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Old Feb 10, 2013, 05:57 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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Hi Pat,

Nice work and great tutorial for Styrospray and the canopy of course.
I just bought some SS this week to use on my project.
I had some idea how to use it from Fahim's website, your tutorial clarified some things for me.
The canopy tutorial is excellent, completely filled in everything I had questions about.

Cheers,
Eric B.
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Old Feb 11, 2013, 10:41 PM
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Got started on the wing. I did the center section first. I made the center section from nacelle to nacelle constant chord. Some 3-views show a slight taper but I simplified it.

I'm using the "laser method" for building wings. It combines the best features of a built up and foam cored wing. I'll do this one a little differently. Instead of using many thin rib blanks (see my blog for links to earlier builds done this way) I'll use a solid core but make cuts to make the ribs and remove much of the core. This is very similar to a method described in Keith Sparks' Building with foam.
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Old Feb 12, 2013, 01:13 AM
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Absolutely amazing Pat, something I have never tried building with foam thanks for the master class, Ken
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Old Feb 12, 2013, 07:16 AM
Now in TN!
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Nice work Pat

J
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Old Feb 12, 2013, 07:57 AM
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Originally Posted by heli_madken View Post
Absolutely amazing Pat, something I have never tried building with foam thanks for the master class, Ken
Thank you for the kind comment. I've certainly been enjoying your HS 129 build. That's like a master class in balsa!

You can, of course, use this technique with balsa sheeting. As you increase the size of the wing the benefits of balsa's combination of compressive and tensile strength compensate for it's higher per sq ft. weight. Foam is cheap, light weight, and available in big sheets so it's what I prefer to use at this scale.

The really nice thing about this technique is that it's easy to design a wing. I start by drawing (no CAD here!) in ribs where I need them for internal structure and then just fill in the spaces between. There's no need to draw each rib; really handy for tapered wings. The hot wire templates have the dihedral and washout angles built into them. If I needed to add wood ribs for say, a retract mount, I'd trace the top of the rib after the first cut and trace the bottom after the second cut.
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Old Feb 12, 2013, 08:05 AM
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Originally Posted by J Morgan View Post
Nice work Pat

J
Thanks John.

Talk about a master class in building with foam! Your F-16 is off the hook! (Literally in this case.)
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Old Feb 12, 2013, 08:21 AM
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USA, MA, Swansea
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Fantastic work. One of the most interesting new ways to build I have seen for some time now. The only thing I am not a fan of $$Tree foam. I am now using MPF foam. Although availability of $$Tree foam may be the only option for some in isolated areas to get their hands on easily. I like your table foam cutter a lot too.
*Neons**Bob
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Old Feb 12, 2013, 08:48 AM
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Originally Posted by **neons** View Post
Fantastic work. One of the most interesting new ways to build I have seen for some time now. The only thing I am not a fan of $$Tree foam. I am now using MPF foam. Although availability of $$Tree foam may be the only option for some in isolated areas to get their hands on easily. I like your table foam cutter a lot too.
*Neons**Bob
$Tree foam is readily available but you do have to pick through the box to find sheets without ripples. If MPF offered 1/8" sheets I'd order a box today for wing skins (listening MPF?)

IIRC, the cutter's basic design is right out of Keith Spark's book. Just a 2x4 with holes drilled into it for 1/4" steel rods screwed to a piece of melamine coated shelf stock with a saw kerf to allow the hot wire to sink below the level of the board. Works great for squaring up foam blocks. Rest the wire on a couple of spacers to take horizontal slices off a blank like I did for the rudders.
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Old Feb 12, 2013, 10:13 AM
The "pro" in procrastination
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Canada, ON, Kingston
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Great stuff, Pat. I'd seen your "laser method" before, but your tutorial on the canopy is a new one for my "techniques" folder. I can see it's got broad application to many vacform tasks, such as cowlings, nacelles and fuselage parts. Thanks for sharing your secrets!

Steve
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Old Feb 12, 2013, 11:32 AM
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Very cool. So you are saying this is cheaper and lighter than using a solid foam core and sheeting with say 1/16" balsa?

