Why Jet Engines Are Rarely Used in Small Uncrewed Aircraft

Why Jet Engines Are Rarely Used in Small Uncrewed Aircraft

The Evolution of Aircraft Propulsion

In the early years of aviation, the concept of flight was closely tied to propeller-driven internal combustion engines and biplane wing configurations. A photograph of a modern Airbus A380 shown in 1915 would have seemed inconceivable, as aviation pioneers of the time believed that flight necessitated large wings, visible propellers, and open cockpits. However, aircraft design evolved rapidly over the following decades. By the end of World War I, the era of open cockpits and biplanes was waning, and the interwar period witnessed significant advancements in internal combustion engines. This progress culminated in the development of the Rolls Royce Merlin V12 engine, which powered iconic World War II fighters such as the Supermarine Spitfire and the British P-51 Mustang.

Following 1945, the aviation industry embraced jet engines, marking a transformative shift toward pressurized cabins and high-thrust, lightweight gas turbines. These engines, now more efficient and powerful than ever, have become the cornerstone of both commercial and military aviation.

Propulsion Choices in Small Uncrewed Aircraft

Despite the dominance of jet engines in manned aviation, small uncrewed aircraft—commonly known as drones—have not followed the same path. Contemporary small drones almost exclusively utilize electric motors paired with large external propellers, a design reminiscent of early manned flight. This reliance on electric propulsion, while advantageous in terms of simplicity and cost, has exposed significant limitations. Battery technology has not advanced sufficiently to support extended flight durations or substantial payload capacities, posing challenges for many commercial and industrial applications. Consequently, startups and manufacturers often struggle to develop competitive platforms that meet operational demands.

Hybrid powerplants, which combine electric motors with fossil fuel engines, present a potential solution by extending range and payload capabilities. However, these systems introduce additional complexity, requiring the integration and management of two distinct power sources. Despite these challenges, propeller-driven designs remain prevalent, much like the biplane’s dual-wing configuration once dominated early aviation.

Barriers to Jet Engine Adoption in Small Drones

Given the proven efficiency, reliability, and favorable thrust-to-weight ratios of jet engines, their scarcity in small uncrewed aircraft raises important questions. The primary obstacles are both technical and economic. Jet engines are costly to manufacture and maintain, particularly at the small scales necessary for drone applications. Their mechanical complexity results in higher operational expenses and subjects them to more rigorous regulatory scrutiny. Moreover, integrating jet-powered drones into existing airspace would necessitate substantial updates to air traffic management systems, further complicating their adoption.

These factors have influenced market preferences, with manufacturers and operators favoring electric propulsion systems that are more affordable and easier to incorporate into compact platforms. Nonetheless, some companies are pursuing the development of specialized small jet engines or advancing hybrid propulsion technologies that seek to combine the advantages of jet and electric power.

For example, Kratos Defense & Security Solutions, Inc., headquartered in Jupiter, Florida, has been developing small jet engines for defense applications for over a decade. Yet, until production costs decline and regulatory challenges are resolved, jet engines are expected to remain uncommon in the realm of small uncrewed aircraft. For the foreseeable future, the drone industry continues to reflect the early days of aviation, with propellers maintaining their central role.