Lycoming O 235Edit

The Lycoming O-235 is a family of small, four-cylinder, air-cooled aircraft engines produced by Lycoming Engines. Designed for light general aviation, these engines are part of Lycoming’s venerable lineup of horizontally opposed (or “flat”) engines that have powered countless two- and four-seat aircraft since mid-20th century. With a displacement of roughly 235 cubic inches, the O-235 family is known for its simplicity, reliability, and straightforward maintenance, qualities that have kept it in service in many fleets long after newer designs entered the market. The engine has powered a range of popular trainer and light aircraft, most famously the Cessna 152 among others in the light-aircraft category of General aviation.

The O-235 family embodies a design philosophy that emphasizes robust, time-tested engineering and ease of service. Like other Lycoming engines, it uses a horizontally opposed cylinder arrangement, air cooling, and a simple, rugged four-stroke cycle. The powerplant is typically mounted with a fixed-pitch propeller on many installations, and it has supported both carbureted and, in some variants, fuel-delivered configurations to accommodate different airframes and mission profiles. The broad compatibility of the O-235 with light-aircraft airframes and its availability in spare parts have contributed to its long service life in flight training fleets and recreational aviation.

Design and development

Layout and components

The core layout is a four-cylinder, horizontally opposed configuration with air cooling. This arrangement provides a compact, smooth engine with relatively good access for maintenance and inspection.
The crankcase is typically a cast aluminum unit housing the crankshaft and main bearings, with steel cylinder sleeves and cast-iron or chrome-plated piston rings. The use of dual magnetos for spark delivery is common, reflecting Lycoming’s emphasis on redundancy and reliability.
Accessory hardware—such as the oil pump, fuel system components, and ignition system—are mounted to a separate accessory housing or integrated into the crankcase, depending on the model variant.

Fuel and induction

The O-235 family encompasses variants that are carbureted, as is common for many light trainers and sport aircraft, as well as installations that use fuel delivery systems configured for aviation use. This flexibility allowed the O-235 to serve a variety of airframes with differing performance and certification requirements.
Ignition is provided by a two-spark, dual-magneto arrangement in line with Lycoming conventions, ensuring continued operation should one magneto fail. Spark control and timing are coordinated with the engine’s camshaft-driven valve train.

Performance and maintenance

Horsepower output for O-235 variants typically sits in the low-to-mid range for light aircraft, with most installations delivering roughly about 100–125 horsepower depending on the exact suffix and installation. The precise figure is determined by the airframe’s propeller, carburetion or injection configuration, and certified operating limits.
Time between overhauls (TBO) and maintenance intervals reflect Lycoming’s long-standing emphasis on serviceability. In practice, many O-235 installations are scheduled on standard general aviation maintenance cycles, with oil changes and inspections performed at regular intervals and during annual or 100-hour inspections, whichever applies to the aircraft in question.
In operation, operators stress the importance of proper cooling, regular magneto checks, and fuel system maintenance to prevent issues common to air-cooled, carbureted engines, such as icing and fuel-delivery malfunctions in certain conditions.

Variants

The O-235 family comprises several variants that differ in suffix, configuration, and installation specifics. The common thread is a 235 cubic inch displacement, four-cylinder layout, and air cooling. Depending on the airframe and year of manufacture, some installations use carburetors while others employ aviation-grade fuel delivery systems. The most widely recognized example in popular aviation literature and in-flight training fleets is associated with the Cessna 152 airframe, where the O-235-L2C designation is found in numerous references.
Because the exact suffix conveys installation and certification details, the horsepower, fuel delivery method, and ancillary equipment can vary. Operators should consult the specific engine data sheet and airframe flight manual for precise numbers and limits.

Applications and usage

The O-235 has been used in a range of light, piston-powered aircraft designed for training, leisure flying, and light utility missions. Its four-cylinder, air-cooled design makes it well-suited to two- to four-seat airframes that prioritize simplicity, low maintenance, and reliable takeoff and climb performance within the light general aviation category.
The best-known airframe commonly associated with the O-235 is the Cessna 152, where this engine played a central role in making flight training affordable and accessible for decades. The engine has also appeared in other light aircraft configurations, especially those developed in the postwar era of general aviation expansion, where standardized, readily reparable engines helped fleets stay airborne with modest operating costs.
In the broader landscape of aviation propulsion, the O-235 sits among the family of Lycoming opposed-aircraft engines, along with larger siblings and successors that continued to shape light-aircraft performance and maintenance practices.

Operational history and legacy

Introduced during the mid-20th century as part of a broad wave of general-aviation propulsion development, the O-235 contributed to the democratization of flight by enabling affordable trainer and recreational aircraft. Its mixture of durability, serviceability, and widespread support in the aftermarket helped it endure for many decades.
While newer powerplants have since superseded the O-235 in many fresh designs—owing to advances in fuel efficiency, power-to-weight ratios, and certification pathways—the engine remains in service in a sizeable population of aging trainer and private aircraft. Availability of parts, knowledge, and maintenance expertise for Lycoming’s O-series engines continues to support ongoing operations in various fleets around the world.
The engine’s reputation for straightforward maintenance and robust performance has made it a staple in aviation training environments, where consistent, predictable behavior under a range of flight conditions is valued by instructors, students, and maintenance technicians alike.