Aircraft General Knowledge - Airframe, Systems and Powerplant
This domain tests how the airframe carries and controls loads and how the systems and engine behave in flight. Expect questions on structures, hydraulic, electrical, fuel and vacuum systems, and on the piston powerplant with its propeller.
Airframe
- Most light training aircraft are semi-monocoque: stressed skin riveted to stringers, frames and spars carries the loads.
- Primary controls are ailerons, elevator and rudder; flaps and trim tabs are secondary. A trim tab moves in the opposite direction to the surface it trims.
- Ailerons are rigged differentially, with more up than down travel, to reduce adverse yaw.
Systems
- Hydraulics: reservoir, engine-driven pump, accumulator for pressure surges, relief valve, selector, actuators.
- Electrical: alternator, battery, bus bar, circuit breakers. The ammeter shows charging or discharge state, not battery capacity.
- Fuel: tanks, selector, strainer, drain sumps for water and sediment, primer. Always drain and check before the first flight of the day.
- Vacuum system drives the attitude and heading gyros.
Powerplant
- Horizontally opposed four-stroke engine; induction through a carburettor venturi where fuel is metered by the mixture control.
- Two magnetos give independent ignition; a magneto check drop of more than about 150 rpm or an excessive difference between magnetos is a reject.
- Carburettor icing is most likely at 0 to 21 degrees C with high humidity, and at reduced power on descent.
- A constant-speed propeller maintains rpm by varying blade angle through a governor.
Worked example
On descent with power reduced, rpm falls and the engine runs rough. Apply full carburettor heat: the roughness may briefly worsen as ice melts, then clear. Leave heat on, use some power, and do not lean the mixture during heat application.
Traps
Engine roughness on one magneto is an ignition fault, not an icing fault. Carburettor heat bypasses the filter, so avoid it on dusty desert strips on the ground.