The Lockheed Altair was a development of the Lockheed Sirius. The Altair was one of the first aircraft designs with a fully rectractable undercarriage.
The first five Altairs were converted Siriuses. Another six Altairs were built from scratch: three by Lockheed, two by Detroit Aircraft Corporation, and one by AiRover. The AiRover Altair, dubbed The Flying Testbed, was powered by a Unitwin engine, which used two engines to drive a single shaft. The Unitwin was used in the Vega Starliner, which never went into production.