What are rotary engines used for?

Today, rotary engines are used primarily in unmanned aerial vehicles (UAVs/drones), compact range-extender generators for electrified vehicles, small portable and stationary generator sets, select light aircraft and motor gliders, and a handful of niche automotive and motorcycle applications. Historically, a different kind of “rotary engine” powered many World War I aircraft. This article explains both meanings of the term and where each type fits now.

Two meanings of “rotary engine”

In modern usage, “rotary engine” usually refers to the Wankel rotary—a pistonless internal-combustion design where a triangular rotor spins inside an epitrochoid-shaped housing to produce power. That layout is compact, smooth, and has high power density. Historically, “rotary engine” also described an early radial aircraft engine whose entire cylinder block spun around a fixed crankshaft; those powered many WWI planes but were phased out as fixed radial and inline engines improved.

Where rotary engines are used today

The following list outlines the main contemporary applications of Wankel and other rotary-combustion engines, explaining why they remain relevant despite their niche status.

• UAVs and drones: Militaries and industry use small Wankel engines for propulsion due to their power-to-weight ratio, compact form factor, and low vibration. Notable examples include the U.S. Army’s RQ-7 Shadow, which has long flown with a UEL AR741 Wankel engine, and the Schiebel Camcopter S-100, powered by an Austro Engine AE50R rotary. Several manufacturers (e.g., Rotron Power, AIE in the UK) supply rotary engines tuned for aviation gasoline or heavy fuels (JP-5/JP-8).
• Range extenders for electrified vehicles: Because they are compact and smooth, rotary engines work well as series-hybrid generators. Mazda reintroduced the technology in 2023 with the MX-30 R-EV (Europe/Japan), using an 830 cc single-rotor solely to generate electricity for the battery. Other automakers have trialed similar concepts in prototypes.
• Portable/stationary generators and APUs: Defense and emergency-response customers use small rotary engines in lightweight generator sets where portability and quiet, low-vibration operation matter. U.S. defense contracts in recent years have also backed development of next-generation rotary combustion designs (such as LiquidPiston’s X-Engine architecture) for compact gensets and hybrid-electric UAV propulsion.
• Light and experimental aircraft: Self-launching or sustainer motor gliders and some experimental planes have adopted small Wankels because of their smoothness and packaging. The AE50R lineage, for example, has been integrated into several motor gliders and UAVs.
• Automotive performance (niche and historic): Mazda’s RX-7 and RX-8 popularized the Wankel in road cars and racing; the 4-rotor Mazda 787B famously won Le Mans in 1991. While no mass-market rotary sports car is currently on sale, rotary engines persist in enthusiast circles and concept cars as potential range extenders or multi-fuel generators.
• Motorcycles (limited): A few production bikes, like the Suzuki RE5 (1970s) and Norton rotary models (1980s–1990s), used Wankel engines for smoothness and compactness; today they remain specialty or historic examples rather than mainstream products.

Taken together, these uses play to the rotary’s strengths—compactness, smoothness, and power density—while avoiding some drawbacks that limited its mass-market automotive run.

Historical uses: the original WWI “rotary engine”

From roughly 1909 through World War I, many aircraft flew with true rotary radial engines (for example, Gnome, Le Rhône, and Clerget designs) where the entire engine rotated around a stationary crankshaft. These engines offered excellent air-cooling and power-to-weight at the time, but suffered from high fuel/oil consumption and significant gyroscopic effects that complicated handling. They were rapidly supplanted in the 1920s by more efficient, fixed radial and inline engines. Today, the term “rotary engine” generally refers to the Wankel unless the historical WWI context is specified.

Why choose a rotary engine—and why not

The following advantages explain why rotary engines persist in certain roles despite their niche market share.

• High power-to-weight and compact packaging make them ideal where space and mass are at a premium (UAVs, range extenders).
• Very smooth operation and low vibration benefit sensitive avionics and electric drivetrains.
• Mechanically simple with few moving parts, aiding maintenance in certain use-cases.
• Fuel flexibility: some modern rotary units can be configured for aviation gasoline, gasoline, and certain kerosene/heavy fuels used by militaries.

These strengths align well with aerospace, portable power, and hybrid-electric applications, where efficiency can be managed by operating at steady generator speeds.

Conversely, these limitations have curtailed broader adoption, especially in mainstream road cars.

