|
|
Introduction | |
page 1 | |
|
|
Introduction The study of structures determines how the aerodynamic loads (the pressures and forces) on the aircraft are distributed so that no one part of the plane is pushed beyond its limit and breaks. This includes both the predicted performance of the aircraft and unexpected events such as gusts of wind or overspeeding the airplane (operating above the normal flight speeds). As far as the four forces of flight are concerned, the science of structures directly affects the weight of the aircraft. The goal for the structural designers is a plane that is as light as possible, yet strong enough to withstand the aerodynamic loads. Aircraft structural design varies from other structural fields because of this requirement that the plane be both lightweight and strong. The weight of the aircraft in the calculation of the four forces of flight is the total weight of the plane: the aircraft itself, the passengers and crew, the baggage and freight, and the fuel. This total weight must be balanced by the lift for the airplane to fly. Structural designers, then, refer to different weights as they work on a new airframe: the empty weight, which is the weight of the aircraft and all its components; the payload weight, which is the total for the passengers, crew, and baggage and freight; and weights associated with the various portions of the flight such as takeoff weight, average cruising weight, or landing weight. These last values are the sum totals of the empty weight, the payload weight, and the weight of the fuel at the time. As an airplane is prepared for a flight, several tradeoffs in weight may take place. There is a limitation on the maximum takeoff weight versus the runway length, for example. Even though an airplane could fly with a heavy load to its destination, it may not have enough runway to get airborne! A heavy payload may also decrease the range, or distance the aircraft can fly, because the heavier payload must be offset by less fuel weight. With less fuel, the plane can't fly as far. For a heavy payload and a long range, an aircraft would have to be designed with a higher structural weight with possibly larger, heavier wings or a larger, heavier engine to meet the takeoff and landing requirements. The higher structural weight contributes to an even higher total weight for the aircraft! The ability of the airplane to withstand the aerodynamic forces during flight is the other important part to the science of structures. The aircraft structural designer builds with 2 goals in mind: the first is to minimize the loading on an individual piece so that it will last for a long while, and the second is to coordinate all the pieces so that if one unit fails, the other units can absorb the load. This first goal is called safe life, and it pertains to having as small a load, or force, as possible on an individual component of the structure. Over time, even small loads can wear out a component. The structural designer works so that the time for this fatigue failure is beyond the expected lifetime of the airplane, or at least until well after the part is scheduled for replacement. Fail safe is the second goal, and it means that the overall airframe is designed so that one failure in one component doesn't cause the whole airplane to come apart.
Web Hosting Provided By The National Business Aviation Association. Explore Space ... Not Drugs! |
