Exam code: CADA / CADHPass mark: 70% · 1.5 hrsFixed & Rotary specific streams
Aerodynamics is one of the 7 CASA CPL/PPL theory subjects under CASR Part 61 MOS Schedule 3.
Every topic below is drawn from the same syllabus registry that drives Aero Academic's Knowledge
Deficiency Report — including which regulatory citations are confirmed against the published MOS
text and which are still awaiting review.
Topics covered in depth
Angle of Attack & the Lift Curve
How CL, drag and the lift/drag ratio change as angle of attack increases to the stalling angle and beyond — read off the CL, CD and CL/CD graphs. The shared aerodynamic basis for an aeroplane wing and a helicopter rotor blade.
CASR Part 61 MOS Schedule 3 (AD) 2.1.1 (p.397) — Effect of changing angle of attack up to the stalling angleVerified“Explain the effect of changes in angle of attack up to the stalling angle on the following: (a) pressure changes above and below an aerofoil; (b) changes in airflow characteristics streamlined to turbulent; (c) lift and drag; (d) the boundary layer.”
CASR Part 61 MOS Schedule 3 (AD) 2.1.2 (p.397) — Identifying angles of attack on the CL, CD and CL/CD graphsVerified“With reference to CL, CD, CL/CD graphs identify angles of attack associated with the following: (a) minimum drag – maximum level flight speed; (b) maximum lift – stalling angle; (c) best CL/CD – best glide range and still air range.”
Common exam mistakes
The stall is defined by angle of attack, not by airspeed — a wing can stall at any speed or attitude.
Past the stalling angle, more angle of attack gives LESS lift, not more.
Best glide range and minimum drag occur at the SAME angle of attack — the best CL/CD point.
Recovery from a stall is to reduce angle of attack first; power and attitude do not un-stall a wing.
On a helicopter the retreating blade meets the lowest relative airflow and reaches this stalling angle first.
How Bernoulli's theorem of constant energy flow — kinetic energy (dynamic pressure) trading against potential energy (static pressure) — explains accelerating flow through a venturi and the pressure difference an aerofoil generates as air speeds up over the upper surface.
CASR Part 61 MOS Schedule 3 (AD) 2.2.1 (p.396) — Bernoulli's theorem — energy exchange through a venturi and over an aerofoilVerified“Apply Bernoulli's theorem of constant energy flow to describe how an aerofoil produces lift, limited to the variation of kinetic energy (dynamic pressure) and potential energy (static pressure) as air flows through a venturi or over a aerofoil.”
Common exam mistakes
Total energy (dynamic + static pressure) stays constant along a streamline — it is exchanged, not created.
Faster airflow over the upper cambered surface means LOWER static pressure there, not higher.
A venturi speeds up the flow through its narrowest section by the same energy trade, before the air ever meets a wing.
Bernoulli explains the pressure difference; it is not the complete picture of lift on its own — reaction/downwash also contributes.
Vortex Ring State & Loss of Tail Rotor Effectiveness
Two helicopter-specific descending-flight hazards: vortex ring state (settling with power), where the main rotor re-ingests its own tip-vortex downwash in a steep low-speed descent, and loss of tail rotor effectiveness, where relative wind direction starves the tail rotor of authority — the conditions that lead into each and the recovery action.
CASR Part 61 MOS Schedule 3 (AD) 2.2.3 (p.400) — Vortex ring state and loss of tail rotor effectiveness — conditions and recoveryVerified“Explain the meaning the following, including the conditions leading thereto and appropriate recovery action: (a) vortex ring state (settling with power); (b) loss of tail rotor effectiveness (LTE).”
Common exam mistakes
Vortex ring state needs power applied AND a steep, low-airspeed descent together — power alone or descent alone does not cause it.
Recovery from vortex ring state is to fly out of the disturbed downwash — forward cyclic to gain airspeed, not simply pulling more power, which can worsen the sink rate.
LTE is a loss of tail rotor authority relative to the wind, not a mechanical tail rotor failure — the tail rotor is still working.
LTE is most likely at low airspeed with a left/right crosswind or tailwind component (main-rotor-direction dependent), not necessarily at high power.
Vortex ring state affects the main rotor system; LTE affects the tail rotor — the recognition cues and recovery actions are different for each.
How a small, uncorrected bank and yaw excursion on an aeroplane with directional stability stronger than its lateral (dihedral) stability grows over time into a steepening, accelerating spiral — the relationship between directional and lateral stability that produces spiral instability, and its effect on control.
CASR Part 61 MOS Schedule 3 (AD) 2.6.2 (p.398) — Relationship between directional and lateral stability — spiral instabilityVerified“Describe the relationship between directional and lateral stability (spiral instability) and state the effect of spiral instability on the control of an aeroplane.”
