Aircraft Components & Structure


  • The airplane is controllable around its lateral, longitudinal, and vertical axes by deflection of flight control surfaces
  • These control devices are hinged or movable surfaces with which the pilot adjusts the airplane's attitude during takeoff, flight maneuvering, and landing
  • They are operated by the pilot through connecting linkage by means of rudder pedals and a control stick or wheel [Figure 4]
Flight Control SUrfaces
Figure 4: Flight Control Surfaces

Trim Tabs:

  • Trim refers to employing adjustable aerodynamic devices on the aircraft to adjust forces so the pilot does not have to manually hold pressure on the controls
  • This is done either by trim tabs (small movable surfaces on the control surface) or by moving the neutral position of the entire control surface all together
    • Trim tabs are likely to be on the aileron, elevator and rudder
  • Trimming is accomplished by deflecting the tab in the direction opposite to that in which the primary control surface must be held
  • The force of the airflow striking the tab causes the main control surface to be deflected to a position that corrects the unbalanced condition of the aircraft
  • Because the trim tabs use airflow to function, trim is a function of speed. Any change in speed results in the need to re-trim the aircraft
  • An aircraft properly trimmed in pitch seeks to return to the original speed before the change due to its stability
  • Trimming is a constant task as soon as you change any power setting, airspeed, altitude, or configuration
  • Proper trimming decreases pilot workload allowing for attention to be diverted elsewhere, especially important for instrument flying
  • In the pattern, if you have trimmed appropriately, you shouldn't have to use back stick at all, which should also prevent you from exceeding approach speed/on-speed

Servo Tabs:

  • Servo tabs are similar to trim tabs in that they are small secondary controls which help reduce pilot workload by reducing forces
  • The defining difference however, is that these tabs operate automatically, independent of the pilot
  • There are two types of servo tabs:
    • Servo Tabs: tabs that move in the opposite direction as the control surface
    • Anti-Servo Tabs: also called an anti-balance tab, are tabs that move in the same direction as the control surface

Wing Bracing
Figure 3: Wing Bracing

Fixed-Wing Controls and Components:

