Backplates and bees

Hello Paul , what Fred said and the plastic ones can warp easier than the metal, seal is a necessity to make one perform at it's best !! What are you working on ??

I find the air passage through the tank more important.

Aluminum safe sealant takes care of air leaks... mostly.

Screens don't help max RPM but do make the engine harder to get trash in the reed.

Yes the diameter of hole in the back plate matters. I simply choose to not fuss with it especially since I mostly run plastic backs and it is very easy to damage the hole so the engine won't run. Anyways the plastic backs are already larger holes than the oldest backs.

Phil

Thanks for your answers guys.

I knew there were variations in the cylinders and glow heads, but now I am discovering that the backplates also have some differences. Would be nice if an expert could write on those differences on the nice Cox engines Wikipedia page.

In fact I just bought a .049 on eBay. I thought it was a QRC but now I understand it is made up of various Bees parts. As soon as I receive the engine I will take a few pictures to show you the parts.
I originally bought it for my almost finished Li'l Jumpin' Bean.

I also own a GB and a BW, both powering 1/2A RC models. I bought my GB mark II at Bernie's but I don't like the plastic backplate. So I may put on it the metal backplate of this engine I just bougth, if it is compatible.

Speaking of fuel leakage, I do have some problems with my GB and BW. I almost sorted out the problem by putting a short piece of tubing on the tank upper fuel inlet. My BW has a metal backplate. But I don't remember having any leakage issues with my Babe Bees when I was young and hairy and flew control line models - and I was not very careful back then.

Coming back next week with the pictures.

Paul

Here are the pictures.

It seems to be a QRC without the muffler and with a hot glow head.


I have cleaned up the engine.


The cylinder has slit exhaust ports, 2 bypass ports, no bypass booster, no SPI, no tapered grind and no number engraved so this leads us to a post 96 QRC.



The glow head is clearly a #1702.


The "venturi" diameter is 3.5mm the same as this plastic backplate I bought at Cox International for a stunt tank.

I think the QRC had the 1702 glow head as standard to offset the power loss the muffler causes. On the other hand, my very brief tests (with standard bees with similar cylinders to yours) revealed that in my case the muffler did not cause a power loss, and the 1702 head did not give any advantage. I cross-tested all the combinations... The only thing the 1702 caused that the engine was a bit harder to start and a lot more sensitive and finicky about the needle setting. I used 10/25/65% fuel mix.

I think you may have measured the diameter of the recess on the backplate where the venturi is seated, that should be the same in all backplates as all backplates and all tanks are interchangeable (AFAIK). The differences are in the beginning of the venturi, I think Roddie recently posted a picture of pair of Golden Bee tanks with different venturi diameters.

Have you compared the tank venturis on your BW and QRC?

KariFS wrote:Have you compared the tank venturis on your BW and QRC?

Thanks for the answer. No not yet. I will do that after my next flying session when I will clean my BW.

Paul_BB wrote:Here are the pictures. It seems to be a QRC without the muffler and with a hot glow head.



I have cleaned up the engine.



The cylinder has slit exhaust ports, 2 bypass ports, no bypass booster, no SPI, no tapered grind and no number engraved so this leads us to a post 96 QRC.

Not sure, but I gather that the QZ with 5 cc tank was replaced by the non-throttled Q-R/C with 8 cc tank some time down the road, may be a decade later? Peter Chinn did a write up on the QZ in May 1967 Aeromodeller.

sceptreflight.com Model Engine Tests/Cox 049 QZ

Eliminating SPI and adding an additional transfer flute (like yours) made it run more efficiently when muffled. With SPI and muffled, there would be recirculating of the inert exhaust gases diluting the fuel charge and reducing power. Description of the cylinder appears to match Peter's description.

My early 1980's R/C Bee had decent power and flew my single channel 36" span Minnie Mambo with authority. AFAIK it had the Q-R/C cylinder, but I'd have to check whether it had slit exhaust or not. KRD quick blip throttle was nice as it added a new perspective to rudder only flight. I had it set up where the throttle ring was fully closed except for the little peep cut out for idle, Pushed fully ahead exposing 1/3rd the cylinder exhaust for medium RPM, and full throttle midway.

I looked at this forum's article on cylinder descriptions, but wasn't clear on when slit cylinders were introduced. A friend gave me a donor engine from his Cox Sportavia R/C powered glider that he flew in late 1970's. It has slit cylinders. Black Widow that I have from the early 1990's has the plastic tank back and your has metal. Since Estes built post 1995 engines with parts only from Cox, I think your specimen could go back earlier than 1996.

The fact yours has signs of very little wear (light mounting marks) and metal tank back with anodized tank shows me that you have indeed gotten a prize.

