Questions about OK Cub .049s...

Mike Mulligan Fri Jun 26, 2015 6:08 pm

HI Guys,

I have a couple of OK Cub .049s, two with tank mounts and one beam mount. I have never run one of these and I was wondering how they performed. I have heard that they are not as powerful as the Cox engines, but other than that I have no info. I notice the prices for these things on the 'bay seem to be pretty low, which might indicate that demand (read popularity) is pretty low.

I have one of them bolted to an (unfinished) hollow log model, and another on a little scratch-built stunter (also unfinished) that uses an old Hyper-Viper wing. I like 1/2A models a lot, but all of my small engine experience has been with Cox hardware so I'm kind of wondering what to expect.

Any advice on fuels, props, plugs, etc. would be greatly appreciated!

Thanks in advance!

Mike

Ken Cook Fri Jun 26, 2015 8:05 pm

Mike I was never impressed with the performance from the .049. I witnessed a few in the Musciano events and I can say with all honesty they're even worse. Hollow Log planes don't fly well to begin with and it takes a lot of work to make them fly well and horsepower is key. I have a few members who totally revamped the Golden Hawk out of molded balsa and carbon fiber. Back onto topic, I would polish the crank for starters. I would ditch the needle valve. It's amazing it even works. I've seen Cox spraybars and needles retro fitted for greater needle accuracy. As far as nitro is concerned, I would keep the nitro in the 35% range because they do handle nitro well. I'm a fan of 5" props on .049 engines. I just find them to unload the engine and keep the run and power consistent. The OK cub .049's without the tank is the engine I'm referring to. I have no experience with the tanked engines.

Oldenginerod Sat Jun 27, 2015 6:45 am

Mike, it depends which .049 model you have. The first model used an alloy radial mount tank as an option, but was also beam mounted. If it has the red plastic tank and no beam mount it's the .049A. The .049B is effectively the same as the A only with no tank and both beam and radial mount. I've never had much luck making the first .049 model run well. 049As can run pretty well if you get a good one, but there were some real quality issues. I've not had much success with the plastic tanks sealing or mounting solid. The Bs that I've run seem to do a good job on the bench, but I haven't flown one. They don't seem to cope well with a large prop, so 5", as Ken suggests, is probably a good choice. Mine run fine on 25% nitro and just use a standard short hot plug. I get about 14,000 rpm out of them, maybe a little more.

Rod.

rsv1cox Sat Jun 27, 2015 12:39 pm

I'm glad to see this discussion regarding these engines. I have scads of them of every variety but have never ran one. Dreary rain filled day here in WV, a good day to fire one up.

These are so cheap on ebay, even new one's go for a song. They seem to be well supported for parts etc. This one looks to be the first model with the metal tank. Might it be the best of the lot?

http://www.ebay.com/itm/OK-Cub-049-Control-Line-Model-Airplane-Engine-with-firewall-fuel-tank-/131541241885?pt=LH_DefaultDomain_0&hash=item1ea078101d

Oldenginerod Sat Jun 27, 2015 1:32 pm

rsv1cox wrote:This one looks to be the first model with the metal tank. Might it be the best of the lot?

I don't believe so. They had poor port timing and often the crankshaft port was finished poorly. They were long stroke so they never really got up and sang in my experience with them. The tank for these also fits the .074 which had a very similar crankcase. I believe the .049B which followed was a far better engine for functionality. The latest crop of .049s & .06s with the rear reed valve were better still.

Rod.

GWILLIEFOX Sat Jun 27, 2015 7:14 pm

I fouled up the formatting on my test runs. The OK Cub listed below is an original long stroke. Below it are runs of the .049B

The bottom of the 049s is marked "CUB" or "049-". The Cub is the first mass produced .049 OK just called it a Cub, not an .049. As was said it is a long stroke; .390" bore x .415" stroke. It was originally equipped with and Arden glow plug.

All other OK .049s have a .390"bore x .360" stroke. Last fall I ran some tests to see just how fast these engines were and what effect plugs had. I ran a Cub and an 049B.

