PPL Aircraft General Knowledge cheat sheet

Primary structure carries flight, ground and pressurisation loads and must be damage-tolerant; secondary structure (fairings, cowlings, access panels) carries only aerodynamic or minor loads.

Semi-monocoque construction: skin takes shear and part of the bending, stringers and frames stabilise the skin against buckling, and a few heavy spars/keel beams take concentrated loads.

Fail-safe design assumes a detectable crack can exist without catastrophic failure until inspection; safe-life design retires the part at a fixed life; damage tolerance sets inspection intervals from crack-growth analysis.

A stressed-skin wing upper surface works mainly in compression, the lower surface in tension; this is why upper-surface fatigue, disbonds and corrosion are critical inspection areas.

Control surfaces are mass-balanced (leading-edge weights or internal balances) to keep the surface's centre of gravity ahead of the hinge line and prevent flutter.

Aircraft bolts are graded (AN, MS, NAS); grip length must equal the combined thickness of the parts so the shank, not the threads, bears the shear load.

Corrosion types to recognise: surface/general, galvanic (dissimilar metals plus electrolyte), pitting, intergranular, exfoliation (delamination of clad sheet) and stress corrosion in high-tension fittings.

Flying-control travel and rigging are checked against published tolerances; a mis-rigged or free-played surface causes trim error, buffet and reduced flutter margin.

Four-stroke cycle: intake, compression, power, exhaust; the piston is driven through two crankshaft revolutions per cycle, so one power stroke per cylinder per two revolutions.

Mixture ratio: stoichiometric is about 15:1 air-to-fuel by mass; best power is rich of peak (roughly 12:1), best economy lean of peak; excessively lean mixtures raise cylinder head temperature and risk detonation.

Detonation is uncontrolled explosive combustion after spark ignition (high CHT, high manifold pressure with low rpm or lean mixture); pre-ignition is ignition before the spark, usually from a hot spot such as a glowing deposit or plug.

A constant-speed propeller absorbs constant power by increasing blade angle with rpm; manifold pressure is the power demand indicator, rpm the setting, and the two must be moved in the correct order to avoid overboost or overspeed.

Carburettor icing can occur at ambient temperatures well above freezing (roughly -7 to +21 degrees C with high humidity); carburettor heat raises the mixture temperature and enriches it because heated air is less dense.

Hydraulic system: pressure = force / area; a smaller piston moves further with less force, a larger piston moves less with more force, and the system pressure is set by the relief valve, not by pump displacement.

Electrical and pneumatic anti-ice/de-ice systems draw significant power; boot de-ice removes ice after accretion, thermal anti-ice prevents it, and both cost engine bleed air or alternator capacity.

Moment = mass x arm; total moment divided by total mass gives the centre of gravity arm, expressed from the datum.

Adding mass forward of the CG moves the CG forward; adding mass aft moves it aft; the shift equals (added mass x distance from old CG) / new total mass.

Maximum take-off mass, maximum landing mass, maximum zero-fuel mass and maximum ramp mass are separate limits; the most restrictive one governs the planned fuel load.

Forward CG limit: nose-heavy aircraft need more tail-down force, giving higher stall speed, longer take-off run, heavier stick forces and better stall/spin recovery.

Aft CG limit: shorter take-off and higher cruise speed but reduced longitudinal stability, lighter control forces, longer landing flare and a greater tendency to enter a spin with poor recovery.

Load sheet checks: dry operating mass plus traffic load gives zero-fuel mass; adding take-off fuel gives take-off mass; subtracting trip fuel gives landing mass.

Floor loading limits (kg per unit area or per running metre) apply to cargo and must be checked independently of the total mass and CG limits.

Density altitude rises with pressure altitude, temperature and humidity; it degrades engine power, propeller/thrust and lift, so take-off and climb performance fall and true airspeed for a given IAS rises.

Take-off distance required is the greater of the all-engines and engine-failure cases, screened to 35 ft; landing distance required is from 50 ft to a full stop, and both are factored by regulation (for example 1.15 or 1.43).

V speeds: V1 decision speed, VR rotation, V2 take-off safety speed, VY best rate of climb, VX best angle of climb, VNE never-exceed, VNO maximum structural cruising, VFE flap-extended, VLE/VLO gear speeds.

