Aircraft Materials, Hardware, and Transmissions Flashcards

Vocabulary terms and definitions from the lecture notes covering aircraft fabrics, composites, corrosion, hardware (rivets, bolts, screws), bearings, gears, and chains.

Bias

A line running at $45$ degrees to the warp and fill of a fabric, created when fabric strands are pulled.

Warp

The longitudinal threads that run the length of a fabric roll ($0^{\circ}$ direction); they are the strongest direction and must be parallel to the direction of flight.

Fill (woof or weft)

Threads that run perpendicular ($90^{\circ}$) to the warp, interweaving with them to form the fabric.

Selvage Edge

A tightly woven edge parallel to the warp that prevents threads from unraveling; it is removed before the fabric is used.

Pinked edge

An edge cut in a series of v-shapes to prevent fabric from unraveling.

Greige (raw fabric)

Polyester fabric as it is removed from the loom, which is unshrunk, unbleached, and not dyed.

Anti-chafe tape

Tape used on sharp protrusions, rib caps, and metal seams to provide a smoother surface and prevent fabric tears.

Reinforcing tape

A flat woven polyester material available in $\frac{1}{4}$\,inch, $\frac{3}{8}$\,inch, and $\frac{1}{2}$\,inch widths with a strength of $150\,lbs$.

Rib lacing cord

Cord used to secure aircraft covering to the cap strips of the ribs, preventing the fabric from pulling away during flight.

Aircraft Dope

Cellulose-based coatings (Nitrate or Butyrate) used to protect fabric from moisture, sunlight, and pollution.

Envelope Method

A fabric covering method where covers are pre-sewn to fit a particular aircraft surface.

Blanket Method

A covering method used for aircraft with a VNE greater than $150\,mph$, where the fabric blanket is sewn together along the trailing edge.

Matrix

The bonding material in a composite that completely surrounds the fibers and transfers stress to them.

Thermoplastic Resins

Resins that use heat to form a shape and can be reheated and reshaped, such as Acrylic (Lucite or Plexiglas).

Thermosetting Resins

Resins that are cured using a catalyst or heat and cannot be reshaped or returned to liquid form once cured.

Microballoons

Small plastic or glass spheres added to resin to reduce overall weight and lower stress concentrations without adding strength.

Pot Life

The time span a resin remains liquid and workable after the catalyst has been added, affected by temperature and catalyst proportion.

Delamination

The separation of fabric layers in a laminate, which may have no visible external signs.

Disbonds

The separation of a composite material from another material to which it was adhesively bonded.

Kissing bond

A tight or weak disbond that is particularly difficult to detect.

Galvanic Corrosion

Corrosion that occurs when dissimilar metals are in direct electrical contact in the presence of an electrolyte.

Stress Corrosion

Corrosion caused by the combined action of stress (such as an interference fit) and a corrosive environment, leading to rapid crack growth.

Pitting Corrosion

Localised anodic areas that form pits, often identified by clumps of white powder on the surface of the metal.

Intergranular Corrosion

Corrosion occurring between metal grains, often caused by improper heat treatment (delayed quenching).

Filiform Corrosion

Corrosion that propagates beneath a protective organic coating, starting at a coating defect.

Fretting Corrosion

Corrosion occurring between two tightly fitted surfaces that move against each other, often indicated by "smoking rivets."

Exfoliation Corrosion

An extreme form of intergranular corrosion occurring in extruded materials where the metal separates or delaminates along grain boundaries.

Microbiological Corrosion

Corrosion in fuel tanks caused by fungus (microbes) that produces scum and holds water against the structure.

Icebox rivets

Aluminium alloy rivets (Types D and DD) that must be heat treated and stored in a freezer to remain soft enough for driving.

Blind rivets

Fasteners such as CherryMAX or Huck-Lok used when access is available to only one side of the structure.

Rigid Tubing Dash Number

Identification number based on outside diameter (OD) in $\frac{1}{16}$ inch increments (e.g., $-4 = \frac{4}{16}$\,inch).

Flexible Hose Dash Number

Identification number based on the inside diameter (ID) of the hose in $\frac{1}{16}$ inch increments.

Lay Line

A colored stripe running the length of a flexible hose used to identify the hose and ensure it is not twisted after installation.

Pitch (Screws)

The distance from one thread to the next, measured parallel to the axis of the screw.

Lead

The distance a thread advances in one complete turn; for single-start threads, it is equal to the pitch.

Grip Length

The unthreaded portion of a bolt shank, which should match the combined thickness of the materials being joined.

Plain Washers (Standard)

AN960 series washers used to provide a smooth bearing surface under nuts.

Split Pins (Cotter Pins)

Locking devices used to secure castellated nuts on drilled bolts.

Plain bearings

Bearings with no moving parts (sleeves or bushes) made of a material softer than the shaft to reduce friction.

Babbitt

A soft lining alloy of tin, lead, copper, and antimony used in plain bearings.

Oilite Bush

A self-lubricating bush made from sintered metal that can hold lubricant in up to $30\%$ of its volume.

Rolling element bearings

Anti-friction bearings containing balls or rollers between inner and outer races.

Needle Roller Bearings

Bearings with rollers that are much longer than their diameter, used for heavy radial loads in compact spaces.

Tapered Roller Bearings

Bearings designed to support heavy combined radial and thrust loads, commonly used in aircraft wheels.

Diametrical Clearance

The small clearance between a bearing or shaft maintained to allow for lubricant flow and thermal expansion.

Staking

A method of deforming housing metal around a bearing to help retain it against axial loads and vibration.

Spur Gear

A gear with straight teeth parallel to the shaft axis used to connect parallel shafts.

Helical Cut Gear

A gear with teeth cut at an angle to the shaft axis, offering smoother and quieter operation than spur gears.

Herringbone Gear

A double helical gear made of two opposite helical gears joined to cancel out axial thrust.

Bevel Gears

Gears with teeth cut on a conical blank used to transmit power between intersecting shafts.

Hypoid Gears

Gears similar to spiral bevel gears where the shaft axes do not intersect, requiring Extreme Pressure (EP) lubricant.

Worm Gears

A gear system consisting of a worm screw and worm wheel providing high gear reductions; it becomes self-locking at reductions greater than $20:1$.

Speed Ratio

The ratio of driving RPM to driven RPM, calculated as $\frac{\text{Teeth on Driven Gear}}{\text{Teeth on Driving Gear}}$, though aircraft convention often expresses it as Output:Input.

Gear Ratio

The ratio indicating torque production on the output shaft relative to the input, calculated as $\frac{\text{Teeth on Driven Gear}}{\text{Teeth on Driving Gear}}$.

Idler Gears

Intermediate gears used to change rotation direction or bridge distance without changing the speed or gear ratio.

Epicyclic (Planetary) Gears

A gear system consisting of a sun gear, planet gears, a spider (carrier), and a ring gear, used as aircraft engine reduction gearing.

Backlash

The clearance or "play" between two meshing gear teeth, typically between $0.003$ and $0.004$ inches.

Roller Chain

The most common type of aircraft control chain, where rollers rotate freely around bushes.

Pitch (Chains)

The distance between the centers of adjacent rollers in a chain.