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Happy postage stamp mounting

Post  getback on 6/18/2014, 1:16 pm

I have seen some old post from 2011/2012 and couldn't find any of the carl goldberg mounts like I have the cash for extras now . but I do have a few of these engines I hate I cant do anything with them as far as mounting and running on a plane////// is anyone figured a easy inexpensive way to make an adaptable mounting system ? Thanks ahead Getback  sunny  Airplane  sunny
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Post  OVERLORD on 6/18/2014, 2:45 pm

Hi Eric,

Have a look at the pictures below. They were posted by Jim in the Speed Contest Discussion thread on 24 november 2013.

postage stamp mounting Backpl10

postage stamp mounting Backpl11

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Post  JPvelo on 6/18/2014, 4:06 pm

The best thing to do with a postage stamp backplate is press out the fine thread needle valve. Install the needle valve in a product or horseshoe backplate and run it on bladder pressure .

Jim
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Post  roddie on 6/18/2014, 6:40 pm

I'm going to try to make a two-piece mount on a CNC router. The biggest obstacle will be the air-intake clearance when mounted.. and using a strong-lightweight material. I'm thinking about making "twin"; either PVC or acrylic "ears" that mount to the backplate spacing holes; either side of the NVA/air-intake and extend outward approx. 5/16" with mounting-holes to accept #3-4 wood screws. The 2-56 crankcase screws may have to be custom-cut to length using a Dremel-tool.. but this will depend on how deep I countersink the holes for the screw-heads. I'll try to design the mounts to accept standard-length Cox screws if I can.

I recently got called back to work at the company I worked at several years ago; where I was able to design several custom Cox engine mounting-plate configurations; as well as some nice precision parts custom made for my models. They even have all my old CAD design files saved on their server.
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Happy Re: postage stamp mounting

Post  JPvelo on 6/18/2014, 7:43 pm

Congratulations Roddie, that's great news man!!
Maybe you can make some side cash turning out some of those cool cnc wheels lol! 

Jim
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Post  getback on 6/18/2014, 9:11 pm

DAMMIT! Thanks Overlord , I remember reading this also.....Jim I got that and looks like could be some vibration in that's a lot to do for a extended mount , maybe just removing the fine threaded nva would be the better option   Very Happy Very Happy Very Happy Very Happy Roddie Good news man I will be watching to see what you come up with..... Eric
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Happy RE:postage stamp mounting

Post  rat9000 on 6/19/2014, 4:47 pm

Roddie-thats fantastic news,that kind of CNC talent seems to be getting harder to find along with machinists and toolmakers and good mechanics,I'm in for some wheels.rat


Last edited by rat9000 on 6/19/2014, 10:31 pm; edited 1 time in total (Reason for editing : I'm in getbacks thread)
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Post  sdjjadk on 7/17/2014, 6:24 pm

OVERLORD wrote:Hi Eric,

Have a look at the pictures below. They were posted by Jim in the Speed Contest Discussion thread on 24 november 2013.

postage stamp mounting Backpl10

postage stamp mounting Backpl11

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What airplane is that in the pics?
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Happy Re: postage stamp mounting

Post  roddie on 7/18/2014, 6:10 am

Thanks guys.. It's good to be back to work.. especially in a familiar surrounding with people I worked with several years ago. I just took some measurements off a 290 backplate that I have.. and am trying to figure out the best way to design a simple lightweight mount. I have sheet PVC in several thicknesses, and  I think I can make up a couple of mounts in different configurations to try. The Bee's crankcase screw pattern is 17/32" square on center. I'm shooting for a one-piece mount drilled with that hole pattern, that "keys" into the backplate with a central bore for the venturi protrusion, a slot for the spraybar.. and "ears" for mounting radially to a firewall. Maybe I'll put a radius-cut on the backside for breathing. The 10mil (3/8" nominal) thickness material should work. We'll see.
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Happy Re: postage stamp mounting

Post  JPvelo on 7/18/2014, 7:38 am

Sdjjadk,
That plane is the "290 special", a reed valve profile proto designed by Dale Kirn. Will try and post a photo of the full plan later.

Jim
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Happy Re: postage stamp mounting

Post  RknRusty on 7/18/2014, 11:51 am

I missed the back to work part. Good going, Roddie.
Rusty

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Post  JPvelo on 7/18/2014, 10:17 pm

postage stamp mounting IVPK36a
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Happy Re: postage stamp mounting

Post  batjac on 7/19/2014, 12:45 am

Well, it's a good thing I don't have a 290 backplate, or I'd be wanting to build one of these also.  But, the plans are now in my plans directory in the event that I do someday end up with a 290 backplate.