Climb gradient (%) = 100 x (height gained / horizontal distance); for light aircraft use approximately 100 x (rate of climb in ft/min) / (groundspeed in kt x 101).

Stall speed varies as the square root of load factor and of mass: Vs at load factor n = Vs(1g) x square root of n; a 30 degree bank gives n = 1.15, a 60 degree bank gives n = 2.

Headwind increases the climb angle over the ground for a given rate of climb but does not change the rate of climb itself; wind affects the ground distance, not the air performance.

Runway slope, surface condition (dry, wet, contaminated) and braking action change accelerate-stop and landing distances; contaminated runway corrections can exceed 50 percent.

Fuel plan components: taxi fuel, trip fuel, contingency (usually 5 percent of trip), alternate fuel, final reserve (30 minutes holding at 1500 ft for commercial jets) and extra fuel.

Endurance = usable fuel / fuel flow; range = endurance x groundspeed; specific range (nm per kg) is highest at the speed for best lift/drag ratio, not at maximum speed.

Triangle of velocities: true heading plus wind vector gives true track and groundspeed; true heading corrected for variation and deviation gives magnetic and compass heading.

Point of no return (equal-time point) is reached when time to destination equals time back to base; the equal-distance point is where distance to destination equals distance to base.

ISA: sea-level temperature 15 degrees C, pressure 1013.25 hPa, lapse rate 1.98 degrees C per 1000 ft up to 36,090 ft (tropopause, -56.5 degrees C).

Pressure altitude = indicated altitude with 1013 set; true altitude = pressure altitude corrected for temperature error, roughly 4 percent per 10 degrees C of ISA deviation.

In-flight monitoring compares planned fuel at each waypoint with actual fuel; a persistent shortfall means recalculating the equal-time point and considering a diversion.

Pitot-static: the airspeed indicator uses total minus static pressure, the altimeter uses static pressure only, and the vertical speed indicator uses the rate of change of static pressure through a calibrated leak.

Altimeter errors: position/static-source error, instrument error, temperature error (cold air means the aircraft is lower than indicated, roughly 4 ft per 1000 ft per degree C of ISA deviation) and pressure-setting error.

Airspeed definitions: IAS is what the instrument shows, CAS corrects for position and instrument error, EAS corrects CAS for compressibility, TAS corrects EAS for density altitude.

A blocked pitot tube with a clear static source makes the ASI behave like an altimeter; a blocked static source freezes the ASI, altimeter and VSI at the values when the blockage occurred.

Gyroscopic instruments: rigidity in space gives the attitude and heading indicators their reference; precession is the apparent drift caused by applying a force, and is used deliberately in rate gyros.

The directional gyro drifts (apparent wander, about 15 degrees per hour times the sine of latitude) and must be realigned with the magnetic compass in level, straight flight.

Magnetic compass errors: variation (geographic), deviation (aircraft magnetism), dip (turning and acceleration errors in a turn toward the poles) and northerly/southerly turning error.

An artificial horizon shows pitch and roll from a vertical gyro; tumble limits and caging protect it during unusual attitudes, and it must be erect before flight.

Ohm's law and power: V = I x R, P = V x I = I squared x R; series resistances add, parallel resistances combine as 1/R total = sum of 1/R.

Aircraft DC supply is typically 14 V (12 V battery) or 28 V (24 V battery); the alternator/generator must exceed the bus load to recharge the battery after start.

Alternator output is controlled by the voltage regulator; a failed regulator can cause overvoltage, which the overvoltage relay protects against by taking the alternator off line.

The ammeter shows current into or out of the battery, not total alternator output; a loadmeter shows the alternator's total output.

Bus bar distribution allows essential services to be fed from a separate essential bus; the battery master and alternator switches control the source, not the individual consumers.

Circuit protection: fuses and circuit breakers protect the wiring, not the equipment; a breaker that pops repeatedly indicates a fault and must not be repeatedly reset.

Magneto ignition is independent of the aircraft electrical system; a live magneto requires the ignition switch to ground the P-lead, so a broken P-lead means the engine can fire with the switch off.

Bonding and shielding control static discharge and electromagnetic interference; a failed bonding strap causes radio noise and can allow a static spark at refuelling.