ATPL Aero & Systems cheat sheet

Limit load is the maximum load expected in service; ultimate load is limit load multiplied by the factor of 1.5, and the structure must withstand ultimate load without failure for 3 seconds.

Design manoeuvring speed VA is the speed at which full deflection of the flight controls produces the limit load factor; below VA the wing stalls before structural limit load is reached.

Load factor n = L/W = 1/cos(phi) in a level banked turn, so a 60-degree bank gives n = 2.

The V-n diagram is bounded by the positive and negative limit load factors, the manoeuvring speed VA, the design dive speed VD and the stall boundary.

Gust load factor increment is proportional to gust velocity and to airspeed, and inversely proportional to wing loading (W/S); higher wing loading reduces gust response.

Fail-safe design allows load paths to redistribute after failure of a primary element; safe-life design retires components at a calculated fatigue life.

Structural fatigue is driven by cyclic loading; the number of cycles to failure falls as stress amplitude rises (S-N curve), and corrosion accelerates crack growth.

Primary structure carries flight, ground and pressurisation loads and failure would be catastrophic; secondary structure failure affects safety but not catastrophically.

Pascal's law: pressure applied to a confined fluid is transmitted undiminished in all directions, so F1/A1 = F2/A2 for an ideal system.

Hydraulic power = pressure x volume flow rate (P = p x Q); for a given actuator speed, flow determines rate and pressure determines force.

System pressure is set by the pressure relief valve or pump regulator; the relief valve protects against overpressure and is not a normal pressure-control device.

A constant-pressure (variable-displacement) pump varies its output flow to hold system pressure; a constant-delivery pump needs a relief valve or unloading valve.

Accumulators store hydraulic energy in a gas-charged chamber, damp pressure surges, absorb thermal expansion and provide reserve for emergency operation.

Hydraulic fluid viscosity falls as temperature rises; excessive temperature increases internal leakage and reduces volumetric efficiency.

Selector valves direct flow to actuators; check valves permit one-way flow; restrictors and fuses limit flow in the event of a downstream line failure.

Air in hydraulic fluid causes spongy actuator response and pump cavitation; cavitation damages pumps and reduces flow.

Cabin pressure differential is the difference between cabin pressure and ambient pressure; it is limited by the structural design differential pressure.

Cabin altitude is the equivalent altitude corresponding to cabin pressure; pressurisation normally holds cabin altitude around 8000 ft or lower at high aircraft altitude.

Outflow valves control cabin pressure by regulating the rate at which air leaves the cabin; the inflow rate is set by the air-conditioning packs.

Cabin rate of climb or descent is limited (typically about 500 ft/min climb and 300 ft/min descent) for comfort and to avoid ear discomfort.

Air-cycle machines cool bleed air by compressing it, cooling it in a heat exchanger and expanding it through a turbine; the turbine also drives the compressor.

Bleed air for pressurisation and air-conditioning is taken from engine compressor stages or the APU; bleed air is hot and must be precooled before use.

The safety relief valves protect the fuselage against overpressure and negative pressure differential if the normal outflow control fails.

Air-conditioning packs regulate temperature by mixing hot bleed air with cooled pack air through a bypass or trim-air valve.

Ohm's law: V = I x R; electrical power P = V x I; for AC, real power P = V x I x cos(phi).

A generator's frequency is f = (p x N)/120, where p is the number of poles and N is rotational speed in rpm; AC frequency must be held near 400 Hz for aircraft systems.

A bus tie or busbar distributes power; essential and emergency buses are supplied from the battery or emergency generator if main generation is lost.

A contactor or relay switches high-current loads; circuit breakers protect wiring against overcurrent and are resettable, while fuses are not.

The battery supplies power for starting, emergency loads and ground operations; its capacity is rated in ampere-hours and it must be charged at a controlled rate.

A generator control unit regulates voltage, protects against overvoltage, undervoltage, overfrequency and reverse current, and controls paralleling.

DC generators need a reverse-current cut-out; AC generators are paralleled by matching voltage, frequency and phase.

Bonding and grounding provide a low-resistance return path and protect against static discharge and lightning damage.

Primary flight controls are ailerons, elevators and rudder; secondary controls are flaps, slats, spoilers and trim.

An autopilot has a command channel and a feedback channel; the servo drives the control surface and the position or rate feedback closes the loop.

Fly-by-wire replaces mechanical linkage with electrical signalling and computers; it can provide envelope protection, load alleviation and normal-law reversion.

In a fly-by-wire aircraft, normal law protects against exceeding load factor, angle of attack and bank limits; alternate or direct law progressively removes protection.

A yaw damper suppresses Dutch roll by feeding yaw rate back to the rudder; it is required for aircraft with weak natural Dutch roll damping.

Trim balances steady control forces; a mistrim condition causes persistent stick force and must be corrected before autopilot engagement.

A servo tab moves the control surface by aerodynamic force; an anti-balance tab moves opposite to the surface to increase feel.

