Helmut (or Helmuth) John Stieger was born in Zurich, Switzerland, on 18 April 1902. He was educated as the Swiss Federal Polytechnic before travelling to England to attend the Imperial College of Science in London. During his studies he found time to gain his RAeC Aviators Certificate, No. 8039, on 4 October 1926 at the de Havilland Aircraft Co., flying a D.H. Moth.

Stieger’s first employment after college was with William Beardmore and Co. in Dalmuir, where he was involved in the design and analysis of the enormous Inflexible monoplane. Stieger had always been a proponent of the monoplane over the biplane, and possibly it was the massive nature of the Inflexible’s wing structure that led him to create a novel, lightweight, single spar structure, the Stieger Mono-Spar wing system, the basis of which was a single warren girder or plate spar, which was used to take the flexural loads, with pyramidal tie-rod bracing systems to absorb the torsional strains. With a minimum of other structures, this wing was thus light in weight and yet very strong. This received patent 306220 “Improvements in or connected with wings for aircraft” on 21 February 1929 (following Application number 19270032753 on 5 December 1927), in the names of Stieger, A.E.L. Chorlton and R.A. de Haga Haig, Beardmores' Aircraft Manager and Chief Designer respectively. This was followed by related patents 325041 “Improvements in spars and shafts” (applied for on 7 December 1928 and granted on 13 February 1930), 325465 “Cantilever spars for aircraft” (applied for on 7 December 1928 and granted on 20 February 1930) and 335603 “Improvements in or connected with wing and aileron construction for aircraft” (applied for on 27 June 1929 and granted on 29 September 1930).

With the closure of Beardmore’s Aircraft Department in February 1929, the Mono-Spar Co. Ltd. was formed in June of that year, with H. J. Stieger as director and chief designer. Along with the aforementioned Chorlton and de Haga Haig as co-directors was stockbroker Charles William Hayward (later Sir Charles William Hayward, CBE KStJ).

Following the building of the ST-1 test wing by Beardmores and the ST-2 test wing and ST-3 experimental aircraft by Glosters, the Monospar Company (by now without the hyphen) moved into offices and works at Croydon Airport, where General Aircraft was formed to acquire the construction rights for the Monospar System from the Mono-Spar Company for aircraft up to 3000 lbs, with Stieger Chairman and Managing Director.

The creation of General Aircraft and the input of finance from the Pacific Trust led to changes at the top of the company. In 1933 Stieger relinquished his position as chief designer to his deputy, F. F. Crocombe and Eric Gordon England replaced Stieger as managing director from 19 June 1935, following which he left the company altogether and moved to Brough to join Blackburn Aircraft. In a move to support further expansion, Blackburn had established a new factory at Dumbarton, which was completed in 1937. This new enterprise was put under the leadership of Major Bumpus, with Steiger as assistant works manager.

Post war, Stieger returned to Brough and, following retirement, was appointed sheriff of Kingston upon Hull for 1959 – 60.

Helmut John Stieger died on 1 October 1989 in Beverley, Humberside.

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