Loading & Performance
Area IV of the Remote Pilot ACS — one Task, three knowledge elements, and the smallest area on the test. It is also the one where the numbers are yours rather than the FAA's: there is no published performance chart for most small unmanned aircraft, so the manufacturer's data and your own records are the whole source.
Effects of loading changes — UA.IV.A.K1a
Every gram you add is thrust the motors have to produce continuously. Adding payload to a small unmanned aircraft does all of the following at once, and they compound:
- Endurance falls — more current to hold a hover, so less time on the same battery. This is the effect that bites first.
- Climb rate and acceleration fall — less thrust margin above the weight.
- Stopping distance grows — more momentum to arrest, which matters when the aircraft is being flown to a fixed point.
- Wind tolerance falls — a multirotor holds position by tilting, and tilting to fight wind uses thrust it no longer has spare.
- The margin for a motor failure disappears. On a quadcopter there is none to begin with; on a hexacopter or octocopter, loading is exactly what decides whether the remaining motors can hold the aircraft up.
§ 107.3 defines a small unmanned aircraft system as under 55 pounds on takeoff, including everything on board — payload, battery, and anything attached. Exceed it and you are not flying under Part 107 at all.
Balance, stability and centre of gravity — UA.IV.A.K1b
A multirotor's flight controller will trim out a modest CG error by running some motors harder than others. That is precisely why an out-of-balance aircraft is dangerous rather than merely untidy: it flies normally while quietly consuming the margin you were relying on.
- The motors on the heavy side run continuously hotter and draw more current, so the pack depletes faster than the flight time you planned.
- Those motors reach full authority first. In a gust, the aircraft runs out of correction on one side before the other.
- The aircraft yaws or drifts when the controller saturates — often the first the pilot knows of it.
Check CG with a hover in ground effect before every mission that changed the payload. Level, hands off, no drift. On a fixed-wing sUAS the consequence is more familiar: CG too far aft reduces longitudinal stability, CG too far forward increases stall speed and takes elevator authority away from the flare.
Using performance data — UA.IV.A.K2
Manufacturer figures are quoted in the manufacturer's best case: no wind, a standard day, a new battery, a hover at low altitude. Every one of those assumptions is generous.
| Condition | What it does to the quoted number |
|---|---|
| High density altitude | Less thrust per motor; endurance and climb both fall |
| Wind | Continuous tilt to hold position; the return leg costs more than the outbound |
| Cold | Reduced usable battery capacity — sometimes dramatically |
| Battery age | Capacity falls with cycles; a pack at 200 cycles is not a pack at 20 |
| Payload | Endurance falls faster than weight rises |
Keep your own numbers. The single most useful performance record for a small unmanned aircraft is a log of what each pack actually delivered, in the conditions it delivered it. That is real performance data for your aircraft, and it beats a brochure figure every time.
Set a reserve and treat it as a hard floor rather than a target. Part 107 sets no fuel-reserve rule — which means nothing stops you flying a pack flat except your own discipline.