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Happy some progress

Post  roddie on 7/22/2014, 8:29 pm

Well.. here's my 1st attempts at a one-piece 10mil PVC mount for the Cox 290 back-plate. It will be refined further.. but I wanted some opinions. I'm using a CNC table router to cut the material.. and all the work that you see in these photos is on the front side of the mount. I will make a jig-block that the mount will fit snugly in, for counter-boring the case holes on the backside.. as well as a radiussed slot for the air intake between the firewall.

postage stamp mounting 7-22-110
postage stamp mounting 7-22-111
postage stamp mounting 7-22-112
postage stamp mounting 7-22-113

The outer "firewall" mounting hole counter-bores will be opened up a little more.. probably to clear the head of a #4 socket-head wood screw.
postage stamp mounting 7-22-114

This version (below) has a .500" through-hole that would allow for breathing through the slot for the NVA/fuel-line.. rather than a radiussed breather slot on the backside.
postage stamp mounting 7-22-115

I did this today on my lunch hour. Later versions will be cleaned-up a lot better with rounded "inlay" corners. The finished parts will also be sanded to remove the "fuzz" that you see here.

I'm also going to try a 2-piece mount.. which might provide for more breathing; without having to mill the backside. So far; this mount design caters to running the NVA/fuel-line horizontally on the airplane, which could have a fairly narrow firewall of only .750" wide by 1.250" vertically.

I will be making some cool new wheels too.
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Happy Re: postage stamp mounting

Post  anm2 on 7/22/2014, 11:35 pm

Roddie,

That all looks good to me. Those look like they will be very sturdy. How heavy are they? Can't wait to see one mounted on a plane! Andy
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Post  getback on 7/23/2014, 9:08 am

Nice work Roddie , is the idea to counter sink the holes in the mount and use longer screws to sandwich it all to the engine so it will have a mount on a mount as to say  Wink ?If so I would consider the length of the 8cc tank bee style screws that way they will be ready available. Are you going to produce some of these for sell ? Getback Popcorn 
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Post  roddie on 7/23/2014, 7:11 pm

getback wrote:Nice work Roddie , is the idea to counter sink the holes in the mount and use longer screws to sandwich it all to the engine so it will have a mount on a mount as to say  Wink ?If so I would consider the length of the 8cc tank bee style screws that way they will be ready available.  Are you going to produce some of these for sell ? Getback Popcorn 

Thank you Eric, I have both 8cc and 5cc tank screws in my parts stock. I'm thinking that the 5cc length screws will do the job. I'll check a couple of cases (for variances) by bottoming-out the screws through the postage-stamp.. and take some measurements to see how deep to counter-bore my plate.. and add maybe 3/32" for clearance. I also may source some custom-length socket-head 2-56 machine screws for this application. If all goes together well.. I'll either sell some with the custom screws.. or specify the Cox OEM ones to use.

Andy, I'm working on making the mount as light as possible.. while still having it be reasonably strong. I really like the idea behind the "290 special's" 2-piece metal mount. This would be VERY easy for me to make. I would design it differently though. I would form a perpendicular "Z" which could be mounted to a conventional plywood firewall. If I make the plates from .040" aluminum.. they'll be super lightweight. This may actually be the better way to go, because it would allow for very easy fuel-line changes and ample breathing. I already have the case-hole spacing measurements saved in a CAD file.. and just need to design a 4-hole plate with scores for bending... and space the firewall screw-holes to be easily accessible with a screwdriver.. with any cylinder orientation. Four standard Cox "prod." back-plate screws would secure the 2 mounts through the back-plate to the case... and mounting to the firewall would be the builder's-choice for whatever #4 screws they wish to use.
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Happy Cox "290" 2-piece mount

Post  roddie on 7/24/2014, 10:20 pm

Well.. I liked the idea behind the "290 Special's" 2-piece mount shown in the drawings earlier in this post.. so I cut some at work today. They're a little "crude".. but are really easy to make. The important things are the hole-spacing, plate width/length and a "bending jig" (which I haven't made yet..) which sets the thrust angle.

