Weight, Balance, and Loading
The arithmetic behind every load sheet
Weight and balance questions are simple arithmetic wrapped in terminology. Learn the vocabulary cold: datum (reference point), arm (distance from datum), moment (weight × arm), empty weight (includes unusable fuel and full oil), useful load (max gross minus empty weight), and EWCG.
Standard weights appear constantly: aviation gasoline 6 lb/gal, oil 7.5 lb/gal, water 8.35 lb/gal. Compute total weight and total moment, then divide moment by weight to get CG in inches from datum, and compare against the envelope.
Effect of CG position is a classic instructional point. A forward CG increases stall speed and takeoff distance, is more stable, and improves spin recovery, but may reduce elevator authority and cruise speed. An aft CG raises cruise speed and reduces stability, and can make stall and spin recovery difficult or impossible.
Rule of thumb for shifting weight: distance moved = (ΔCG × total weight) ÷ weight moved. Rearranged: weight to move = (ΔCG × total weight) ÷ distance available.
Trap: answers that add unusable fuel as if it were usable, or that ignore the difference between maximum ramp weight and maximum takeoff weight.
Worked example: 3,200 lb aircraft, current CG 82.0 in, desired 84.0 in. You have stations at 40 in and 120 in. Move how much? weight = (2.0 × 3,200) ÷ 80 = 80 lb forward-to-aft.