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Cox Engine of The Month
What needle is this? w/pic
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wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: What needle is this? w/pic
Terry, the aluminum needles I believe were for the early plastic "horseshoe" backplates. I have one with the longer needle.
This backplate used a circlip reed-retention and I believe that mine had the thin (.001") Copper-Beryllium star-shaped reed originally. I believe that my needle (and most likely yours..) have the std./coarse 80 threads-per-inch.
Here's a photo of a pair of Cox Brass needles, that shows the difference between a coarse (80tpi) needle and a fine (128tpi) needle.
The early Cox "Postage-Stamp" (190/290) reed-valve product-engine's backplates had the fine-thread needle-valves.. and ran external fuel tanks.. prior to the development of the "Horseshoe" backplate product engines.. the latter of which had radial mounting-provisions for running on a small balsawood model's standard ply-firewall.
This backplate used a circlip reed-retention and I believe that mine had the thin (.001") Copper-Beryllium star-shaped reed originally. I believe that my needle (and most likely yours..) have the std./coarse 80 threads-per-inch.
Here's a photo of a pair of Cox Brass needles, that shows the difference between a coarse (80tpi) needle and a fine (128tpi) needle.
The early Cox "Postage-Stamp" (190/290) reed-valve product-engine's backplates had the fine-thread needle-valves.. and ran external fuel tanks.. prior to the development of the "Horseshoe" backplate product engines.. the latter of which had radial mounting-provisions for running on a small balsawood model's standard ply-firewall.
Re: What needle is this? w/pic
Thanks for the info, Roddie.
Now that I know what hey are, maybe someone can use 'em.
Now that I know what hey are, maybe someone can use 'em.
wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: What needle is this? w/pic
My pleasure Terry!
The backplate that you have there, is the Cox "Postage-Stamp" type.. and its needle has a custom-knob fitted to the top. Those backplates were usually orphaned/discarded once the model that utilized them broke.. because they fit into a slot.. and had no other type of mounting-provision. Carl Goldberg models made an adapter to use that backplate/engine on a standard radial-mount plywood firewall. Sometimes they show-up on eBay.. but have long been out of production.
It does however have a very desirable fine-thread NVA... and many modelers extract the NVA for use in other engines where they need extra-fine resolution/fuel-mixture control.. such as with a pressure-bladder system.
These backplates were fitted to Cox's early "product-engines" (#'s 190/290) "290" being a seperate "off-the-shelf" replacement engine for a model that originally came with the 190.. from what I understand. There's threads here on the forum.. that are quite interesting reads.
You seem like a guy who enjoys "tinkering".. so I'll include some info on how I made my own 2-piece mounts for running that backplate and superb needle on an airplane. It merely requires a little measuring.. and making two Z-bent metal plates with holes drilled in the right places.
Those are .040" sheet-aluminum plates, cut and drilled to match the 17/32" spacing of the 2-56 case-screws without any modification to the plastic backplate itself.
You could run that backplate on your GB... with the fuel-tank/system of your choice if you wanted.
Some interesting comparison photos..
Adapter-plates "can" fit the standard vertically-oriented Bee backplate area on a firewall.
If you'd like, I can provide you with all the measurements. I mailed a few sets of these plates along with the proper length case-screws to a few members here on the forum. One member "Getback" (Eric) experienced a stress-fracture along a bend-point on one of the aluminum plates. I made these plates on a CNC router and also made bending-jigs to form the Z-bends. Eric's issue might have been an isolated condition.. therefor; a light-gage/mild-steel might be a better choice. It would come with a weight-penalty though.
The backplate that you have there, is the Cox "Postage-Stamp" type.. and its needle has a custom-knob fitted to the top. Those backplates were usually orphaned/discarded once the model that utilized them broke.. because they fit into a slot.. and had no other type of mounting-provision. Carl Goldberg models made an adapter to use that backplate/engine on a standard radial-mount plywood firewall. Sometimes they show-up on eBay.. but have long been out of production.
It does however have a very desirable fine-thread NVA... and many modelers extract the NVA for use in other engines where they need extra-fine resolution/fuel-mixture control.. such as with a pressure-bladder system.
