Helicopter Flight Performance and Planning - Mass, Balance and Performance
This domain tests whether the helicopter can safely lift the load, keep the centre of gravity within limits and perform in the prevailing density altitude, wind and surface conditions.
Mass and balance
Use datum, arm and moment. Moment = mass × arm. Total mass is the sum of empty mass, crew, passengers, baggage and fuel; CG = total moment ÷ total mass. Forward CG may reduce autorotation flare authority; aft CG may reduce cyclic authority and tail-rotor margin. Never exceed maximum gross mass or individual compartment limits.
Performance
Performance depends on pressure altitude, temperature, humidity and wind. Density altitude combines these into the altitude the helicopter ‘feels’. Hover performance is quoted in ground effect (IGE) and out of ground effect (OGE). Translational lift improves performance after effective translational lift. Consider slope, surface, obstacle clearance, headwind/tailwind, fuel for diversion and reserve.
Worked example
Empty mass 700 kg at arm 2.5 m; pilot 80 kg at 2.0 m; fuel 60 kg at 2.8 m. Moments: 1,750 + 160 + 168 = 2,078 kg·m. Total mass = 840 kg. CG = 2,078 ÷ 840 = 2.47 m. If the limit is 2.30–2.60 m, the loading is within limits. Recalculate after fuel burn because CG can move.
Traps
Using mass instead of moment; forgetting fuel or baggage; assuming IGE hover performance applies in a confined area; and ignoring density altitude on a hot, humid day.