Aircraft Construction and Design

Aircraft Construction Intro

• An aircraft is a device used or intended to be used for flight, according to Title 14 of the Code of Federal Regulations (14 CFR).
• Aircraft categories for airmen certification include airplane, rotorcraft, glider, lighter-than-air, powered-lift, powered parachute, and weight-shift control aircraft.
• Title 14 CFR part 1 defines an airplane as an engine-driven, fixed-wing aircraft supported by the dynamic reaction of air against its wings.
• Advanced avionics aircraft have a GPS navigation system with a moving map display, plus another system like autopilot.
• Light Sport Aircraft (LSA) have their own handbooks detailing aerodynamics and control.

Aircraft Design, Certification, and Airworthiness

• The FAA certifies aircraft, aircraft engines, and propellers, ensuring they meet airworthiness standards in Title 14 CFR.
• These standards aim to ensure aviation products are designed without unsafe features.
• Airworthiness standards are different based on the categories of aviation products.
• Normal, Utility, Acrobatic, and Commuter Category Airplanes follow 14 CFR part 23.
• Transport Category Airplanes follow 14 CFR part 25.
• Normal Category rotorcraft follow 14 CFR part 27.
• Transport Category Rotorcraft follow 14 CFR part 29.
• Manned Free Balloons follow 14 CFR part 31.
• Aircraft Engines follow 14 CFR part 33.
• Propellers follow 14 CFR part 35.
• Aircraft with no airworthiness standards, such as gliders and powered lift, are special classes of aircraft.
• For special classes of aircraft, the airworthiness standards are a mix of requirements from 14 CFR parts 23, 25, 27, and 29.
• The FAA issues a Type Certificate (TC) for products meeting airworthiness standards, along with a Type Certificate Data Sheet (TCDS).
• A TCDS specifies an aircraft, engine, or propeller's design and operational characteristics, accessible to the public on the FAA website.
• Light sport aircraft are designed to a consensus of standards agreed upon in the aviation industry, not to FAA airworthiness standards.
• A TC is issued to light sport aircraft as a whole, including the airframe, engine, and propeller.
• Aircraft can be manufactured one at a time using design drawings or through an FAA-approved manufacturing process.
• During manufacturing, parts are inspected for conformity to the approved design.
• After the aircraft is manufactured, it undergoes inspection, and the FAA issues an airworthiness certificate
• Having an airworthiness certificate means the complete aircraft meets the design and manufacturing standards, and is in a condition for safe flight.
• An 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 either "Standard" (white for normal, utility, acrobatic, commuter, or transport category aircraft) or "Special" (pink for primary, restricted, and limited category aircraft, light sport aircraft, provisional airworthiness certificates, special flight permits, and experimental aircraft).
• Information can be found in Chapter 9, in 14 CFR parts 175-225, and on the FAA website

Lift and Basic Aerodynamics

• Understanding basic aerodynamic concepts is vital to understanding how aircraft components and subcomponents work.
• Four forces act on an aircraft in straight-and-level flight which are thrust, lift, weight, and drag.
• Thrust is the forward force produced by the powerplant/propeller, opposing drag and generally acts parallel to the longitudinal axis.
• Drag is a rearward force caused by the wing, fuselage, and other objects, opposing thrust and acting rearward parallel to the relative wind.
• Weight combines the load of the aircraft, crew, fuel, and cargo, pulling the aircraft downward due to gravity, opposing lift, and acting vertically through the center of gravity (CG).
• Lift counters weight, produced by air's dynamic effect on the wing, acting perpendicular to the flight path through the wing's center of lift (CL).
• An aircraft moves in three dimensions and is controlled by moving it about its axes: longitudinal (roll), lateral (pitch), and vertical (yaw).
• The longitudinal axis extends from nose to tail through the CG.
• The lateral axis extends across the aircraft through the wingtips, also passing through the CG.
• The vertical axis passes vertically through the CG.
• The CG is where the aircraft's mass or weight centers, affecting stability in flight.
• An aircraft is dynamically unstable when the CG moves rearward.
• If fuel tanks are in front of the CG, it's important to set the CG with an empty fuel tank.
• The CG is computed during initial design and construction and is affected by onboard equipment, aircraft loading, and other factors.

