Flight Performance and Planning: Mass, Balance, Performance and Flight Planning
Mass and balance
Every performance question begins with mass and centre of gravity. Know empty mass, payload, fuel mass and maximum take-off mass, and how to compute the CG position by the moment method: multiply each mass by its arm, sum the moments, divide by total mass. The trap is forgetting to include fuel in the CG calculation, or using the wrong arm for a seat row. Aft CG reduces static stability and pitch authority; forward CG increases stall speed and landing distance and can limit rotation.
Performance
Separate take-off, climb, cruise and landing performance. Density altitude is the key concept: high altitude, high temperature and high humidity all reduce air density and therefore power and lift. Learn the four factors affecting take-off distance - mass, density altitude, wind and runway slope - and the direction of each effect. A frequent trap is confusing indicated with true airspeed when computing groundspeed; only TAS and wind give groundspeed.
Flight planning
Know how to compute heading from true course, wind correction angle and magnetic variation, then add deviation for compass heading. Fuel planning must include taxi, trip, reserve and contingency. The exam often asks for endurance: fuel available divided by hourly consumption.
Worked example
Aircraft mass 600 kg at arm 0.30 m, pilot 80 kg at arm 0.10 m, fuel 60 kg at arm 0.50 m. Moments: 180 + 8 + 30 = 218 kg·m; total mass 740 kg; CG = 218/740 ≈ 0.295 m from the datum. Check this against the envelope before declaring the loading acceptable. As a rule of thumb, adding mass ahead of the datum moves the CG forward, and the shift is larger when the added mass is far from the datum.