Chapter 3: Aircraft Construction
An aircraft is any device that is used for flight. This includes airplanes, rotorcraft, gliders, lighter-than-air, powered-lift, powered parachute, and weight-shift control aircraft.
An airplane as an engine-driven, fixed-wing aircraft that is supported in flight by the dynamic reaction of air against its wings.
Lift and Basic Aerodynamics
Four forces act upon an aircraft in relation to straight-and level, unaccelerated flight. These forces are thrust, lift, weight, and drag.
Thrust is the forward force produced by the powerplant/ propeller. It opposes or overcomes the force of drag.
Drag is a rearward, retarding force and is caused by disruption of airflow by the wing, fuselage, and other protruding objects. Drag opposes thrust and acts rearward parallel to the relative wind.
Weight is the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift and acts vertically downward.
Lift opposes the downward force of weight, is produced by the dynamic effect of the air acting on the wing, and acts perpendicular to the flight path.
Center of Gravity
The center of gravity (CG) is the specific point where the mass or weight of an aircraft may be said to center. If the aircraft could be suspended or balanced at the CG, it would remain relatively level.
The position of the CG of an aircraft determines the stability of the aircraft in flight. The CG is computed during initial design and construction. However, it is further affected by the installation of onboard equipment, aircraft loading, and other factors. Managing weight and balance is a critical preflight task for pilots.
Dimensions of Movement
An aircraft moves in three dimensions. It is controlled by moving it about one or more of its axes.
The longitudinal, or roll, axis extends through the aircraft from nose to tail, with the line passing through the CG.
The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the CG.
The vertical, or yaw, axis passes through the aircraft vertically, intersecting the CG.
All control movements cause the aircraft to move around one or more of these axes and allows for the control of the aircraft in flight.
The FAA certifies three types of aviation products: aircraft, aircraft engines, and propellers.
Having an airworthiness certificate means the complete aircraft meets the design and manufacturing standards, and is in a condition for safe flight. This airworthiness certificate must be carried in the aircraft during all flight operations. The airworthiness certificate remains valid as long as the required maintenance and inspections are kept up to date for the aircraft.
Airworthiness certificates are classified as either “Standard” or “Special.” Standard airworthiness certificates are white. Special airworthiness certificates are pink, and are issued for primary, restricted, and limited category aircraft, and light sport aircraft.
An aircraft moves in three dimensions and is controlled by moving it about one or more of its axes. The longitudinal, or roll, axis extends through the aircraft from nose to tail, with the line passing through the CG. The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the CG. The vertical, or yaw, axis passes through the aircraft vertically, intersecting the CG.
Most airplane structures include a fuselage, wings, an empennage, landing gear, and a powerplant.
The fuselage is the central body of an airplane and is designed to accommodate the crew, passengers, and cargo.
The wings are airfoils attached to each side of the fuselage. The principal structural parts of the wing are spars, ribs, and stringers. These are reinforced by trusses, I-beams, tubing, or other devices, including the skin.
The empennage includes the entire tail group and consists of fixed surfaces, such as the vertical stabilizer and the horizontal stabilizer. The movable surfaces include the rudder, the elevator, and one or more trim tabs. A second type of empennage design does not require an elevator. Instead, it incorporates a one-piece horizontal stabilizer that pivots from a central hinge point. This type of design is called a stabilator.
The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations or skis for landing on snow. Wheeled landing gear consists of three wheels — two main wheels and a third wheel positioned either at the front or rear of the airplane. Landing gear with a rear mounted wheel is called conventional landing gear.
The powerplant usually includes both the engine and the propeller. The engine provides power to turn the propeller, electrical power, a vacuum source for some flight instruments, and cabin heat.
A propeller is a rotating airfoil that produces thrust through aerodynamic action.
The subcomponents of an airplane include the airframe, electrical system, flight controls, and brakes.
The airframe is the basic structure of an aircraft and is designed to withstand all aerodynamic forces, as well as the stresses imposed by the weight of the fuel, crew, and payload.
The main drawback of truss structure is its lack of a streamlined shape. Monocoque construction uses stressed skin to support almost all loads much like an aluminum beverage can. Although strong, monocoque construction is not highly tolerant to deformation of the surface. Semimonocoque construction uses a substructure to which the airplane‘s skin is attached.
Composite construction offers two advantages: extremely smooth skins and the ability to easily form complex curved or streamlined structures. A very smooth, compound curved, aerodynamic structure made from composites reduces drag. However, in a composite structure, a low energy impact, such as a bump or a tool drop, may not leave any visible sign of the impact on the surface. Underneath the impact site there may be extensive delaminations, spreading in a cone-shaped area from the impact location.
The performance instruments indicate the aircraft‘s actual performance. Performance is determined by reference to the altimeter, airspeed or vertical speed indicator (VSI), heading indicator, and turn-and-slip indicator. The performance instruments directly reflect the performance the aircraft is achieving.
The control instruments display immediate attitude and power changes and are calibrated to permit adjustments in precise increments. The instrument for attitude display is the attitude indicator.
The navigation instruments indicate the position of the aircraft in relation to a selected navigation facility or fix. This group of instruments includes various types of course indicators, range indicators, glideslope indicators, and bearing pointers.
Commercial Pilot & Flight Instructor Test Questions
The three axes of an aircraft intersect at the center of gravity.
Action of the elevators moves the plane on its lateral axis.
Action of the ailerons moves the plane on its longitudinal axis.
Which type of flap creates the least change in pitching moment? Split.
Which type of flap creates the greatest change in pitching moment? Fowler.