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Post  Cox International Wed Aug 27, 2014 1:29 pm

OOPS!

Definitely wrong picture  Embarassed  Embarassed  Embarassed
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Post  Cox International Wed Aug 27, 2014 2:05 pm

Pictures are now corrected:

http://coxengines.ca/cox-.049-propeller-grey-4.5-x-4.html

Surfer_kris,

My apologies for not listening to you when you first posted this. On your next order with us please mention this confused and we shall include 3 of those little beasts for you at no charge Hand Shake
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Post  Surfer_kris Wed Aug 27, 2014 2:18 pm

Oh, that explains why they looked so similar then... lol!

Thank you for the offer, I will include that in the next order. Smile

Another question, do you have any recommended rpm limits for these props?
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Post  Cox International Wed Aug 27, 2014 2:28 pm

Probably around 40,000 RPM with the compound we used.

Don't let the message on the hub scare you. Back in time they were made with a weaker compound.

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Post  1/2A Nut Sun Aug 31, 2014 5:10 pm

Bernie, you said you noted the .049 reed engine does 20k +  with the 4.5x4  
Out of the teflon, copper, crystal clear plastic, stainless steel and mylar reeds which reed material has been shown to helps provide the highest rpm?

Thank you, also let us know when the 4x2.5 props are ready for sale.

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Post  1/2A Nut Sun Aug 31, 2014 6:15 pm

Hey guys cox made some CL dog fighters meant to be combat with streamers here is the triplane with a reed .049 note the prop size 4.0D x 2P written on the other blade of this RH prop is the word COX
The prop dia is suits the plane as the wee lil plane is small like a Lil Stinker.
The cylinder has the twin slits I would imagine to help protect the plastic. Very interesting prop choice and without question the least amount of prop pitch in relation to diameter ever mass produced for a cox .049 reed engine. This engine has to pull a streamer and must screaaam with this prop - have not ran it as of yet I would guess 25k ish. unloaded. If anyone has flown the biplane or the triplane let me know I would like to hear how well it did. I would imagine this prop would work very well with the Pee Wee engine too.

Cox prop question - Page 3 Imag0011
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Post  Cox International Sun Aug 31, 2014 8:10 pm

1/2A Nut wrote:Bernie, you said you noted the .049 reed engine does 20k +  with the 4.5x4  
Out of the teflon, copper, crystal clear plastic, stainless steel and mylar reeds which reed material has been shown to helps provide the highest rpm?

Thank you, also let us know when the 4x2.5 props are ready for sale.

Small Cox Logo

The Beryllium Copper ones are the least suited as they are prone to "float" and likely the reason that Cox discontinued them. Steel, Mylar and the crystal ones (still not sure what they are made of) would all work. The preference out there seems to be the Mylar version but, if you ask 3 Cox engines users, may get 3 different answers.

Of course we will post when we get the props Smile
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Post  RknRusty Sun Aug 31, 2014 8:25 pm

Among Cox reedy enthusiasts, I have heard significantly more people that think mylar runs fastest, however will become bowed over a fairly short time. For a speed contest, after trying steel(also bows), solid teflon, woven teflon, copper, and mylar, but not crystal, I am 100% in the mylar camp.

The bow does not appear to me to affect it for sport use, and I can't say whether it hurts or helps RPMs. It seems to continue to seal just fine after short and long term bowing.
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Post  roddie Sun Aug 31, 2014 10:18 pm

I got curious about the thickness of the different reeds. About 5 years ago, I stocked-up on new Mylar, Teflon and Steel reeds.. and measured the thickness using a vernier caliper. I also had the older "star-shaped" reeds of Copper and Mylar. The "thickest" reed was the "Teflon" @ .010".. Both of the Mylar (star and oval) are .005".. The Steel reed is .002".. and the Copper is .001". How would the "much thicker" Teflon reed function with a tighter circlip clearance/fit? I've heard it mentioned, that the reed should not bind once the circlip is installed. The .009" difference in thickness between the Teflon and the Copper is quite a bit. Maybe that's why the Copper reed tends to "float" as Bernie mentioned? The Steel @ .002" is probably much more rigid than the Copper.. yet it's .003" thinner than the Mylar.

The "flex" between the different materials is probably a big factor.. but the circlips are all the same size wire diameter. I would think that the reed is meant to be held "stationary" by the circlip.. because of these wide variations in reed thicknesses. Pressure-differential valves "in general" don't float "radially" during their operation. The "disc" comes off the "seat" and reseals on a "linear" path.. without any radial movement happening.

