What makes the BW the strongest stock reedie?

That is an amazing run for a stock BW. Normally they turn 17K's.

Assuming it's all stock, then you got really lucky with factory fits. The 1973 BW is my favorite Bee type engine. I think a stock BW class would be a great addition to the Tach Race. If that happens you should send yours in!

That's fast considering it was a 4" pitch. You better enter that one in next year's tach race, it'll blow the doors off the rest of them.
Rusty

Never seen a Black Widow with that piston, didnt they stop using the three piece way before the Widow came out?

The Widow improved on the Golden Bee that had a single transfer port. with two transfer ports and larger Venturi it had more power. I have read that it had improved timing but don't know for sure.

Frankly, I'm surprised that it has a 3-piece piston Andras. I thought that those were very early issue on the Babe Bee's.. but I could be wrong.

I've posted these photos countless times.. but maybe you haven't seen them. They are of my two Golden Bees. I don't know the production-years of either.. and only noticed the difference between them recently.




The "right-side" parts have a larger .082" (2.08mm) air-intake opening. Unfortunately; I never kept track of which cylinders originally came with the engines. I'm pretty certain that both engines had the "non-slit" exhaust ports and thin-wall cylinders. I would assume that the "left-side" parts; which have a .0625" air-intake, were mated with a single-bypass cylinder.. and the "right-side" parts were mated with a dual-bypass cylinder. Note that the larger intake parts are NOT modified. The screen is in place on the backplate.. and the gold-anodizing can be seen down through the throat of the venturi. Both engines were in my family since new.

I've had a theory that the "right-side" parts were very late production Golden-bee. Maybe Cox did a short production-run of high-output Golden Bees.. just prior to the release of the Black Widow??? Cox did some funky things over the years. Maybe I have a rare engine.. I don't know when production ceased on the Golden Bee engine.. or whether Cox made "both engines" for a time, before discontinuing the Golden Bee. It very well could be; that a run of "BW" tanks were mistakenly gold-anodized. Rather than scrap them; Cox may have decided to fit them with GB anodized crankcases.. and "BW" backplates and cylinders??

Martin Hepperle's site states of the "Golden Bee"; "The cylinders have one bypass-port, a later version came a throttle-ring (#120-1) and had two bypass-ports. Due to the longer tank.. the GB has a slightly larger venturi-diameter (4.37mm vs. 3.57mm) at the reed-valve". My "smaller-intake" measures 3.97mm at the reed.    and the larger measures the 4.37mm.



3.57mm= 9/64".. 3.97mm=5/32" and 4.37mm=11/64". Nothing is mentioned regarding the orifice in the backplate.

Do any of the BW's have any "boost-ports" ground into their cylinders? None of my Bee cylinders (Babe Bee or Golden Bee) have boost-ports. Again; Mr. Hepperle's site states of the Black Widow; "The cylinder came with generous bypass flutes and extended port timing".

There's no doubt that the larger intake will produce more power. The original GB.. was basically a Babe Bee with a stunt-vented tank that held an additional 3 cc's of fuel. I'd love for this mystery to be solved.. but I've posted these photos many times.

Long ago I compared a #1 BW cylinder to a dual port Bee cylinder. They looked the same, but with my caliper, I found the bypass ports in the #1 were considerably deeper. Not longer or wider, just cut deeper into the side wall. I've never heard that mentioned, nor have I ever gone back and compared any others.

I didn't catch the 3 piece piston comment. Do you have a picture? An early BW would not have one. That's an early 50's thing. They are also not swaged, it's just a ball socket piston with a ball con rod and a snap in ring to hold it all together.

Thank you to all for the detailed answers.
So I gather the BW secret maybe around the venturi...

I may have misused the 3-piece piston denomination that now I realize was in the Thermal Hopper and other grannies.

The piston I talk about was in all older engines in the 60-s and 70-s with the socket  apparently swaged into the crown. Later engines had the socket machined from the parent material of the piston itself and have a flat crown. Compare the crowns of the BW and a Surestart:


On the rpm well I have always noted the COX engines spin the black 5x4 faster than the 5x3 and did not expect so...my favorites are the 5x4-s of Bernie pictured here with a 5x3:

Maybe the reason is the wider cord of the 5x3 than the 5x4? The 5x3 also looks to be a bit longer than the 5x4 so the 5 inch diameter is just nominal on the 5x4?

http://www.mh-aerotools.de/airfoils/cox_venom.htm

The Cox Venom is the strongest .049 reed engine.
Had large transfer ports and additional boost ports.
Due to the design speed was limited to 22,000 r.p.m. on the ground, only 1000 ever made.