These backplates were fitted to Cox's early "product-engines" (#'s 190/290) "290" being a seperate "off-the-shelf" replacement engine for a model that originally came with the 190.. from what I understand. There's threads here on the forum.. that are quite interesting reads.
You seem like a guy who enjoys "tinkering".. so I'll include some info on how I made my own 2-piece mounts for running that backplate and superb needle on an airplane. It merely requires a little measuring.. and making two Z-bent metal plates with holes drilled in the right places.
Those are .040" sheet-aluminum plates, cut and drilled to match the 17/32" spacing of the 2-56 case-screws without any modification to the plastic backplate itself.
You could run that backplate on your GB... with the fuel-tank/system of your choice if you wanted.
Some interesting comparison photos..
Adapter-plates "can" fit the standard vertically-oriented Bee backplate area on a firewall.
If you'd like, I can provide you with all the measurements. I mailed a few sets of these plates along with the proper length case-screws to a few members here on the forum. One member "Getback" (Eric) experienced a stress-fracture along a bend-point on one of the aluminum plates. I made these plates on a CNC router and also made bending-jigs to form the Z-bends. Eric's issue might have been an isolated condition.. therefor; a light-gage/mild-steel might be a better choice. It would come with a weight-penalty though.
Re: What needle is this? w/pic
Must be some atmospheric condition floating brain waves or sumpin', Roddie.
Just moments ago I was in my "shop" looking at that backplate, thinking it might/could replace the GB tank.
I have several sizes of old small Perfects, allowing better control over flight time and balance point.
And yes, I can and do tinker!
MOF, the pic with the ruler is enough to let me sort it out.
Veggie can will do for stock. I admit, the bends may take a few trials.
Thanks for the kickstart!
Just moments ago I was in my "shop" looking at that backplate, thinking it might/could replace the GB tank.
I have several sizes of old small Perfects, allowing better control over flight time and balance point.
And yes, I can and do tinker!
MOF, the pic with the ruler is enough to let me sort it out.
Veggie can will do for stock. I admit, the bends may take a few trials.
Thanks for the kickstart!
wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: What needle is this? w/pic
My plates measure .785" square.. with an on-center 7/32" 4-hole pattern. A rat-tail file can be used to trim the radius on one edge where the venturi protrudes. That edge receives the case-screws that tighten the backplate/gasket/case together.
The Z-bend is .25" from the edge on both sides. You can pad the jaws of an avg. bench-vise to gage the .25" depth for the bend.
I made fixture-blocks to be compressed in a bench-vise.
The 785" measurement is the distance between two parallel protrusions on the rear/mount side. Making the pair of plates "square" with the 1/4" bends.. just happened to work-out and still have ample clearance for the air-intake when mounted.
The Z-bend is .25" from the edge on both sides. You can pad the jaws of an avg. bench-vise to gage the .25" depth for the bend.
I made fixture-blocks to be compressed in a bench-vise.
The 785" measurement is the distance between two parallel protrusions on the rear/mount side. Making the pair of plates "square" with the 1/4" bends.. just happened to work-out and still have ample clearance for the air-intake when mounted.
Re: What needle is this? w/pic
Nice work, Roddie, simple and neat - thanks for the clear pix too.
A "make-do" man after me own heart, no doubt.
"We don't need no stinkin' store-bought mounts!"
BTW, I was informed the needles also fit "a KK (?) spraybar for TDs".
A "make-do" man after me own heart, no doubt.
"We don't need no stinkin' store-bought mounts!"
BTW, I was informed the needles also fit "a KK (?) spraybar for TDs".
wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: What needle is this? w/pic
Here is an alternative way to mount one of these engines, a little easier as it only requires one bend per mount. The thread is about an entire model, a "290 Special", the mounts can be seen at the end.
https://www.coxengineforum.com/t9988-i-couldnt-wait-anymore
https://www.coxengineforum.com/t9988-i-couldnt-wait-anymore
KariFS- Diamond Member
- Posts : 2002
Join date : 2014-10-10
Age : 52
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