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2-3
Figure 2-4. Airplane components.
Figure 2-5. Truss-type fuselage structure.
independent of airspeed
Nose-down forcedependent upon airspeedNose-up forceFixedVariableVertical forces acting on an airplane in flightLiftCG too far aftnose-down forceInsufficient elevatorIf the CG is too far aft, there might not be enough elevator nosedown force at the low stall airspeed to get the nose down for recovery.LiftCGCG too far forwardnose-up forceInsufficient elevatorIf the CG is too far forward, there will not be enough elevator nose-up force to flare the airplane for landing.CGLiftFigure 2-3. Center of gravity.
Figure 2-3. Center of gravity (CG).
Major Components
Although airplanes are designed for a variety of purposes, most of them have the same major components. [Figure 2-4] The overall characteristics are largely determined by the original design objectives. Most airplane structures include a fuselage, wings, an empennage, landing gear, and a powerplant.
Fuselage
The fuselage is the central body of an airplane and is designed to accommodate the crew, passengers, and cargo. It also provides the structural connection for the wings and tail assembly. Older types of aircraft design utilized an open truss structure constructed of wood, steel, or aluminum tubing. [Figure 2-5] The most popular types of fuselage structures used in today’s aircraft are the monocoque (French for “single shell”) and semimonocoque. These structure types are discussed in more detail under aircraft construction later in the chapter.
Wings
The wings are airfoils attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Each fulfills a certain need with respect to the expected performance for the particular airplane. How the wing produces lift is explained in Chapter 4, Aerodynamics of Flight.
Wings may be attached at the top, middle, or lower portion of the fuselage. These designs are referred to as high-, mid-, and low-wing, respectively. The number of wings can also vary. Airplanes with a single set of wings are referred to as
2-4
Figure 2-6. Monoplane (left) and biplane (right).
Figure 2-7. Wing components.
monoplanes, while those with two sets are called biplanes. [Figure 2-6]
Many high-wing airplanes have external braces, or wing struts, which transmit the flight and landing loads through the struts to the main fuselage structure. Since the wing struts are usually attached approximately halfway out on the wing, this type of wing structure is called semi-cantilever. A few high-wing and most low-wing airplanes have a full cantilever wing designed to carry the loads without external struts.
The principal structural parts of the wing are spars, ribs, and stringers. [Figure 2-7] These are reinforced by trusses, I-beams, tubing, or other devices, including the skin. The wing ribs determine the shape and thickness of the wing (airfoil). In most modern airplanes, the fuel tanks either are an integral part of the wing’s structure, or consist of flexible containers mounted inside of the wing.
Attached to the rear or trailing edges of the wings are two types of control surfaces referred to as ailerons and flaps. Ailerons extend from about the midpoint of each wing outward toward the tip, and move in opposite directions to create aerodynamic forces that cause the airplane to roll. Flaps extend outward from the fuselage to near the midpoint of each wing. The flaps are normally flush with the wing’s surface during cruising flight. When extended, the flaps move simultaneously downward to increase the lifting force of the wing for takeoffs and landings. [Figure 2-8]
2-5
Plain flap
Basic sectionSplit flapSlotted flapFowler flapSlotted Fowler flap
Figure 2-8. Types of flaps.
Figure 2-9. Weight-shift control aircraft use the shifting of weight for control.
Figure 2-10. Empennage components.
Alternate Types of Wings
With the Federal Aviation Administration’s (FAA) recent addition of the LSA category, various methods are employed to control flight and to produce lift. These methods are discussed in Chapter 4, Aerodynamics of Flight, which provides information on the effect controls have on lifting surfaces from traditional wings to wings that use both flexing (due to billowing) and shifting (through the change of the aircraft’s CG). Handbooks specific to each category of LSA are available for the interested pilot. LSA illustrate various lifting surfaces and control methods. For example, the wing of the weight-shift control aircraft is highly swept, and the shifting of weight to provide controlled flight. [Figure 2-9]
Empennage
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. [Figure 2-10]
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Pilot's Handbook of Aeronautical Knowledge飞行员航空知识手册(29)
