Landing Gear (ATA 32)

PURPOSE OF LANDING GEAR

• Structural Support: Landing gear provides essential structural support to the aircraft during ground operations.

• Maneuverability: It facilitates the aircraft's maneuverability on the ground, enabling it to taxi, turn, and park.

• Load Absorption: Landing gear serves as a means to absorb and distribute unusual loads experienced during landing and ground operations, ensuring safety and stability.

DESIGN CONSIDERATIONS

• Maximum strength

• Minimum weight

• High reliability

• Low cost

• Airfield compatibility

3 COMMON LANDING GEAR ARRANGEMENTS

1. Tail Wheel (Conventional Gear): Main gear forward, requiring a tailwheel for support.

2. Tandem Gear: Main and tail gear aligned along the aircraft's longitudinal axis (rare).

3. Tricycle Gear: Main gear behind the center of gravity, nose gear at the front (common in modern aircraft).

TWO CATEGORIES OF LANDING GEAR

1. Fixed Gear: Remains exposed to slipstream, causes parasite drag.

2. Retractable Gear: Stows in fuselage/wing compartments, reduces parasite drag during flight.

THREE MAIN PARTS OF LANDING GEAR

• strut

• wheels

• brake

4 TYPES OF LANDING GEAR STRUTS

1. Leaf Spring Gear: Utilizes flexible spring materials to absorb and dissipate landing impact gradually.

2. Rigid Gear: Early aircraft used welded steel struts that directly transferred shock loads to the airframe, often with pneumatic tires for cushioning.

3. Bungee Cord: Struts flex upon landing impact, with bungee cords absorbing and gradually releasing loads to the airframe.

4. Shock Struts (Air/Oil or Oleo Struts): Self-contained hydraulic units using air or nitrogen combined with hydraulic fluid to absorb and dissipate shock loads during landing.

AIRCRAFT BRAKES

• Brakes slow and stop aircraft, hold it during engine run-up, and aid in taxiing.

• Typically, main wheels have brakes; nose/tail wheels do not.

4 COMMON AIRCRAFT BRAKE TYPES

1. Single Disc Brake: Floating-disc, fixed caliper brake.

2. Dual and Multiple Disc Brake: Heavy-duty, used with power brake control valves or boost master cylinders.

3. Segmented Rotor-Disc Brake: Multiple-disc brake with segmented rotors for improved cooling and prolonged braking.

4. Carbon Brake: Utilizes pure carbon discs, offering weight savings and effective heat dissipation, eliminating extended cooling periods.

AIRCRAFT TIRES AND TUBES

2 TYPES OF TIRE CLASSIFICATION

1. Tubeless: These tires have an inner liner approximately one-tenth of an inch thick, serving as an air container.

2. Tubed: Tube-type tires lack this liner but have a smoother inside to protect the tube from chafing.

TYPES OF TIRES

The United States Tire and Rim Association recognizes 9 types of aircraft tires, with 3 being of primary concern:

1. Type III: The most popular low-pressure tire.

2. Type VII: Extra-high-pressure tires, standard for jet aircraft.

3. Type VIII: Used for high-performance jet aircraft with extremely high takeoff speeds. They feature extra-high inflation pressure and a low profile.

TIRE CONSTRUCTION

• Bead: Tire edge on the wheel.

• Carcass: Layer above the inner liner with textile fiber cords.

• Tread: The rubber that contacts the road.

• Sidewall: Protects cords, displays tire info.

INFLATION

• Heat is aircraft tire's enemy.

• Designed to withstand heat from flexing.

• Inflation pressure critical, check daily and before flight.

• Remove if tread is cut over half a rib width.

HYDROPLANING

• occurs when water builds between vehicle wheels and the road, leading to a loss of traction, making the vehicle unresponsive to control inputs.

Fuel System(ATA 28)

AIRCRAFT FUEL

• Aviation Fuel: A liquid containing chemical energy, released as heat energy through combustion and converted to mechanical energy by the engine.

• Fuel Source: Aircraft engine fuels are petroleum products derived from crude oil by refineries, classified as inflammable liquids.

