Module 11A.1 — Aeroplane aerodynamics, flight controls and other aerodynamic devices

Module 11A at a glance

Module 11A (turbine aeroplanes) is taken by A1 and B1.1. Under the EASA single Module 11 (Reg. (EU) 2023/989) the paper is A1: 108 questions / 135 min; B1.1: 140 questions / 175 min (UK retained 11A: A 108, B1 140). Sub-module 11.1 is level 1 for A1 and level 2 for B1.1.

11.1(a) Aeroplane aerodynamics and flight controls

Axes and controls

Axis	Motion	Primary control	Stability
Longitudinal (nose to tail)	Roll	Ailerons (and roll spoilers)	Lateral
Lateral (wingtip to wingtip)	Pitch	Elevators / stabilator / trimmable horizontal stabiliser	Longitudinal
Normal / vertical	Yaw	Rudder	Directional

All three axes pass through the centre of gravity.

Roll control

• Ailerons move differentially: the down-going aileron increases lift on its wing; the up-going one reduces it.
• Adverse yaw: the down aileron creates more induced drag, yawing the nose away from the turn. Countered by differential aileron (up-going travel greater than down-going), Frise ailerons (leading edge of the up aileron protrudes below the wing, adding drag), rudder coordination, and roll spoilers.
• Large jets often have inboard (all-speed) and outboard (low-speed) ailerons; outboard ailerons are locked out at high speed to avoid aileron reversal (wing twist from aileron load reverses the intended roll).
• Roll spoilers (flight spoilers) rise on the down-going wing only, reducing lift and adding drag — they also assist roll and avoid wing twisting.

Pitch control

• Elevators hinged to a fixed tailplane.
• Stabilator (all-moving tailplane) — the entire surface moves; usually with an anti-servo (anti-balance) tab to give feel.
• Variable-incidence (trimmable) horizontal stabiliser (THS) — moved by a screw jack for pitch trim on large aircraft; elevators provide manoeuvre control.
• Canards — foreplanes ahead of the wing providing lift and pitch control.

Yaw control

• Rudder on the fin. On large aircraft, a rudder limiter (ratio changer or travel limiter) reduces maximum rudder deflection as speed increases to protect the fin structure.
• Yaw dampers automatically apply small rudder inputs to damp Dutch roll and coordinate turns.

Combined surfaces

Surface	Function
Elevons	Combined elevator + aileron (tailless/delta aircraft)
Ruddervators	V-tail surfaces: moved together for pitch, differentially for yaw
Flaperons	Ailerons that also droop together as flaps
Tailerons	Differentially moving stabilators for roll (military)

High-lift devices

Device	Location	Effect
Plain, split, slotted, Fowler flaps	Trailing edge	Increase camber (and area for Fowler) → higher C_L max, lower stall speed; increase drag
Slats	Leading edge (movable)	Create a slot, re-energise upper-surface boundary layer, increase stalling angle
Slots (fixed)	Leading edge	As slats but permanent
Krueger flaps	Inboard leading edge lower surface	Increase camber and C_L max
Droop leading edge	Leading edge	Increases camber

Drag-inducing devices

• Speed brakes / flight spoilers — deployed symmetrically in flight to increase drag and descent rate without speed increase.
• Ground spoilers / lift dumpers — deploy fully on touchdown to dump lift, putting weight on the wheels for braking effectiveness, and add drag.
• Fuselage-mounted airbrakes (petals) on some types.

Trim and tabs

Tab	How it moves	Purpose
Trim tab	Set by pilot; moves opposite to the required control surface movement	Removes steady stick force
Balance tab	Linked to move opposite to the control surface automatically	Reduces stick force (aerodynamic assist)
Anti-balance (anti-servo) tab	Moves in the same direction as the surface	Increases stick force / feel (e.g. on stabilators)
Servo tab	Pilot moves only the tab; the tab's aerodynamic force moves the free-floating surface	Reduces forces on large surfaces
Spring tab	Spring in the linkage; tab assistance increases with stick force/speed	Light forces at high speed, direct control at low speed
Fixed tab (ground-adjustable)	Bent on the ground	Corrects a permanent out-of-trim (e.g. wing heaviness)

Control surface bias: on some aircraft a surface (e.g. rudder or aileron) is rigged slightly off neutral to counter a known asymmetry such as propeller torque.

Key fact: A trim tab moves opposite to the direction the control surface must be held; an anti-balance tab moves in the same direction as its surface to increase feel.

11.1(b) Other aerodynamic devices

Balancing

• Aerodynamic balance: part of the surface ahead of the hinge line (inset hinge, horn balance, internal balance panels in a sealed chamber) — the airflow on the forward part helps move the surface, reducing pilot force.
• Mass balance: weights ahead of the hinge line bring the surface CG to (or ahead of) the hinge line to prevent flutter — a self-excited oscillation that can destroy the surface. After painting or repair, surfaces must be re-balanced to the manual limits.

Wing-flow devices

Device	Purpose
Wing fences	Chordwise plates on swept wings that block spanwise flow towards the tips, delaying tip stall
Saw-tooth (dog-tooth) leading edge	Discontinuity creates a vortex that acts like a fence and controls spanwise flow
Vortex generators	Small blades mixing high-energy free-stream air into the boundary layer — delay separation, improve control effectiveness, reduce shock-induced separation
Stall wedges / stall strips	Sharp strip on the inboard leading edge that makes the root stall first, preserving aileron control and giving buffet warning
Leading-edge devices	Slats, slots, Krueger flaps (above) used as boundary-layer control
Winglets / wingtip devices	Reduce induced drag from tip vortices

Key fact: Mass balance prevents flutter; aerodynamic balance reduces control forces. Don't mix them up.

Typical maintenance links

• Flight control surface rigging and balance checks after repair/painting (11.3.4, 11.9).
• Inspection of vortex generators and stall strips — missing VGs may be dispatch items in the CDL.
• Ensuring correct sense of operation after control work (independent inspection).

Exam tips

• Adverse yaw → differential/Frise ailerons, spoilers.
• Outboard ailerons locked at high speed → avoids aileron reversal.
• Rudder limiter reduces rudder travel with increasing speed.
• Fence/saw-tooth = stop spanwise flow; stall strip = root stalls first.