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Building Tips and technical articles. => 1/2 A building. => Topic started by: philip metzner on January 26, 2010, 01:04:36 AM
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Between cox cylinders with the large exhaust ports and dual intake transfer ports, whats the difference? I have always kept the piston matched to the cylinder, but used the assemblies interchangeably. The two blackwidows i have were actually car engines. I put prop drive washers and ordered blackwidow tanks and carbs for them and installed hi compression heads. Did a factory black widow have something more?
I also have a collection of the cylinders with the slit exhaust ports and have ignored them. How do they run?
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Phillip, I am far from an expert on this subject but I will give you my take. If I am wrong on any count please correct me.
First on those slits. I never have liked the way they look as they seem so restrictive but so far as I know they do not affect performance in normal running.
The most important differences between the cylinders are the gas transfer ports inside.
A good place to see and read of the differences is here: http://www.mh-aerotools.de/airfoils/cox_frameset.htm
from the menu on the left choose "TECHNICAL DATA" and you will find this about mid page.
Robert
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Larry Renger is really someone who can authoritatively answer this question.
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The big differences that I know of are:
Some engines have only one transfer port (inside the cylinder, between the exhaust ports). This was to cut costs, and it cuts power, too.
TD engines have boost slots cut into the transfer ports, and they're tapered. I've only heard of this -- I never owned a TD 049 (I have a TD 09, but it lacks the boost slots -- perhaps it's a Medallion cylinder).
Most of these engines use sub-piston induction, i.e. the bottom of the piston goes above the bottom of the exhaust port on the top of the stroke. This puts a bit of fresh air into the crankcase _if_ you're not using a muffler, and lets the 'normal' induction path be small without harming induction too much. But it means that you can't cowl the engine too tightly, or muffle it, unless you don't have sub-piston induction.
There are at least three different head designs (normal, high compression, and Texaco) plus the 'early' version that won't fit current (post mid fifties) engines.
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Here are a few points as I remember them. Some may be incorrect:
Transfer ports: Since the time of the Space Bug Junior, Cox has used one transfer port for sport engines and two for power (Space Bug and Thermal Hopper at that time). The single transfer port worked better with the smaller venturi which provided easier starting and better fuel draw...good for beginners. I believe this was carried through until near the end.
The extra boost in the TD cylinders was an improvement, not on the first ones.
The exhaust slot top and bottom locations were/are positioned for timing. Which way they are pointing is arbitrary.
TD cylinders were tapered for higher performance. Early Black Widows used TD cylinders.
Black Widows used the "stunt vented" tank setup from the Golden Bee, but with a larger venturi for power.
Toward the last, I THINK ESTES used the Sure Start front end on an unvented plastic tank for the Black Widow, as well as the BabeBee and the Texaco.
George
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We need to get Warren Leadbeatter who is a member of this forum involved in this conversation.
Until he responds the next best thing is to review his Wikipedia page. I use this all the time.
http://en.wikipedia.org/wiki/Cox_engines
I do find that I run accross cylinders that do not fit the table still. It does however get the majority of them. For any of you that still have questions on Exhaust, Bypass and Boost ports.. this will help.
Mark
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Hi guys,
Firstly, let me say the info on the Wikipedia page is simply an amalgamation of information I obtained from three main sources. ie (1) Larry Renger, (2) Martin Hepperle's http://www.mh-aerotools.de/airfoils/cox_frameset.htm (http://www.mh-aerotools.de/airfoils/cox_frameset.htm) and (3) Mark Boesen's 049collectors forum http://groups.yahoo.com/group/049Collectors/ (http://groups.yahoo.com/group/049Collectors/).
I do have a collection including almost every type of Cox engine ever made so I have been able to make some of my own comments and observations as well as confirm information obtained from my various sources.
To answer the question, Larry is the best person to answer this question as he worked at Cox as a design engineer and is responsible for many engines and RTF planes, including the Black Widow and Venom engines.
However, I will have a go in case Larry is over answering Cox questions. To quote Larry on the 049 collectors forum "The original split exhaust was made to prevent fires. The open exhaust can blow flaming fuel out and start the plane on fire. This can’t happen with the slit exhaust."
From what I have learned, standard slit exhaust cylinders have No sub piston induction. This is handy for using a muffler as mufflers degrade SPI engine performance considerably.
Early slit exhaust cylinders were same porting as Black Widows, ie dual bypass no booster grooves. Later ones came out with a single bypass booster groove on each bypass port. However I have seen single bypass slit exhaust cylinders too. These would not be very good unless you want a lower power engine. I believe that the booster groove is an attempt to put back what the slit exhaust and lack of SPI takes away. Not sure if this is true in reality.
The exception to the above is the original Killer Bee. Slit exhaust, dual bypass, one booster groove on each bypass, tapered cylinder, lightened piston and sub piston induction and stronger balanced crank shaft to handle extra power.
The killer Bee cylinder can be easily identified as it has a wider lower slit and you can see the SPI gap when the piston is moved to TDC.
The Venom used a cylinder similar to the Tee Dee, but it had one large bypass booster on each bypass. ie much bigger than slit exhaust bypass booster groove. (see pic) The problem with the Venom was that the piston was made too light.
The Tee Dee 049 and 051s had dual bypass ports with dual booster grooves (one on each side of each bypass port, tapered grind, lightened piston, SPI but NEVER slit exhaust. The 051 has a single groove in the skirt of the piston for identification purposes.
So which is best (for power), from top to bottom, Tee Dee (number 4), Venom, Killer Bee, Black Widow (number 1), Dual bypass Slit exhaust then Single bypass (number 2). IMHO.
Cheers
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I do find that I run accross cylinders that do not fit the table still. It does however get the majority of them. For any of you that still have questions on Exhaust, Bypass and Boost ports.. this will help.
Mark
Hi Mark
Yes I come across unexplained odd cylinders all the time. Saw a couple of funny ones recently... a cylinder and piston that looked like Tee Dee 051 (groove / ring on piston skirt) but with Number 10 stamped on the cylinder. And a 051 cylinder with single boost groove with what appears to be a letter "A" stamped in the exhaust groove.
The table you refer to was based on the one from an article by Larry Renger in M.A.N. and covers mainstream production engines. ie what the engine mentioned "should have" It doesnt cater for odd bods, faulty, homemade or otherwise.
Also remember that you could once buy blank cylinders and cut your own exhaust ports and bypass grooves, which many people did apparently. Would love to get my hands on a Tee Dee 049 cylinder with schnerle porting and single exhaust port, like in the .15 Special MkII
Cheers
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Warren,
Thanks for all of this. Have you seen a #4 Cylinder where it is marked in the side of the cut for the Exhaust window rather than below it like most Cylinder markings?
Mark