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Old Oct 24, 2011, 04:40 PM
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Jim.Thompson's Avatar
Australia, NSW, Bellingen
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Fuselage Plug with Fin questions.

I have plans to construct a fuselage plug with included fin for my first X tail moulded glider.
I am going to use laminated MDF sheet for the fuse.
My question is how do I construct the fin and what material to use?
My first thought was to shape the fuselage to a satisfactory degree of symmetry and shape then hot wire cut the fin, glass and glue it to the MDF plug. Fillets can then be added and faired out etc.
Just to clarify, I do not have access to a CNC machine. This will be a hand shaped plug.

Jim.
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Old Oct 24, 2011, 06:00 PM
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Jim, that is how I would add a fin.
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Old Oct 24, 2011, 11:43 PM
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Thanks Adam. I really cannot see any other way to do it actually.

Jim.
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Old Oct 25, 2011, 10:29 AM
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Jim,

I carve my plugs from basswood. I do the same carve the fuselage to satisfaction and then I make the fin from aircraft plywood. Then shape-fill-finish like the rest of the plug. Of course any joint may be a source of damage when the plug is removed from the mold. Therefore, make sure your connection of the fin to the fuselage is sound. I have never had good results using foam as a plug material.

My 2 cents.

Dan
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Old Oct 25, 2011, 04:27 PM
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Originally Posted by dkane View Post
Jim,

I carve my plugs from basswood. I do the same carve the fuselage to satisfaction and then I make the fin from aircraft plywood. Then shape-fill-finish like the rest of the plug. Of course any joint may be a source of damage when the plug is removed from the mold. Therefore, make sure your connection of the fin to the fuselage is sound. I have never had good results using foam as a plug material.

My 2 cents.

Dan
Dan,

How do you shape an airfoil section from the plywood? Do you use external templates?

Jim.
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Old Oct 26, 2011, 01:12 AM
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Jim

i used ply wood to carve out a fin, using airfoil templates on either side, and then its lots of sanding. whats great about it is the plywood sheets form contour lines on the plug which help to gauge accuracy when sanding.

i prefer foam though, much faster as i have a cnc , two layers of 160g, fast hardner, and in the hot box for 3 hours and its ready for filling
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Old Oct 26, 2011, 09:35 AM
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Originally Posted by Jimbello View Post
Dan,

How do you shape an airfoil section from the plywood? Do you use external templates?

Jim.
Jim, if you need a specific airfoil, it can be roughed out via CNC or templates. I have done both with good success. As was stated, because of the layers in the ply you have good reference lines from side to side due to the shape. If you need a quick and dirty fin similar to what you would have done with balsa sheet, rough it out on a belt sander and use a contour gauge to verify the shape.

One more note, depending on how you do your fuselage plug, you can have a nice flat surface if you make it in halves and your splitter is simply a solid sheet vs. cutting out the shape and sinking it in. I have done this a couple of times, it allows you to lay up both mold halves at the same time (I know longer process on the day of making the mold, but you don't need to let one side cure before moving on to the next).

Again, if you are comfortable with foam go ahead. My personal preference is wood.

Dan
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Last edited by dkane; Oct 26, 2011 at 09:41 AM.
Old Oct 26, 2011, 03:34 PM
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Quote:
Originally Posted by dkane View Post
Jim, if you need a specific airfoil, it can be roughed out via CNC or templates. I have done both with good success. As was stated, because of the layers in the ply you have good reference lines from side to side due to the shape. If you need a quick and dirty fin similar to what you would have done with balsa sheet, rough it out on a belt sander and use a contour gauge to verify the shape.

One more note, depending on how you do your fuselage plug, you can have a nice flat surface if you make it in halves and your splitter is simply a solid sheet vs. cutting out the shape and sinking it in. .................. My personal preference is wood.

Dan
Thanks Dan. I like the benefits of the plywood for the fin as you describe. I'm tentatively thinking that the centre of the full plug laminate might be good plywood. Then the outer layers could be MDF to provide sufficient width for the fuselage body.
I will be making my plug in one piece. This avoids any problems of alligning the two halves! And also its easy to rout full length allignment keys as described by Adam of WyoWindworks. (et.al.).



Jim.
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Last edited by Jim.Thompson; Oct 26, 2011 at 03:37 PM. Reason: Additional question.
Old Oct 26, 2011, 03:44 PM
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Further challenges.

Just to clarify, this project is planned to be a bladder joined fuselage (with included fin) as described over in the inflation bladder thread. The plan is to have a full flying stab. I am wondering how I am going to install the bellcrank for the full flying stab into the fin after the fuse is made in one go?
This is off the main topic of the thread I know, apologies for that.

Jim.

edit: I have realised that the bellcrank installation will not be the problem that I first thought it would be.
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Last edited by Jim.Thompson; Nov 19, 2011 at 01:25 PM. Reason: Answer to bellcrank question.
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