I suppose if you wanted to upgrade it, both Cox International and Ex Model Engines have Tee Dee .049 cylinders with SPI.

That head is correct for a QRC. It supposed to make up for the lack of SPI.

Yes, Peter Chinn mentioned the cone-like head chamber for higher performance versus the hemispherical for the Babe Bee. Those plus the additional intake flute on the cylinder made my R/C Bee a performer on Minnie.

I'm guessing that Cox Hobbies prior to Estes probably went with the non-SPI dual exhaust slit cylinder due to reduced costs in manufacturing and making the sport engines suitable for muffling. Someone like Larry Renger might be able to further clarify details.

Nice looking engine Paul, appears the muffler was taken off from git go no marks at all , and very little use ... I personally don't care for the slit cylinders At the beginning of me trying to get one slit to run i never did so that's probably the reason ??

Hi Paul, The Lil' Jumping Bean is a nice little model. I don't have any plastic back-plates for the integral-tanked Cox engines.. but I do not like them for a few reasons. #1 being that they're not as durable as the metal back-plates. I also don't like the fitting for the internal fuel-line/pick-up. The old metal back-plates have a distinct "barb" to hold the fuel-line secure. The newer plastic ones don't. If the fuel-line falls-off this fitting; you won't know it. Your engine will run for a short time.. until the fuel moves away from that un-connected fitting; which would happen very quickly once airborne.

I personally use small-size "Dubro" silicone fuel-line in my tanked-engines. Its "elasticity" grips the barb on the metal back-plates.. and stays-put. Be sure to cut/size your fuel pick-up line; so that it draws fuel from the extreme outer-side of the tank-wall.. outboard to the flight-circle.

The later Cox "ARF" model-airplanes used a plastic "horseshoe" back-plate which I highly recommend. This later back-plate has four holes for radial-mounting.

This is what it looks like..



You would use an external fuel-tank with this type of back-plate. It's compatible with your Bee engines.. and uses shorter 2-56 size screws to mount it to the crankcase. The Bee (reed-valve) engines draw fuel very reliably. Don't hesitate to try one of these on a little stunt-model.

Thanks everybody for your comments, write up and for the piece of history. My engine is not in pristine condition. One fixing bracket on the backplate is a little bit bent as well as one of the fuel tank screws. But overall, I am largely satisfied with the deal. I have just ordered the dis-assembly and assembly tools as well as the piston reset tool. I want to thoroughly clean up the crankcase and crank.

Cox engines are wonderful. I suppose we have all spent our adolescence flying Cox model airplanes.

I'll come back next week with the air intake comparison between this engine and the original BW I bought on eBay last year.

Here are the pictures for means of comparison of the BW and QRC backplates. Note : I have thrown away the QRC backplate debris screen, I have ordered a new one.


BW right - QRC left



The QRC air intake is larger than that of the BW


#3 and #8 are engraved on the BW and the QRC backplates respectively


Note that the fuel inlets on the BW backplate have been sealed

Paul_BB wrote:Here are the pictures for means of comparison of the BW and QRC backplates. Note : I have thrown away the QRC backplate debris screen, I have ordered a new one.


BW right - QRC left. The QRC air intake is larger than that of the BW

This would be understandable. The BW has SPI, so it obtains a puff of fresh air into the crankcase when piston is near TDC. The QRC doesn't have SPI and as such must get the same amount of air from the venturi opening. But since it is an earlier back, perhaps originated with the first Golden Bees?  

Note that the fuel inlets on the BW backplate have been sealed

Looks like a machinist modified the die by plugging holes. I forgot where I read it, but IIRC it was an earlier back for the Golden Bee with stunt tank, might have carried into the BW. Or, if an Estes era engine, assembled from left over parts spares. Brand new, the bright gold colored backs contrasted with the anodized tank would make this cosmetic flaw hardly noticeable.

Perhaps one of the Cox guru's will be by to clarify the mystery.

GallopingGhostler wrote:
This would be understandable. The BW has SPI, so it obtains a puff of fresh air into the crankcase when piston is near TDC. The QRC doesn't have SPI and as such must get the same amount of air from the venturi opening. But since it is an earlier back, perhaps originated with the first Golden Bees?  

Looks like a machinist modified the die by plugging holes. I forgot where I read it, but IIRC it was an earlier back for the Golden Bee with stunt tank, might have carried into the BW. Or, if an Estes era engine, assembled from left over parts spares. Brand new, the bright gold colored backs contrasted with the anodized tank would make this cosmetic flaw hardly noticeable.

Perhaps one of the Cox guru's will be by to clarify the mystery.

Thanks for the explanations GallopingGhostler.

