Aircraft types and missions

Why this matters

No drone type is best for every job. A quadcopter easily hovers to photograph a building’s windows, but surveying hundreds of hectares of paddy fields drains its battery before it finishes. A fixed-wing aircraft flies long and far but cannot stop in mid-air and needs somewhere to take off and land. Choosing the right aircraft for the mission from the start saves both money and time.

Types of unmanned aircraft

The 2026 (B.E. 2569) CAAT announcement groups remote pilot ratings by aircraft category: Rotorcraft (including multirotors and helicopters), Aeroplane, Powered lift and Lighter-than-air, covered further in module 5.

The four forces and flying a quadcopter

Every aircraft is subject to lift, weight, thrust and drag. On a multirotor, rotor thrust both lifts and pushes: when the drone tilts, part of the thrust pushes it sideways, like a person leaning forward and starting to walk.

In ArduPilot’s Quad X layout, motors 1 (front right) and 2 (rear left) spin counter-clockwise, and motors 3 (front left) and 4 (rear right) spin clockwise.

• Up or down: speed up or slow all motors together
• Roll and pitch: speed up the motors on one side and slow the other, so the aircraft tilts
• Yaw: a spinning propeller twists the body the opposite way. In a steady hover, the torques of the counter-clockwise and clockwise pairs cancel. Speed up one pair and slow the other, and the torque imbalance turns the aircraft

If motors are wired in the wrong order or propellers fitted upside down, the drone flips as soon as it lifts off. This is why each motor is tested individually, with propellers removed, as the manual requires before the first flight.

import math

g, rho = 9.81, 1.225                  # m/s², kg/m³ (standard sea-level air)

quad_mass, motors = 1.4, 4            # kg
hover_per_motor = quad_mass * g / motors
print(f"quad {quad_mass} kg: each motor must give {hover_per_motor:.2f} N ({hover_per_motor / g * 1000:.0f} gf) to hover")

wing_mass, wing_area, cl = 2.5, 0.5, 0.8   # kg, m², lift coefficient
v_min = math.sqrt(2 * wing_mass * g / (rho * wing_area * cl))
print(f"fixed-wing {wing_mass} kg: lift equals weight at {v_min:.1f} m/s ({v_min * 3.6:.0f} km/h)")

quad 1.4 kg: each motor must give 3.43 N (350 gf) to hover
fixed-wing 2.5 kg: lift equals weight at 10.0 m/s (36 km/h)

Choosing an aircraft for the mission

Score each option against the criteria that matter to the mission, weighted by importance. Check must-have conditions first: if the mission must hover, options that cannot hover are excluded at once.

options = {"multirotor": (3, 1, 3, 3), "fixed-wing": (0, 3, 1, 2), "VTOL": (3, 3, 3, 1)}
missions = {
    "building inspection": {"weights": (0.4, 0.1, 0.3, 0.2), "must_hover": True},
    "5 km² field mapping": {"weights": (0.0, 0.5, 0.2, 0.3), "must_hover": False},
}
for name, m in missions.items():
    scores = {}
    for opt, s in options.items():
        if m["must_hover"] and s[0] == 0:
            continue                                   # fails the must-have condition
        scores[opt] = sum(w * v for w, v in zip(m["weights"], s))
    ranked = sorted(scores.items(), key=lambda kv: kv[1], reverse=True)
    print(f"{name}: " + ", ".join(f"{o} {v:.2f}" for o, v in ranked))

building inspection: multirotor 2.80, VTOL 2.60
5 km² field mapping: VTOL 2.40, fixed-wing 2.30, multirotor 2.00

Module lab

Common mistakes

Summary

• Each aircraft type trades off hover, endurance, take-off space and complexity
• A multirotor tilts with differential thrust and yaws with the torque of its counter-clockwise and clockwise pairs
• Thrust per motor in a hover is $mg/n$, and a wing needs enough speed to carry the weight
• Choose aircraft by must-have conditions first, then a weighted table

Check your understanding

1. A 3.0 kg hexacopter hovers. How much thrust must each motor give ($g=9.81$)?
2. If the wing area doubles, how does the speed at which lift equals weight change?
3. In ArduPilot’s Quad X layout, which motors spin clockwise?
4. For close-up photos of a building’s windows, which aircraft type should be used, and why?
5. Why does a fixed-wing aircraft fly longer than a multirotor with the same battery?