Common exam mistakes
Spiral instability comes from directional (weathercock) stability being strong relative to lateral (dihedral) stability — not from a general lack of stability.
A laterally-strong, directionally-weak aeroplane tends toward Dutch roll instead — the opposite imbalance.
Uncorrected, the aircraft does not return to wings-level: bank, yaw rate, airspeed and rate of descent all increase together, tightening into a spiral.
It is a one-way divergence away from the disturbed condition, not an oscillation — unlike Dutch roll, it does not repeat back and forth.
Recovery is the same as any spiral dive: close the throttle, roll wings level with coordinated aileron and rudder, then ease out — pulling back before levelling the wings tightens the spiral and raises g.
Three helicopter-specific hazards that share a common thread — each starts from a small disturbance that a rotor system can amplify rather than damp: ground resonance, where an unbalanced rotor disc rocks the airframe through the skids/wheels on the ground; mast bumping, where excessive rotor flapping in a low-G condition lets the hub strike the mast; and dynamic roll-over, where one skid or wheel acts as a pivot the rotor thrust cannot overcome past a critical bank angle. Conditions leading to each and the correct recovery.
CASR Part 61 MOS Schedule 3 Unit 1.3.3 CADH 2.7.1 (p.396) — Ground resonance, mast bumping and dynamic roll-over — conditions and recovery (CPL)Verified“Explain the following phenomena and the conditions that can lead to them arising and the appropriate recovery actions to be taken when they arise: (a) ground resonance; (b) mast bumping; (c) dynamic roll-over.”
CASR Part 61 MOS Schedule 3 Unit 1.1.3 RBKH 3.7.1 (p.364) — Ground resonance, mast bumping and dynamic roll-over — conditions and recovery (RPL/PPL)Verified“Select from a list the statement which best describes: (a) ground resonance; (b) mast bumping; (c) dynamic roll-over; (d) the conditions leading to: (i) ground resonance; (ii) mast bumping; (iii) dynamic roll-over; (e) the appropriate recovery action for each condition in paragraph (d).”
Common exam mistakes
Ground resonance needs the rotor disc unbalanced (blades bunched instead of evenly spaced, e.g. from a hard landing on one wheel) AND the skids/wheels in contact with the ground — it does not occur in flight, and the recovery is an immediate lift-off (to fly clear of the ground contact feeding it) or an immediate shutdown, not waiting it out.
Mast bumping is a two-bladed teetering (semi-rigid) rotor problem, triggered by a low-G or negative-G condition followed by an abrupt cyclic input — the rotor thrust that normally resists excess flapping is briefly gone, so the hub can flap far enough to strike the mast.
Recovery from a low-G condition is smooth aft cyclic first to reload the rotor disc, not lateral cyclic — rolling the cyclic while unloaded is what drives the flapping that causes mast bumping.
Dynamic roll-over needs one skid or wheel planted as a pivot point (e.g. a snagged skid, or sliding sideways during pickup/set-down) plus a bank angle past which rotor thrust can no longer arrest the roll — it is a ground-contact hazard, not an in-flight one.
The recovery from dynamic roll-over is to reduce collective (put weight back on the ground) and level the cyclic, not to pull more power or try to fly out of it — more lift with the pivot still planted steepens the roll.
Behind the Power Curve, Power Pushover & Pilot-Induced Oscillation
Three helicopter handling hazards that unfold as airspeed, power or the pilot's own control inputs work against the aircraft over time: flying behind (on the backside of) the power curve, where slowing further demands more power rather than less; power pushover, where an abrupt forward-cyclic pushover combined with reduced power briefly unloads the rotor disc; and pilot-induced oscillation, where the pilot's own out-of-phase corrections sustain and grow an oscillation the aircraft did not start. Causes, effects, avoidance and recovery for each.
CASR Part 61 MOS Schedule 3 (AD) 1.1.5 (p.402) — Causes, effects, avoidance and recovery for power pushover, flight behind the power curve, rotor vibration on take-off, negative flight load manoeuvres, high-speed flight, ground resonance, pilot-induced oscillation, and lift-off/low-airspeed high angle of attackVerified“Explain the causes and effects of, and avoidance and correct recovery procedure for, the following: (a) power pushover; (b) flight on backside of the power curve; (c) flight behind the power curve; (d) rotor vibration on take-off; (e) negative flight load manoeuvres; (f) high-speed flight; (g) ground resonance; (h) pilot-induced oscillation; (i) lift off/low airspeed and high angle of attack.”