I have to get Sparky's book.
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Old Feb 12, 2013, 12:36 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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Again excellent work on the wing.
Thank you for going into such detail.
I have marked this blog thread as an excellent tutorial in foam, it has become my favorite way to build in the last few years.

Eric B.

PS, I also have Keith Sparks book, it has given me a lot of inspiration.
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Old Feb 12, 2013, 01:03 PM
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Quote:
Originally Posted by Steve Merrill View Post
Very cool. So you are saying this is cheaper and lighter than using a solid foam core and sheeting with say 1/16" balsa?

I have to get Sparky's book.
Foam is certainly cheaper than 1/16" balsa. About 1/4 the cost for bulk balsa per square ft. and much less if you're buying select, contest grade balsa. The weight of 1/4" XPS is about the same as a medium to light grade of 1/16" balsa per sq ft. $Tree foam is about 2/3 of that. More weight savings come at the finishing step, unless you use an iron on film, filling and sealing balsa adds more weight than prepping foam to paint. The numbers I use, based on several builds where I've carefully kept records, is 20 g/sq ft for foam vs. 25 g/sq ft. for light (but not super light) 1/16" balsa. Both would be just the skin ready to paint covered in either paper/wbpu or glass/epoxy. Not a tremendous difference but there's a lot of area on a wing and every little bit helps.

The solid foam core vs. laser method depends on the volume of the wing. Below is a chart I made based on measured data and calculations of the weight of a 1lb EPS foam core at several sizes (NACA 23015 airfoil and Do-335 wing I think).

I no longer have the original notes but I assume the laser wing is foam covered and the solid core wing is 1/16" balsa. The point is as the size of the wing goes up, the weight of a solid core rises faster than the area. A built up wing saves a lot of weight when you get to giant size planes.

Sparky's book is good. I haven't seen the second edition but I assume it's better than the first (which I have.) What's nice is he presents a complete system from design to finish where you could build a plane from scratch from a decent 3-view. Are there better ways to do certain things? Sure, but much of that is personal preference; would you rather spend your time sanding or making elaborate hot wire templates? Stuff like that. At least you get enough of a background to start building then you can settle in on your favorite ways of doing things.
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Old Feb 13, 2013, 07:04 AM
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The airplane on my Avatar here on RCG has a solid core foam wing, sheeted with balsa, and covered with Monokote. I had the cores made for me, and they were not cheap. Will have to try this method.
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Old Feb 13, 2013, 08:26 AM
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Here's a shot of the 1/4" balsa leading edge. I dropped the wing back into the hot wire bucks to hold the wing while I planed the LE to shape.

I glued a 2.5 mm bamboo round to the TE. It really makes the foam TE stiff and durable. The bamboo rounds came from a roll up blind from the home center clearance bin.

I'll sand the foam down to the bamboo and after some filling it will be ready to cover.
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Last edited by pmullen503; Feb 13, 2013 at 11:38 AM.
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Old Feb 16, 2013, 06:44 PM
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I marked the wing and cockpit cutouts using a tracing of the wing center section and a full size printout of the cockpit I traced from a 3-view. The wing airfoil is NACA 2412 root to tip with 2 degrees wash out and 1 degree positive incidence. I've found the 2412 to be a good sport airfoil with less drag and more aerobatic than a Clark Y but still with good lift.

Before making the cockpit cutout I marked the canopy frame. It was much easier with the fuselage intact. I then transferred the lines to the canopy. It took me three tries but I finally got a reasonably good canopy.

I added an additional bulkhead below the wing and the servo mount in a way to firm up the area that I'll grip for hand launching. I'm planning to mount the ESC's on the underside of the center wing section in the area ahead of the elevator servo. That way all I'll have to disconnect is the elevator servo to separate the wing from the fuselage. If I need to, I can hide some cooling air intakes and exits under the wing, similar to the Aeronaut He-219.
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Last edited by pmullen503; Feb 17, 2013 at 07:34 AM.
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