Re: Cox prop question

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...

**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

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?

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.

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 ,

..... 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

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.

**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

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 ?

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.

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

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

I was expecting you to reply-back; telling me to go "make you a sandwich" and then stand in the corner for awhile.. Smile

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.

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.

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

Shawn

**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!

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.

1/2A Nut Sun Sep 14, 2014 5:37 pm

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

Paranoid

Cox International Mon Sep 15, 2014 11:07 am

1/2A Nut wrote:Hey Bernie has the folks in California started a run yet?

No idea. Once they run them it only takes a few hours for 2,000 props.

They have to squeeze this miniscule production run in between two "real" production runs.

Cox International Thu Sep 25, 2014 1:39 pm

The props were shipped today and should arrive in aprx. 10 days Smile

batjac Thu Sep 25, 2014 1:42 pm

WooHoo! Now to select which plane gets one first.

The Excited Mark

Cox International Thu Sep 25, 2014 2:03 pm

Dilemma easily solved ... buy them in bulk lol!

1/2A Nut Thu Sep 25, 2014 2:46 pm

Wooot thank you for the update Bernie! Small Cox Logo

Cox International Tue Sep 30, 2014 3:26 pm

Here they are:

http://coxengines.ca/cox-.020-racing-propeller-4-x-2.5.html?&cat=44

and in 3-packs:

http://coxengines.ca/cox-.020-racing-propeller-4-x-2.5-3.html

batjac Wed Oct 01, 2014 12:05 am

Okay. My order's in...

The Early Adopter Mark

Cox International Wed Oct 01, 2014 9:00 am

batjac wrote:Okay. My order's in...

The Early Adopter Mark

Thanks and we received several orders overnight Smile

1/2A Nut Wed Oct 01, 2014 7:58 pm

Good idea with the multi 3 packs!!
I just made a double order along with some other needed goodies. Small Cox Logo

WTG Bernie,
Let us know if you decide to go with a run of the competition greys the material is great for reworking / shaping with a fine file and buffs up to a shine.

Example done with the 3 x 1.25

batjac Wed Oct 01, 2014 8:54 pm

1/2A Nut wrote:
WTG Bernie,
Let us know if you decide to go with a run of the competition greys the material is great for reworking / shaping with a fine file and buffs up to a shine.

Example done with the 3 x 1.25

Do you get a measurable difference in thrust doing this? And how do you determine the shape to file? Using an APC as a template?

The Curious Mark

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