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Development of Aircraft Structures | |
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The very early airplanes were built from very lightweight materials such as bamboo, wood, and fabric. They were designed much like bridges, with beam and truss construction. The wings on the Wright Flyer form a truss; the two wings used wires and bars diagonally (at an angle) to strengthen the wing against aerodynamic forces. Other airplanes used this construction, too. The insides of wings were also a type of truss construction. The bars inside were called spars. Wires were used on the diagonals to strengthen the wing. The spars, plus the spar caps at each end, were shaped to give the wing aerodynamic features. This shape is often called the airfoil. The figure below shows the basic construction of the wing of the Sopwith Camel, World War I fighter.
As manufacturing techniques for metals improved in the early 1900's, metal rods and pieces began to replace the wooden components in airplanes. Metal skins, rolled very thin, were used because they were less affected by weather than the fabric skins. The ribs and spars of the plane were made by riveting many pieces together. When aluminum alloys became available at the end of the 1920's, ribs and spars were often stamped (cut) out of whole aluminum sheets. When an airplane flies it has stress or loads on its frame. At first, the wood or metal frame took all of the stress. The fabric or thin metal skin was not strong enough to take any of the load. Later, thicker metal skin was put on airplane frames. This thicker skin was able to share the stress. The metal frame could then be made of lighter metal. The planes then weighed less overall! As metals were used on airplanes more often, the basic design of airplanes also changed. The original biplane design (two wings) with struts and bracing wires, was no longer efficient at the higher speeds that were coming into the field. The spars and wires caused more drag at the higher speeds. Using metal skins to carry some of the load (of the frame) made the biplane design no longer necessary or desirable. Monoplanes (single wing) create much less drag than a biplane. Also, the monoplane did not have the struts and wires sticking out, like the biplane. Design work continues in the field of aircraft structures for a better
balance of weight and strength. New structural designs are helped with
better manufacturing methods. This has produced better structural parts
and alloys (metals).
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