The circlip-style reed-holder design has a "tang" in the center. Depending on which way you hold it; you will see that it protrudes one way or the other.. in relation to the "outer-circle" part of the clip, which seats in a groove around the seat. The circlip should be installed; so that this "tang" protrudes "away" from the reed/seat.. allowing the reed to flex away from the seat when there is a vacuum in the crankcase (piston moves "up" in the cylinder..) After installing a reed and a circlip-style retainer.. I hold the assembly up to my mouth.. and gently "blow" against the reed with my lips tightly sealed around the valve. If I don't feel any resistance.. this indicates that the reed is not seating properly.. (sometimes it "whistles") Oftentimes; removing and re-installing the reed/circlip will establish a reliable seal. Repeat the process as many times as it takes (swap-out a different reed/circlip) to achieve a good seal.. before you continue assembling the engine. This (along with cleanliness...) is the single most important thing to get right.. for a "reliable-running" Cox reed-valve engine.


Last edited by roddie on Sun Aug 31, 2014 10:25 pm; edited 2 times in total
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Post  Cribbs74 Sun Aug 31, 2014 10:19 pm

Steel or Mylar,

I prefer steel, only because it seems more robust. It does hold a shape like the Mylar as Rusty mentioned. They both do a fine job though.
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Post  roddie Sun Aug 31, 2014 10:47 pm

I recently assembled a "postage-stamp" backplate/engine to test the mounts I made. I could not get Mylar reeds (tried two.. with two different circlips) to seat properly. An "old" Copper star-shaped reed sealed the best. Do you suppose that Cox later reduced the "height" of the seat.. to accommodate the new "thicker" Mylar reed, with the development of the horseshoe backplate? I can't recall if I've had issues with running Mylar reeds in my old "tanked" Bee's. Huh...
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Post  Cribbs74 Sun Aug 31, 2014 10:52 pm

All I know is that the Mylar or steel reed does not play nice with the clip style reed retainer. I have to sand my clips when using a mylar or steel reed to allow them to move freely.

The plastic style reed retainer works well with the Mylar or steel so my guess is Cox went with the Mylar when they changed the retainer.

Ron
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Post  roddie Sun Aug 31, 2014 11:24 pm

Cribbs74 wrote:All I know is that the Mylar or steel reed does not play nice with the clip style reed retainer. I have to sand my clips when using a mylar or steel reed to allow them to move freely.

The plastic style reed retainer works well with the Mylar or steel so my guess is Cox went with the Mylar when they changed the retainer.

Ron

I guess that would make sense Ron. Maybe I need to "spec-out" the Cox overhaul kits that were available during the time that they were producing the new-style "plastic" reed-holder for their product engine.. against the "Bee's"... overhaul kit; to see if the reeds were different? Was Cox producing a "tanked" reed-valve engine by the time that they switched to that plastic reed-holder? The "Black-Widow" was the last of the tanked-Bee's wasn't it? Did it utilize a Mylar reed/circlip?
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Post  roddie Mon Sep 01, 2014 10:55 am

I feel a little stupid.. Embarassed After reading Rod's thread where he asked about gaskets for the plastic reed retainer.. it occurred to me that  the reed will still function properly within a specified gap between the seat and retainer . So now I wonder.. given BOTH style retainers.. if Cox designed the gap-size between the reed-seat and the inner-face of the plastic retainer or circlip (once seated) to allow for reeds of varying thicknesses to be used? This gap would have to be .010"+ for the thicker "Teflon" type reed to function.

Furthermore.. Rolling Eyes Being that the Mylar type reed is .005" in thickness.. would it be possible to use "thinner" reeds in multiples? Where the fragile Copper-style reed is only .001" thick.. and prone to floating/creasing.. could "two" be stacked together and still function properly? There's more than likely enough of a gap to try using a Copper reed, with a Mylar reed in front of it. This might "stabilize" the Copper reed better.. and give it more support?

These ideas/questions have probably been tried/asked by others.. but it's always good to re-hash through a topic.. to have a better understanding of why something will or won't work.
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Post  getback Mon Sep 01, 2014 11:29 am

one of mine I feel sure is an older BW I was waiting on a back plate that was plastic and broke I think it had a mylar reed in it no circlip , Cox prop question - Page 3 Wp_20125..... I got a metal one and need to ck the air intake to make sure it is correct sized per.....1973 Black Widow (Cat#150 - Manufactured May 1973-Jan 1996)

During the 70s a couple of Cox engineers were playing around with different coloured Babe Bee and Golden Bee parts and came up with an all-black engine with a red spinner. They hopped it up a bit with a dual bypass cylinder from a Super Bee (#1), a black Golden Bee tank and a slightly larger (0.062") venturi intake. The Black Widow was born. These engines were marketed as a High Powered Combat Engine. On later Black Widows the red rubber spinner was replaced by a red anodized aluminum Tee Dee style spinner. In the late 1990s some Black Widows were produced with the a dual bypass slit exhaust cylinder. The slit exhaust was to prevent fires. According to an Aeromodeller engine test done in August 1974 the Black Widow on 25% Nitro output power was 0.08 bhp (60 watts) at 15,000 rpm with a max. torque of 6 oz.in at 9,000 rpm    

http://upload.wikimedia.org/wikipedia/en/4/4d/WLBlackWidow.jpg



Cox Black Widow1973 Black Widow (Cat#150 - Manufactured May 1973-Jan 1996)  Speaking of circlips I lost one the other day and went to my stock had two in a unmarked package they were both made flat as to not have no relief so I did fix that were it would extrude out Shocked . don't know who made them and never seen this before .. Eric
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Post  Cox International Mon Sep 01, 2014 11:33 am

It is our understanding that the “gap” between retainer and reed is not that important. What is important is that the reed seals on upstroke.

