Atmospheric Flight

Structure

All the different pieces of an airplane must be held together by a sound structure, like a frame in a building or the chassis of a car. The structure must be strong enough so that the airplane doesn't break when the aerodynamic forces are applied, and it must be stiff so that the pieces maintain their correct aerodynamic position during flight. Remember that aerodynamic forces depend on the orientation of the wing (especially the angle of attack) so stiffness against twisting is particularly important. The amount of force also depends on the flight speed. Design regulations include a "never exceed" velocity, and the manufacturer does not guarantee that the vehicle structure will survive loads at faster speeds.

It is generally possible to make structures stiffer and stronger by using more material. It is expensive to buy the extra material, but it can be worth it to avoid worrying about structure failure. Unfortunately, for airplanes, the weight of the material is much more important than cost, because any extra weight in the body of the airplane means less weight is available for payload (passengers or cargo). Airplane designers need to make things just strong enough. An airplane that is too strong cannot carry payload efficiently.

Airplanes are made of materials that are stiff, strong and light. Early airplanes were made from fabric and lightweight, but strong wood. Later they were constructed of lightweight sheet metal. Now airplanes are made up of a mix of fabricated metal and composites that provide strength without adding tremendous weight.

Great care is taken to figure out just where the loads occur within the structure so as to maintain the airplane's center of gravity.

This is a picture of the X-33 under construction.

For this Mars airplane problem, the relative weights of alternative designs will not be calculated. Be aware that smaller airplanes are generally lighter, and since the Mars airplane will not be designed as a full-scale airplane, it can be built of lighter weight material from which an ordinary Earth-bound airplane could not be constructed.

Table of Contents