Country of origin:

New Zealand

Description:

Two-seat agricultural biplane

Power Plant:

One 448 kw (600 hp) Pratt & Whitney R-1340-AN1 Wasp nine-cylinder radial air-cooled engine

Specifications:

History:

The Murrayair MA-1 was a redesign and reconstruction of the Boeing Stearman Model 75 Kaydet biplane trainer as a two-seat crop-dusting aircraft performed under contract to Murrayair Ltd of Hawaii by engineers at Air New Zealand, some 9,000 examples of the Stearman having been built as trainers during World War II, many finding their way into agricultural duties subsequent to their retirement from military service. Major changes to the Stearman, other than the installation of a larger engine, included strengthening of the undercarriage, a planned increase in wing area from 27.63 m² (297.4 sq ft) to 37.90 m² (408 sq ft) by the insertion of a new aluminium centre-section in the upper wing, and the original flying-wires being replaced by aerofoil shaped struts.

The hopper formed an integral part of the front fuselage, the position formerly occupied by the front cockpit. The rear cockpit, which became fully enclosed, had two-seats side-by-side for the pilot and loader/driver. The pilot’s seat was raised to increase visibility. Initial calculations allowed an increase in max take-off weight of nearly 1,588 kg (3,500 lb) to 2,835 kg (6,250 lb).

The aircraft was a strut-braced biplane with forward staggered wings of unequal span and NACA 2213 wing section. Structure was conventional two-spar in five sections, the centre-section of the upper wing being of aluminium structure and the outer top wing and both lower wing sections being of spruce laminated spars and ribs, duralumin channel-section compression struts and steel tie-rod internal bracing with fabric covering. The ailerons were of duralumin construction with fabric covering and were only on the lower wings.

The fuselage was of rectangular welded chrome molybdenum steel tube frame with fibreglass panels except over the engine which had a metal cowling initially. The tail unit was a conventional single fin, and the rudder of welded chrome molybdenum structure with fabric covering.

The prototype N101MA (c/n 001) made its first flight at Mangere in Auckland, New Zealand  on 27 July 1969. It was later dismantled and shipped to Honolulu to complete trials for FAA certification. At this time testing was carried out without the engine cowling or baffles. It was later taken to Texas where it operated from Harlingen. By that time it had accumulated 2,300 hrs.

Early reports refer to a “quick in-field adjustment for maximum swathe width and removable vanes for cross country ferry.” Also, there was an aerofoil section beneath the spreader. Another feature was a four-bolt attachment for the fuselage sections which facilitated ease of maintenance and repair.

Subsequently, some 25 examples were converted for Murrayair in Hawaii by Emair in Harlingen, Texas, this Company being a subsidiary of Murrayair, these being known as the MA-1. At some stage the name Agronemair MA-1 Paymaster was given to the type and it seems all 27 production MA-1s (c/ns 002 to 029) were supplied to American operators, no further examples being seen in this region. Early production aircraft were N302MA (c/n 002), N103MA (c/n 003), N104MA (c/n 004), N305MA (c/n 005) and N306MA (c/n 006). Engine was the Pratt & Whitney R-1340 driving Hamilton Standard constant speed 6101A-12 or AG-100 blades.

The Boeing Stearman received considerable alteration. This involved the installation of the more powerful Pratt & Whitney R-1340 Wasp engine, which was available in some numbers from retired air force North Americn Harvards, a substantial increase in wing area, strengthening of the undercarriage, and redesign of the forward fuselage to accommodate the crew of two, and the chemical hopper. The wing area was increased by the insertion of a new aluminium centre-section incorporating the fuel tank in the upper wing; and the flying-wires were replaced by aerofoil-shaped struts. The fuselage was also lengthened and strengthened to accommodate the larger engine and fibreglass panels replaced the fabric on the side panels. The hopper formed an integral part of the front fuselage in the position formerly occupied by the front cockpit. The rear cockpit, which was fully enclosed, accommodated two side-by-side, the second seat being for the loader/driver.

The hopper was designed by engineers at Air New Zealand Ltd and manufactured by Kendricks Plastiglass of Wanganui, was of fibreglass construction, and was capable of holding 1,360 kg (3,000 lb) of chemicals. The hollow steel support struts for the hopper, and all other fuselage tubes, were filled with linseed oil for anti-corrosion protection. The hopper was of fibreglass construction and was boxed in as a precaution against corrosion of its support tubes by pesticide.

At some stage the Murrayair Company was acquired by George Roth and Emair. The Company became known as Emair and subsequently operated as a division of Emroth Co. Further development and redesign took place. This involved the installation of a Wright R-1820 radial engine of 900 kw (1,200 hp) but de-rated to 671 kw (900 hp). This new aircraft had redesigned wings, a larger vertical tail and the hopper enlarged by 95 litres (21 Imp gals).

This model, known as the MA-1B Diablo 1200, was first flown in August 1975 and Type Certification was received in May 1976. Five were built in Hawaii and then tooling was transferred to Harlingen in Texas where they were built by Emair. A total of 23 examples was completed (c/ns 30 to 52) until production concluded in 1980. Aircraft conversion took place at Harlingen, Texas, some 48 examples being reported to have been completed, a number of the earlier EA-1s being updated to MA-1B Diablo configuration fitted with a Wright R-1820 engine. Three examples, including N88910, are stored engineless and wingless at the Pacific Aviation Museum in Honolulu.