Aft hold floor limit and aft CG together
An aircraft is being loaded for a cargo flight. Before cargo, mass is 4,650 kg and CG is 4.68 m; aft CG limit is 5.02 m. The aft hold has a floor load limit of 600 kg/m². A 420 kg crate measures 0.80 m × 0.90 m and is planned for station 7.40 m. A second 280 kg crate measures 0.60 m × 0.50 m and is planned for station 7.90 m. Both are to be tied down to approved floor fittings. The loading supervisor has calculated only the total mass and says the aircraft is below MTOM. The crew notices that the aft CG limit may be close and that the second crate's footprint looks small. No ballast is available, but the 420 kg crate can be moved forward within the hold. The hold floor is flat and approved for palletised loads; the crates have no integrated spreader plates.
1. Calculate the combined CG with both crates at the planned stations and state whether the aft limit is exceeded.
Read the worked answer
Total mass = 4,650 + 420 + 280 = 5,350 kg. Moment = 4,650×4.68 + 420×7.40 + 280×7.90 = 21,762 + 3,108 + 2,212 = 27,082 kg·m. CG = 27,082 / 5,350 = 5.062 m. The aft limit is 5.02 m, so the CG is 0.042 m aft of the limit. The load is not acceptable as planned.
2. Check the area load for each crate and state what spreading is needed for the 280 kg crate.
Read the worked answer
Area load = mass / footprint. 420 kg crate: 0.80×0.90 = 0.72 m²; 420/0.72 = 583 kg/m², below 600. 280 kg crate: 0.60×0.50 = 0.30 m²; 280/0.30 = 933 kg/m², above 600. Minimum footprint = 280/600 = 0.467 m². For example, spreading it over 0.80×0.60 = 0.48 m² gives 583 kg/m². A spreader board or pallet must transfer the load to the floor, and the crate must still be tied down.
3. Find a forward shift of the 420 kg crate that brings the CG to 5.02 m or less, and recompute the CG for that shift.
Read the worked answer
Move the 420 kg crate forward by d. New CG = (27,082 − 420d)/5,350 ≤ 5.02. 27,082 − 420d ≤ 26,857; 420d ≥ 225; d ≥ 0.536 m. Moving it from 7.40 m to 6.80 m (d = 0.60 m) gives moment 27,082 − 252 = 26,830 kg·m and CG = 26,830/5,350 = 5.015 m, within the aft limit. Check the new station is within the hold, the floor limit is still met, and the forward limit is not approached.