Module 11B.1–11B.3 — Piston aeroplanes: flight controls aerodynamics and airframe structures

Module 11B at a glance

Module 11B (piston aeroplanes) is taken by A2 and B1.2. EASA paper (single Module 11, Reg. (EU) 2023/989): A2 72 questions / 90 min; B1.2 100 questions / 125 min (UK retained 11B: A 72, B1 100). B1.2 is examined at levels 2–3, A2 mostly level 1. Several turbine-only items are not in 11B: air-cycle air conditioning and bleed air supply, fly-by-wire and active load control, fuel jettison/inerting/trim tanks, pneumatic hydraulic generation, anti-icing (hot air) and rain repellent, air–ground sensing, and 11.18–11.21.

11.1 Theory of flight (A2 level 1, B1.2 level 2)

Controls and devices on piston aeroplanes

• Ailerons (often differential or Frise type to counter adverse yaw), elevator or stabilator (with anti-servo tab), rudder; ruddervators on V-tail designs (e.g. some Beechcraft Bonanza models).
• Flaps: plain, split, slotted or Fowler; electrically or manually (lever and cable) operated; flaperons on some light designs.
• Trim tabs (cable-driven trim wheel or electric trim), ground-adjustable fixed tabs on ailerons/rudder to correct wing heaviness or yaw.
• Spoilers/speed brakes are rare (some motor-gliders and high-performance singles).
• Balance: mass balance weights (often lead in the horn or a balance arm) and horn balances; re-balance after repair or repainting to prevent flutter.
• Stall strips on inboard leading edges make the root stall first; vortex generators (kits) improve low-speed handling; wing fences are rare on straight wings.

Propeller effects (piston-specific handling)

Effect	Cause	Result (clockwise propeller viewed from the cockpit)
Torque reaction	Engine turns propeller one way; aircraft rolls the other	Roll/yaw to the left
Slipstream (spiralling)	Spiral slipstream strikes the fin on one side	Yaw to the left
P-factor (asymmetric blade effect)	At high angle of attack the down-going blade has a higher angle of attack	Yaw to the left at high power/low speed
Gyroscopic precession	Pitching or yawing the rotating propeller	E.g. raising the tail on take-off in a tail-wheel aircraft yaws left

Designers counter these with engine offset (side thrust), fin offset, rudder trim tabs or rudder bias. Twin-engine aircraft have a critical engine (the one whose failure most affects directional control — usually the left on conventional twins) unless they have counter-rotating propellers.

11.2 Airframe structures — general concepts (level 2 for A2 and B1.2)

The same ATA 51 concepts apply as for turbine aircraft:

• Zones and stations: fuselage stations, water lines, buttock lines, wing stations, zone numbering (100–800).
• Electrical bonding (bond straps across hinges, engine mounts, fuel system components), lightning protection (bonding, static wicks; composite aircraft need embedded conductive mesh).
• Structural classification (primary, secondary, tertiary), safe-life / fail-safe / damage tolerance (many light aircraft were designed safe-life; some have life-limited wing spars or mandatory spar inspections by AD).
• Stresses: tension, compression, shear, bending, torsion; hoop stress in pressurised piston twins; fatigue (e.g. flight-school aircraft with high cycles).
• Drainage and ventilation: drain holes in the lower fuselage, control surfaces and fabric covering (grommets); ventilation of battery boxes and fuel areas.
• Construction methods (B1.2 level 2): stressed-skin semi-monocoque aluminium (most common), riveting (solid and blind rivets), bonding (metal-to-metal), surface protection (Alclad, anodising, chromate conversion, primers), symmetry checks (rigging after heavy landing).

Light-aircraft structure types

Structure	Features	Maintenance points
Metal semi-monocoque (aluminium alloys)	Skins, stringers, formers, spars, ribs	Corrosion (especially seaplanes, coastal), cracks at spar caps and wing attach fittings, loose rivets ("smoking rivets")
Welded steel tube (truss) with fabric	4130 chromoly tube fuselage; fabric-covered (cotton/linen historically, now polyester such as Ceconite)	Internal tube corrosion (lower longerons), fabric strength testing (punch tester), UV deterioration, doped/coating finishes
Wood	Spruce spars, plywood ribs/skins, glued joints (resorcinol, epoxy)	Moisture/rot, glue joint failure, compression failures, check with moisture meter
Composite	Glass/carbon fibre sandwich (foam/honeycomb), monolithic laminates	Delamination (tap test), UV/heat limits (white paint), lightning protection mesh, matrix cracking

Part-66 B1 Group 3 ratings carry limitations for structure types (metal, composite, wooden, metal tubing with fabric, pressurised) unless experience is shown — this mirrors these structure types.

11.3 Airframe structures — aeroplanes (A2 level 1, B1.2 level 2)

Fuselage, doors and windows

• Construction and pressurisation sealing (pressurised piston twins such as some Cessna 340/421, Piper Malibu): sealed cabin section, pressure bulkheads, sealed control-cable and wire penetrations, inflatable or compressed door seals.
• Wing, stabiliser, pylon/engine and undercarriage attachments: wing attach fittings and carry-through spar; strut-braced high wings (Cessna) — lift struts and their attach fittings (corrosion inside struts is a known AD subject).
• Seat installation: seat rails with stops — seat rail cracks and worn locking holes have caused seats to slide back during take-off (classic AD for light aircraft); seat belts and shoulder harnesses.
• Doors and emergency exits: cabin doors with latches and secondary latches; emergency exits on larger twins; safety devices and cargo loading are level 1 for B1.2.
• Windows and windscreens: stretched/cast acrylic (Perspex/Plexiglas); clean with approved cleaners and soft cloths (no solvents — crazing), cover when parked; crazing and cracks limits; stop-drilling of cracks only as allowed.

Airborne towing devices (level 1)

Glider tow hooks (e.g. tail-mounted release with cable to the cockpit), banner tow hooks — check release function under load, weak links, structural attachment and placards.

Wings, stabilisers, control surfaces, nacelles

• Wings: single or twin spar, ribs, skins; fuel storage in integral (wet) tanks or bladder/rigid tanks between spars; landing gear and engine nacelle attachments on twins; flap/aileron hinges.
• Stabilisers: tailplane and fin, often light-alloy or composite; stabilator pivot and hinge fittings.
• Flight control surfaces: light alloy (often corrugated skins), fabric-covered or composite; balancing — mass and aerodynamic; drain holes in trailing edges.
• Nacelles/engine mounts: welded steel tube engine mounts bolted to the firewall via rubber vibration isolators (shock mounts); firewall of stainless steel or galvanised/terne-plate steel with sealed penetrations; cowlings with cowl flaps.

Key fact: The engine firewall must stop a fire spreading from the engine compartment; any hole made for cables or pipes must be sealed with fireproof grommets/sealant.

Exam tips

• B1.2 levels are higher than A2 — expect "why" and "how" questions on construction and control devices.
• Know propeller left-turning tendencies and the critical engine.
• Fabric, wood and composite inspection methods (punch test, moisture, tap test).
• Seat-rail and lift-strut corrosion are classic light-aircraft inspection items.