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. 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. 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. 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. The Monospar ST-11 was developed from the ST-10, with retractable landing gear, and two were built for export to Australia. 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. ==Design==

The General Aircraft Monospar was a family of unorthodox touring and utility aircraft. The principal feature of the Monospar was its innovative monospar construction method, which was applied not only to the wing but also the fuselage of the aircraft. Accordingly, the structural weight of the aircraft was only 26 percent of the all-up weight, which a considerably lower percentage than was typically found amongst its contemporaries in its size and weight class. For conventional aircraft of the era, the structural weight made up a high proportion of the overall weight of the aircraft; by reducing the structural weight, the ratio of useful payload to all-up weight could be positively increased, meaning that the aircraft could carry a greater useful load without negatively impacting performance. The wing comprised three pieces, the centre section of which was integral with the fuselage and contained the engine mountings, the struts of which acted as the king-posts in the wing bracing system. The wing structure consisted of a single main spar that was strong in its ability to bend but was braced against torsion by two sets of spiral bracing wires, that ran around the wing in opposing directions. A modified form of the wing's monospar construction was used for the fuselage; its primary structure member was a square-section beam of relatively shallow depth, composed of duralumin, that was placed at the bottom of the fuselage and anchored to the wing spar of the center section. The four corner booms of this beam were of built-up D-section and were joined by an outer cover of stamped duralumin sheeting that formed lattices, akin to the main wing spar web. This cover braced the fuselage beam while the free edges overlapped the top and bottom booms. The flight controls were duplicated and of the conventional stick and rudder-bar type. ==Operational history==

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

;Monospar ST-3 :Experimental cantilever monoplane, powered by two British Salmson AD.9 engines; one built. ;Monospar ST-4 :Cantilever touring monoplane, powered by two 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. ;Monospar ST-10 :Improved variant with two 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 ==Operators==

; • Portuguese Navy ; • South African Air Force ; • Spanish Republican Air Force, 1936 from LAPE ; • Spanish Air Force ; • Turkish Air Force Civil operators ; • Australian Transcontinental Airways (ATA), 1935–1936 ; • VASP, 1933–1938 ; • Inner Circle Air Lines, 1935-1935 ==Incidents==

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, 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. Renfrey walked for two days towards Ryan's Well, a watering hole on the Overland Telegraph Line around , to seek assistance. Three men (one of several search parties sent out to look for the men) 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. ==Surviving aircraft==

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