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Cox Engine of The Month
Scratch build BRM - a first
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Scratch build BRM - a first
I built a Bamboozle in '60, a Li'l Satan in '68 and the Nats Memorial Flite Streak in '97.
I decided I had to start somewhere if I was ever going to build planes, so for my first scratch build, I've taken elements from a couple of online plans for the Baby Ringmaster to come up with my own, 23.5" ws.
The components (basswood LE and center):
The sub-assemblies glued up, shaping done:
Tomorrow, dope and tissue base coats.
I decided I had to start somewhere if I was ever going to build planes, so for my first scratch build, I've taken elements from a couple of online plans for the Baby Ringmaster to come up with my own, 23.5" ws.
The components (basswood LE and center):
The sub-assemblies glued up, shaping done:
Tomorrow, dope and tissue base coats.
wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: Scratch build BRM - a first
Looking great Terry, your own design. Postage stamp Cox, where are you going to locate the fuel tank?
Bob
Bob
rsv1cox- Top Poster
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Re: Scratch build BRM - a first
Fuel tank will go under the OB wing, Bob.
wha-tah-hey- Rest In Peace
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Join date : 2013-12-04
Location : Elgin, Al
Re: Scratch build BRM - a first
wha-tah-hey wrote:Fuel tank will go under the OB wing, Bob.
1/2-3/4 oz wedge?
rsv1cox- Top Poster
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wha-tah-hey- Rest In Peace
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Re: Scratch build BRM - a first
Looks good. That tank is only going to last about a minute...
Cribbs74- Moderator
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Re: Scratch build BRM - a first
Yeah, I thought it might do 'til I measured it, Ron.
I found a 1/2 oz wedgie in my parts box that'll work.
I found a 1/2 oz wedgie in my parts box that'll work.
wha-tah-hey- Rest In Peace
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Re: Scratch build BRM - a first
Looking GOOD Terry !! Coming together quickly , bee watching the progress ..
getback- Top Poster
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wha-tah-hey- Rest In Peace
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Location : Elgin, Al
Re: Scratch build BRM - a first
I've got a couple of those little tanks... cute little buggers!
Balloon-tanks are something you might want to try.. Not a bladder.. but an airtight "collapsing" vessel that needs no vent.. and isn't particularly sensitive to location (elevation). The pick-up tube usually has multiple "notches" cut into it, to assure flow if a passage becomes blocked by the collapsing balloon.
I like the looks of the model. My 24" span designs fall close to that weight Terry. About 4.5/5oz. Keep us posted on the progress!
Balloon-tanks are something you might want to try.. Not a bladder.. but an airtight "collapsing" vessel that needs no vent.. and isn't particularly sensitive to location (elevation). The pick-up tube usually has multiple "notches" cut into it, to assure flow if a passage becomes blocked by the collapsing balloon.
I like the looks of the model. My 24" span designs fall close to that weight Terry. About 4.5/5oz. Keep us posted on the progress!
Re: Scratch build BRM - a first
A 1/8 oz. tank is 3.7 cc, a little less than 3/4 of a Babe Bee's 5 cc tank capacity. Might be a choice for free flight or .020's. A 1/4 oz. tank is 7.4 cc, a touch less than a Black Widow's 8 cc tank. 1/3 oz. is 9.9 cc. 1/4 or 1/3 oz. would be more suitable.
GallopingGhostler- Top Poster
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wha-tah-hey- Rest In Peace
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Re: Scratch build BRM - a first
Terry. You refer to this as a Baby Ringmaster, but I'm pretty certain the "Baby" has a built up wing and the slab wing version is known as a "Beginners" Ringmaster. Anyway, it's scratch built so I suppose you can call it whatever you like.
Rod.
Rod.
Oldenginerod- Top Poster
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Re: Scratch build BRM - a first
Right you are, Rod.
I call this one the BRM Special.
I call this one the BRM Special.
wha-tah-hey- Rest In Peace
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Re: Scratch build BRM - a first
Looking good. Should be a good flier. I really like the decals you produced.
NEW222- Top Poster
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Re: Scratch build BRM - a first
Yes those are really nice decals! I tried about a week ago to joing there group but never heard anything back from them.
Canso.
Canso.
Canso07- Gold Member
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Re: Scratch build BRM - a first
Thanks, guys.
Canso - seems it took a while to hear from them when I joined a few months back.
Not sure, but I may have had to contact admin.
Canso - seems it took a while to hear from them when I joined a few months back.
