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Old Aug 29, 2007, 12:01 AM
aclosedmouthgathersnofoot
freeble's Avatar
Mansfield, Vic, Aust
Joined Aug 2007
228 Posts
Question
dihedral joint

hey everyone,
i'm currently doing my first build and am wondering how you make strong dihedral joint in the centre of the wing? is it also possible to shape or bend the balsa somehow to get the correct angle so as not to weaken the wing with a joint?
any suggestions welcomed!
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Old Aug 29, 2007, 09:16 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
13,187 Posts
Fibre glass works well for dihedral joints. 6 oz. cloth a little wider than the fuselage. Epoxy finishing resin you can get at marinas. I use a playing card for a spatula. Pour about a quarter size glop on the wing and squegee it out with the card. If it looks shiny, it's not spread out thin enough and your just adding weight. Depending on the size of the plane you can use lighter weight cloth. With the glassing method, you don't need a dihedral joiner. Don;t quite know what you mean about bending balsa.
Gord.
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Old Aug 29, 2007, 09:59 AM
aclosedmouthgathersnofoot
freeble's Avatar
Mansfield, Vic, Aust
Joined Aug 2007
228 Posts
thanks for the advice gord. i remember reading something ages ago about soaking balsa in something which made it shapeable, as i say it was a long time ago and i forget the details. you also mention a dihedral joiner, is this a tool or jig for dihedral joints?
thanks again
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Old Aug 29, 2007, 11:02 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
13,187 Posts
Dihedral joiner is usually a piece of plywood cut to a shallow V with the correct angle that the wing calls for. Long enough to go at least from the centre rib to the next rib and glued to the wing spars. Used to strengthen between the wings. For shaping balsa, water works just as well as anything. Some use water with ammonia but I find in unnecessary. For instance I built a P40 Warhawk about the size of the GWS planes, slightly bigger. Carved and sanded pink foam to shape of fuse. Cut 1/16 balsa to roughly the shape of one side of the fuse. Soaked in the tub for about 20 mins. Wrapped around the side of the fuse with horse leg bandages, these are light cloth strips about 3 in. wide. You could cut some strips from scrap cloth. Rubber bands will leave a mark in the soft wood. Let sit overnight to dry out. The wood expands quite a bit when you wet it, and shrinks back when it dries is why you can't glue it to the fuse when it's wet. Peel it off the next day like half an eggshell. Do the other half the same way. Cut the upper and lower centre lines to exact shape. Use aliphatic resin wood glue although any carpenters glue would work. I don't cover the wood with glue as it would add a lot of unnecessary weight. I use a zig zag sawtooth pattern bead on the foam, lay the wood on, wrap lightly with the bandages and let dry overnight. Do the other side th same way. I use light spackling compound to fill any defects then sand to finish. Hope this helps.

Gord.
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Old Aug 29, 2007, 11:33 AM
An itch?. Scratch build.
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South Wales U.K.
Joined Mar 2003
13,785 Posts
It does depend on the model and what you're going to do with it, but as I often like removable/split wings for transport I sometimes use wood dowels running in paper tubes for plug-in wings.

The one in the picture below, (own design for stooging around and aerial photography), actually was the two wing halves just butted together with two layers of clear tape on the bottom joint and one layer on the top.
The original idea was to undo the top tape and use the bottom tape as a hinge to fold the wings, (underside to underside), for carrying the model in the car boot, (trunk).The model has been looped regularly, not problems.

As for joining two pieces of balsa together for l.e., spars, t.e. dihedral breaks etc, do a good tight scarf joint, (angled overlap).
Any doubts, try a test piece and try and break it, the wood will usually go before the joint.
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Old Aug 29, 2007, 08:09 PM
aclosedmouthgathersnofoot
freeble's Avatar
Mansfield, Vic, Aust
Joined Aug 2007
228 Posts
thanks fellas, i knew i'd get great advice using this forum! gord you jogged my memory...it was ammonia that i'd read about ages ago. i think i'll hedge my bets and try both methods as i have built two of the same wing (always be prepared!).
thanks again
p.s gord, if you don't mind me asking,where did you get plans for the P40? i've been trying to get as many warbird plans as possible and the P40 is such a beautiful plane. so far i have plans for MK V, VIII & XVI Spitfires, P47 D Thunderbolt and North American P51-b to name a few but am always looking to expand my options (as much as the wife will allow!)
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Last edited by freeble; Aug 29, 2007 at 08:18 PM.
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Old Aug 29, 2007, 08:50 PM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
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There is a Russian website that has the best three views I've found but my computer took a dump and lost all my favorites. If any one knows that website, let me know. I get good drawings and blow them up with a calculator and ruler and a roll of butcher paper. I enjoy that as much as the building and flying. Couple of others were the Vought Cutlass, about the same size as the P 40 and a 9 ft. W.S. FW 190 D9. Homade retracts for that one made from electric screwdriver motor,gearboxs.
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Old Aug 30, 2007, 12:03 AM
aclosedmouthgathersnofoot
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Mansfield, Vic, Aust
Joined Aug 2007
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well if you have Autodesk on your pc you are more than welcome to my plans, they are .Dwg & .Dxf files so if you don't have Autodesk there is freeware on www.autodesk.com
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Old Aug 30, 2007, 12:28 AM
Rocket Programmer
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United States, AZ, Mesa
Joined Jul 2007
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You can soak balsa in water and let it dry in a form, but it weakens it severely, and that method is only suitable for static models or non-structural (cosmetic) parts.
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Old Aug 30, 2007, 12:35 AM
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Quote:
Originally Posted by jasmine2501
You can soak balsa in water and let it dry in a form, but it weakens it severely, and that method is only suitable for static models or non-structural (cosmetic) parts.
Hi Jasmine,

Could you expand on this? I've never heard of that before!

Thanks,

Chuck
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Old Aug 30, 2007, 12:54 AM
Rocket Programmer
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United States, AZ, Mesa
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There's some information about it here:
http://www.smarttoolsinc.com/Model_K...onArticle.html

He talks about how you don't really have to steam it or soak it, and this might be a better method. Again, it does weaken the wood. I used this method to make balsa wood strips to make realistic-looking hull boards for ships. If the bend doesn't have to be too extreme and there are structural factors which will hold it in shape, you can just bend it, then wet it, and it will keep it from cracking about 75% of the time. The other 25% of the pieces you just have to throw away. Variations in the grain mean it doesn't always work, and steam-bending is used on thicker pieces... the process can be used to bend super-thick pieces of wood for furniture, which is how one of these is made, I think.

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Old Aug 30, 2007, 01:04 AM
is it supposed to smoke??
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canada alberta outside edmonton
Joined Apr 2007
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i would steam over soak id say soak would be way worse imo. but hey make some ribs under for support and you should be ok
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Old Aug 30, 2007, 08:06 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
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Both ways work equally well. Your soaking the wood with water either method. Steam is just faster, as your using heat and pressure. To many other factors involved as far as splitting the wood. Hardness, direction of the grain, how long it soaks, experience etc. Semi soft, straight grain wood bends like cardboard with no loss of strength. This P 40 is about 10 yrs old and has't split yet. The article above doesn't mention about it weakening the wood.

Gord.
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