Build a Piper J-3 Cub for Flying Aces Competition

By SAM 27 Member Tandy Walker of Arlington, Texas

Sue and Tandy Walker with Tandy's Class A Lanzo Bomber.

 

Flying Aces J-3 Cub

by Tandy Walker

As you know, when I got interested in building a Flying Aces Club (FAC) model, I decided on the small AT-6 after reading an article about the AT-6 FAC competition in Flying Models. I ordered the plans and a canopy from Richard Zapf and proceeded with the fuselage construction to the point shown below.

It was then I started receiving several e-mails from a number of experienced FAC modelers suggesting that I had selected a somewhat difficult subject to make fly because (1) it was a low wing, (2) because it was relatively small with only a 21" wing span, and (3) it was going to be heavy with all of those stringers. The basic message that kept coming through was that I was doomed for flight failure with the AT-6 as my first FAC model. Therefore, I put the AT-6 project aside to be finished at some later time.

A year or so earlier (before the AT-6) I was told by Ed DeLoach to contact Mike Midkiff to help me get started in FAC modeling and to help me select a suitable "first" FAC model to build. I did and Mike was more than willing to help. We met over at Roy's hobby shop in Hurst and he selected the Herr Piper J-3 Cub kit for me to build, which was a larger model with about a 36" wing span. Then we went over to Mike's house and went through the kit. He made several changes such as reducing the wing dihedral and raising the location of the rubber motor pin at the back of the fuselage to change thrust line. However, I was still working on my Class A T-Bird free flight at the time so I did not start the J-3 Cub project and that has now been a couple of years ago.

Since then, I have completed the Class A T-Bird, finished up my full size Lanzo Bomber, built the FAC AT-6 fuselage, and recently built a 1/2A fuselage for the Fubar 43X. As I was considering my next building project, I decided to go back and work on the FAC J-3 Cub for a while before I start this winter's long term building project, whatever that is going to be

So Saturday afternoon I framed up the first fuselage side as shown below. The laser cut parts for a scratch builder are a real treat.

Then Sunday after church (and before the Cowboy game) I framed up the second side as shown below. Oh yes, notice the raised hole for the rubber motor aft pin that Mike Midkiff recommended.

This Cub is going to be a fun model to build. However, I keep thinking about the up and coming winter project so I have to be careful not to stop work on the Cub too soon..........................Tandy

I have spent the better part of the day assembling the two sides, adding cross members, diagonals and bulkheads. The picture below shows an interim step in the progress with the two central bulkheads installed, a few aft cross members, and the two sides sanded and glued at the tail post.

Two pieces of 3/16" I.D. aluminum tubing were cut to a 3/32" length and filed smooth. These were CA'd into the 3/32" balsa side members for the rubber motor pin as shown below

A proper length of 3/16" wooden dowel that serves as the rubber motor pin slides into the aluminum inserts snugly as shown below.

This is a proof view looking through the front bulkhead opening and down through the center line of the fuselage. It shows the clearance of the rubber motor with respect to the modified structural cross members. The cross members that were cut out had the same shape as the bottom cross members seen below.....................................Tandy

This is later in the day with four side diagonals glued in and all of the bulkheads installed as shown below. I have removed excess wood from several of the bulkheads as suggested by Mike MidKiff back when we went through the kit.

The Cub is a well designed model from a structural stand point, however, I have several issues with the laser cut parts. (1) The laser cut software file did not account for the width of the laser cut itself, so the cut parts are all slightly undersize and the notches are all oversize. :O< (2) Of course the laser cut is perpendicular to the plane of the sheet balsa so all part edges are square. However, there are many joints where the edges of the parts need to beveled to obtain a good fit. If the edges are sanded with the proper slope, then the part becomes too small. (3) And then there are the unsightly laser burned edges $#@&. My concern is that the brownish charring is going to show through the beautiful cub yellow tissue. Some of the outer edges can be lightly sanded to remove some of the charring, but many edges are just not accessible. I guess these issues seem picky to most of you, but I have been a self demanding scratch builder for many many years and I am picky! However, on this project I decided to just use the laser cut parts, undersize, burned edges, and all and do the best I can. I will just have to wait and see how it turns out....................................Tandy

There was a construction set back today when it was discovered that all of the top longeron cross members were in the line of the rubber motor as a result of raising the rubber motor pin in the back of the fuselage. The 3/32" cross members had to be cut out and some new 3/32" arches were made to replace the two rear cross members. The most forward cross member was cut out and a piece of 3/32" square balsa was glued across the bulkhead up from the top longeron about a 1/2" as shown above.

   

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