In case you don't know.. the 2-56 screws that mount this "postage stamp" back-plate to the crankcase are .300" (or 7.6mm) in length, measured from under the head. These mounts shown, are made from .040" (1mm) sheet aluminum.

postage stamp mounting 7-24-110


I had to use a rat-tail file for venturi clearance.. but will add a radius-cut in the CAD file. Incidentally.. this back-plate's venturi measures .173" (4.4mm) in diameter.
postage stamp mounting 7-24-111
postage stamp mounting 7-24-112


A pair of these weighs 2 grams... a lot lighter than the airplanes that the "290" was mounted in...
postage stamp mounting 7-24-113
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Happy Re: postage stamp mounting

Post  roddie on 7/26/2014, 2:45 pm

Next week at work.. I will make a bending jig from a PVC block with a "slot" cut to the correct depth. This will make the 90 degree "Z" bends in the two plates uniform in length. The plates are also much longer overall, than they need to be... and I will shorten them up so that after they're bent; the venturi will "just clear" the firewall.

I'll post more photos of my progress next week. I'm sure that there are plenty of you who have the "290" backplate (that haven't cannibalized it for it's fine-thread NVA)  Laughing... that would enjoy running it on a model.

Design consideration/question; Do you feel it would be advantageous to have the mount's hole pattern at the firewall, "match" the pattern of a "Cast" .049 backplate (mounted vertically/"needle-up") That spacing is .750" wide.. and 1.050" vertically (on center). Some kits come (or came) with plywood firewall stock that was pre-punched with that pattern for the Cox Bee's. The postage-stamp backplate, I am orienting "horizontally" which is the way I would think most people would want to run it for using an external fuel tank or bladder.

I often design my own airplanes, so I will be making "some" of these mounts similar to what's shown on the "290 Special" drawing that is pictured earlier in this thread, with a hardwood block that accepts screws from the top and bottom. (i.e. only a single bend in the mounts, at the backplate) This makes for an extra streamlined frontal area.


Last edited by roddie on 7/26/2014, 3:05 pm; edited 1 time in total
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Happy Re: postage stamp mounting

Post  JPvelo on 7/26/2014, 3:00 pm

Roddie,
Ideally you could make two versions, one that uses the tanked bee type mount pattern and one that uses the horseshoe pattern. If your only going with one I would say make the bee type since it is the more common pattern.

Jim
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Happy Re: postage stamp mounting

Post  roddie on 7/26/2014, 3:28 pm

JPvelo wrote:Roddie,
Ideally you could make two versions, one that uses the tanked bee type mount pattern and one that uses the horseshoe pattern. If your only going with one I would say make the bee type since it is the more common pattern.

Jim

Yea.. I agree Jim. If I were making these for myself.. I wouldn't change much of what I already have.. but other people may be interested.. and it may make mounting on a model that previously had another engine difficult. I'll have to re-design the plates "trapezoidal" to get the .750" hole spacing clearance on the firewall side.

sort of like this

postage stamp mounting Trapez10
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Post  roddie on 7/26/2014, 6:15 pm

It's not necessary that the 290 backplate be cut .750" square with a razor saw as shown on this drawing, to use the mounts shown. It would be a lot of work, and the metal-plate mounts will fit in-between the molded "ears" on the backplate if they're cut to the correct width. Whereas this model is a "racer".. it's done for maximum streamlining. The wheels shown here would induce much more drag than a stock un-modified backplate ever would.

postage stamp mounting 290_sp10
postage stamp mounting 7-24-114
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Post  roddie on 8/5/2014, 11:07 pm

I shortened-up the 2-piece mount plates for the 290 backplate by .375" and once they're bent-up; they should locate the backplate snugly against a firewall, with enough clearance for breathing and access to R & R a fuel line if needed. I should have modified the CAD program to cut-in the radiuses to clear the protruding venturi.. but that can be done with subsequent runs.. if enough modelers have interest in these. A few swipes with a rat-tail file works fine for the ones shown here.  

postage stamp mounting 8-5-1410


These "shorter" plates don't weigh much...

postage stamp mounting 8-5-1411

and a "290" backplate weighs half of what the "horseshoe" does...

postage stamp mounting 8-5-1412
postage stamp mounting 8-5-1413

Still less weight than the "horseshoe" with both plates.

postage stamp mounting 8-5-1414

sometimes "every gram" makes a difference.. when balancing/trimming a competition model.

Think about this when you consider removing that nice fine-thread NVA.. from the "290".. for use in the heavier "horseshoe".
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Happy Re: postage stamp mounting

Post  getback on 8/6/2014, 8:52 am

I am up for a couple sets Roddie , I have several engines I don't even know if they run for lack of mounting!! Good job Dude ! Eric  Very Happy Fireworks 
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Post  Kim on 8/6/2014, 11:06 am

Me too Roddie! Let me know if I need to PM the info !!
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