be sure of the displacement.

Ken, as far as running, when my situation stabilizes, intend to do. Regarding Eddy's comment on RPM limited to 15K-16K, following web article gives some clues as to why.

https://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=304 Adrian's: OK Cub Reed Valve Models

Adrian's .06R OK Cub Reed Valve Engine description, power curves and props

On 10% nitro, brake horsepower (BHP) peaked at 11,000 RPM. So, given the props Adrian indicated, figuring about 1K RPM drop on the bench would unload in flight to around peak. So, an APC 7x4 would be optimal.

On 30% nitro, BHP peaked at 12,000 RPM. Again, one would want to select a prop with about a 1K RPM static drop, so that it would unload in flight to near peak BHP. Again, Adrian's data shows an APC 7x4 would be optimal.

Not all props are equal. I'm thinking the Masters Airscrew props have a bit more resistance (slightly lower RPM) than the APCs. Perhaps a Master's 6x4 might be optimal, too.

I know some are into tach racing, to see how fast one can get an engine to turn. One can boost RPM, but in this case with the OK .06R, you then put the engine beyond it's best thrust capability.

Some time back, I equipped a 40 inch wingspan Hobby Shack Cessna 180 with a 1965 Enya .09-III TV. Peter Chinn in his engine review stated that running a prop smaller than a 7x4 was impractical, because it would take the engine beyond its maximum HP. This I found out was true.

When I fitted it with an APC 7x3 prop, the plane designed for a Cox .049 Bee flew very .049 like. But when I put an APC 7x6 prop on, then it flew like it had a .09 on it, became a wonderful sport plane.

I also found out something interesting with hand starting. It became more manageable with wooden props, was more finicky in starting with heavier plastic props, but with wood, was quick starting and easier to needle. So, some engines don't like a heavier high inertia prop.

I really enjoy these types of posts. I find them very rewarding in terms of always learning new characteristics and traits of the vintage engines. Eddy, you need to post more. I always enjoy your feedback and experiences. George, I found many similarities that I already encountered with Adrian's post. Number 1 being the yellow Fireball, I never had a lot of success with red hot Fireball plugs. The posts seemingly always leak, the filament gets sucked out of the plug cavity and I actually ruined a engine as a result of this. I still have some reds but I use caution as to where I use them. The funny thing is that I've had some last and I've had some go south quickly.  There's no telling when it can happen  or how to differentiate. So, yellow it's been on the OK engines with terrific success. I've also noted the run excels when using Cox type glow heads. I never used a high comp head, just the standard. I found the OK engines do like the nitro and there's no harm in doing so. George, you mention this quite often about the 4 pitch props. OK engines as I've found really do benefit from the older period 4 pitch propellers and they can sing along just fine with a 6x4.