Airframe Structures and Flight Controls
Airframe load paths
A candidate must be able to trace loads from the wing spar through the centre section and fuselage frames, and explain why a semi-monocoque structure uses stringers, frames and skin together rather than skin alone. Know the difference between a truss, a monocoque and a semi-monocoque fuselage, and what a fail-safe or damage-tolerant design means in practice. Recognise the empennage: vertical fin and rudder, horizontal stabiliser and elevator, and the stabiliser/elevator split on a trimmable tailplane.
Primary and secondary controls
Primary controls are ailerons, elevator and rudder; secondary controls are flaps, slats, spoilers, trim tabs and leading-edge devices. Be clear on differential aileron, Frise aileron, mass balance, and why control surfaces are balanced both statically and aerodynamically. Traps include confusing a balance tab with an anti-balance tab, and forgetting that a spring tab assists the pilot while a servo tab moves the surface itself.
Traps in questions
Questions often mix up the purpose of a dorsal fin (directional stability), a ventral fin (keel effect) and a wing fence (spanwise flow control). Another common trap is the direction of trim tab movement relative to the control surface. Remember that the tab moves opposite to the surface it is trimming: to trim nose-down, the elevator moves down and the trailing-edge tab moves up.
Rule of thumb
If a question asks which component carries a particular load, ask whether the load is bending, shear or torsion. Spars carry bending, skin carries torsion and shear, and frames and stringers stabilise the skin against buckling.