UAV vs UAS and systems thinking

Why this matters

People call everything a “drone”, but when the video freezes in flight you must ask whether the problem is in the aircraft, the radio link, the camera or the app on the tablet. Treat a drone as just “a small aircraft” and you fix the wrong thing. This course therefore starts by seeing a drone as a system of parts working together.

The whole course uses one hypothetical case: a student team preparing a photo survey of a campus building with a quadcopter, from understanding the system, through simulator practice and mission planning, to checking readiness before a real flight. The Python code of every module can be downloaded from /downloads/uat-201/.

UA, UAV, UAS and RPAS

The International Civil Aviation Organization (ICAO) defines these terms as follows:

UAS is therefore wider than the aircraft, just as a “rail system” means not only the trains but also the track, stations, signalling and staff.

Elements of a UAS

• Aircraft (UA): frame, propulsion, flight controller and sensors such as the IMU, GNSS and barometer
• Payload: the equipment that does the job, such as a camera, thermal camera or spray tank
• Remote pilot station (or ground control station, GCS): the transmitter and software such as QGroundControl or Mission Planner
• C2 link (command and control link): the data link between aircraft and station for commanding and monitoring the flight
• Crew: pilot, observer and camera operator
• Support: batteries, chargers, spares, manuals and records

The two widely used open flight-control software projects are ArduPilot and PX4. Ready-made drones from manufacturers (COTS, commercial off-the-shelf) are easy to use but usually offer less freedom to modify or replace parts than self-built systems.

The three rotation axes

An aircraft rotates about three axes; pilots and flight-controller logs use these terms constantly.

• Roll: rotation about the fore–aft axis; the aircraft banks left or right
• Pitch: rotation about the left–right axis; the nose goes down or up
• Yaw: rotation about the vertical axis; the heading changes

The direction the nose points (heading) can differ from the direction actually travelled (track) in wind or sideways flight.

Units before calculations

Numbers from battery labels, sensors and logs often come in different units; convert them before using a formula.

import math

capacity_mah, v_nominal = 5000, 22.2
capacity_ah = capacity_mah / 1000
energy_wh = v_nominal * capacity_ah
print(f"{capacity_mah} mAh = {capacity_ah} Ah; energy {energy_wh:.0f} Wh = {energy_wh * 3600:,.0f} J")

heading_deg = 90
print(f"{heading_deg} deg = {math.radians(heading_deg):.6f} rad")

5000 mAh = 5.0 Ah; energy 111 Wh = 399,600 J
90 deg = 1.570796 rad

Data rate matters too. If the station receives a position five times a second, a fast drone moves a long way between updates.

speed = 10.0                     # m/s
for rate_hz in (10, 5, 1):
    print(f"telemetry {rate_hz:>2} Hz: drone moves {speed / rate_hz:.1f} m between updates")
link_loss_s = 2.0
print(f"a {link_loss_s:.0f} s link loss at {speed:.0f} m/s = {speed * link_loss_s:.0f} m without new data")

telemetry 10 Hz: drone moves 1.0 m between updates
telemetry  5 Hz: drone moves 2.0 m between updates
telemetry  1 Hz: drone moves 10.0 m between updates
a 2 s link loss at 10 m/s = 20 m without new data

The screen always shows the past. The slower or patchier the data, the more the pilot sees a position that does not match reality. This is why the law requires keeping the aircraft in sight, and why you must know what the system does when the link is lost (module 4).

Module lab

Common mistakes

Summary

• The UA is the aircraft; the UAS adds the station, C2 link, payload, crew and support
• Systems thinking traces problems to the right subsystem
• Roll, pitch and yaw are rotations about three axes, and heading can differ from track
• Convert units before calculating; the distance between updates is speed divided by data rate

Check your understanding

1. How does a UAS differ from a UA?
2. How many Wh does a 14.8 V 2200 mAh battery hold?
3. What is 45° in radians (4 decimal places)?
4. A drone flies at 8 m/s with position data at 4 Hz. How far does it move between updates?
5. The video freezes, but the drone still hovers in place. Which subsystem is the likely cause?