page_title: Straight-twin engine
section_title: Aviation use
hierarchical_section_title: Straight-twin engine / Aviation use
caption_attribution_description: English: A Rotax 503 aircraft engine display by Aero Propulsion Technologies at the Challenger Winter Rendezvous, Montebello, Quebec
context_page_description: A straight-twin engine, also known as straight-two, inline-twin, vertical-twin, or parallel-twin is a two-cylinder piston engine which has its cylinders arranged side by side and its pistons connected to a common crankshaft. Compared to V-twins and flat-twins, straight-twins are more compact, simpler, and usually cheaper to make, but may generate more vibration during operation.
  Straight-twin engines have been primarily used in motorcycles, but are also used in automobiles and in powersports applications. Automobiles with straight-twin engines are usually very small and include city cars and kei cars. Recent examples of cars with straight-twin engines include the Tata Nano and Fiat Group automobiles using the TwinAir engine. Powersports applications include use in outboard motors, personal water craft, all-terrain vehicles, snowmobiles, and ultralight aircraft.
  Different crankshaft angles are used in four-stroke straight-twins to achieve different characteristics of firing intervals and engine balance, affecting vibrations and power delivery. The traditional British parallel twin had 360° crankshafts, while some larger Japanese twins of the 1960s adopted the 180° crankshaft.
context_section_description: Inline-twin engines, such as the Hirth 2704 are commonly used in Ultralight, single seat gyrocopters and small homebuilt aircraft  originally sourced from snowmobiles. Another popular inline-twin two-stroke engine was the Cuyuna 430-D, also a modified snowmobile unit which produced 30 hp (22 kW). More modern ultralights tend to use engines such as the Rotax 503 or Rotax 582 which are designed for the purpose.
  Inline-twin engines are sometimes also used in large scale flying model aircraft.
caption: A Rotax inline aircraft engine
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