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Old Jan 18, 2013, 09:48 PM
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Underside of Star Ship

A couple of images showing how I strengthened the underside of the Harpy Cat.

I noticed that with the original design it was easy for the back end of the plane to twist under stress. My attempt to rectify the situation was to glue three strips of foam to the underside as demonstrated by the images below.

I also included an image of the location of the servo for controlling the elevons and ailerons.

As it works out, the COG is located immediately behind the servo or 16" from the nose.
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Old Jan 22, 2013, 06:38 PM
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Strengthening the vertical tail assembly

In order to strengthen the twin boom tail assembly I opted for an extra layer of foam rather than the more expensive carbon rod option.

As you can see in the image below I simply made a couple foam plates and laminated each to create a stronger vertical stabilizer.

You can use carbon rod if you don't like the look of the extra plates.

Also note the "strakes" attached to the horizontal stabilizer.
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Old Jan 22, 2013, 06:52 PM
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Final decorative details

To give the plane an interesting look I opted to add wing cannons and some sort of propulsion system protruding from the upper surface of the wing.

The wing cannon assembly was made by laminating two 6mm Depron foam shapes into an appealing body where the gun would protrude from. A half circle was added to the tail end and a "dart" was added to the top to give the shape a little more complexity. The larger barrel is made of wooden doll rod with a small recoil system made of CF rod.

The propulsion system was composed of several parts.
  • A rectangle three sided box made of foam then sanded to shape.
  • Foam circles cut and sanded.
  • Small triangles positioned between the circles, topped off with a foam rod connecting the two units visually.

Note in the finished image bits of black between the "spokes" of the propulsion system. This was intentional. I tried to simulate grime by applying a coat of diluted black acrylic paint, brushed on with a soft artist brush.
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Old Jan 22, 2013, 07:21 PM
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Getting ready to paint

One of the early frustrations I had with painting foamy models is that the enamel paint I used (Valspar enamel) ate the foam. That bugged me. All that work on creating an interesting model with a finish that looked like the surface of the moon. Then I read of a little trick while reading RCGroup forums that completely changed my mood about painting foam.

After spackling with DAP Lightweight Spackle and sanding, I apply a coat or two of Minwax Polycrylic clear satin to the foam. I slather it on all exposed surfaces, let it dry, sand and repeat if necessary. This does a couple of things for my model:
  1. Acts as a barrier so I can apply enamel spray paint preventing it from eating the foam.
  2. Improves the final look of the painted surface.

After the Polycrylic dries I use Valspar enamel spray paint to cover the entire model. I then apply Tamiya acrylic model paints, applied from an airbrush or Liquitex artist acrylic paints with an artists brush.
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Old Jan 22, 2013, 07:41 PM
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Impressions

Just before painting but after I've applied the clear Minwax Polycrylic I make impressions into the foam using several tools and found objects. The goal is to add a little pseudo complexity with little effort.

Pictured are a few of the tools I use to make lines in the foam, odd shapes, etc.

I purchased the dental tools from a local flea market. Other objects include wire nuts, screwdriver tips, sharpened end of hollow brass tube, square aluminum tubes and just about anything you have laying around the garage that has an interesting shape.
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Old Jan 22, 2013, 08:18 PM
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Stenciling

I enjoy creating my own "decals." The method is simple but requires a little patience in creating them. Your efforts will be rewarded.

You can create single or multilayer stencils to achieve your goals. The easiest stencils to create involve bold lines without a lot of intricate details.

The images below show how I created a three layer symbol. The first stencil is for the base layer of white paint. The second stencil for the middle red layer and the third for the top black layer. Here's how I did it.

I created the symbol with the free program Inkscape. I then printed the image three times. After printing I penciled in "registration marks" to help properly align each stencil used. I then covered each stencil with 2" clear packing tape to add strength and to help keep the paper from tearing while cutting out the shapes with an Exacto blade. Finally the tape helps prevent the paper from curling when I spray paint from airbrush or spray can.

I then cut out the pertinent shapes for each stencil. As you can see in the images below, I cut out a large square in my first stencil. This became my white background. On the second stencil I cut out the shapes that would be red. Finally I cut out the shapes that would be black. I then sprayed a light coating of Elmer's' Multipurpose spray adhesive on the back of each stencil allowing me to stick each stencil in place while I airbrushed.
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Old Jan 22, 2013, 08:26 PM
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Other stencil work

These images show other stencil options.

One of the easiest stencil projects comes from looking up different types of fonts, importing them to your PC then printing out various words and letters with your favorite word processor.

The #36 imaged below was from a fancy font set. I printed the number in two different font sizes, applied 2" inch packing tape mentioned in the last post then cut out each stencil. Finally the adhesive mentioned in the last post was applied. The larger font became my white background, the smaller the black foreground.

The alien lettering is from an alien font, typing the most interesting shapes then printing, taping, cutting, etc. Obviously these are single layer stencils.
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Old Jan 22, 2013, 08:31 PM
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That's about it.

If you've made it this far I hope you found something that inspired or interested you.
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Old Jan 23, 2013, 10:26 AM
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DontTellTheWife,

I'm impressed with your redesign and inspired to at least build a Harpy Cat. I especially like how you improved on the original design, intentional or not. Very nice build.

Ksqm
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Old Jan 23, 2013, 06:04 PM
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Ksqm:

Thanks for the kind words. I thoroughly enjoyed this project and was happy with the outcome.

I learned quite a bit from this project and will apply what I learned on a plane I'm developing. If it turns out how I hope, I'll share it with the foam scratch-building community in the form of a build log.
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