Not sure, but I may have had to contact admin.
wha-tah-hey- Rest In Peace
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Join date : 2013-12-04
Location : Elgin, Al
Re: Scratch build BRM - a first
Hi Terry! Those decals look GREAT! They'll add a nice touch to your custom-model! I have a question regarding your current engine configuration. Do you know the origins of that red horseshoe-style backplate? I'm assuming that it's a stock/ARF product-engine type backplate. They run just fine with an external-tank of your choice. The earlier Cox designs used a circlip-style reed-retainer (same as the tanked-Bee engines).. and in later years; was redesigned without the wire circlip.. for a "cap-style" retainer with a thin flange that mated with a case-gasket. You may want to experiment with different reeds for proper function. There's a design "cross-over" point; where Cox switched from their standard .001" copper-reed.. to the .005" Mylar. Cox did this before they redesigned the retainer-system. This is "my own" observation.. and subject to speculation.. but test your reed-function prior to test-running your engine. If your backplate uses a wire-retainer.. it may require the .001" Copper "star-shape" reed. I have a backplate that had this arrangement. It's my assumption.. that Cox switched to a lower-grade plastic at some point.. which would not stand-up to the pressure of the circlip bearing on the thin molded area which retained it.
Take a look at this backplate.. I have a couple more with the same condition.
Your backplate may not exhibit this issue. The very early Cox 190/290 "Postage-Stamp" backplates are made from a very dense-plastic that doesn't seem to degrade this way. I have custom-mounts that I made for those.. just in case you have any that you'd like to resurrect! The "posties" have a fine-thread (128 TPI) needle valve.. which is very nice! If you ever want to experiment with a pressure-bladder feed.. you'll want to use one of those backplates.
Needle comparison.. 80TPI-left (Cox later standard-issue) 128TPI-right (early Postage-stamp issue)
Just a little food for thought.
Take a look at this backplate.. I have a couple more with the same condition.
Your backplate may not exhibit this issue. The very early Cox 190/290 "Postage-Stamp" backplates are made from a very dense-plastic that doesn't seem to degrade this way. I have custom-mounts that I made for those.. just in case you have any that you'd like to resurrect! The "posties" have a fine-thread (128 TPI) needle valve.. which is very nice! If you ever want to experiment with a pressure-bladder feed.. you'll want to use one of those backplates.
Needle comparison.. 80TPI-left (Cox later standard-issue) 128TPI-right (early Postage-stamp issue)
Just a little food for thought.
Re: Scratch build BRM - a first
The backplate came on one of a "twofer" on eBay - $22.50 total, Roddie, both with the fine thread, mylar reed/wire clip - hadda thin the clip a bit to get it to seal properly.
It turns a 5-4 TD @ 17.3K on Cox 15%, which I think isn't too shabby.
The 2nd has a slit cylinder and it's down ~1.5K, same prop/fuel.
It turns a 5-4 TD @ 17.3K on Cox 15%, which I think isn't too shabby.
The 2nd has a slit cylinder and it's down ~1.5K, same prop/fuel.
wha-tah-hey- Rest In Peace
- Posts : 264
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Location : Elgin, Al
wha-tah-hey- Rest In Peace
- Posts : 264
Join date : 2013-12-04
Location : Elgin, Al
Re: Scratch build BRM - a first
roddie wrote:Yes.. I remember now. Good deal.. and either one should haul that model no problem! The only "older" horseshoe backplate in my collection is a white one with an aluminum needle. I have no idea where it came from.. probably was thrown-in when I bought some other hobby stuff years ago.
Interesting, Roddie, I have the same also, was given to me as gift by a modeller into electrics now. It powered his Cox Sportavia ARF 25-30 years ago. I thought it interesting it had an aluminum needle just like yours. Only thing different is I mounted an Ace R/C exhaust throttle sleeve.
wha-tah-hey wrote:Dry weather finally so I've started painting. Trim color will be red.
Really looking good now, Terry. I bet it will look awesome when finally completed.
--
George, Clovis NM US
GallopingGhostler- Top Poster
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Re: Scratch build BRM - a first
Thanks, George.
I shoulda mentioned - if I'm artistic enough, it'll have black pin-striping to set off the red trim.
I shoulda mentioned - if I'm artistic enough, it'll have black pin-striping to set off the red trim.
wha-tah-hey- Rest In Peace
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Re: Scratch build BRM - a first
Looks Good man !! looks like you decided to sow the hinges>? the red will set it off for sure.
getback- Top Poster
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Re: Scratch build BRM - a first
Sewn hinges are simple, easy, quick, flexible, long-lasting and plenty good for a 1/2A machine like this.
What more could you ask for, right?
What more could you ask for, right?
wha-tah-hey- Rest In Peace
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