Aft CG on a Winter Departure
Your aircraft is a four-seat, single-engine touring aircraft with a maximum take-off mass of 1,150 kg and a CG range of 0.95 m to 1.25 m aft of the datum. The basic empty mass is 680 kg at an arm of 1.00 m. Today’s load sheet shows pilot and front passenger 150 kg at 0.80 m, two rear passengers 150 kg at 2.30 m, baggage 40 kg at 3.40 m, and usable fuel 120 kg at 1.40 m. The aircraft is parked at a Norwegian airfield with outside air temperature −6 °C; the runway is 1,050 m long and dry. The commander is under time pressure because the destination forecast is deteriorating. The baggage compartment is the only baggage stowage, and the rear seats are already occupied. Before start, you must confirm the loading is legal and decide whether any change is needed before departure.
1. Calculate the take-off mass and CG position. State whether the loading is within limits and identify the limiting item.
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Moment calculation
| Item | Mass (kg) | Arm (m) | Moment (kg m) |
|---|---|---|---|
| Basic empty | 680 | 1.00 | 680 |
| Front occupants | 150 | 0.80 | 120 |
| Rear occupants | 150 | 2.30 | 345 |
| Baggage | 40 | 3.40 | 136 |
| Fuel | 120 | 1.40 | 168 |
| Total | 1,140 | 1,449 |
CG = 1,449 / 1,140 = 1.271 m. The mass is 10 kg below MTOM, but the CG is 0.021 m aft of the 1.25 m aft limit. The loading is not legal. The aft baggage and rear occupants are the dominant aft moments; the aircraft cannot depart as loaded.
2. The only available option is to move 30 kg of baggage from the aft baggage compartment at 3.40 m to a forward cabin stowage at 0.50 m. Recalculate and determine whether the flight can depart. If not, propose another change.
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Moving 30 kg from 3.40 m to 0.50 m changes moment by 30 × (0.50 − 3.40) = −87 kg m. New moment = 1,449 − 87 = 1,362 kg m; mass remains 1,140 kg; CG = 1,362 / 1,140 = 1.195 m. This is inside 0.95–1.25 m. Also check zero-fuel: mass 1,020 kg, moment 1,194 kg m, CG 1.171 m, still inside. The move is acceptable only if the forward stowage is approved, floor loading is respected, and the load is secured. If not, offload aft baggage: removing 20 kg gives mass 1,120 kg and CG 1.233 m, but confirm zero-fuel CG and document the change.