General Aircraft Monospar

In 1929, the Monospar Company Ltd was formed to pursue new techniques of designing cantilever wings, based on the work of Swiss engineer Helmuth J. Stieger, who headed the company. Helmuth John Stieger was born in Zurich in 1902, and educated at the Swiss Federal Polytechnic, and then at the Imperial College of Science in London. While working as a designer for William Beardmore and Company, he formed his own ideas about wing design, and evolved an improved method of building and stressing wings, for which he was later granted a British Patent in December 1927. The principle behind this Patent No. 306,220 was that the wing needed only one spar with torsion loads resisted by an efficient system of strong compression struts, with triangulated bracing in the form of thin wires. The design was revolutionary and very light for its strength.[1]

Based on this design, The Monospar Company designed a twin-engined low-wing aircraft designated the Monospar ST-3, that was built and flown in 1931 by the Gloster Aircraft Company at Brockworth, Gloucestershire. After successful testing of the Monospar ST-3, a new company General Aircraft Ltd was formed to produce aircraft that used the patented Monospar wing designs.[2]

The first production design was the Monospar ST-4, a twin-engined low-wing monoplane with a fixed tailwheel landing gear and folding wings for ground storage.[3] Powered by two Pobjoy R radial engines, the first aircraft (G-ABUZ) first flew in May 1932, and was followed by five production aircraft. The Monospar ST-4 Mk.II, an improved variant with minor differences, followed with a production run of 30. In 1933, the Monospar ST-6 appeared, a similar aircraft to the ST-4, with manually retractable landing gear and room for an extra passenger. The Monospar ST-6 was only the second British aircraft to fly with retractable landing gear (the first, the Airspeed Courier, was flown a few weeks earlier). Another Monospar ST-6 was built, and two ST-4 Mk.IIs were converted. GAL then produced a developed version, the Monospar ST-10, externally the same but powered by two Pobjoy Niagara engines, an improved fuel system, and aerodynamic refinements.[2][4] The Monospar ST-11 was developed from the ST-10, with retractable landing gear, and two were built for export to Australia.[1][5][6] A production batch of ten Monospar ST-12 aircraft was based on the ST-11, but with de Havilland Gipsy Major engines and fixed landing gear.[1]

The Croydon factory closed down in 1934, and a larger factory was opened in 1935 at London Air Park, Hanworth.[7]

The Monospar ST-10 prototype (G-ACTS) won the 1934 King's Cup Air Race with an average speed of 134.16 mph.[8] Only one other ST-10 was built.[1][9]

GAL Monospar ST-4

Monospar ST-3

Experimental cantilever monoplane, powered by two 45 hp (34 kW) British Salmson AD.9 engines; one built.[10]

Monospar ST-4

Cantilever touring monoplane, powered by two 85 hp (63 kW) Pobjoy R radial engines, seven built.

Monospar ST-4 Mk.II

Improved variant of Monospar ST-4, 22 built, two later converted to ST-6 standard.

Monospar ST-6

As Monospar ST-4, with manual retractable landing gear, two built plus two conversions from ST-4 Mk.IIs.

GAL Monospar ST-11 (VH-USN) with pilots Collins and Wylie, after flight from UK to Australia, February 1935

Monospar ST-10

Improved variant with two 90 hp (67 kW) Pobjoy Niagara engines, two built.

Monospar ST-11

Development of Monospar ST-10, with retractable landing gear, two built.

Monospar ST-12

Fixed landing gear variant with two de Havilland Gipsy Major engines, ten built.

General Aircraft ST-18 Croydon

Ten-seat transport with two Pratt and Whitney Wasp Junior engines, one built.

Monospar ST-25 series

Development of Monospar ST-10

 Portugal

• Portuguese Navy

 South Africa

• South African Air Force

 Spanish Republic

• Spanish Republican Air Force, 1936 from LAPE

 Spain

• Spanish Air Force

 Turkey

• Turkish Air Force

• One Monospar ST-12 (registration VH-UTH) is on display at the Newark Air Museum, England

Monospar ST-10 3 view from l'Aerophile magazine, January 1933

Data from The Illustrated Encyclopedia of Aircraft [12]

General characteristics

• Capacity: four
• Length: 26 ft 4 in (8.03 m)
• Wingspan: 40 ft 2 in (12.24 m)
• Height: 7 ft 10 in (2.30 m)
• Wing area: 217 sq ft (20.16 m²)
• Empty weight: 1,840 lb (835 kg)
• Gross weight: 2,875 lb (1,304 kg)
• Powerplant: 2 × de Havilland Gipsy Major 4-cylinder inverted inline piston engine , 130 hp (97 kW) each

Performance

• Maximum speed: 158 mph (254 km/h, 137 kn)
• Range: 410 mi (660 km, 360 nmi)
• Service ceiling: 21,000 ft (6,400 m)

On 6 September 1935, a Monospar ST-12 operated by Australian Transcontinental Airways suffered engine failure, and made an emergency landing on Woodgreen Station in the Northern Territory. Reports vary slightly,[13] but the plane was said to be carrying the pilot J. Maher, with two passengers, Renfrey and Maloney, and a young crocodile that was being transported to Adelaide.[lower-alpha 2] Renfrey walked for two days towards Ryan's Well, a watering hole on the Overland Telegraph Line around 40 mi (64 km), to seek assistance. Three men (one of several search parties sent out to look for the men[14]) motoring across the desert found him, and took him to Aileron telegraph station. In the meantime, Don Thomas from Alice Springs drove to Woodgreen to pick up Purvis Sr and two "blackfellows", one of whom managed to track down the plane based on the description of the location given by Renfrey. Maher and Maloney had only six oranges between them for food, but they survived until they were rescued by shooting and eating the crocodile.[15]

• General Aircraft ST-18 Croydon

Related lists

• List of Interwar military aircraft
• List of aircraft of the Spanish Republican Air Force