Autopilot disconnect must be possible by a readily accessible means, and the autopilot must not oppose deliberate pilot override.

Tyre ply rating indicates load capacity; the tyre must be inflated to the specified pressure and inspected for cuts, wear and flat spots.

Brake energy is proportional to the kinetic energy absorbed: KE = 1/2 m v^2, so stopping distance and speed dominate brake heating.

Carbon brakes retain strength at high temperature; steel brakes are cheaper but have lower heat capacity.

An anti-skid system modulates brake pressure to prevent wheel lock; a locked wheel gives lower friction and loss of directional control.

The landing gear must withstand the design sink rate at maximum landing weight; the shock strut absorbs energy by compressing gas and oil.

A shimmy damper prevents rapid nose-wheel oscillation; worn torque links or low tyre pressure can cause shimmy.

Brake temperature must be monitored; excessive temperature can cause tyre fusible plug melting, brake fade or fire.

The parking brake is normally a separate valve that traps pressure; it must be released before take-off to avoid brake drag and overheating.

Fuel mass = volume x density; fuel density falls as temperature rises, so volume must be corrected for temperature when calculating mass.

The fuel system must supply fuel to the engines at the correct pressure and flow in all normal attitudes and at the maximum fuel imbalance allowed.

Fuel tanks are vented to atmosphere to prevent overpressure and to allow fuel to flow; blocked vents can cause tank collapse or fuel starvation.

A fuel boost pump supplies positive pressure to the engine-driven pump and provides backup if the engine pump fails.

Fuel imbalance limits are set to control lateral centre of gravity; crossfeed allows fuel to be transferred between tanks.

Water in fuel is drained from sump drains before flight; water is denser than fuel and collects at the lowest points.

Fuel quantity is measured by float, capacitance or ultrasonic systems; capacitance gauges measure dielectric change and need calibration for fuel type.

Jettison systems must be capable of dumping fuel at a controlled rate to reduce landing weight; jettison must not create a hazard or exceed structural limits.

Ice accretion increases drag, reduces lift and adds weight; the critical areas are wing leading edges, tailplane, engine intakes, pitot heads and windscreen.

Thermal anti-ice uses hot bleed air or electrical heating; de-ice uses cyclic inflation of boots to break ice off the protected surface.

Pitot and static heaters prevent blockage of pressure sensors; a blocked pitot tube causes airspeed indication errors.

Fire detection uses heat, smoke or rate-of-rise sensors; a fire loop must be tested before flight and the warning must identify the zone.

A fire extinguisher bottle is discharged into the affected zone; the agent is usually halon or an inert gas, and the bottle must be checked for pressure.

Smoke detection in cargo compartments uses photoelectric or ionization sensors; cargo smoke procedures require isolation of ventilation and discharge of the suppression agent.

Windscreen rain protection uses wipers, rain repellent or bleed-air heating; heating also prevents windscreen icing and fogging.

Engine fire detection must survive the fire environment long enough to give warning; the fire handle closes fuel, bleed and hydraulic shut-off valves.

Four-stroke cycle: induction, compression, power and exhaust; the crankshaft turns twice per complete cycle.

The mixture control sets fuel/air ratio; best power is slightly rich of stoichiometric, best economy is lean of peak EGT.

Detonation is uncontrolled rapid combustion causing high cylinder pressure and temperature; pre-ignition is ignition before the spark, often from a hot spot.

The propeller converts engine power into thrust; thrust falls as airspeed rises for a fixed-pitch propeller at constant rpm.

Propeller pitch is the angle between the blade chord and the plane of rotation; coarse pitch suits high speed, fine pitch suits take-off and climb.

A constant-speed propeller uses a governor to vary blade pitch and hold selected rpm as load changes.

Carburettor icing can occur at ambient temperatures well above freezing because of venturi cooling and fuel evaporation.

Engine power is limited by manifold pressure and rpm; overboosting can cause detonation and structural damage.

Thrust is the rate of change of momentum: F = m_dot x (V_jet - V_in) plus the pressure thrust term (p_exit - p_ambient) x A_exit.

Specific fuel consumption is fuel flow divided by thrust; lower SFC means better efficiency.

The Brayton cycle efficiency rises with pressure ratio; turbine inlet temperature limits thrust and is monitored by EGT or TIT.

A turbofan produces most thrust from the bypass stream; bypass ratio is bypass mass flow divided by core mass flow.

Engine surge is an unstable compressor condition with reverse flow and loud bangs; it is caused by stall of compressor blades and is countered by bleed valves.

Engine monitoring uses EGT, N1, N2, fuel flow and oil pressure/temperature; exceedance of any limit requires action and reporting.

Thrust falls with altitude because of reduced air density; it also falls with increasing Mach number due to ram effects and temperature rise.

Reverse thrust is produced by redirecting the bypass or exhaust flow; it is most effective at high speed and must not be used below the specified speed.