S41a Flivver (oz14733)

 

S41a Flivver (oz14733) by Thayer Syme 2004 - plan thumbnail

About this Plan

S41a Flivver. Free flight model for indoor flying. Wingspan 24 in, wing area 119 sq in. For electric power with DJ Aerotech MPS-1 geared motor. Uses foam construction.

Note this plan is available as a free download from the FlyRC site (see Datafile).

Update 1/10/2023: Added article, thanks to RFJ.

Quote: "Lightweight electric for small spaces. Gryffin Aeroworks S-41a Flivver, by Thayer Syme.

Over the last several months, I have been thinking more and more about designing a new model for indoor and backyard flying. A trip to Toledo and an upcoming article on indoor airfoils by Jef Raskin provided just the sparks I needed to get going. Now that I was committed, what was this plane going to look like?

I've long been a fan of the early English ultralight designs from the 1920s and 30s. Gryffin Aeroworks was not a company of the era, but it sure sounds like it could have been. The S-41a Flivver was clearly inspired by that era and keen observers will likely recognize several influences. Interestingly, full-scale airplanes of this type are regaining popularity, as pilots look for inexpensive quick-building designs to sate their hunger for flight. That sounds awfully familiar.

MATERIALS: With little spare time for the project, a sheet foam structure made the most sense. This model had to be quick to build. I chose Zepron foam from Air Dynamics for the basic building material. Made in the US, Zepron is similar to the Depron foam that is so popular in Europe. Zepron also has a light surface skin, which adds stiffness and ding resistance, and it is a perfect material for 'doodling' with new designs.

Zepron is easily formed using the heat of a covering iron or heat gun. I made a balsa form for the wing and inserted it, along with a wing blank, into the oven. Zepron heat forms at a relatively low temperature, so it may take some experimenting to find a setting that works for you. I would recommend 150 degrees for your first try.

Building the Flivver was almost a non-event. I printed my drawings at full size; then cut parts from Zepron sheets with a new X-acto blade. I had a complete set of parts within five or ten minutes.

Before you glue anything together, make some decisions about markings. I used some art markers to detail the wing and tail 'structure.' I got ahead of myself and mounted the wings before coloring the fuselage. If I get around to it someday, some trim strips of colored tissue will be applied with a glue stick.

I used PK Industries NI1000E foam-safe odorless CA to assemble the fuselage. For final airframe assembly, I used the faintest dabs of PK Industries 30-minute epoxy. Faster epoxy works as well, but I appreciated the extra time for alignment and attaching multiple parts. Whatever you use, go sparingly with the glue. There is no need to add extra weight. Even the smallest amount of glue will be stronger than the foam it is securing.

Make sure that you hinge the elevator before gluing the fin and stab onto the fuselage. It is captured in the fin cutout once the glue cures. I bought some 3M Blenderm adhesive bandage tape for the hinges..."

Supplementary file notes

Article.

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S41a Flivver (oz14733) by Thayer Syme 2004 - model pic

Datafile:

S41a Flivver (oz14733) by Thayer Syme 2004 - pic 003.jpg
003.jpg
S41a Flivver (oz14733) by Thayer Syme 2004 - pic 004.jpg
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User comments

Looks similar to a Heath or Church Midwing, but I don't think this is a scale model, per se. (Unable to find scale documentation) A very attractive model, nonetheless.
D A - 11/08/2023
Ah, good point. Ok have unset the scale tag on this one now. Thanks.
SteveWMD - 11/08/2023
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