[1] The HP-20 was designed by Schreder for the FAI 15 Metre Class.
The HP-20 prototype was just complete when Schreder lost interest in the project and moved on to work on the HP-21 instead.
The sole example of the HP-20 was built by Schreder in his workshop in Byran, Ohio and first flew in 1981.
The design shares a similar fuselage to the HP-19, but has a different double-tapered wing of smaller area, 102 sq ft (9.5 m2) versus 113 sq ft (10.5 m2) for the HP-19.
[1] Even though Richard Schreder died in August 2002, in April 2011 the sole HP-20 was still registered to him.