Aircraft Fundamentals
Core concepts
An aircraft in steady flight balances four forces: lift, weight, thrust and drag. Lift rises with angle of attack, airspeed squared, air density and wing area, up to the stall. Induced drag falls as speed increases; parasite drag rises with speed squared. Primary controls are ailerons (roll), elevator (pitch) and rudder (yaw); flaps raise lift and drag, and trim tabs relieve stick forces.
Structures may be truss, monocoque or semimonocoque. Stressed-skin semimonocoque designs use spars, ribs, stringers, formers and bulkheads. Common materials include 2024 and 7075 aluminum alloys, rivets, and composite or honeycomb structures. Know the corrosion types - surface, galvanic, pitting, intergranular, exfoliation and stress - and that dissimilar metals plus moisture drive galvanic attack.
Weight and balance uses a datum, arms and moments: moment = weight x arm; CG = total moment / total weight. The CG must stay inside forward and aft limits. A forward CG raises stall speed and gives a nose-down tendency; an aft CG reduces static stability. Standard sea-level atmosphere is 15 C and 29.92 inHg, with roughly a 2 C per 1,000 ft lapse rate.
Traps
Questions deliberately confuse angle of attack with airspeed, mix up induced and parasite drag, or ask which control moves for a given motion. Weight-and-balance items often hide a datum offset or a negative arm.
Worked example
A 2,000 lb aircraft has its CG at 30 in. Add 200 lb at arm 40 in. New moment = (2,000 x 30) + (200 x 40) = 68,000 lb-in; new weight = 2,200 lb; new CG = 68,000 / 2,200 = 30.9 in - the CG moves aft.