Flight Performance and Planning
Core framework
Performance for helicopters is about the power available versus power required across the flight envelope. You must understand the Hover Performance diagram (in-ground-effect vs out-of-ground-effect), the height-velocity (dead man's) curve, and the factors that degrade performance: density altitude, weight, wind, and surface conditions.
Concepts to master
Density altitude rises with altitude, temperature and humidity - all reduce performance. Know the difference between IGE and OGE hover ceilings, maximum take-off/landing weight, and the effect of wind on translational lift. For planning, understand fuel required (trip + reserve + contingency), mass and balance (CG limits, datum, moment arms), and take-off/landing distance data.
Traps
- Mixing IGE (higher ceiling) with OGE (lower ceiling) - questions often reverse them.
- Forgetting humidity raises density altitude even at constant temperature and pressure.
- Treating the H-V curve as a prohibition rather than an avoidance region.
- Miscomputing CG: moment = weight × arm; total moment ÷ total weight = CG position.
Rule of thumb
"Hot, high, heavy, humid = poor performance." Any one of these raises power required or lowers power available; combine them and margins vanish quickly.
Worked example
A helicopter has empty weight 1,000 kg at arm 2.0 m and a pilot of 100 kg at arm 1.0 m. Moments: 2,000 + 100 = 2,100 kg·m. Total weight 1,100 kg. CG = 2,100 ÷ 1,100 ≈ 1.91 m from datum - check this lies within the CG envelope.