Its looks like you might have a 4.5x4 prop there?
What is the total length of it?

The older 5x4 would not withstand revs around or above 20 krpm. The pitch changes and they bend forward....

A grey cox 5x3 prop would be a much better reference prop, in that respect.

The two pictured pistons are made the same, as far I know, there is just a machining difference on the top.

Thanks, Kris, I will measure both when I hit home this evening..I was rushing in the morning and could not do that. One thing for sure is that both have a dia 5" printed in the stem of the blades..if your screen resolution is good enough you may see that. But I would ask Bernie to chime in as I bought both from COX Int'l:

https://coxengines.ca/cox-.049-propeller-grey-5-x-3.html
https://coxengines.ca/cox-.049-propeller-5-x-4.html

The older pistons in my engines are all consistently the same as far as the top of the crown is concerned, i.e. showing off like made of 2 parts by swaging, so whether this is the trace of machining on all I am not sure..I remember having read this swaged piston design of COX somewhere but now could not point to where...Paul Gibbault as the one-time COX engineer may know it better.

I see this swage-kind of piston top on all my old 010, 020, 049 , 051 and 09 engines...the 050 R/C and the Surestarts and later TD-s that came in cardboard boxes (not in chrystal box) are the exception, and these were made after the mid 1980-s.The pistons in these all have flat tops.

balogh wrote:I took her out dancing in my garage this afternoon and tached her swaying Bernie's 5x4 black prop at 19,7k on my home fuel blend having 20% nitro, and with high comp head...similar reedies like the old stock postage stamp ones I have would do this job at around 500 rpm less or so (those are also real beasts but I do not exactly remember the numbers they ran when tached).

Back in the late 1960's, early 1970's, there were a few plans for entry level 1/2-A CL racing, I think they called it proto? These planes used the postage stamp engines, because they were decently powerful. Back in the 1960's, Carl Goldberg saw an opportunity for owners to make use of those engines once the RTF plane was totalled. Without convenient mount lugs due to the postage stamp back, Carl offered a nylon mount for a small cost. Bernie at Cox International had a stash of those recently but sold out.

BW has been always advertised as the strongest reedie - refer to its instruction sheet - maybe with the Killer Bee and Venom in exception.

Engines like the Venom and Killer Bee came later. When it came it out around 1974, it was the most powerful Cox production reed valve engine. This is what Peter Chinn had to say in August 1974 Aeromodeller:

sceptreflight.com Model Engine Tests Cox Black Widow

Peter Chinn wrote:THE COX 'BLACK WIDOW' is the latest and most powerful derivative of the American Cox 'Babe Bee' .049 cu. in. (0.82 c.c.) glowplug engine of which millions have been produced and which, through its wide use in ready-made plastic models, has been responsible for introducing more youngsters to the fascination of the miniature two-stroke engine than any other motor.

In presenting this new variation on the Babe-Bee theme, the L. M. Cox Company's objective was to offer an engine better suited to regular aeromodelling applications, with particular emphasis on small control-line stunt and combat models. The engine has therefore been given a larger fuel tank and has a different cylinder with twin transfer ports for extra power. It is not, of course, as powerful as the more expensive 'Tee-Dee' .049 rotary-valve contest engine, but does show a useful improvement over the Babe-Bee and Golden-Bee.

20 years ago, I found that the BW could power my Q-Tee at 6,500 feet (1,981 m). (Air density at that elevation is 11.6 psia versus 14.7 at sea level. With a 21% loss in air pressure one could expect a corresponding loss in HP.) At that elevation, 5x4 props power was marginal, barely puttered along. The Masters 6x3 props flew it at a decent speed. This is considering that the Q-Tee has generous wing area, it flies on its wing, which also helped. The BW is decently powerful. One thing I noticed as sea level was there was not much difference in flight between a 5x4 and 6x3 prop, but is more pronounced at elevation.

balogh wrote:On the rpm well I have always noted the COX engines spin the black 5x4 faster than the 5x3 and did not expect so...my favorites are the 5x4-s of Bernie pictured here with a 5x3:



Maybe the reason is the wider cord of the 5x3 than the 5x4? The 5x3 also looks to be a bit longer than the 5x4 so the 5 inch diameter is just nominal on the 5x4?

