AP 118 · No. 10 Section II · Aircraft Plate 61 / 228

Plate 61 of 228 · Between the wars · Four-seat twin-engined light transport and air taxi

General Aircraft Monospar ST-12

General Aircraft Monospar ST-12 (1935), painted as VH-UTH ‘Captain Cook’, built in 1935 and imported into Australia for New England Airways, which flew it from Sydney, later owned by Airlines of Australia, Butler Air Transport and the Tasmanian Aero Club among many others, flown from Sydney to England in August and September 1961 by its owner Dr John Morris with B. J. Harrison, acquired by Newark Air Museum in 1968 and restored there over more than 50 years until 2021; the only surviving ST-12: General Aircraft’s four-seat light twin of 40 ft 2 in span, built round H. J. Stieger’s patented single-spar ‘Monospar’ wing, with a fixed divided undercarriage and two 130 hp de Havilland Gipsy Major engines, shown complete with the wings spread, standing tail-down on its main wheels and tail wheel, as restored at Newark in the blue and white scheme Dr Morris gave it in 1958: teal blue overall with a white cabin top and rear decking, white cowling fronts, red spinner caps, black yellow-tipped airscrews, red ‘VH-UTH’ on the rear fuselage and the starboard upper wing, and a white kangaroo above ‘AUSTRALIA’ on the fin (side view from a side-on photograph of VH-UTH at Moorabbin, c.1960, with the wing and tail planform from the NACA Aircraft Circular 164 three-view of the ST-4 and the details from photographs of VH-UTH at Newark).

3D model

Turn it over

A procedural model built in Blender from published dimensions, drawings and photographs, painted as VH-UTH ‘Captain Cook’, built in 1935 and imported into Australia for New England Airways, which flew it from Sydney, later owned by Airlines of Australia, Butler Air Transport and the Tasmanian Aero Club among many others, flown from Sydney to England in August and September 1961 by its owner Dr John Morris with B. J. Harrison, acquired by Newark Air Museum in 1968 and restored there over more than 50 years until 2021; the only surviving ST-12: General Aircraft’s four-seat light twin of 40 ft 2 in span, built round H. J. Stieger’s patented single-spar ‘Monospar’ wing, with a fixed divided undercarriage and two 130 hp de Havilland Gipsy Major engines, shown complete with the wings spread, standing tail-down on its main wheels and tail wheel, as restored at Newark in the blue and white scheme Dr Morris gave it in 1958: teal blue overall with a white cabin top and rear decking, white cowling fronts, red spinner caps, black yellow-tipped airscrews, red ‘VH-UTH’ on the rear fuselage and the starboard upper wing, and a white kangaroo above ‘AUSTRALIA’ on the fin (side view from a side-on photograph of VH-UTH at Moorabbin, c.1960, with the wing and tail planform from the NACA Aircraft Circular 164 three-view of the ST-4 and the details from photographs of VH-UTH at Newark). Drag to orbit, scroll or pinch to zoom · download .glb (821 KB)

Data plate

Specification

First flight, number built and top speed are for the whole family (); engine, crew and dimensions are for the General Aircraft Monospar ST-12 (1935) modelled here.

History

The Monospar ST-12

The Monospar was the idea of H.J. Stieger, a Swiss engineer working for William Beardmore and Company, who in 1927 patented a way of building a wing round a single main spar, braced by a pyramid of wires and struts so that the spar took the bending loads and the bracing the twisting ones. It promised a light, stiff structure, and the Monospar Company was formed in 1929 to exploit it. Gloster built the first aircraft to the design, the twin-engined ST-3, at Brockworth in 1931, and in the finished Monospars the structure made up only about a quarter of the all-up weight.

General Aircraft Ltd was set up at Croydon to put the design into production, and its first type, the ST-4, a four-seat low-wing cabin monoplane with two Pobjoy radials, flew in May 1932. A run of ST-4s and improved ST-4 Mk IIs followed, then the ST-6 with a retractable undercarriage and the cleaner ST-10, whose prototype won the 1934 King’s Cup air race at 134.16 mph. The ST-11 added retractable gear to the ST-10, and the ST-12 of 1935 kept the fixed undercarriage but swapped the Pobjoys for two 130 hp de Havilland Gipsy Majors, which lifted the top speed to about 158 mph. Ten ST-12s were built as the company moved from Croydon to a larger factory at Hanworth, where the ST-25 Jubilee and Universal took the line on.

Four ST-12s went to Australia in 1935, where twin engines meant a great deal over long stretches of empty country. New England Airways named its three after explorers, ‘Captain Cook’, ‘Captain Phillip’ and ‘Captain Flinders’, and flew them from Sydney into northern New South Wales and Queensland. Australian Transcontinental Airways’ VH-UTZ came down between Barrow Creek and Alice Springs on 6 September 1935 after an engine failed, and its pilot and passengers survived several days in the outback before they were found. Monospars also served with the Portuguese Navy, the South African and Turkish air forces and both sides in the Spanish Civil War.

This airframe

General Aircraft Monospar ST-12 VH-UTH

VH-UTHThe airframe modelled

VH-UTH (c/n ST12/36) was registered to New England Airways in May 1935 and named ‘Captain Cook’. It passed to Airlines of Australia when that company was formed in 1936, and in July that year, carrying the former Prime Minister Billy Hughes, it lost its way in bad weather between Sydney and Brisbane and struck a fence landing at Beaudesert; Hughes broke his collarbone. It then changed hands at least fourteen times, flying with P.H. Moody Air Taxis at Rockhampton, Butler Air Transport in Sydney and the Tasmanian Aero Club at Launceston, among others. In 1958 Dr John Morris of Forestville, New South Wales, bought it and painted it blue and white with a kangaroo on the fin, and on 17 August 1961 he and B.J. Harrison left Sydney in it for England, arriving on 20 September. Sold in 1964, it stood outside at several aerodromes until Newark Air Museum acquired it in 1968, one of its first aircraft. Its restoration, much of it done by the Cotswold Aircraft Restoration Group, took more than 50 years and was finished in 2021. The model shows it as restored, complete with the wings spread, standing tail-down on its main wheels and tail wheel: teal blue overall with a white cabin top and rear decking, white cowling fronts, red spinner caps, black airscrews with yellow tips, red ‘VH-UTH’ on the rear fuselage and the starboard upper wing, and a white kangaroo above ‘AUSTRALIA’ on the fin. The side view follows a side-on photograph of VH-UTH at Moorabbin taken about 1960; the wing and tail planform come from the NACA Aircraft Circular 164 three-view of the ST-4, which shares the ST-12’s span and length, and the details from photographs of the aircraft at Newark.

See it at Newark Air Museum

Where to see one

In the gazetteer

The gazetteer records the Monospar ST-12 in one UK collection. The airframe modelled here is marked.

Every airframe and serial All 228 plates

Profiles and models are procedural interpretations built in Blender from published dimensions, three-view drawings and photographs of each airframe. Treat the museum aircraft as the reference.