OK Cub
5" Kaysun OK long plug 13,800
5" Kaysun Arden long plug 14,100

6x3 gray TD OK long plug 9,600
6x3 gray TD Arden long plug 10,000

7x 31/2 gray TD OK long plug 5,800
7x 31/2 gray TD Fox long plug 6,700
7x 31/2 gray TD Arden long plug 8,000

.049B
5" Kaysun OK short plug 16,400
6x3 gray TD OK short plug 11,600
7x 31/2 gray TD OK short plug 8,900

The original Cub used long plugs. It was designed to be used with the Arden plug as it was the only one available and it does like it.

Ken Cook Sat Jun 27, 2015 9:11 pm

I have some Arden plugs in my O&R .23's. As old as those things are it amazes me they still work. A real testament to the quality of things made from years back. Ken

gcb Sun Jun 28, 2015 1:27 am

One problem some had is a nearly flat needle that goes blubbering rich to over lean in less than a full turn. For these, I added some taper to solve the problem.

As mentioned above, Cubs have a lower compression ratio so they like a good amount of Nitro.

Remember these were developed ~1950 and early fifties so don't expect modern power. They have powered countless models designed to use the power available from them.

Good luck with them.

George

jayd3 Wed Jul 01, 2015 1:28 am

I have some Cubs as well and have only ran the .024 which ran quite well ,I will be trying some of the others, but as the last poster said we have to remember these were made in the 1950's with designs going back to pre war so we can't expect modern power from the materials and machine work of that time even if it was the very best at the time, just as you can't expect late model Norvel performance from a Cox.
There is quite a history behind the OK Cub just as there is behind Cox with more than a few similarities.

Jayd

chevyiron420 Wed Jul 01, 2015 12:18 pm

My opinion on these engines and similar types is to judge them each by performance. In other words, get them on a test bench and give them a good break in. I found that cubs need a lot of break in.
About 12 years back I was trying to get kids involved in cl flying and needed engines that I could afford to give away. At the time Ted Brebeck (sp) was selling A engines for 14.95 new in bag. I bought some as well as plugs and other parts. Most of the engines I got had a carb extension, restriction in them. I always ended up drilling them out some. Most of mine would equal a single port babe bee in performance. There are some engines that use a glow head that will interchange with a cox head, and as you would expect they are faster.
I have a B engine on a baby ring that I cut a second bypass in the crankcase and that woke it up some! I tanked the thing to fly for five minutes and used it to practice stunts with. I cant imagine how much run time is on it, but its a lot. I have flown the airframe ragged but the engine is like new still.

GallopingGhostler Wed Jul 01, 2015 8:50 pm

Following I think provides a reasonable comparison in performance.

GWILLIEFOX Engine Tests (25% nitro?):

OK Cub .049A (with tank)

PROP	PLUG	RPM
5" Kaysun	Arden long	14,100
5" Kaysun	OK long	13,800
6x3 gray TD	Arden long	10,000
6x3 gray TD	OK long	9,600
7x3-1/2 gray TD	Arden long	8,000
7x3-1/2 gray TD	Fox long	6,700
7x3-1/2 gray TD	OK long	5,800

OK Cub .049B (without tank)

PROP	PLUG	RPM
5" Kaysun	OK short	16,400
6x3 gray TD	OK short	11,600
7x3-1/2 gray TD	OK short	8,900

Peter Chinn Engine Test (15% nitro):

Cox QZ .049 (Aeromodeler May 1967, adjusting for un-muffled use)

PROP	PLUG	RPM
6x3 Top Flite	Cox Head	14,300
6x4 Top Flite	Cox Head	11,800
7x3 Top Flite	Cox Head	10,000

H.R. Warring Engine Test (15% nitro):

Cox Babe Bee .049 (Aeromodeler May 1961)

PROP	PLUG	RPM
6x3 Top Flite	Cox Head	14,400
6x4 Top Flite	Cox Head	13,000
7x4 Top Flite	Cox Head	10,000

Summary from test reports using a 6x3 prop:

	OK "A"	Frog .049	OK "B"	Wen-Mac Roto-matic	Babe Bee	McCoy Red Head	Cox QZ	Black Widow	Testors 8000	Cox Tee Dee
BHP		0.037		0.055	0.056	0.062	0.065	0.078	0.094	0.105
BHP RPM		12,000		14,500	13,000	14,800	15,000	15,500	18,000	22,000
6x3 RPM	10,000	10,600	11,600	14,000	14,400	14,200	14,300	14,600	15,700	18,400

Overall I think these comparisons are relatively reasonable representations. Since the QZ is the start of the heritage of the Sure Start with elimination of SPI and designed by the masters Bill Atwood and Dale Kirn, it set the standard and I think that more or less this would be about where the Sure Start would fit.

