UPSC Prelims 2025 Q42: UAV Types, Hovering and Power — Explained
With reference to Unmanned Aerial Vehicles (UAVs), consider the following statements:
I. All types of UAVs can do vertical landing.
II. All types of UAVs can do automated hovering.
III. All types of UAVs can use battery only as a source of power supply.
How many of the statements given above are correct?
- Only one
- Only two
- All the three
- None
Answer: (d) None
Statement-wise explanation
- I: incorrect — Only rotary-wing UAVs (multicopters, unmanned helicopters) and hybrid VTOL designs can land vertically. A conventional fixed-wing UAV gets lift from air flowing over its wings, so it needs forward speed. It lands on a runway or is recovered by belly landing, parachute or net. MALE drones such as the Heron or the MQ-9B take off and land on runways like ordinary aircraft.
- II: incorrect — Hovering means staying at one point in the air with zero forward speed. Rotorcraft can do this because their rotors make lift directly. A fixed-wing UAV stalls if it stops moving forward, so it can only circle (loiter) over a target, and no autopilot can make it hover. Since fixed-wing UAVs cannot hover at all, not all UAVs can hover automatically.
- III: incorrect — Small multicopters mostly run on lithium-polymer batteries, but many UAVs do not. The Heron uses a piston engine, the MQ-9 Reaper/MQ-9B a turboprop and the Global Hawk a turbofan, all burning liquid fuel. Other UAVs use solar power (high-altitude pseudo-satellites such as Airbus Zephyr), hydrogen fuel cells, or petrol-electric hybrid systems. Liquid fuel stores far more energy per kilogram than batteries, so long-endurance UAVs are not battery-only.
How to eliminate
All three statements start with "All types of UAVs". UAVs come in very different designs, so this absolute word should make you suspicious straight away. One counter-example settles each statement, and a single basic fact supplies all of them: fixed-wing drones need forward motion to stay airborne. That means they cannot hover (II is wrong) and they usually need a runway or a recovery system to land (I is wrong). For III, remember any large military drone, such as the Heron or the Predator/Reaper family, which flies for 24 hours or more on fuel, not batteries. Once you see that the mental picture of a 'drone' as a small quadcopter is wrong, all three statements are clearly wrong. The facts to remember: lift from wings needs forward speed; lift from rotors allows hovering and vertical take-off.
Know more
How UAVs are classified by how they make lift
An Unmanned Aerial Vehicle (UAV) is an aircraft with no pilot on board. It is flown remotely or autonomously. 'Drone' and 'UAS' (Unmanned Aircraft System, meaning the aircraft plus its ground station and data link) are used loosely for the same thing.
| Type | Lift from | Vertical take-off/landing | Hover | Typical power | Examples |
|---|---|---|---|---|---|
| Multirotor | 4–8 rotors | Yes | Yes | Li-Po battery | Quadcopters for agriculture, photography |
| Single-rotor (unmanned helicopter) | Main rotor | Yes | Yes | Fuel or battery | Heavy-lift and naval drones |
| Fixed-wing | Wings + forward speed | No (runway, catapult, hand-launch; net/parachute recovery) | No, only loiters | Fuel (piston, turboprop, jet), some battery | Heron, MQ-9B, Rustom/TAPAS |
| Hybrid VTOL | Rotors for take-off, wings for cruise | Yes | Yes | Battery + fuel, or battery | Mapping and surveillance VTOLs |
Trade-off: rotorcraft can hover and need no runway, but they use a lot of energy and have short endurance (usually under an hour on battery). Fixed-wing UAVs fly longer and farther but cannot hover.
Other power sources: solar cells (HAPS, built to fly for weeks in the stratosphere), hydrogen fuel cells, and tethered drones powered by cable from the ground.
Military classes: MALE (Medium Altitude Long Endurance) and HALE (High Altitude Long Endurance) drones are fixed-wing and fuel-powered.
Indian regulation: the Drone Rules, 2021 sort drones by maximum all-up weight: nano (up to 250 g), micro (250 g–2 kg), small (2–25 kg), medium (25–150 kg) and large (over 150 kg). They also set up the Digital Sky platform, UINs for drones and remote pilot certificates.
In the news
Drones were heavily in the news before Prelims 2025: the Drone Rules 2021 and the PLI scheme for drones, Namo Drone Didi in agriculture, India's 2024 deal for MQ-9B drones, and wide use of drones in the Russia–Ukraine and West Asia conflicts. The question checks whether aspirants know that 'drone' covers more than the small battery quadcopter.
NCERT Concepts to Revise
- Drone Rules 2021: India's Drone Rules 2021 classify UAVs by weight rather than design, a reminder that 'drone' covers a very wide range of aircraft.