Solid Air UL-Bau Franz is a German aircraft manufacturer based in Hundheim, Rheinland-Pfalz.

The company specializes in the design and manufacture of ultralight trikes.

[1] The company has been noted for its innovative designs and use of materials to improve maintainability.

The Solid Air Diamant Twin has an unusual side-by-side configuration cockpit and a plywood engine mount laminated to a fibreglass structure to create a firewall.

The Solid Air Diamant LP incorporates a two-point wing mounting that allows the carriage to be flared like a conventional airplane on landing.