In the early 1970s, William Lear, the founder of Learjet, designed the Lear Fan-2100 as a lightweight and fuel-efficient composite aircraft. The design was not completed before Lear’s death in 1978.
The Lear Fan design was unique because it was made entirely with graphite epoxy and Kevlar composite materials.
Using composites enhanced the structure's strength while keeping the overall weight half of a conventional aluminum airframe. The aircraft's weight gave it a faster speed, and it was designed to be more economical than the competition.
With a designed empty weight of just 1860kg, the aircraft could carry up to nine people, including two pilots. The pressurized cabin concept enabled the service ceiling of 12500m, making the flight comfortable and fast for passengers.
The aircraft featured a four-bladed propeller in the rear powered by two Pratt & Whitney turboprop engines. Each engine generated 650 shaft horsepower of takeoff power.
The engines ran on independent shafts to ensure the safety and reliability of a multi-engine system. A single-engine handling capability was designed in case of an engine failure. The purpose-built gearbox allowed power transmission from two individual engines (and shafts) to a single propeller.
Another unusual feature of the Lear Fan-2100 was its Y-shaped tail aircraft with two stabilizers pointing upwards, with an addition of a short vertical stabilizer pointing downward. The downward-pointing stabilizer protected the propellor from ground strikes during unusual takeoffs and landings.
While three prototypes underwent a series of ground and flight tests, the design was met with structural issues, particularly with the pressurization of the all-composite fuselage. The fuselage structure showed design flaws during test flights.
The manufacturer planned to build a new factory in Belfast, Northern Ireland, to produce the Lear Fan-2100. The British government sponsored the factory to boost employment in the region, but the aircraft never entered production.
The reliability of the combining gearbox was also questioned by the Federal Aviation Administration (FAA), leading to a refusal of the airworthiness certification of the prototype. The aircraft never entered production. The program was terminated in 1985.
The three prototypes are displayed at different sites across the United States: at the Museum of Flight in Seattle, Washington, the Frontiers of Flight Museum in Dallas, Texas, and in front of the Civil Aerospace Medical Institute in Oklahoma City, Oklahoma.