Major Components

• Most airplanes have common major components: a fuselage, wings, an empennage, landing gear, and a powerplant.
• The fuselage is the central body, accommodating the crew, passengers, and cargo, and provides structural connection for the wings and tail.
• Older aircraft used an open truss structure made of wood, steel, or aluminum tubing.
• Monocoque and semimonocoque structures are the most popular types of fuselage structures used in today's aircraft.
• Wings are airfoils on each side of the fuselage, providing the main lifting surfaces.
• They can be attached at the top, middle, or bottom of the fuselage, referred to as high-, mid-, and low-wing designs.
• Airplanes with a single set of wings are monoplanes, while those with two sets are biplanes.
• Many high-wing airplanes have external wing struts transmitting flight and landing loads to the fuselage, called semi-cantilever.
• A few high-wing and most low-wing airplanes use a full cantilever wing without external struts.
• Spars, ribs, and stringers are the main structural parts of the wing and are reinforced.
• The wing ribs determine the wing's shape and thickness (airfoil).
• Fuel tanks are either integral to the wing's structure or consist of flexible containers inside the wing.
• Ailerons and flaps are attached to the rear of the wings as control surfaces.
• Ailerons extend from the midpoint of each wing outward, moving in opposite directions to roll the airplane.
• Flaps extend outward from the fuselage, moving downward simultaneously to increase lifting force for takeoffs and landings.
• The shape and design of a wing depends on the type of operation and is tailored to specific types of flying.
• This includes considering the effects of controls on lifting surfaces from traditional wings to weight-shift control aircraft.

Empennage

• The empennage includes the tail group: the vertical stabilizer, the horizontal stabilizer and the movable surfaces: the rudder, the elevator, and one or more trim tabs.
• The rudder attached to the vertical stabilizer, which is used to move the airplane's nose left and right during flight.
• The elevator is attached to the back of the horizontal stabilizer and is used to move the nose of the airplane up and down during flight.
• Trim tabs: Small movable parts on the trailing edge control surface to reduce control pressures, and can be on the ailerons, rudder, and/or elevator.
• A stabilator incorporates a one-piece horizontal stabilizer that pivots from a hinge point, eliminating the need for an elevator.
• An antiservo tab is used to makes the stabilator less sensitive, and maintains the Stabilator in the desired position.

Landing Gear

• Landing gear provides support when parked, taxiing, taking off, or landing.
• The most common type of landing gear consists of wheels.
• Can be equipped with floats for water operations or skis for landing on snow.
• Wheeled landing gear has two main wheels and a third wheel, that can be at the front or rear of the aircraft.
• Conventional landing gear has a rear-mounted wheel.
• Tailwheel airplanes have conventional landing gear.
• Tricycle gear has the third wheel located on the nose.
• A steerable nosewheel or tailwheel allows for aircraft control on the ground.
• Rudder pedals are used to moved most aircraft, whether nosewheel or tailwheel.
• Additionally, some aircraft are steered by differential braking.

Powerplant and Subcomponents

• The powerplant contains the engine and the propeller, which functions to turn the propeller.
• The powerplant generates electrical power, vacuum, and heat in single-engine planes, and is covered by a cowling or nacelle.
• The cowling or nacelle streamlines airflow and help cooling.
• The propeller translates the engine's rotating force into forward thrust.
• The propeller is mounted on the front of the engine, and is a rotating airfoil that produces thrust.
• There are two significant factors involved in the design of a propeller, effecting its effectiveness: the blade angle, and the pitch of the blade.
• The blade angle helps reduce the possibility of a stall, while pitch effects efficiency.
• Subcomponents of an airplane include the airframe, electrical system, flight controls, and brakes.
• Aerodynamic forces and payload stresses are withstood by the airframe.
• An aircraft electrical system generates and distributes electrical power.
• The electrical system includes alternating current (AC) generators, auxiliary power units (APUs), and external power.
• The devices and systems that govern flight path are the flight controls, typically hinged, trailing-edge surfaces like elevators, ailerons, and the rudder.
• Airplane brakes consist of hydraulically-squeezed caliper pads against a rotating rotor, slowing the wheels.

Types of Aircraft Construction

• Aircraft fuselage construction evolved from wood truss structures to semimonocoque shell structures.

