Aircraft General Knowledge
Aircraft General Knowledge covers the airframe, powerplant, systems and flight instruments a PPL pilot must monitor and interpret.
Airframe, engine, propeller
Most light trainers are semi-monocoque aluminium structures. Primary controls are ailerons, elevator and rudder; flaps and trim are secondary. The piston engine is a four-stroke: induction, compression, power, exhaust. Mixture controls fuel/air ratio; lean for altitude and rich for climb or high power. Carburettor ice can form at 0-20°C with high humidity; apply carb heat and expect a temporary power drop. Dual magnetos provide independent ignition. A fixed-pitch propeller rpm follows engine rpm; a constant-speed unit maintains selected rpm via a governor.
Instruments
Pitot-static: ASI, altimeter, VSI. Gyroscopic: attitude indicator, heading indicator, turn coordinator. The magnetic compass has variation, deviation, turning and acceleration errors. The ASI has position, density and compressibility errors; the altimeter must be set to QNH or standard pressure.
Worked example
During a climb the static port blocks. The pitot pressure still falls with altitude, but the static pressure in the instrument case is trapped at the lower value from the blockage altitude. The pressure difference decreases, so the ASI under-reads; the altimeter remains frozen; the VSI reads zero. Expect the ASI to over-read in a descent. Reason from trapped static pressure, not from airspeed alone.
Traps
Carburettor heat is not a cure for all rough running. A magneto check drop that is excessive or rough means no takeoff. Do not treat the heading indicator as a magnetic instrument; reset it to the compass in level flight. Instrument indications must be cross-checked before you act.