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The skinny on the Cox Queen Bee .074

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The skinny on the Cox Queen Bee .074

Old 03-29-2005, 03:59 AM
  #51  
Big Al-RCU
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Default RE: The skinny on the Cox Queen Bee .074


ORIGINAL: Japanman

Tim,
I would have said that there MUST be a significant reverse flow to cause the reed to close. Otherwise, what will close it?

J.M
J.M., what you say makes sense, but wonder if the reverse ‘pressure’ (which moves the reed) closes it before the actual flow is significant? Also I’ve always wondered what controls the total opening of the free floating reed as used by cox. And what is the effect and is it critical? Don’t know if it is the free travel or the flexibility of the material (or probably both) but neither seem to be tightly controlled. What is the RPM tradeoff between less travel vs. increased flow (opening)? I’m thinking that many of my problems with cox reedies over the years were due to my lack of understanding of the overall principles of the reed valve. No wonder I had problems with my pee wee’s after hammering out the crumpled up brass reeds.
al
Old 03-29-2005, 08:10 AM
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Tim Wiltse-RCU
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Default RE: The skinny on the Cox Queen Bee .074

JM,

The reed is flat to start with and it wants to stay flat. It's the negative pressure change inside the crankcase that pulls the reed open and the intake charge in. As soon at the pressure is equal again it snaps shut its not "pushed shut".

Later,
Tim
Old 03-29-2005, 09:04 AM
  #53  
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Default RE: The skinny on the Cox Queen Bee .074

The reed is flat to start with and it wants to stay flat. It's the negative pressure change inside the crankcase that pulls the reed open and the intake charge in. As soon at the pressure is equal again it snaps shut its not "pushed shut".

Later,
Tim
Do you mean with the stock cox reedy or in the V Reed setup? In all my cox reedys the reed just floats between the "reed stopper" wire/plastic and the reed seat.

One of the reasons I started to play with the Vreed setup is the positive stop that this has over the stock cox reed- e.g the Vreed is attached at one end and has to be bent to be open and hence will spring closed.

Big Al:
Also I’ve always wondered what controls the total opening of the free floating reed as used by cox. And what is the effect and is it critical? Don’t know if it is the free travel or the flexibility of the material (or probably both) but neither seem to be tightly controlled. What is the RPM tradeoff between less travel vs. increased flow (opening)?
I wonder about the amount of movement too- I would have thought that too much reed lift would mean that to get the reed to close, quite a lot of reverse flow out the carb must happen. This is assuming that the reed lifts all the way to the stopper, but seeing as quite a large volume of air/fuel has to pass the reed to get into the crankcase, you`d think it would.
I imagine finding near optimium reed lift would be quite easy if a vairable reed stopper can be fabricated. then it is just a matter of trying the reed stopper at greater and greater lift and watching the revs climb and fall. Would be good to try with say 3 different props- something like 4x3 5x3 and 6x3 to get a feel for whats happening.

I found with my v reed blocks that the reed lift required was really a lot less than I though it would be- in the range of 1.5mm (1/16" )
this is a different kettle of fish though as even with the reeds slightly open it is quite a straight trajectory and the reeds make a neat nozzle which may not produce a lot of drag., as you can see if you look at C.P`s diagram (but imagine it reversed.)

`tis all much interesting stuff.

J.M
Old 03-29-2005, 01:57 PM
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Default RE: The skinny on the Cox Queen Bee .074

It's my understanding that the COX reed is setup to lift entirely away from its' seat. Is the 90 degree tang that is bent in the retainer wire suppose to hold the reed tight against the backplate so the outer ends can flap? This product engine has a full floating reed that is in a plastic cage. This cage allows a ton of room for the reed to lift away from the seat. I have had similar experience to BIG AL with overhauling reed engines.
Old 05-19-2005, 08:36 PM
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Default RE: The skinny on the Cox Queen Bee .074

Wow! I missed out on one heck of a thread while I was on vacation (at work)! I found the discussion about what causes a reed to close, and about back paulses in the intake tract to be very interesting. I agree with everyone's opinion a little... I agree with I think it was Tim, that there is no reversion (back flow) in a (proper) reed valve engine, but I agree with others that there is a "pressure differential" that forces the reed closed. How could pressure close the reed but there be no backflow? Simple: On the upstroke of the piston, a pressure differential (meaning less pressure than atmospheric) is created which opens the reed, and accelerates air through the intake tract and into the crankcase. This column of air has great momentum and causes a higher than atmospheric pressure on the reed and into the engine. When the piston hits TDC, and begins it's way down, it creates high preassure in the crankcase. This preassure eventually reaches a level higher than atmospheric pressure, and higher than the pressure created by the rushing column of air entering the engine. This causes the reed to close, but the rushing column of air and it's incredible momentum are still acting on the reed and are still higher than atmospheric pressure, so no air is actually pressed back through the carb. This momentum of air also works to in a way "supercharge" the engine when all conditions are correct. The effectiveness of this depends on the length, cross-sectional area, and taper of the intake tract. These conditons are all used to tune an engine for a specific RPM rang, much like a tuned exhaust pipe. In my testing on reed valves, I use a relatively large diameter intake tract, and I have found that it wants to be as short as I can make it.

Wink
Old 03-29-2020, 04:08 PM
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ok cox 074 guys I have a question will the muffler fit on my 051
Old 03-30-2020, 07:07 AM
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No. It shares the cylinder thread size with the .09. One of those mufflers might match IDK. You could check with Cox International for stock.
Old 03-30-2020, 01:08 PM
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Yes if you use rubber grommets like this guy did with his .049. How well does is work, I don't know.



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