Truss Structure

• A main drawback of truss structure is a lack of streamlined shape.
• During construction, longerons are welded to form a braced framework, called bulkheads.
• Additional struts are needed to resist stress that can come from any direction.
• As technology progressed, aircraft designers began to enclose the truss members.
• Was accomplished with cloth fabric, which eventually gave way to lightweight metals such as aluminum.

Monocoque

• Construction uses stressed skin to support almost all loads.
• The monocoque strong, although is not tolerant to deformation of the surface.
• The construction carries external skin rather than by an open framework.
• Jack Northrop constructed a monocoque fuselage for the Lockheed S-1 Racer in 1918.
• The technique utilized two molded plywood half-shells that were glued together around wooden hoops or stringers.

Semimonocoque

• It uses a substructure to which the airplane's skin is attached.
• The substructure, which consists of bulkheads and/or formers of various sizes and stringers, reinforces the stressed skin.
• The main section of the fuselage also includes wing attachment points and a firewall.
• A new emerging process of construction is the integration of composites or aircraft made entirely of composites.

Composite Construction History and Materials

• Composite use in aircraft dates to WWII with soft fiberglass insulation in B-29 fuselages.
• By the 1950s, European sailplane manufacturers were using fiberglass as primary structures.
• By 2005, 35 % of new aircraft were constructed of composite materials.
• The term composite means materials such as fiberglass, carbon fiber cloth, and Kevlar™ cloth.
• Composite construction offers smooth skins, and has the ability to easily form complex curved or streamlined structuresComposite materials are fiber-reinforced matrix systems.
• The matrix is the "glue" used to hold the fibers together, but the fibers carry most of the load. There are many different types of fibers and matrix systems.
• In aircraft, the most common matrix is expoxy resin, which has good high-temperature properties.

Advantages and Disadvantages of Composites

• The most common reinforcing fibers used in aircraft construction are fiberglass and carbon fiber.
• Fiberglass has good tensile and compressive strength and impact resistance, and is easy to work with.
• Their lighter weight is the most frequently cited advantage.
• A very smooth, compound curved structure made from composites reduces drag.
• They provide good performance in a flexing environment such as helicopter rotor blades.
• Composite construction comes with the disadvantage of a lack of visual proof of damage.
• Low-energy impacts on composites may not have visible damage.
• High-energy impacts result in a puncture and a severely damaged structure.
• Heat damage to the resin may occur, weakening epoxies.
• Painted white to minimize this issue, as heat will damage the resin.
• Fluid spills on composites are generally not a problem with epoxym resin.
• If low costs, auto gas with ethanol can be combined with polyester resin can be a problem.

Lightning Strike Protection and The Future of composites

• Lightning strike protection is an important consideration in aircraft design.
• A lot of energy is delivered when struck by lightning.
• Aircraft needs to have enough electricity to spread the energy.
• Electricity is conducted through aluminum.
• Fiberglass is an excellent electrical insulator, while carbon fiber conducts electricity easier than aluminum.
• Additional electrical conductivity needs to be added to fiberglass, and is done with metal meshes bonded to the skin surfaces.
• Composites have design flexibility and corrosion resistance.
• Because of this, they will undoubtedly will led to more innovative aircraft designs in the future.

Instrumentation

• Most GA aircraft were equipped with instruments, and were recently replaced by multiple liquid crystal display (LCD) screens.
• This has been accomplished through the utilization of solid state instruments that have a failure rate far less than those of conventional analog instrumentation.
• Whether an aircraft has analog or digital (glass) instruments, the instrumentation falls into three categories: performance, control, and navigation.

Performance, Control, and Navigation Instruments

• The performance instruments indicate the aircraft's actual performance: the altimeter, airspeed or vertical speed indicator (VSI), heading indicator, and turn-and-slip indicator.
• The control instruments display immediate attitude and power changes and are calibrated to permit adjustments in precise increments.
• The navigation instruments indicate the position of the aircraft in relation to a selected navigation facility or fix.
• This is comprised of indicators that Display GPS, radio range, and landing system.

Global Positioning System (GPS) and Chapter Conclusion

• GPS is a satellite-based navigation system composed of a network of satellites placed into orbit by the United States Department of Defense (DOD).
• A GPS receiver must be locked onto the signal of at least three satellites to calculate a two-dimensional position (latitude and longitude) and track movement.
• This chapter provides an overview of aircraft structures.
• Pilots are also encouraged to subscribe to or review the various aviation periodicals that contain valuable flying information.