McMullan Aircraft Design


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Birth of an Airplane

JayBird Design Page

Page 4

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IMPORTANT: All drawings, photos, and information presented on these web pages are the sole property of Jay S. McMullan and are © 2002. Nothing on these pages can be copied or reproduced in any way without the written, expressed permission of Jay S. McMullan and/or his assigness.

Building a Wood Fuselage

On this page, I've kind of jumped ahead some. Since I have already done much of the preliminary calculations and sizing of the airplane, I jumped ahead to drawing the fuselage. This is where it really gets fun for me.

If you have ever built a flying model airplane out of balsa sticks, you will see that a full size wood airplane can be built the same way. Wood is one of the best building materials for an airplane even in the days of aluminum and composite construction. With the JayBird, I will used Clear Vertical Grain Douglas Fir. Many wood airplanes have been built out of Spruce in the past which is an excellent, lightweight, strong material. Spruce is cost prohibitive in our society. Douglas Fir is much less expensive. It is also quite a bit stronger than Spruce but it is also heavier. For me, the trade offs are acceptable.

Wood airplanes are generally built by first building a ladder type truss. When both sides of the airplane are built, they are joined together at the front of the fuselage and then the back of each side is pulled together to give the airplane the streamlined shape. Then each of the horizontal formers are glued into place. Before the first fuselage side is built, the builder must have a perfectly flat work surface so that each side will be perfectly flat and square.

With the JayBird, we will basically be building a tub or a structure that looks kind of like a canoe with one flat end. This tub will carry all of the fuselage loads. The cowling, windshield and turtle deck are all mainly on the airplane to streamline the structure.

The JayBird uses the basic truss design that most wood airplanes use.

In the drawing above, the bottom two images show what the fuselage tub will look like when completed. The bottom image shows how the side structure is layed out in the beginning steps of construction. The top and bottom longerons are laid out on an extremely flat table. Then the vertical formers are glued into place. Two sides are built, a left and a right side. When the glue is completely cured, each side is laid upside down on the top longeron and the front, horizontal formers are glued and clamped in place. The first four formers are glued into place. When the glue is cured, the back of each side is pulled together and the rest of the horizontal formers glued in place. After all of this comes the tedious task of cutting and gluing in gussets at each joint. The gussets will increase joint strength immensely.

The drawings above were done in AutoCad. The JayBird is being designed in 2D, or two dimensions. Then the airplane will be "built" with a 3D parametric modeling software. By designing the airplane in three dimensions, I will be able to make sure parts fit perfectly without having to build an actual prototype of the airplane. Also, by doing this, I can know what the airplane will weigh when it is built and by using finite element analysis programs with the 3D drawings, I can see if there weak spots in the airplane or if there are parts that are "over-built". I can also run wind tunnel tests on the airplane without having ever built a prototype. The cost savings are substantial by using modern computer software!

When the fuselage tub is completed, the firewall, instrument panel and turtle deck can be added. The tub will be covered with 1/8 inch Birch plywood. Then, fiberglass cloth and resin will cover that. This will give an incredibly light and strong structure.

The beginning stages of building the fuselage tub is drawn and actually "built" using 3D modeling computer programs.


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