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Old Aug 21, 2010, 08:17 PM
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Independence, KY and Brandon, MS
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The Comet Stinson SR-7 - Another Free Flight conversion project - Video Addeded

Earlier this year I decided to revisit a model from my youth and built a rubber powered Free Flight Comet 25 span Stinson SR-7. It became such a good flier that I decided an RC version was in order. Between the recently released Pat Tritle Stinson SR-10 kit and the ParkZone Stinson Reliant I guess I am in good company in terms of wanting an RC Stinson. As a result, I thought I would do a build log of the project.

The Comet kit dates way back to the 30s and has held up well over time in terms of the overall balance between scale and flyability. The Comet designers certainly took some liberties relative to scale fidelity, but the model does retain the distinctive lines of the full scale airplane while providing for a very good flying platform.

With the availability of the great gear these days my thought was a fairly simple conversion of the Free Flight design could be accomplished. My Free Flight Stinson weighs just under 40 grams without a rubber motor. Using something like a brick receiver/servo package and one of the popular brushed RTF motor packages, my goal is to build an RC Comet Stinsion that does not exceed 45 grams flying weight.

My equipment choices are the Specktrum AR6400 receiver, the motor/gear drive from the ParkZone Micro P-51, and a 150 mah lipo cell. I plan to only use rudder and elevator flight controls so the AR6400 is over kill, but it may get used in a future project that will need the added channels.

Now on with the project. I use iron-on transfer paper to transfer the parts to sheet balsa. After cutting out the parts I began construction with the fuselage. Both sides get built over the plan. The second side is built on top of the first side to make sure they are exactly the same.

Once each side is built they are joined using the formers in the center of the fuselage section. Once that is complete the sides are joined at the rear and the remaining formers are added.

With the fuselage sides joined the nose section gets built. I developed a simple jig to help that process. The transition from the rectangular fuselage cabin area to the round nose requires something more in my opinion than eyeballing cracking and bending longerons as called out on the original plan. The jig holds the round forward former while nose longerons and stringers are added. Once the nose is completed the jig is removed and the remaining stringers are added to the fuselage. Also added is the cabin roof and the landing gear support plate.
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Last edited by PaulBrad; Oct 10, 2010 at 08:58 PM.
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