Flight performance, loading and weight and balance
Domain 2 - Flight performance, loading and weight and balance
This domain tests whether you can use POH data and loading calculations to predict whether a flight is legal and safe. Expect density altitude, takeoff/landing distance, climb, and CG questions.
Performance rules
- Density altitude is pressure altitude corrected for temperature. High density altitude reduces engine power and propeller thrust, increases true airspeed for a given IAS, and lengthens takeoff and landing ground roll.
- POH figures are normally based on gross weight, ISA sea level, level paved runway and zero wind. Correct for aircraft weight, wind, runway slope, surface and temperature.
- A headwind reduces ground roll; a tailwind increases it. The effect is not linear, so use the POH chart rather than a simple rule.
- Climb performance is affected by weight, density altitude and configuration. Best rate of climb (Vy) gives most height in least time; best angle (Vx) gives most height over least ground distance.
Weight and balance
- Use datum, arm and moment. Moment = weight × arm. CG = total moment ÷ total weight.
- Check maximum takeoff weight, maximum landing weight and the CG envelope at takeoff, in flight and at landing. Fuel burn moves CG, so check the forward and aft limits after burn.
- A forward CG increases stall speed and reduces performance; an aft CG reduces static stability and can make stall recovery harder.
Worked example
Empty weight 600 kg at arm 1.0 m; pilot 80 kg at 0.5 m; passenger 80 kg at 0.5 m; fuel 100 kg at 1.5 m. Total weight = 600 + 80 + 80 + 100 = 860 kg. Total moment = 600 + 40 + 40 + 150 = 830 kg·m. CG = 830 ÷ 860 = 0.965 m. If the envelope is 0.90–1.20 m, the loading is within limits.
Traps
Mixing kilograms and pounds; using empty weight instead of basic empty weight; forgetting fuel or baggage; checking only takeoff CG; using IAS in a performance chart that requires TAS; ignoring a tailwind or slope correction.