Ronald Valentine (the engine builder) apparently makes his engines with zero gap between retainer and reed (circlip version), so that the reed cannot rotate at all.

The gaps on the OEM Cox engines is all over the place and we have used the red, black, grey and metal retainers with all combinations of reeds and they all seem to work fine.

The one thing one must be mindful of is using the black backplate with the red retainer as there is not enough gap in the centre, and an additional gasket must be placed underneath the retainer.
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Post  Cribbs74 Mon Sep 01, 2014 12:48 pm

I politely disagree.

Every engine I have built that had a mylar/steel reed that did not rotate ran like crap. Once I removed material from the clip and freed up the reed the engine ran fine.

I am not smart enough to explain the science behind it, but if the reed ends are clipped tight against the tank then the reed itself is forced to flex in the center to open and close.

This may work for the copper reed since it's so thin however, the Mylar and Steel reeds are thicker and less flexible. I have experimented with this over and over. The newer plastic reed retainer negates the whole issue.

So in a way you are correct, but it really depends on which reed you choose to work with.

Ron
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Post  Cox International Mon Sep 01, 2014 1:02 pm

The reeds is supposed to flex (only?) in the middle... methinks?

Have never tried the "no-gap" version myself but Roland Valentine builds high-performance Cox engines, is an old-school machinist and that he once mentioned.

But then, again, what do I really know ?

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Post  roddie Mon Sep 01, 2014 1:08 pm

Cox International wrote:It is our understanding that the “gap” between retainer and reed is not that important. What is important is that the reed seals on upstroke.

You mean on the "down-stroke" of the piston right? The down-stroke pressurizes the crankcase; forcing the reed to seal against it's seat. The upstroke creates "vacuum" in the crankcase.. sucking the reed away from the seat.. to let in the fuel/air-charge for the next combustion cycle.
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Post  Cox International Mon Sep 01, 2014 1:18 pm

Yes, of course, downstroke lol.

That's what happens when I drop into the office on a holiday Monday Sad

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Post  roddie Mon Sep 01, 2014 1:37 pm

Cox International wrote:Yes, of course, downstroke lol.

That's what happens when I drop into the office on a holiday Monday Sad


lol! I was expecting you to reply-back; telling me to go "make you a sandwich" and then stand in the corner for awhile.. Smile
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Post  sdjjadk Thu Sep 04, 2014 9:45 pm

1/2A Nut wrote:Hey guys cox made some CL dog fighters meant to be combat with streamers here is the triplane with a reed .049 note the prop size 4.0D x 2P written on the other blade of this RH prop is the word COX
The prop dia is suits the plane as the wee lil plane is small like a Lil Stinker.
The cylinder has the twin slits I would imagine to help protect the plastic. Very interesting prop choice and without question the least amount of prop pitch in relation to diameter ever mass produced for a cox .049 reed engine. This engine has to pull a streamer and must screaaam with this prop - have not ran it as of yet I would guess 25k ish. unloaded. If anyone has flown the biplane or the triplane let me know I would like to hear how well it did.
Cox prop question - Page 3 Imag0011
I have owned a couple of the DR-1's and I have owned a couple of the Sopwith's and they all flew great! They were super stable and easy to fly but yet maneuverable enough to easily perform loops.
It's a little dusty, but here are a couple of pics of my never flown DR-1 from the 70's with the original 4.5x4 faux wood grain prop.
Cox prop question - Page 3 Dscn5710
Cox prop question - Page 3 Fokker10
The faux wood grain props came on the Dog Fighter Series planes back in the 70's and they re-released them back in the 90's with the same style prop but in black.

Also, Bernie sells the direct replacement L.H. props for the Dogfighter Series.
http://coxengines.ca/cox-.049-propeller-4.5-x-4-left-hand.html


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Post  RknRusty Thu Sep 04, 2014 10:05 pm

I've always loved a DR1 Tripe. My best build as a kid was a static model when we were studying WW1. My history teacher LOST it! GRrrrrr!

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Post  1/2A Nut Thu Sep 04, 2014 11:47 pm

Yes I have some of those sexy wood looking and black swept right hand props.
I wonder where this prop came from then 4 x 2 seems best for a .020??
Perhaps they used this at some point to improve ground clearance.
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Post  1/2A Nut Sun Sep 14, 2014 5:37 pm

Hey Bernie has the folks in California started a run yet?

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