Mass, Balance & Stability

B. reduces longitudinal stability, lightens the controls and improves range (less tail download and drag)

Aft CG: smaller static margin (less stable, more manoeuvrable, lighter stick forces) and less tailplane download, so less induced drag and fuel burn - better range. Behind the aft limit it becomes dangerously unstable.

The question was recalled without its options; these options were written to it.

A. extremely stable and will require excessive elevator control to change pitch

A forward CG makes the aeroplane very stable but the elevator must be moved a lot to change pitch (heavy controls, higher stall speed).

C. Be caused by a centre of gravity which is towards the rearward limit.

Neutral stability occurs when the CG reaches the neutral point, which lies behind the aft CG limit - so it is associated with a CG towards the rearward limit.

A. higher stalling speed

With the CG forward the tailplane must supply a larger download, so the stalling speed rises.

A. become heavier, making the aeroplane more difficult to manoeuvre in pitch

Moving the CG forward makes the aeroplane more stable and the elevator control heavier, so it is harder to manoeuvre in pitch.

B. the position of the CG relative to the neutral point, with the tailplane providing the restoring moment

The further the CG is ahead of the neutral point (static margin), the more stable; the horizontal tailplane provides the restoring moment. Moving the CG aft reduces stability.

The question was recalled without its options; these options were written to it.

A. Increases

A higher mass needs a higher lift coefficient / speed for the same lift: the stalling speed increases.

D. High gross mass and forward centre of gravity

Stalling speed is highest with high gross mass and a forward CG.

B. the point through which the total weight of the aircraft acts

All the individual weights can be replaced by one force, the total weight, acting through the CG. CG arm = total moment / total mass.

The question was recalled without its options; these options were written to it.

C. The manufacturer

The manufacturer establishes the CG limits (approved by the authority).

D. An increase in drag, due to excessive elevator trim

A nose-heavy aeroplane needs nose-up elevator trim, which adds drag.

D. stability increased, pitch stick forces increased

A very forward CG makes the aeroplane too stable: large elevator forces/deflection are needed to rotate and flare, and there may not be enough elevator authority.

The question was recalled without its options; these options were written to it.

B. required more trim elevation which will increase the fuel consumption

A forward CG needs more nose-up trim (elevator down-load), which increases drag and fuel consumption.

A. elevator, with auto-trim relieving the sustained load

The pitch channel drives the elevator servo; the auto-trim moves the stabiliser to remove the steady elevator load so the AP can disconnect without a jolt.

C. be greater, drag will increase and endurance will decrease.

A heavier aeroplane at the same speed needs a higher angle of attack, so drag increases and endurance falls.

B. the structure, engines, fixed equipment, unusable fuel and full operating fluids

BEM + variable load (crew, catering, etc.) = DOM; + traffic load = ZFM.

The question was recalled without its options; these options were written to it.

A. 2.17 m aft of datum

Moments: 1000 x 2.00 = 2000; 200 x 3.00 = 600; total 2600 kg m. Mass 1200 kg. CG = 2600 / 1200 = 2.17 m.

B. a higher stalling speed, longer take-off and landing runs, poorer climb, and reduced structural safety margins

More weight needs more lift: higher stall speed and approach speed, longer runs, lower climb gradient and ceiling, and the structure is loaded beyond its design limits.