A prop is nothing more than a rotating wing (why we call helicopter blades "rotary wings"). Prop blade airfoil is a lifting surface. Your example goes to show that not all props are equal although may be classified with the same size. The additional "wing area" helps to explain the difference. Also, differences in diameters goes to show that the numbers aren't precise but can vary.

Personally, I go more by how it performs in the air. I don't have a tach and as such cannot give quantitative values. Once in the air, I see how it performs with the prop. If it does well, then I make sure I have sufficient replacements of the same. I'd be interested to hear on which was the better performing prop in the air.

balogh wrote:....On the rpm well I have always noted the COX engines spin the black 5x4 faster than the 5x3 and did not expect so...my favorites are the 5x4-s of Bernie pictured here with a 5x3:

Maybe the reason is the wider cord of the 5x3 than the 5x4? The 5x3 also looks to be a bit longer than the 5x4 so the 5 inch diameter is just nominal on the 5x4?

The diameter of 5x3 is 127mm = 5 inches and the widest cord is 17mm.

The 5x4 is a bit shorter in dia. 123mm= 4,84 inches with the widest cord 14mm..this may explain why the BW swinged it at 19,7k

Yes, the load of a prop is highly dependent on the diameter, so yes the smaller diameter will indeed have a large influence on the prop load.

Incidentally, I think this could possibly also explain the high revs you reported from your .051 engine, was that on the same prop?

Yes I have the 5x4 on most of my 049....051 engines.

If I remember correctly, the original Black Widows used TD piston/cylinder sets. Later ones dropped the cylinder tapering step but kept the timing.

George

I wonder why the Black Widow doesn't have ports that allow air to flow in under the piston, sub-induction or whatever it is called.  Maybe it was made without it to slow down dives and would need it for racing.

I flew a TD with a stunt control line club.  One of them told me to put a Black Widow cylinder on the TD for stunt.  The reason is that in stunt one does not want to speed up too much down hill.  With the Black Widow cylinder the mixture becomes richer at higher RPM, limiting speed.  You could hear it sort of strangle when flying downward.  I think the resistance in the fuel feed is mostly viscous, while in the TD the carburetor has a real venturi that sucks harder as the air flow increases.  The resistance in the fuel line is more like proportional to the flow, while the suction in the real venturi is proportional to the square of the flow.  The TD takes in fresh air below the piston, increasingly with speed, so it runs up to high RPM, while the Widow cylinder doesn't have the under intake so it runs at nearly constant speed.

The reed valve engines have a different sort of carburetor.  I have flown the BW with the TD cylinder, but can't say what difference it made.  I expect that it also goes faster down hill with sub-induction, though probably less so.

Probably one reason the reed valve engines are so easy to start and to tune is that the carburetor chamber isn't a real venturi.  That is it doesn't work by  Bernoulli's principle, in which the momentum of the air takes it  away from the jet, pulling in fuel.  It works by the suction caused by the small intake opening.  That suction probably increases less with flow, but it may have the same effect as with the TD, to some extent.

Added: I know Cox called the reed valve carburetor space a "venturi", but that was because it sounded better.

The original #1-stamped open-exhaust BW cylinders before 1996 all have SPI. Some #1 stamps may be missing(or hard to locate), but they're still the same. After that, the split exhaust with additional boost flutes came out without SPI. Claims are that the boost flutes performed as well as the original open exhaust SPI cylinders. That's arguable.
Rusty

1996 is the year that Estes Industries purchased Cox. Following is an excerpt from:

Wikipedia: Cox Model Engine

Wikipedia wrote:In 1996 Cox sold to Estes Industries / Centuri Corp. and moved to Penrose, Colorado. Things changed quite considerably from here on. Cox as the hobbyists of the world knew it had gone. The high reputation Cox engines had declined. One by one each product item was withdrawn from sale as stock ran out. Engine parts from different engines were mixed and matched making hybrid engines that performed very poorly compared to the Cox engines from previous years.

I gather that Estes was assembling engines from left over production parts. As the higher quality SPI cylinders were in short supply, they started substituting other assemblies, including the RTF Sure Start cylinders, which must have been scads of them. Also, they did not do as good of job matching pistons to cylinders, so some fits were loose losing compression.

