Avro 531 Spider

The Avro 531 Spider was a single-seat British fighter prototype of the last year of the First World War, built by Avro. It was a sesquiplane, a biplane whose lower wing is much shorter than the upper, and it took its nickname from the rigid Warren truss interplane struts, welded steel tubes set in triangles in place of the usual flying and landing wires. In tests it showed exceptional performance, handling and pilot visibility, but by the time it flew the War Office had already chosen the Sopwith Snipe for mass production, so no order followed. A more refined Avro 531A was apparently never completed, although some of its components seem to have been used to build the Avro 538, a racing aircraft that proved to have a faulty wing spar and served the company as a hack from May 1919 to September 1920.