GallopingGhostler wrote:

Paul_BB wrote:


BW right - QRC left. The QRC air intake is larger than that of the BW

This would be understandable. The BW has SPI, so it obtains a puff of fresh air into the crankcase when piston is near TDC. The QRC doesn't have SPI and as such must get the same amount of air from the venturi opening. But since it is an earlier back, perhaps originated with the first Golden Bees?  

That's interesting George. It's made me re-think why my two Golden Bees have different size air-intakes/tubes. It's a mystery that I'll probably never solve.. since I can't identify which cylinder came with which engine. The parts were mixed-up long ago.

Roddie, actually considering if one were to participate in a vintage or nostalgia event, such minute details wouldn't really matter, except to the most scrutinizing individual who had a deeply intimate knowledge of it.
(Could be wrong, but I gather these are certainly not antique auction shows. )

Might have bearing in a museum where someone wanted to be as technically and as historically accurate as possible.

Seeing that more and more engines are being released through  estate sales and auctions due to a baby boomer death, and many at such reasonable prices leads me to conclude that it is better to make use of it to our own satisfaction, because our loved ones may not appreciate them as much as we do, and we can't take it with us when we pass on.

One of the bigger frustrations for any OCD guy EVEN with New in Box Original Cox engines ...obviously later with Estes it got more pronounced to have various mix matches

BUT this is true...even if I do not have photos to prove it

Way back when the just released and much advertised Black Widows where introduced IIRC around 1970~72...MY local Base Exchange got 25 of them

I suspect I was one of maybe 3 guys interested as they stayed mostly on the shelf for a full year

One day ( I think late 1972) they were all in a end cap bin for $1.00 liquidation sale and that day I did not buy my monthly comic book series--- instead brought home 3 new BWs

I only ever used one--- and two got stored until 2012 when I came BACK

Point is of my three Cox initial production versions two have vastly different back plate openings

My oh my this stuff would have been some much easier if MFGs back in the Day had serial numbers and kept track of LOTs and design changes

fredvon4 wrote: Way back when the just released and much advertised Black Widows where introduced  IIRC around 1970~72...MY local Base Exchange got 25 of them. I suspect I was one of maybe 3 guys interested as they stayed mostly on the shelf for a full year. One day ( I think late 1972) they were all in a end cap bin for $1.00 liquidation sale and that day I did not buy my monthly comic book series--- instead brought home 3 new BWs. I only ever used one--- and two got stored until 2012 when I came BACK. Point is of my three Cox initial production versions two have vastly different back plate openings.

I recall BX pricing around then. I picked up a Cox Babe Bee to power my 22" span Sterling Beginner Eindecker in 1973, while in AIT ("A" school). It cost me all of a couple bucks, ditto with the .020 Pee Wee for my 27" TopFlite RC Schoolboy trainer at the Naval Exchange in Naval Amphibious Base, Little Creek, VA (Virginia Beach area. Back then, the exchanges did not take a portion of profits and passed onto morale, welfare and recreational [MWR] functions. Cost savings to the max were passed on to us, basically it was "cost plus" like a Sam's Club.)

That is an interesting factoid, Fred. Are the BWs' cylinders ported exactly the same, or is there a corresponding difference there as well?

My oh my this stuff would have been some much easier if MFGs back in the Day had serial numbers and kept track of LOTs and design changes.

They used to produce these engines by the tens of thousands annually. Costs were so competitive, that not having to stamp serial numbers kept costs down I imagine. There was very little incentive to serialize a very low cost engine, IMO.

Herkimer actually had serial numbers on their Cub .049 for about the first year or so, until they figure there was really no need to do so.

GallopingGhostler wrote:I recall BX pricing around then. I picked up a Cox Babe Bee to power my 22" span Sterling Beginner Eindecker in 1973, while in AIT ("A" school).

I learned to fly CL with the Sterling Eindecker in 1975. But my first CL plane was the Cox PT-19. Unfortunately I crashed it the first time I flew it due to PIO (Pilot Induced Oscillations).

George I do not know if the internals were different.
I think the day I bought them I was still a dependent (Army Brat) and the BX, now that I better remember, was actually the Navy Exchange on Alameda Navel Air Station

I just remember taking each engine in hand and doing a look over of each. I was mildly curious that one of the three had the visibly larger air inlet on the back plate. They were repackaged (put back in the twist wire hold down in the package) and I set two of the three in my closet for some day....
The one I used replaced my tanked Bee on the nose of my first Lil Satan
I never did try to think why, or if it was, or was not, better that way.

I was still too ignorant to even know how precision the Cox engines were. Thus ended my curiosity

I intended to build more models and use all three but before that happened I got drafted and Army life got in the way

In fact in 2012, when I offered the two unused BWs in a trade for a couple of used TeeDee .051s, I did not remember that (air inlet size) discovery or let the new owner know one of the two was slightly different