Two further prototypes were produced in 1984; the last, fourth, was fabricated in 1985.

The first prototype, (serial N91) flew in 1917, with a further five prototypes being produced.

Two further prototypes of the larger design were also built followed by at least 9 development aircraft.

A further two prototypes were completed in mid-1983.

Despite this, a further five prototypes were ordered for evaluation.

In addition, further prototypes are aimed more at consumer acceptance than bare-bones competition requirements.

Two further prototypes followed by 25 production aircraft.

It was followed by further four prototypes, in order to test different engines.

Two further prototypes, meant to be direct preproduction vehicles, were delivered in November 1965.