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Old Dec 15, 2011, 07:13 PM
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Creating the Skip Stewart Prometheus Pitts

Hello all

Long story short, I've been itching for a nice electric biplane and after exhausting my search skills online I just couldn't find anything I really wanted. I found this thread - http://www.rcgroups.com/forums/showthread.php?t=1101221 and thought, "hmmmm, that's a good idea!" My dad had the same plane - a 42.5" Pitts Challenger ARF .40 and (according to him) it flew great. Yes, it's a nitro kit, but mine is going to be electric-powered. Soooooo, I ordered one and thought up a game plan. I've always been a fan of Skip Stewart, and really like his Prometheus S-2S....project underway!

I started this project by contacting the man himself (that's right, Skip Stewart!) and informing him of my intention, and asked if he could provide anything useful. He was overly gracious, sending me plans, scale drawings, graphics packages...everything I would need to re-create his iconic aircraft! Way cool , many thanks to Skip!!!

After looking over all of Skip's information while also looking at the untouched kit, I determined that I would need to do several significant modifications to achieve the results I wanted. Those are: 1) remove covering, 2) square off the wingtips, 3) re-make the rudder and elevators, 4) re-make the engine cowling, 5) re-cover in the Prometheus paint scheme, sponsorship logos, and graphics. Here we gooooo!
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Old Dec 15, 2011, 07:15 PM
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Step one: Remove covering.

This went very smoothly; the covering peeled right up. No heat, no special tricks...just find a corner, pull, and off it comes. Entire kit stripped in about 10 minutes.
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Old Dec 15, 2011, 07:19 PM
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Step 2: re-make the rudder and elevators.

This took a little graphics work on the computer, and some good old-fashioned eyeballing. Skip supplied a plan-view drawing of the rudder, so I basically measured the rudder on the kit, then scaled the file of his rudder to size so that the plans would print out to-scale.
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Old Dec 15, 2011, 07:22 PM
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Once the new rudder was built, I cut the rudder stab off at the top to accept the new rudder.
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Old Dec 15, 2011, 07:25 PM
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I had to eyeball the elevators, since there wasn't a plan to copy from. I basically just looked at several top/bottom views of the real Prometheus, and "winged" the shape and size.
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Old Dec 15, 2011, 07:32 PM
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Step 3: Square off the wingtips.

The kit's wingtips are balsa blocks glued to a horizontal plywood rib, which is then glued to the vertical wingtip rib. Initially, I attempted to remove the wingtips by de-bonding them, which worked on the first wingtip. I then tried on a second wingtip and could not de-bond it.
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Old Dec 15, 2011, 07:36 PM
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Then it dawned on me....just leave the wingtips glued on, and cut off all but 1/8" to square them. D'oh!
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Old Dec 15, 2011, 07:42 PM
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If you're paying attention, you already know that the ailerons are too short to reach the end of each wing. Remember those rib trailing edge pieces? Glue them to the ends of the ailerons, and sand smooth. Voila!

Hint! Ensure you glue these pieces to the OUTSIDE ENDS of the ailerons, so that the pre-cut hinge slots maintain alignment. You'll realize the mistake if you glue them to the insides of the ailerons.
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Old Dec 15, 2011, 07:46 PM
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The real Prometheus has no canopy visibility cut-out in the trailing edge of the top wing, so neither will this model. I glued a scrap piece of balsa in and sanded smooth.
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Old Dec 15, 2011, 08:04 PM
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Step 4: Re-make the engine cowling.

Why, you ask? Because the cowling that comes with the kit is just downright ugly, and (in my opinion) totally defeats the purpose of attempting to copy the Prometheus. The cowling on the S-2S is unique, and I want this model to look exactly like the real deal. So, I used the kit cowling for measurement purposes and started making a new one.

I acquired the 8"x8" foam block from Hobby Lobby. It was perfect for making the mold for a new cowling. It cuts and sands easy, and is very hard (won't compress). Like most foams, it's melted by acetone and thinners so USE SPARINGLY WHEN CUTTING DOWN YOUR RESIN FOR FIBER-GLASSING!!!
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Old Dec 15, 2011, 08:15 PM
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Glassing is pretty straight-forward. I used 3/4 oz. glass, four layers thick, one layer at a time. Each layer is about 5 pieces, cut and laid as flat as it would lay. The cowling has several compound curves which are difficult to form with the glass. Before you put resin to the glass, cut a top, front, sides, and a bottom, then work each piece. Let each layer dry, sand smooth, and layer again, until about 4 layers thick.
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Old Dec 15, 2011, 08:29 PM
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Currently, 4th glass layer is drying. Once dry, I plan to remove the foam block and apply a layer of thick fiberglass mat to the inside of the cowling.

On a side note, one of the files Skip sent me was a graphics file; it contains all the sponsorship logos, decals, etc. displayed on the real Prometheus. The file is in .ai format - that's Adobe Illustrator - so I downloaded a free trial version of that program from Adobe so I could open and view the file. The download is a full version, not a read-only or limited version, so I was able to hastily learn how to operate the program and scale-down the graphics to fit my model. I then sent the file to a local graphics printing shop and am having them digitally print the graphics onto vinyl, which I will apply after re-covering the airplane. Pics of this to come!
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Old Dec 15, 2011, 08:42 PM
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Your conversion is going great thus far. Very inspiring work. The cowling looks very authentic, even if done by eye-ball!
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Old Dec 15, 2011, 09:21 PM
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The pics really don't do the cowl justice (yet), the foam block just isn't very photogenic. Once finished though, it'll look great!
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Old Dec 16, 2011, 06:57 PM
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After laying the fourth layer, I personally felt like the cowl was still too weak/flexible to remove from the foam block. Rather than spending all day laying more layers of 3/4 oz. glass, instead I went with a single layer of 2 oz. glass. I was concerned that it would not lay nicely across the compound curves, but after cutting 5 pieces (front, sides, top and bottom) and laying each piece just like the 3/4 oz. glass, it laid down quite easily. Cool

If I could go back and start from scratch knowing what I know now, I would've laid a single layer of 3/4 oz. glass, followed by a single layer of 2 oz., then a layer of heavy mat inside. Layer after layer of 3/4 oz. was unnecessary and time-consuming....lesson learned!
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