• Emissions and fuel economy challenges versus modern four-stroke piston engines, particularly under varied loads and cold starts.
• Seal durability and oil consumption concerns, including apex and side seal wear and thermal management.
• Heat rejection and combustion-chamber geometry make clean, efficient burn more complex.
• Regulatory and lifecycle-cost pressures that favor highly optimized piston or electric solutions.

As regulations tightened and efficiency expectations rose, manufacturers concentrated rotary development on roles where its unique benefits outweigh these trade-offs.

Notable examples and recent developments

The items below illustrate how rotary engines are deployed now and where the technology is headed.

• Mazda MX-30 R-EV (launched 2023, EU/Japan): a single-rotor gasoline engine acts solely as a generator in a series-hybrid powertrain, decoupled from the wheels.
• Schiebel Camcopter S-100 UAV: uses an Austro Engine AE50R Wankel powerplant for compact, reliable rotary propulsion in a tactical VTOL drone.
• RQ-7 Shadow tactical UAV: fielded by the U.S. Army with a UEL Wankel engine, demonstrating long-standing military use of rotary power for small aircraft.
• LiquidPiston X-Engine programs: U.S. defense-funded work on compact rotary-combustion generators and UAV power units aims to boost power density and portability for expeditionary power and hybrid-electric flight.
• Mazda 787B (1991): the only rotary-powered winner of the 24 Hours of Le Mans, a historic benchmark for the technology’s performance potential.
• Concepts and research: automakers continue to explore rotary units as flexible, multi-fuel range extenders, including hydrogen-capable concepts showcased in recent years.

Together, these examples show a clear trend: rotary engines have pivoted from mass-market propulsion to targeted roles in aerospace and electrified platforms, while remaining a marker of innovation in concept and niche performance projects.

Summary

Rotary engines, chiefly the Wankel type, are used today in UAVs and drones, compact range-extender generators for electrified vehicles, small portable/stationary gensets, and select light aircraft, with limited presence in niche cars and motorcycles. The older WWI-era “rotary” radial engines are of historical interest only. Rotary designs survive where their compact size, smoothness, and power density deliver clear advantages—especially in aviation and hybrid-electric systems—despite challenges with emissions, sealing, and efficiency that curtailed their mainstream automotive use.

Why were rotary engines banned?

The rotary has never been explicitly banned, the alignment to F1 was the only reason it wasn’t allowed, much like many of the piston engines that had been racing at the time were no longer allowed.

What is the purpose of a rotary engine?

A rotary engine has fewer moving parts than a piston engine, which can lead to improved reliability and reduced maintenance costs. The rotary engine’s compact size and high power-to-weight ratio make it an attractive option for sports cars and other performance-oriented vehicles.

Why are rotary engines not used anymore?

While not a reliability issue, rotary engines are less common today because of fuel mileage issues and emission control. With less precise control over the intake and exhaust event, it’s more difficult to make these run efficiently. That’s not to say that rotary engines have no future in automobiles.

Do any cars still use rotary engines?

Yes, some cars still use rotary engines, though very few. Mazda is the main manufacturer, and they have recently reintroduced a rotary engine in the Mazda MX-30 e-SKYACTIV R-EV as a range extender for its hybrid-electric system. While rotary engines were once abandoned by most manufacturers due to issues with emissions, fuel economy, and durability compared to piston engines, Mazda has found them a good fit for their hybrid applications, providing a compact and reliable power source.
 
The Mazda MX-30 e-SKYACTIV R-EV 

• Function: The rotary engine in the MX-30 serves as a generator to recharge the battery and extend the vehicle’s driving range, rather than directly powering the wheels. 
• Benefits: Mazda considers a rotary unit to be well-suited for this role due to its compact size and ability to provide smooth, reliable performance. 
• Market: The Mazda MX-30 e-SKYACTIV R-EV has been introduced in Japan and Europe. 

Why Most Car Manufacturers Don’t Use Rotary Engines

• Emissions and Fuel Economy: Rotary engines historically struggled to meet modern emissions standards and were less fuel-efficient than traditional piston engines. 
• Durability and Complexity: They can also be less durable and more expensive to manufacture than piston engines, making them less attractive to most automakers. 

The Future of Rotary Engines

• Hybrid Technology: Opens in new tabMazda’s strategy is to leverage the advantages of the rotary engine within a hybrid system, where it can operate at a more constant speed for greater efficiency. 
• Potential for Sports Cars: Opens in new tabWhile the current production rotary engine is for range extension, Mazda has also patented concepts for future rear-wheel-drive sports cars that use a rotary engine with hybrid technology.