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Is there any .049 Transfer & Exahaust, BDT, rod length data available?

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Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  wmazz on Fri Jan 11, 2019 11:53 pm

I am really interested in transfer port duration and Blow Down Time between
cylinders. This data interests me because in many of the posts I have read about
transfer and boost ports, and the lack of a substantial difference between
bench test rpm.

It makes me wonder if some cylinders like the TD 049 (#4) have too much
transfer port duration for bench testing, or is it just friction?

If the transfer ports are too large for a bench test, how many rpm must an
engine unload to take full advantage of the port area? and how to minimize
the time it takes for a TD to unload?

If there isn't any baseline info, does anyone know the connecting rod length
from center to center?


Thanks!

Bill M.

BTW, I am also interested in the geometric compression ratio of the different
Cox glow heads so I can calculate cranking compression (if it applies to miniature
engines).
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  coxaddict on Sat Jan 12, 2019 1:05 am

Hi,
I too am very interested in the design and operation of the Cox .049 engines.
 Compression for this type of two stroke engine begins as the exhaust port is covered, not when the piston starts on its upward rotation. Is the size of the engine determined by bore and stroke?
So is installing a high compression head then adding 3 to 5 head gaskets to lower compression to allow the engine to run with the proper nitro amount counter productive?
Does the high compression head change the exhaust gas exiting dynamics, shrouding the glow element from cooling off because of the incoming air/fuel allowing more power? After all, engines are heat pumps. Paranoid
 I hope someone can enlighten us.  Cox engineers knew how to extract the most power from these "throwaway" engines.
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  wmazz on Sat Jan 12, 2019 2:57 am

Has anyone ever tried a high compression/low nitro head with a squish band
~.004" squish clearance.


Something else I have only read about is the glow head coming loose while
running. Seems more likely on a control than a free flight? But on our race
engine things tend to come loose when the engine is detonating, or the piston
is hitting the head Sad

Recently saw a picture of a cracked piston, detonation destroys, preignition melts.
Could an .049 piston crack from detonation?


Bill M.

I both hate and love detonation Smile
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  roddie on Sat Jan 12, 2019 4:15 pm

Hi Bill and Agustin, I don't know a whole lot about the technical side of our Cox glow engines.. but I'll comment on a few points.. as "food for thought".

Regarding a glow-head coming loose while the engine is running; I've had that happen a few times. In my cases.. it could've been because I didn't tighten it enough to begin with. Many of my .049 cylinders are of the earlier-type which lack "flats" on top, for a wrench. Tightening the glow-head using a single-wrench also tightens the cylinder.. so I tend to use "less force" on that type.

I also suspect that re-using a head-gasket.. rather than installing a new one, might cause the glow-head to loosen.. due to the used-gasket being previously squished-thinner. This is just speculation though.. Maybe previously-used head-gaskets become "work-hardened" and loose some of their ability to keep the head from loosening-up?

You can bench-run an engine using a flywheel (rather than a propeller).. but it's wise to provide some cooling for the cylinder.. and a BALANCED-flywheel. An engine running a flywheel will unwind on the bench.

I'll start a new thread on some of my own recently-discovered info. regarding flywheels for the Cox .049 glow engine.
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  wmazz on Sun Jan 13, 2019 2:12 am

roddie wrote:
I also suspect that re-using a head-gasket.. rather than installing a new one, might cause the glow-head to loosen.. due to the used-gasket being
previously squished-thinner. This is just speculation though.. Maybe previously-used head-gaskets become "work-hardened" and loose some of their
ability to keep the head from loosening-up?

I have had similar experience using copper head and base gaskets on
Kawasaki Jet Ski's. Except the part about coming loose, that would be
very bad. The copper gaskets do compress and become "work-hardened."

Copper gaskets are reusable after they have been annealed (heated, then
tossed into water).

roddie wrote:
You can bench-run an engine using a flywheel (rather than a propeller).. but it's wise to provide some cooling for the cylinder.. and a BALANCED-flywheel.
An engine running a flywheel will unwind on the bench.

I'll start a new thread on some of my own recently-discovered info. regarding flywheels for the Cox .049 glow engine.

I am very interested in that, and I may have to many questions.

I thought about pros & cons of an inertia dyno when Oldenginerod mentioned
testing .020 & .010 engines. But the problem I saw was how to get the engine
to a low rpm, and then measure the acceleration. An inertia dyno or tachometer
would be a simple electronics project using your favorite microcontroller and
display.

Perhaps all the engine needs is to momentarily block the air intake and let it
accelerate up, and log the data.


Bill M.
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  gkamysz on Sun Jan 13, 2019 9:51 am

What is the goal of further developing an entirely ancient design? Modern 1/2A make much more power. While it may be interesting to know, I haven't bothered to accurately measure timing, I'm just not sure much more power can be extracted from a TD. I had doubts about the pipe adapter I made for Brad being effective with a blocked exhaust port, but it seems to be working. A few attempts were made at schnuerle TD's, but there is very little information available about performance.

Tight clearances or specific timing require the ability to modify/produce the parts, so there is little out there in that regard. I think a better engien could have been produced using the threaded cylinder arrangement, but it would take a larger diameter overall to get the porting in there. Of course, very small details can have a big influence, so it's hard to say what will work without a lot ideas, testing, and experience to interpret the results.
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Re: Is there any .049 Transfer & Exahaust, BDT, rod length data available?

Post  wmazz on Sun Jan 13, 2019 3:20 pm

gkamysz wrote:What is the goal of further developing an entirely ancient design? Modern 1/2A make much more power.
While it may be interesting to know, I haven't bothered to accurately measure timing, I'm just not sure much more power
can be extracted from a TD.

Initially my #1 goal is to find a propeller that holds the engine rpm to 22,000
when it unloads. Because published data suggests that is where peak HP is.

I do find the results of bench racing impressive, but I don't see that as a
reliable engine, and so I would rather fine tune the existing engine to its
nearly stock potential for tuning consistency, with pressure, using a bladder.

Goal #2: Similar performance to #1, but using low nitro, or no nitro like an FAI
engine.

gkamysz wrote:
While it may be interesting to know, I haven't bothered to accurately measure timing

It is interesting, and I would like to see if I can gain any practical knowledge
from it by comparing existing cylinder specs.


gkamysz wrote:
I had doubts about the pipe adapter I made for Brad being effective with a blocked exhaust port, but it seems to be working.

That adapter was the first thing I noticed in 1/2anut's thread. I especially liked the
choice of the adapters inside diameter. It looks very professional.

gkamysz wrote:
A few attempts were made at schnuerle TD's, but there is very little information available about performance.

While researching my Kirn Kraft engines, I spoke to a Cox employee who basically
told me the single exhaust port .049 engines didn't test as well as the original design.


gkamysz wrote:
Tight clearances or specific timing require the ability to modify/produce the parts, so there is little out there in that regard.
I think a better engine could have been produced using the threaded cylinder arrangement, but it would take a larger diameter
overall to get the porting in there. Of course, very small details can have a big influence, so it's hard to say what will work
without a lot ideas, testing, and experience to interpret the results.

I am only interested in the benefits of a tight squish, and working with other cylinders,
within the boundaries of what the threaded cylinder will allow. But for the most part,
I believe the engine to be a well tested engine, and that I would not have any new ideas
that remain untested.

The only other goal is to make a better test stand, but not a complicated test stand
with load cells like they sell for electric motors.


Bill M.
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