AMT 1105 – Aircraft Structures & Landing Gear

Introduction to Aircraft Assembly & Rigging

• Aircraft assembly = joining of discrete structures to create a complete airframe.
  • Major sub-assemblies: fuselage, empennage (tail), wings, landing-gear, power-plant.
  • Each is initially fabricated as an independent module, then mated and rigged (precise alignment, incidence, dihedral, wash-out, control-surface travel, etc.) to achieve the designer’s aerodynamic and structural intent.

• Rigging = positioning/adjusting control surfaces & major assemblies so the finished airplane performs to type-certificate data.
  • Involves setting cable tensions, angular offsets, control stops and symmetry; errors here create adverse yaw, roll-coupling, trim drag, and structural overloads.

• AMTs (Aviation Maintenance Technicians) routinely:
  • Disassemble/re-assemble sub-assemblies for inspection or transport.
  • Carry out initial and recurrent rigging after damage repair, control-cable change, or scheduled maintenance.

• Contemporary challenge: maintaining the structural integrity of large fleets of aging aircraft (many were certificated mid-${20^{\text{th}}}$ century) while simultaneously mastering new-build composite and advanced-alloy structures entering service in the ${21^{\text{st}}}$ century.

Evolution of Aircraft Structures

• Historical arc: wood-and-fabric trusses ⟶ metal semi-monocoques ⟶ composite sandwich & honeycomb designs.
  • Continuous progress driven by material science, aerodynamic theory, and power-plant capability.
  • Key milestones summarized chronologically below.

Myth & Imagination Era (Antiquity – $15^{\text{th}}$ C.)

• Greek myth of Daedalus & Icarus: feathers + wax wings melted by the sun; illustrates early intuition but no structural practicality.

• Medieval tower jumps confirmed inadequacy of human-powered flapping; led to concept of mechanical ornithopters (flapping-wing machines).
  • Leonardo da Vinci ( $1486\text{–}1490$ ) produced >35{,}000 words & $500$ sketches on flight; envisioned flapping wings driven by human musculature, proposing articulated spars & pulleys.

Lighter-Than-Air Breakthrough (Late $18^{\text{th}}$ C.)

• Montgolfier brothers ( Joseph & Étienne ).
  • $1782$: observed convective “lift” of hot air; experimented with paper/linen balloons.
  • $21\,\text{Nov}\,1783$ at $1{:}54\,\text{pm}$: first manned flight ( Pilâtre de Rozier & Marquis d’Arlandes )—duration $25\,\text{min}$, distance $5\,\text{mi}$ across Paris.
  • Demonstrations (e.g.
  – $8\,\text{min}$ animal flight) ignited public fascination.

• Jacques Alexandre César Charles: $1\,\text{Dec}\,1783$ hydrogen balloon; linked to Charles’ Gas Law $\bigl(V \propto T\bigr)$.
  • Although balloons contributed little to heavier-than-air engineering, they validated that humans could leave the ground for sustained periods.

Foundations of Aerodynamics (Early–Mid $19^{\text{th}}$ C.)

• Sir George Cayley (“father of the airplane”)
  • $1799$: engraved a silver disk illustrating the modern three-surface concept—fixed cambered wing (lift), separate propulsion system, cruciform tail (pitch/yaw stability).
  • Developed cambered airfoil sections & quantified forces: lift vs. drag diagrams on reverse of the disk.
  • First tri-plane glider $1853$ (carried a human).
  • Introduced wing dihedral, center-of-gravity (CG) studies, and rudder for directional control, decisively separating lift from propulsion and steering research away from ornithopters.

Experimental Glider Period (Late $19^{\text{th}}$ C.)

• Otto Lilienthal (“Glider Man”)
  • Published $1889$ Der Vogelflug als Grundlage der Fliegekunst—systematic study of bird-wing aerodynamics.
  • Constructed willow-frame / fabric gliders; performed >2{,}000 flights $1891$-$1896$, proving controllable, repeatable human flight.
  • Used stabilizing vertical + horizontal fins; his empirical data later aided the Wrights’ 1900–1901 glider iterations.

• Octave Chanute
  • Retired civil engineer; collated global aviation data, publishing $\textit{Progress in Flying Machines}$ $1894$.
  • Advanced structural design by stacking multiple wings supported by wire bracing, achieving high lift with modest span.

Birth of Powered Flight ($1903$)

• Wright Brothers
  • Integrated prior knowledge (Cayley, Lilienthal, Chanute) plus their own wind-tunnel testing.
  • Wright Flyer I (“Kitty Hawk”): twin-spar, spruce truss fuselage, muslin-covered biplane wings; warping for roll control; forward canard for pitch.
  • First sustained, powered, controlled flight $17\,\text{Dec}\,1903$.

Early Monoplane & Metal Evolution ($1909$ – $1910$)

• Louis Blériot
  • Blériot XI $1909$: first successful monoplane, cable-braced via king-post mast; Pratt truss fuselage.
  • Achieved Channel crossing, demonstrating operational viability of single-wing designs.

