404: Airframe Structures

Aircraft is divided into five main sections:

1. Fuselage (aircraft body): includes cockpit and carries passengers/cargo, other parts of aircraft are usually attached to fuselage, shape can vary depending on use of aircraft

2. Wings: generates lift to sustain flight, most aircrafts have one wing surface (but some have more), shape changes depending on use (gliders have long + narrow wings because they’re lighter and need to optimize lift + drag, cargo planes have wide + fat wings that can withstand weight)

3. Empennage (tail section): provides stability to aircraft and usually includes rudder and elevator (control surfaces that control pitch and yaw)

4. Landing gear: supports weight of aircraft when on ground, usually has wheels to move easier on ground and usually combined with shock absorbing systems for landing

5. Propulsion System: includes the following

   1. Engines: produce power, drives propellers on most small aircrafts

   2. Propellers: aerodynamically shaped, create thrust that move aircraft forwards

   3. Cowling: covers engine, helps control flow of air around engine and streamlining (reduces drag)

   4. Engine mounts: connects engine to frame, usually includes shock absorbers

   5. Firewall: sits between engine and aircraft to reduce fire risks

Fuselage

• Three main types of fuselage construction, can be found in other components of aircrafts

• Truss: assembly made of beans/tubes joined together to form frame of fuselage, frame supports loads and covered with coating (fabric/metal/composite materials), main beams are called longerons

• Monocoque: formers and bulkheads (usually oval shaped) create shape of fuselage and a stressed skin is attached to support part of load, similar to a shell

• Semi-monocoque: similar to monocoque but has additional stringers running length of fuselage attached to formers and bulkheads

• Composite construction: use of composite materials in aircraft can reduce need for other structural supports

• Materials combined together to create new material with properties not present in original materials

• Multiple materials frequently sandwiched together in layers and laminated together (uses resin)

• Can be formed/molded into desired shape, results in little need for further interior structure

• Tends to have less need for maintenance, light compared to other materials, very aerodynamic

• Damage to composite aircraft difficult to repair and tend to be expensive

• Very common in gliders, becoming more common in modern aircrafts

Wings

• Definitions:

• Wing Root: part of wing attached to fuselage, widest part of wing

• Wing Tip: end of wing furthest from fuselage, sometimes has modifications to improve flight

• Leading Edge: front of wing, forward facing edge of wing, often rounder/thicker than trailing edge

• Trailing Edge: back edge of wing, often pointy

• Chord: distance from leading edge to trailing edge

• Wing Span: length of wings from wing time to wing tip

• Platform: shape of wings + fuselage from above

• Spar: main structural component of wing that go from wing root to wing tip, aircraft can have more than one spar, often primary spar that is entire length (gives it strength), secondary spars give further structure, supports most of load in flight and resists twisting of wing

• Ribs: runs from leading edge to trailing edge of wing, creates shape of wing (curvature)

• False Ribs: similar to ribs, don’t run full depth of wing, provides supplemental structure and shape to leading edge, usually stops at spar

• Struts: external bracing that holds wing in position, usually seen on non-high performance, high-wing aircrafts can also be seen on low wing models

• Skin/covering: material that covers wing, can be fabric (lighter), metal (resistant but heavy), or combo of materials

• Wing Positions: different wing positions have different advantages + disadvantages

• High Wing: all aircrafts used in ACGP are high-wing, wings affixed to top of fuselage, gives poor visibility above aircraft, common in single engine + non-high performance aircrafts, fuel tanks located in wings and fuel flows to engine through gravity

• Mid Wing: wings connect to center of aircraft

• Low Wing: wings connect to bottom of aircraft, better visibility over aircraft

• Cantilevered Wing: has internal bracing to support instead of external (struts)

• Primary + ancillary controls located on wing:

• Ailerons: usually on trailing edge close to wing tip, helps control aircraft in flight

• Flaps: usually located on trailing edge close to wing root, moving surfaces can move down and up (in some cases) to modify camber of aircraft wing and change flight performance, most small aircrafts equipped with flaps that descend (some gliders designed with “negative” flaps that move upwards)

• Spoilers: found on wing surface, open into airflow and destroy lift being generated by wing, common in gliders

Empennage

• Primary role is to provide stability and control in flight

• Usually includes:

• Vertical stabilizer/fin

• Horizontal stabilizer

• Rudder: usually attached to back of vertical stabilizer, controls yaw

• Elevator: usually attached to horizontal stabilizer and controls pitch

• Trim Tabs: usually found on rudder and/or elevator

Controls

• Stick/control column: usually used to control 2 control surfaces, ailerons and elevator, moving stick left to right causes ailerons to move (stick to right, right aileron goes up, left aileron will go down, aircraft will roll), moving stick forwards and back causes elevator to deflect up and down (stick forward causes elevator to move down, tail of aircraft up, nose down)

• Rudder Pedals: rudder is vertical control surface on tail, usually controlled by set of pedals in cockpit, pushing right rudder pedal will cause rudder to move right

• Trim: compensates for force the pilot is required to exert on the controls, can be adjustable or fixed, adjustable trim can be changed in flight to compensate for force exerted on controls, fixed trim is adjusted on ground to correct for tendencies of aircraft, most aircrafts will have:

• Fixed trim tab on rudder, usually piece of metal extending from rudder can be bent to compensate for turning tendencies of aircraft

• Adjustable trim tab on elevator, usually part of trailing edge of elevator that can be moved independently of elevator, pilot can adjust trim tab as necessary from cockpit, pilot can adjust trim to be more nose down (move tab up) if pilot is exerting lots of pressure pushing stick forward →elevator stays down, will tend to cause tail to go up and nose down