There might be a small merit to using a non-SPI cylinder if one is using a muffler. Then inert exhaust gases induced through SPI would not be diluting the fuel charge, reducing power.

All the Black Widows I have are SPI versions, including a later one with red spinner and plastic back. I remember all the earlier engines that I have, the Pee Wees, .049 Babe Bees, Golden Bees, Black Widows, R/C Bee, postage stamp back 290 RTF, and .020 Tee Dee engines ran right out of the box. (Ditto with Wen Mac / Testors .049's.) I never disassembled and after a few tank fulls, were ready to fly. They were easy to start, easy to adjust, consistent. It was American manufacturing at its best.

I could not agree more..all my genuine old stock COX engines retain the excellent compression over a very long time. (I posted here vids on my 051 with tapered cylinder that I retired after near 300 hrs from my Toucan RC plane and the beast still starts up at the first flip)

Many of my Estes Era engines with cardboard boxes indicating origin from Penrose have much lighter fit when NIB with pistons already dropping through the cylinder etc..they are not too bad but seem sloppier than old stock. I know high engine speed and low piston friction go together but I doubt longevity can be expected from an engine which is loose on fit right out of the box.

Sic transit Gloria mundi.

David Ingham wrote:The reed valve engines have a different sort of carburetor.  I have flown the BW with the TD cylinder, but can't say what difference it made.  I expect that it also goes faster down hill with sub-induction, though probably less so.

Probably one reason the reed valve engines are so easy to start and to tune is that the carburetor chamber isn't a real venturi.  That is it doesn't work by  Bernoulli's principle, in which the momentum of the air takes it  away from the jet, pulling in fuel.  It works by the suction caused by the small intake opening.  That suction probably increases less with flow, but it may have the same effect as with the TD, to some extent.

Added:  I know Cox called the reed valve carburetor space a "venturi", but that was because it sounded better.

No, I believe it is a really a venturi, although its shape is a straight pipe versus a narrowing constriction like many of the larger CL engines. Other half-A's like the front rotary valve Testors / Wen Mac .049, OK Cub .049 A & B, have this. It is easiest to see with the Sure Start plastic backs, although one can also see it with the tank engine backs. The presence of the spray bar in the chamber provides the acceleration of air flow causing a pressure drop that draws the fuel by reducing the area through physical presence of the spray bar. Some larger engines the venturi is a straight pipe, like the Testors .35 McCoy Red Heads. To provide a constriction around the spray bar, they insert a short section of sleeve in that area. My Enya .09-III's have a thin sleeve rolled out of spring steel.

Because of the weaker draw with the smaller limited RPM reed valve engines, tank placement and fuel line length become critical. Leroy Cox solved that problem by offering an integral tank with the reed valve engine. Another company offered an aftermarket machined aluminum special mount plate with clunk on back that allowed one to push a plastic 35mm film canister over its lip for a tank, to which the non-tank engine could be mounted, placing fuel source close to and aligned to the engine.

I agree, the classic Venturi like on a TD is a smooth, gradual, uninterrupted  constriction of the air channel to generate maximum flow speed and depression in its narrowest point where then the fuel suction occurs.

The air intake channel in the reedie backplates would not cause meaningful depression without the spraybar reducing the cross section for the airflow, thus causing the air to accelerate and create depression around the spraybar.

The unrecoverable pressure drop caused by friction in the reedie air intake channel is higher though,  than in the classic venturi, thus the air/fuel charge flowing into the cranckase  is less in the reedie than in a TD even though the move of the piston upward causes the same (or similar, depending on the transfer porting position on the cylinder)  volumetric evacuation in the cranckases of both engines. ...this is why the venturi on the TD-s, and the larger diameter of  Killer Bee air intake and omission of the intake screen mean a lower penalty on the air/fuel charge, helping the engine generate more power than normal Bee engines...and a reminder that especially with the berillium type old stock reeds and circlip that tend to obstruct the smooth airflow, one must make sure this setup creates the smallest possible pressure drop...and a replacement by a stainless steel or mylar reed and cap type reed retainer may help squeeze more power out of the reedies...


ehhhhh, again too much talk from me about the obvious, excuse my gasbag self...

Hello guys and gals,

I have a chance to buy this bw for $70 Cad with shipping . The date inside the box says April 1990 so it's before Estes. Is it good deal? What are they worth?

Thx Canso07.