Which type of SUAS functions best when powered by an internal combustion engine?

• A. Multirotor
• B. Tricopter
• C. Fixed-Wing
• D. Helicopter

Answer: (C)

Endurance and propulsion efficiency drive the best use of an internal combustion engine in SUAS. Internal combustion engines offer high energy density fuel, which is ideal for longer missions. Fixed-wing aircraft take advantage of this because once they’re in forward flight, lift is mainly produced by the wings, and maintaining level cruise requires relatively little additional power. That means the engine can keep the aircraft aloft for a long time without carrying excessively heavy power sources.

Rotorcraft—multirotors, tricopters, and helicopters—must generate lift to hover, which is extremely power-hungry. In small UAVs, batteries and electric motors are favored for this reason, because they provide high thrust-on-demand and clean, compact power for vertical takeoff and hovering. Using an internal combustion engine for sustained hover is less efficient and adds weight and complexity, making long endurance harder to achieve in these configurations.

So, when powered by an internal combustion engine, the fixed-wing design best capitalizes on fuel energy density and aerodynamic efficiency to achieve longer flight times.