Aircraft Structures IIReview of the Aircraft Structures IEngr. Paul Christian Devera
IntroductionAnaircraftis a device that is used, or intended to be used, forflight, according to the current Title 14 of the Code of FederalRegulations (14 CFR) Part 1, Definitions and Abbreviations.Categoriesofaircraftforcertificationofairmenincludeairplane,rotorcraft,glider,lighter-than-air,powered-lift,powered parachute, and weight-shift control.14 CFR part 1 also defines airplane as anengine-driven, fixed-wing aircraftthatissupportedinflightby the dynamicreactionofairagainstitswings. Anotherterm,not yetcodified in 14 CFR part 1, isadvanced avionics aircraft, whichrefers to an aircraft that contains a global positioning system(GPS)navigationsystemwithamovingmapdisplay,inconjunction with another system, such as anautopilot. Thispresentation provides a brief introduction to the structure ofaircraft and uses an airplane for most illustrations.
Lift and Basic Aerodynamics
Lift and Basic Aerodynamics•Thrustis the forward force produced by the powerplant/propeller. Itopposes or overcomes the force of drag. As a general rule, it is saidto act parallel to the longitudinal axis.•Dragis a rearward, retarding force, and is caused by disruption ofairflow by the wing, fuselage, and other protruding objects. Dragopposes thrust, and acts rearward parallel to the relative wind.•Weightis the combined load of the airplane itself, the crew, the fuel,and the cargo or baggage. Weight pulls the airplane downwardbecause of the force of gravity. It opposes lift, and acts verticallydownward through theairplane’scenter of gravity (CG).•Liftopposes the downward force of weight, is produced by thedynamic effect of the air acting on the wing, and acts perpendicularto the flightpath through thewing’scenter of lift.
Aircraft Movement•The figure illustrates the pitch, roll, and yaw motion of the aircraft along the lateral, longitudinal, and vertical axes, respectively.
Center of Gravity (CG) •One of the most significant components of aircraft design isCG. It isthe specific point where the mass or weight of an aircraft may be saidto center; that is, a point around which, if the aircraft could besuspended or balanced, the aircraft would remain relatively level.•The position of the CG of an aircraft determines the stability of theaircraft in flight. As the CG moves rearward (towards the tail) theaircraft becomes more and more dynamically unstable. In aircraftwith fuel tanks situated in front of the CG, it is important that the CGis set with the fuel tank empty. Otherwise, as the fuel is used, theaircraft becomes unstable.
Center of Gravity (CG) The CG is computed during initial design and construction, and is further affected bythe installation of onboard equipment, aircraft loading, and other factors.
Major Components•Although airplanes are designed for a variety of purposes, most of them have the same major components.