PROPERTIES OF FUEL

1. Volatility: Ability to change from liquid to vapor.

2. Flash Point: Temperature for ignition with an external heat source.

3. Fire Point: Temperature for continued burning without external source.

4. Viscosity: Internal resistance to flow.

5. Freezing Point: Temperature where solid particles form.

6. Vapor Lock: AVGAS vaporizes in the fuel line or components between the fuel line and carburetor.

TYPES OF FUEL SYSTEM

1. Gravity Feed Systems: Utilize gravity to transfer fuel from the tanks to the engine.

2. Pump Feed/Fuel Pump Systems: Require a fuel pump to provide fuel pressure for transfer.

FUEL SYSTEM COMPONENTS

1. Tanks: Manufactured from non-reactive materials, with common features including a sump, drain, and top vent to the atmosphere. Some tanks have dump valves for in-flight fuel jettison.

• 4 Common Types of Tanks

  • Rigid Removable Tanks: Older aircraft use welded or riveted gasoline tanks, now largely replaced by integral or bladder-type tanks. Smaller tanks are made of terneplate, a lead-tin alloy-coated thin sheet steel.

  • Integral Fuel Tanks: Maximize fuel storage in minimal space with low weight. Common in light aircraft, they occupy the leading-edge portion of the wing, sealed with a two-part sealant.

  • Bladder Tanks: Prepare the fuel bay with chafe-resistant tape on metal edges and install a bladder made of thin, neoprene-impregnated fabric that is fuel-resistant.

  • Surge Tanks: Not counted in the aircraft's fuel capacity, they serve as a precaution in case main tanks overflow.

2. Fuel Pumps: Engine-driven fuel pumps deliver properly pressured, continuous fuel supply during engine operation. Auxiliary fuel pumps can assist in engine starting and maintain positive pressure at the engine-driven fuel pump inlet.

• 2 TYPES OF FUEL PUMPS

  • Hand-Operated Pumps (Wobble Pumps): Used to back up engine-driven pumps and transfer fuel between tanks.

  • Centrifugal Boost Pump: Popular auxiliary pump driven by an electric motor, installed inside or outside the fuel tank. It uses an impeller to propel fuel into the discharge line.

3. FUEL INJECTORS

   • Description: A specific area in the fuel tank partitioned with a flapper-type valve allowing fuel flow into the collector from the tank.

   • Operation: Utilizes a fuel ejector system based on the venturi principle, providing additional fuel to the collector can regardless of the aircraft's attitude.

4. FUEL VALVES

   • Function: Selector valves are installed in the fuel system to control fuel flow, tank and engine selection, cross-feed, and fuel transfer.

   • Variation: The size and number of ports (openings) differ according to the specific installation.

5. FILTERS

• Importance: Crucial to ensure contamination-free fuel supply for aircraft engines.

• Components: Every aircraft fuel system includes a series of strainers and filters.

• Sampling: Provision for draining fuel samples from all tanks and from the main strainer must be present.

6. FUEL LINES AND FITTINGS

• Materials: Metal tubing is typically aluminum alloy, while flexible hoses are made from synthetic rubber or Teflon.

• Diameter: Tubing diameter is determined by the engine's fuel flow requirements.

• Material Type: Most rigid fuel lines used in aircraft are constructed from 5052 aluminum alloy.

FUEL GRADES

• Definition: Aviation gasoline (AVGAS) is categorized by an octane or performance number (grade) that indicates its antiknock value or knock resistance within the engine cylinder.

• Higher Grade: Higher-grade gasoline can withstand more pressure without detonation.

AIRCRAFT REFUELING AND FUELING

• Two Processes:

  • Over the Wing Refueling: Aircraft are typically refueled over the wing, and the fuel is drained through the tank sump drain.

  • Pressure Refueling: Pressure-fueled aircraft are usually defueled through the pressure fueling port.

VENT SYSTEM

• Fuel Vent: Small pipe for pressure equalization between the tank and the outside.

FUEL DUMPING

• Fuel Dumping/Jettison: Used in emergencies after takeoff or before landing to reduce aircraft weight.

FUEL SYSTEM INDICATORS

1. Sight Glass: Clear tube open to the fuel tank, showing fuel level.

2. Digital Indicators: Converts resistance to a digital signal, displayed on a screen panel.

3. Fuel Temperature Gauge: Alerts pilot to approaching temperatures that could cause fuel system ice.

FUEL CONTAMINATION (most common forms)

• Solid Contaminants: Non-dissolv moing particles in fuel, including rust, scale, sand, and dirt.

• Surfactants: Soap or detergent-like substances occurring naturally or introduced during refining/handling.

• Microorganisms: Over 100 varieties can thrive in free water within fuel systems. Airborne microorganisms constantly expose fuel to contamination. Effects include sludge formation, emulsification, corrosion, and odors.