Cox Pee Wee was rated by Peter Chinn in the March 1976 Aeromodeller report as having 0.035 BHP at 18,500 RPM. It turned a Tornado 5x3 prop at 10,900 RPM. Thus, the OK Cub .049's are more powerful than the Cox .020 Pee Wee, but at the lower end of the spectrum powerwise with the .049's. The OK Cubs are not bad engines, but compared with other .049's that came along later, not quite as powerful.

Not every airplane needs to have a powerhouse of an engine, and thus married to the right airframe, they should prove satisfactory. Many Scientific 1/2-A CL kit planes show an OK Cub "A" or "B" on the plans and box.

I'm sure some may disagree, and numbers can vary due to head or plug used, prop used, fuel used, internal improvements over time, venturi and needle modifications, etc., but that is not my intention. So, if I bent anyone's feelings, my apologies.

roddie Thu Jul 02, 2015 1:46 am

After reading Bob's OK Cub thread and this one.. I have some questions/observations about props for the OK Cub .049 engine. The red 5"D. Kaysun prop's pitch hasn't been mentioned.. nor it's weight. This got me to wondering which props that I have here in my shop, might be selected for my Cub .049B. Looking at the charts shown; RPM#'s for a 6 x 3 (Cox brand stated) seem to average 3500-4000 less than the 5" Kaysun listed.

I have four different 6 x 3 props.. and there is quite a difference in their weight. Maybe none of this matters.. but the only 6 x 3 listed on the Cub .049 chart is the Cox grey one.

I just weighed the four different 6 x 3's that I have.

Cox grey 5gr.
Cox black 5gr.
Zinger (wood) 4gr.
Series "25" (wood) 2gr.

My scale may not be super accurate.. but the wooden series "25" prop is less than half the weight of either Cox variant. I haven't run the series "23" props on any .049 engine yet.. because I have only had them a short time.

To make a fair assessment of performance.. I'm curious as to the pitch and weight of the red 5"D. Kaysun prop. I also have Cox 5 x 2 (2 blade), 5 x 4 (2 blade) and 5 x 3 and 5 x 3.5 three-blade props. Any of these could be slightly cut down and re-balanced to see if performance improves. Maybe the lighter weight wooden props are the way to go on these old engines.. as well as plenty of nitro and castor in their fuel.

The needle valve is a strange arrangement.. externally threaded spray-bar with a split tube collar on the needle. I haven't removed it.. but it makes me wonder if the tube part is threaded.. or whether the aluminum self-taps onto the spray-bar? It was probably a lot cheaper to manufacture, than an internally threaded spray-bar.

GallopingGhostler Thu Jul 02, 2015 2:47 am

Regarding the Kaysun props, since the pitch wasn't given, this is why I didn't use the 5" props for comparison. To be fair, one would use the same fuel, consistent atmospheric conditions with air temperature, humidity and barometric pressure being close, and same prop make and model. Somehow I feel that the Babe Bee RPM is about 1,000 too high.

Yes, the needle is a strange arrangement and I found it prone to leaking air. I was able to stabilize this somewhat by removing the spring and putting a short length of small silicon fuel tubing to help seal the threaded end. It wasn't perfect but I got more consistent runs on my OK Cubs.

Overall it shows that the OK Cubs are toward the lower end of the .049 spectrum. I figure it fits in where one needs more power than a .020 Pee Wee but less than a Golden Bee or Sure Start. Joe Wagner's Dakota F/F Bipe comes to mind.

I don't get to fly lower powered .049 stuff here in NM because of the higher elevation and our windy atmospheric conditions, hence why the academic evaluation. May be one of these days when I live in a place of lower elevation with calm mornings or evenings, would be able to truly enjoy these little jewels of engines.

My Q-Tee with Norvel .061 Big Mig zooms around rather lively, but has great wind penetration. I kind of enjoy its hotter performance as a result.

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