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F-82 Twin Mustang build thread- preliminary Babe_b10
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F-82 Twin Mustang build thread- preliminary

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F-82 Twin Mustang build thread- preliminary Empty F-82 Twin Mustang build thread- preliminary

Post  JPvelo on Wed Sep 18, 2013 8:28 pm

My Brodak Twin Mustang kit showed up today from eBay. It's an older die cut kit but the cuts are clean. It is designed around tanked reedies on plastic mounts:
https://i.imgur.com/uLkOO3o.jpg
I don't care for tanked engines or the chopped off nose look of the plastic mounts. The plan is to extend the nose for a scale outline and mount product backplate engines on an offset mount like this:
https://i.imgur.com/HaJEEtk.jpg
Took a trip to the copy store and blew up a F-82 drawing 300% and got this:
https://i.imgur.com/2SbAdsh.jpg
The scale outline is a little off in back:
https://i.imgur.com/5C6o0gI.jpg
I'll most likely extend the rudders back to the scale outline so I can add 1/2 inch to the elevator. I don't know if I will add balsa on the bottom for a true scale outline. I'm a little leery of adding tailweight after my last twin experience and I don't know if it will make much visual difference when it's 45-52 feet away from me. The cox plastic spinners match the scale of this model perfectly so that's really cool. Don't know how fast I will get this done as I am taking vacation Oct. 1st and moving Nov. 1st, but that's the basic plan for the build.

Jim
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Post  pkrankow on Wed Sep 18, 2013 9:44 pm

That little scoop detail is pretty forward. I expect it to not affect much.

I have read that these build tail heavy to start with. You plan will let you put the motor mount on late in the process and prevent some of this behavior.

Phil
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F-82 Twin Mustang build thread- preliminary Empty Cuttin' wood

Post  JPvelo on Sat Sep 21, 2013 12:06 am

Epoxied the first section of leading edge tonight and started cutting wood to modify the fuselage outline. Here's the direction the project is going:
https://i.imgur.com/6kaop9F.jpg
Modified fuse is on the right, stock kit in the center. As I stated in the last post the fuselage front will be added for a proper scale outline. I am also going modify the offset mount idea shown in the last post for a cleaner look, pics will be posted when I get there. The biggest departure from the stock kit I plan on making is mounting the fuselages to the wing. The plan sandwiches the fuse between ribs and the bottom is added after the fact. I am joining the top and bottom of the fuselages and making a wing cut out so the entire fuse can be slid over the wing and epoxied to the center sheeting. The thought of silkspaning, filling, sanding, and painting two fuselages that are already permanently attached to the wing does not appeal to me, hence the change in mounting procedure.
A question I have about the plan is on orientation of the bellcrank:
https://i.imgur.com/mhBUdvY.jpg
It's reversed from normal, with the pushrod on the inboard side. Can any one tell me why it's installed this way? More importantly is it ok to mount it in the "normal" orientation? The push rod exits the wing next to the outboard side of the inboard fuse. I will probably move it all the way over next to the outboard fuse to keep as much exhaust/castor from the engine out of the exit hole as possible. I hope all the inboard outboard stuff doesn't read to confusing.

Jim
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Post  OVERLORD on Sat Sep 21, 2013 1:00 am

Jim,

You could turn the belcrank around, only the elevator will move the other way. The pushrod is on the inboard side because the stabilizer is located between the 2 fuses only.

Lieven
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Post  roddie on Sat Sep 21, 2013 3:35 pm

JPvelo wrote:
A question I have about the plan is on orientation of the bellcrank:
https://i.imgur.com/mhBUdvY.jpg
It's reversed from normal, with the pushrod on the inboard side. Can any one tell me why it's installed this way? More importantly is it ok to mount it in the "normal" orientation? The push rod exits the wing next to the outboard side of the inboard fuse. I will probably move it all the way over next to the outboard fuse to keep as much exhaust/castor from the engine out of the exit hole as possible. I hope all the inboard outboard stuff doesn't read to confusing.

Jim
That's a little different... I'd be wary of the "R/H" lead-out getting caught on the push-rod in that arrangement. The elev. horn must be mounted on the top instead of the bottom? Does the design "easily" permit modification to run the push-rod below the stab. to a "bottom-mounted" elev. horn, while still locating it along the outboard side of the inboard fuse? It's hard for me to visualize without seeing a full plan view.

Using a carbon-fiber push-rod would help keep tail-weight down too. I'm using .062" dia. solid C-F rod, with short (1/2"L.) pcs. of alum. tubing, CA glued 1/2 way on ea. end for couplings. (a clevis on one end and a short .062" dia. music-wire Z-bend on the other.)

Best of luck with it. I really like twins, and can't wait to see "this one" come together!

Roger







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Post  JPvelo on Sat Sep 21, 2013 4:31 pm

The control horn is on the bottom so it really makes no sense. I am going to move it and flip it and not worry about it. Where do I get a carbon fiber pushrod?

Jim
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Post  roddie on Sat Sep 21, 2013 5:47 pm

JPvelo wrote:The control horn is on the bottom so it really makes no sense. I am going to move it and flip it and not worry about it. Where do I get a carbon fiber pushrod?

Jim
Jim, I bought mine at a local hobby shop.They came 2 per pkg., are 24"L. and approx. 1/16" dia. (I believe .060" dia. is a std. "solid" rod size) There are also "tubes"... which have an i.d. sized for 2-56 Dubro threaded couplers to be glued in.

Here's some info./source

http://www.darrolcady.com/Carbon_Fiber/carbon_fiber.htm

http://www.cstsales.com/carbon_pushrod.html

http://www.midwestproducts.com/store/products/aa9a8bb3-7a34-4161-b281-8f337f65a669/1/Carbon_Fiber.aspx

Your best bet is to read-up on the push-rod assy. types. They are great for saving weight... very strong and rigid.

Here is some good reading on how-to's...

http://www.rcuniverse.com/forum/composites-fabrication-repair-97/10760393-carbon-fiber-push-rods.html
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Post  pkrankow on Sat Sep 21, 2013 7:08 pm

After discovering how tail heavy push rod paint can make a plane, mask the CF rod prior to painting. The larger diameter will pick up more weight from paint than wire.

Removing the paint from the pushrod moved my CG about 1/4 inch.

Phil
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Post  roddie on Tue Sep 24, 2013 7:09 pm

Hey Jim, here's what I'm using for push-rods on an RC model I'm building. Where excess "tail-weight" is a concern with your F-82... I thought you might be interested in this approach. What's pictured is "2" .060" dia. solid carbon fiber rods... 12" in length, with .062" dia. music-wire "Z"-bends coupled with .093" (3/32") dia. aluminum tubing, for my elev./rudder linkages.

Also in the photo, is a pc. of hook & loop mat'l... I may try using small pcs. of it at "midpoint" to support the rods... they are however; very rigid, and may not need support.

My postal scale reads in grams/tenths of an ounce... and without the hook & loop pictured; won't give me a reading. "With" both rods & hook & loop... the scale reads 0.10 oz./3 gr.

The solid .060" dia. carbon fiber rods I bought, were 24" long before I cut them. I used thick CA to assemble what you see in the photo. The music-wire was cleaned and "roughed-up" w/sandpaper prior to gluing-in to the alum. tubing.

F-82 Twin Mustang build thread- preliminary _060_c10
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Post  RknRusty on Tue Sep 24, 2013 7:44 pm


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