  • Components:
    • Fuselage:
      • The fuselage is one of the principal structural units of the airplane. It houses the crew, passengers, cargo, instruments, and other essential equipment. Most present day airplanes have a fuselage made of a combination of truss and monocoque design. In the truss type construction, strength and rigidity are obtained by joining tubing (steel or aluminum) to produce a series of triangular shapes, called trusses. In monocoque construction, rigs, formers, and bulkheads of varying sizes give shape and strength to the stressed skin fuselage [Figure 1]
      • On single engine airplanes the engine is usually attached to the front of the fuselage. There is a fireproof partition between the rear of the engine and the cockpit or cabin to protect the pilot and passengers from accidental engine fires. This partition is called a firewall and is usually made of a high heat resistant, stainless steel
      Aircraft Fuselage
      Figure 1: Aircraft Fuselage
      Wing Construction
      Figure 2: Wing Construction
    • Wings:
      • The wings are airfoils attached to each side of the fuselage and are the main lifting surfaces which support the airplane in flight. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Each fulfill a certain need with respect to performance expected for the particular airplane. How the wing produces lift is explained in subsequent chapters
      • Wings are of two main types - cantilever and semi-cantilever [Figure 2]
        • The cantilever wing requires no external bracing; the stress is carried by internal wing spars, ribs, and stringers. Generally, in this type wing the "skin" or metal wing covering is constructed to carry much of the wing stresses. Airplanes with wings so stressed are called stressed skin types. Treated aluminum alloy is most commonly used as the wing covering [Figure 3]
        • The semi-cantilever wing is braced both externally by means of wing struts attached to the fuselage, and internally by spars and ribs
      • The principal structural parts of the wing are spars, ribs, and stringers. These are reinforced by trusses, I beams, tubing, or other appropriate devices. The wing ribs actually determine the shape and thickness of the wing (airfoil). In most modern airplanes, the fuel tanks are either an integral pat of the wing's structure, or consist of flexible containers mounted inside of the wing structure
    • Empennage:
      • Commonly known as the "tail section," the empennage includes the entire tail group consisting of fixed surfaces such as the vertical fin or stabilizer and the horizontal stabilizer; the movable surfaces including the rudder and rudder trim tabs, as well as the elevator and elevator trim tabs
      • These movable surfaces are used by the pilot to control the horizontal rotation (yaw) and the vertical rotation (pitch) of the airplane
      • In some airplanes the entire horizontal surface of the empennage can be adjusted from the cockpit as a complete unit for the purpose of controlling the pitch attitude or trim of the airplane. Such designs are usually referred to as stabilators, flying tails, or slab tails
      • The empennage, then, provides the airplane with directional and longitudinal balance (stability) as well as a means for the pilot to control and maneuver the airplane
  • Controls:
    • Ailerons: control surfaces which control the aircraft about its longitudinal axis allowing the aircraft to roll
      • The term "aileron" is the French word for "little wing"
      • They are located on the trailing (rear) edge of each wing near the outer tips
      • When pressure is applied to the right on the control wheel or stick, the left aileron goes (deflects) down and the right aileron goes up, rolling the airplane right
      • Therefore, ailerons work simultaneously and in the opposite direction of each other
      • The wing with the lowered aileron goes up because of its increased lift, and the wing with the raise aileron goes down because of its decreased lift (also considered lift in the other direction)
      • This happens because the down movement of the left aileron increases the wing camber (curvature) and thus increases the angle of attack
      • The right aileron moves upward and decreases the camber, resulting in a decreased angle of attack
      • Their primary use is to bank (roll) the airplane around its longitudinal axis
      • The banking of the wings results in the airplane turning in the direction of the bank
    • Slats:
      • Attached to the leading edge of the wings and are designed to be controlled by the pilot or automatically by the flight computer
      • Some aircraft employ aerodynamic slats that when lowered create added lift
      • Slats increase the camber of the wings/airfoil
      • By extending the slats additional lift is created when the aircraft is at slower airspeeds, normally on takeoff and landing
    • Flaps:
      • Attached to the trailer edge of the wings and are controlled by the pilot from the cockpit
      • By extending the flaps additional lift is created when the aircraft is at slower airspeeds, normally on takeoff and landing
      • Slats and flaps are used in conjunction with each other to increase both lift and stall margin by increasing the overall wings camber thus, allowing the aircraft to maintain control flight at slower airspeeds
    • Elevator: control surfaces which control the aircraft about its lateral axis allowing the aircraft to pitch
      • The elevators are attached to the horizontal portion of the empennage - the horizontal stabilizer
        • The exception to this is found in those installations where the entire horizontal surface is a one piece structure which can be deflected up or down to provide longitudinal control and trimming
      • A change in position of the elevators modifies the camber of the airfoil, which increases or decreases lift
      • When forward pressure is applied on the controls, the elevators move downward
      • This increases the lift produced by the horizontal tail surfaces
      • The increased lift forces the tail upward, causing the nose to drop
      • Conversely, when back pressure is applied on the wheel, the elevators move upward, decreasing the lift produced by the horizontal tail surfaces, or maybe even producing a downward force
      • The tail is forced downward and the nose up
      • The elevators control the angle of attack of the wings
      • When back-pressure is applied on the controls, the tail lowers and the nose rises, increasing the angle of attack
      • Conversely, when forward pressure is applied, the tail raises and the nose lowers, decreasing the angle of attack
      • Stabilizer: a control surface other than the wings which provide stabilizing qualities
    • Rudder: control surfaces which control the aircraft about its vertical axis allowing the aircraft to yaw
      • Like the other primary control surfaces, the rudder is a movable surface hinged to a fixed surface that, in this case, is the vertical stabilizer, or fin
      • Its action is very much like that of the elevators, except that it swings in a different plane - from side to side instead of up and down
        • It is used by the pilot to control the direction (left or right) of yaw about the airplane's vertical axis
        • It is not used to make the airplane turn, as is often erroneously believed
      • Rudders are controlled by the pilot with his/her feet
    • Speed Brakes:
      • Designed to slow the aircraft when in a dive or descent, location and style vary with aircraft, and are controlled by a switch in the cockpit
    • Trim Tabs:
      • Movable tabs located on the primary control surfaces i.e., ailerons, elevators and rudder reducing the pilot's workload enabling the aircraft to hold a particular attitude without the need of constant pressure/inputs into the system

Rotary-Wing Components:

  • The major difference between helicopters and fixed-wing is the source of lift
  • Fixed-winged aircraft derive lift from fixed airfoils while helicopters use rotating airfoils known as rotor blades
  • Lift and control are relatively independent of forward speed
  • Controls:
    • Cyclic Stick:
      • Controls movement about the lateral and longitudinal axis of the helicopter
      • It is located centered in front of the pilot's seat and changes the tip path plane of the main rotor for directional flight
      • By changing the tip path plane, the direction of thrust is changed, and the corresponding intended direction of movement or flight is achieved
    • Collective Stick:
      • Always located to the left of the pilot's seat and varies the lift of the main rotor by decreasing or increasing the angle of attack on all rotor plates equally and in the same direction
      • Also used in combination with the cyclic to regulate speed and altitude
    • Rudder Pedals:
      • Controls movement about the vertical axis (yaw) of the helicopter by changing the pitch (angle of attack) of the tail rotor plates
      • This causes more or less force to be developed which is counteracting the torque caused by the main rotors
      • Additionally, by the pilot deflecting the rudder pedals left or right the aircraft heading or direction is changed left or right
  • Components:
    • Rotor Blade:
      • Spinning "wings" which allow for lift on helicopters or "rotor-craft"
    • Main Rotor Assembly:
      • Consists of rotor blades, rotor hub assembly, pitch control rod/links, mast, swashplate and support assembly
      • Some may have scissor and sleeve assembly
      • All of the above items work to change linear (push/pull motion) into rotating control movement
    • Gearboxes/Transmission:
      • Changes direction and provides power produced by the engines via drive shafts to the main and trail rotor assemblies
      • The main transmission also provides mounting pads for accessory mounting such as hydraulic flight control pumps, generators, and rotor brake
      • Most helicopters have a main, intermediate and a tail gearbox


  • The principles of flight are those basic characteristics which act upon an aircraft
  • A balanced aircraft is a happy aircraft (fuel burn, efficiency, etc.)