The design of the MA-1 by Murrayair Ltd., a Hawaii-based operator,
was based on an extensive modification of the Boeing Stearman 75
Kaydet biplane. Air New Zealand, under contract to Murrayair, started
in September 1968 to build the prototype using a Stearman airframe
and the aircraft, N101MA c/n 001, first flew on July 27, 1969.
Subsequently the aircraft was dismantled and shipped to Honolulu,
Hawaii, where FAA certification trials were conducted, leading to the
Restricted Category Type Approval on April 14, 1970.
The agricultural MA-1 was powered by the 600 hp Pratt & Whitney
R-1340-AN1 Wasp radial piston engine, had a larger wing compared to
the Stearman and a 450 gal (1,703 l) hopper in front of the
cockpit. The enclosed cockpit has a bench seat for the pilot, but can
also accommodate a ground-crew member seated on a jump seat. The
hopper could carry 3,000 lb (1,360 kg) of fluid, powder or granular
products for treating crops, etc.
For manufacturing Murrayair formed Emair at Harlingen, Texas and
produced the aircraft as the MA-1 Paymaster. Briefly marketed as the
Agronemair MA-1 Paymaster, 28 aircraft (c/n 002 to 029) were
completed by January 1976.
In the meantime the company was taken over by George A. Roth, Emair
operating as a Division of Emroth Co. and the MA-1 became subject of
a redesign. In addition to the 1,200 hp (derated to 900 hp) Wright
R-1820 radial engine, it had new wings, a larger vertical tail of
different shape and a 25 gal (95 l) enlarged hopper.
The first MA-1B Diablo 1200, as the type became known, flew for the
first time August 1975; Type Approval was gained in May 1976. Emair
produced 23 aircraft (c/n 30 to 52) before production was halted in
1980; several of the MA-1s produced were converted to the MA-1B Diabolo.