• Hugo Junkers
  • J-1 $1910$: first all-metal monoplane.
  • Dur-aluminum truss + metal skin eliminated external bracing, lowering drag and enabling higher speeds; possible due to stronger power-plants delivering requisite \displaystyle T > D (thrust exceeding drag).

Maturation of Metal Airframes (1920s–1930s)

• All-metal semi-monocoque fuselages emerge—primary load carried by:
  • Longerons (longitudinal beams).
  • Bulkheads & frames (transverse rings).
  • Stringers (secondary longitudinals).
  • Skin (stressed covering sharing shear & hoop loads).

• Flying-boat hull expertise translated into streamlined landplane fuselages.
  • Stress-skin designs reduced internal truss mass, enabling larger payload/cabin volumes.

Advent of Composite Sandwich (WW II Era)

• de Havilland Mosquito (first flight $1940$)
  • Fuselage: balsa core sandwiched between birch plywood skins, bonded with casein & later synthetic resins—lightweight yet stiff, with favorable fatigue and radar signature.
  • Precursor to modern foam/honeycomb composite cores.

Key Structural Concepts & Terminology

• Truss: interconnected beams (members experience only tension or compression). Early aircraft = wood truss; modern light aircraft may still use welded-steel tube trusses.

• Semi-monocoque: load shared between skin & underlying framework; dominant form for metal aircraft $\geq$ $1930\text{s}$.

• Monocoque: shell carries nearly all loads; minimal internal framing (e.g., certain pressurized fuselage sections, rocket bodies).

• Stress-skin: hybrid where external skin transmits shear/axial loads; stringers stiffen skin against buckling.

• Composite sandwich: two strong face-sheets separated by lightweight core; bending stiffness scales with $t^{3}$ (face-sheet spacing $t$), giving high stiffness-to-weight.

Relevance for the Modern AMT

• Mixed fleet reality: wood-and-fabric restorations through advanced CFRP (Carbon-Fiber-Reinforced-Polymer) business jets.
  • Need competence in adhesive bonding, doped fabric recovery, riveted-skin repair, and composite scarf patching.

• Aging-aircraft issues:
  • Metal fatigue (S-N curve life), corrosion (galvanic, pitting), and WFD (Widespread Fatigue Damage).
  • Original design life may be $\approx$ $20\text{–}30$ years; many airframes now > $40$ years in service.

• Regulation & documentation: adherence to OEM SRM (Structural Repair Manual), AC $43.13$ guidance, and AD/SB compliance critical for continued airworthiness.

Ethical & Practical Implications

• Public safety hinges on scrupulous structural maintenance; failure modes (e.g.
  inflight structural breakup) are catastrophic.

• Conservation vs. modernization: balancing heritage aircraft authenticity with safe materials—e.g., substituting Sitka spruce with Douglas-fir or composites where original species unavailable.

• Environmental considerations: composite end-of-life disposal, toxic chromate primers in metal protection, and energy intensity of aluminum production.

Quick Reference Dates & Milestones (Chronology)

• $1783$ – First manned balloon (Montgolfier).

• $1799$ – Cayley’s fixed-wing concept disk.

• $1853$ – Cayley’s man-carrying glider.

• $1891$ – Lilienthal’s first controlled glider flight.

• $1903$ – Wright Flyer powered flight.

• $1909$ – Blériot XI Channel crossing.

• $1910$ – Junkers J-1 all-metal monoplane.

• $1920\text{s}$ – Widespread semi-monocoque fuselages.

• $1930\text{s}$ – Stress-skin, larger transports, radial & early turbojet engines.

• $1940$ – de Havilland Mosquito composite sandwich.

Equations & Technical Nuggets

• Basic aerodynamic force balance (level un-accelerated flight):
  $\sum F<em>{z}:\quad L = W$ $\sum F</em>{x}:\quad T = D$

• Lift on a cambered airfoil (thin-airfoil theory):
  $C<em>{L} = 2\pi (\alpha - \alpha</em>{0})$
  • Cayley’s early experiments recognized the proportionality between angle of attack $\alpha$ and lift.

• Structural bending stress (spar design):
  $\sigma = \dfrac{M y}{I}$
  • Drives need for deeper spars or sandwich construction to increase moment of inertia $I$ without weight penalty.

Study Tips

• Memorize chronological order of key inventors & their structural contributions (Cayley ⟶ Lilienthal ⟶ Chanute ⟶ Wright ⟶ Blériot ⟶ Junkers).

• Understand vocabulary: truss, monocoque, semi-monocoque, rigging, empennage.

• Relate historical materials (wood, fabric) to their mechanical properties (anisotropy, susceptibility to moisture) vs. modern alloys (isotropy, fatigue limits) and composites (directional stiffness, delamination).

• Review AC $43.13$ & specific SRM chapters for procedural knowledge on inspection and repair.