Determining sUA Performance
Performance Factors
sUA performance depends on weight, battery state, air density, wind, and aircraft configuration. Key metrics: maximum endurance (time aloft), maximum range (distance), climb rate, and maximum wind resistance. Manufacturers publish these under standard conditions; real conditions change them.
Density Altitude and Wind
High density altitude (hot, high, humid) reduces propeller thrust and lift, increasing takeoff distance and reducing climb and endurance. Wind affects groundspeed: a headwind reduces range over the ground, a tailwind increases groundspeed and can push you past the 87-knot limit or out of visual range. Gusts reduce control margin. Plan for the worst wind and the lowest expected battery.
Planning Calculations
Use the aircraft's published endurance and derate it for wind and temperature. A simple approach: estimate outbound time with headwind, inbound with tailwind, and reserve at least 20–30 percent battery for contingency and landing. Compute groundspeed as airspeed plus or minus wind component.
Traps
Questions often ask whether a tailwind extends range (it increases groundspeed and can reduce total time aloft but risks overshooting and speed violations) or whether density altitude affects electric motors (it does, through propeller thrust). Another trap: confusing endurance (time) with range (distance).
Rule of Thumb
"Plan the outbound leg against the wind and keep a 25 percent battery reserve." If the wind at altitude exceeds the aircraft's rated limit, do not launch.