Common exam mistakes
Behind (on the backside of) the power curve, slowing further needs MORE power, not less — the opposite of normal front-of-curve handling.
Power pushover needs an abrupt forward-cyclic pushover AND reduced power together — recover with smooth AFT cyclic to reload the disc, not lateral cyclic.
The retreating blade, not the advancing blade, is the primary high-speed limit on a conventional rotor — it must fly at a higher angle of attack for the same lift because rotational speed subtracts from, rather than adds to, its airflow.
A pilot-induced oscillation is sustained by the pilot's own out-of-phase corrections, not by the aircraft — relaxing the grip, not applying a bigger correction, breaks it.
Flight Controls & The Three Axes of Flight
The three orthogonal axes of flight (lateral, longitudinal, vertical), primary control surfaces (elevators, ailerons, rudder), movements (pitch, roll, yaw), secondary effects, adverse yaw, and trim tabs.
CASR Part 61 MOS Schedule 3 (AD) 1.1.1 (p.396) — Primary and secondary flight controls — axes and movementsVerified“Explain the function of primary control surfaces: elevators (pitch around lateral axis), ailerons (roll around longitudinal axis), rudder (yaw around normal axis), and secondary flight controls including trim tabs.”
FAA-H-8083-25C (Pilot’s Handbook of Aeronautical Knowledge) Chapter 6: Flight Controls — Flight Controls: Primary Flight Controls and Aerodynamic ForcesVerified
Common exam mistakes
Movement around an axis is perpendicular to that axis: pitch is AROUND the lateral axis, roll is AROUND the longitudinal axis, yaw is AROUND the vertical (normal) axis.
Adverse yaw is caused by induced drag from the downward-deflected aileron on the rising wing, pulling the nose away from the turn.
Rudder does not turn the aeroplane — banking the wings turns the aeroplane by tilting total lift; rudder merely counters adverse yaw to maintain coordinated flight.
Trim tabs relieve control pressures; they are not primary flight controls and move in the OPPOSITE direction to the control surface when trimmed.
The physics of autorotation, rotor RPM preservation, the certified Bell 206 Height-Velocity avoid envelope, and Mayday distress protocols.
CASR Part 61 MOS Schedule 3 Unit 1.9.7 COPH — Helicopter height-velocity diagram and forced landing proceduresVerified“Explain the purpose and avoid areas of the height-velocity diagram and execution of autorotative forced landings.”
Common exam mistakes
Operating inside the low-speed, high-altitude envelope leaves insufficient kinetic energy and altitude to arrest descent before ground impact.
In autorotation, the Total Aerodynamic Force (TAF) vector tilts FORWARD in the driving region (25%–70% span) to drive the blades.
Total engine failure is a MAYDAY (distress) emergency, not PAN-PAN.
Distinguishing hover spin from cruise vertical fin weathercocking, stuck pedal emergencies, throttle steering, and running landings.
CASR Part 61 MOS Schedule 3 Unit 1.9.8 COPH — Loss of tail rotor effectiveness and tail rotor drive failureVerified“Describe indications, aerodynamic behaviour and emergency actions for complete tail rotor drive failure and jammed anti-torque pedals.”
Common exam mistakes
At cruise airspeed (> 60 kt), the vertical stabilizer provides aerodynamic weathercocking stability to prevent yaw.
In a hover, loss of tail rotor drive causes violent, uncontrollable right yaw (in US CCW rotation).
For a stuck pedal landing, use throttle adjustments and shallow approach angle for a running touchdown.
Transition from hover in ground effect to forward flight, induced flow reduction, rotor efficiency gains between 16 and 24 knots, and transverse flow effect.
CASR Part 61 MOS Schedule 3 Unit 1.2.1 CADH — Translational lift and effective translational lift (ETL)Verified“Explain the principles of translational lift, effective translational lift (16-24 kt), and transverse flow effect.”
Common exam mistakes
ETL occurs between 16 and 24 knots as the rotor disc outruns its own recirculating downwash vortices.
Transverse flow effect causes right roll (US rotor) or left roll just before reaching ETL.
Dynamic Lift & Altitude Pressure Gradients
Air density changes with altitude, dynamic pressure ($q = \frac{1}{2}\rho V^2$), true airspeed versus indicated airspeed divergence, and lift coefficient variation.
CASR Part 61 MOS Schedule 3 (AD) 1.2.2 — Dynamic pressure and aerodynamic lift generationVerified“Explain dynamic pressure as a function of air density and velocity, and describe how lift varies with pressure gradient and altitude.”
Common exam mistakes
For a given IAS, TAS increases by roughly 2% per 1,000 ft of altitude due to decreasing air density.
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