General Aircraft Monospar ST-25

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Monospar ST-25
Monospar ST-25 Jubilee of Eloy Fernández Navamuel during the Spanish Civil War[1]
National origin United Kingdom
Manufacturer General Aircraft Ltd, Hanworth
First flight 19 June 1935
Produced 1935–1939
Number built 60
Developed from General Aircraft Monospar ST-10

The General Aircraft Monospar ST-25 was a British 1930s light twin-engined utility aircraft.

Design and development[edit]

The Monospar ST-25 was a low-wing cantilever monoplane with a fabric-covered metal structure. The monospar name came from the use of a single spar in the wing structure, that had been developed by H J Stieger. The cabin was enclosed with five seats. It was based on the GAL Monospar ST-10, with the addition of a folding seat for a fifth passenger, extra side windows, and the addition of a radio receiver. On 19 June 1935, the prototype (G-ADIV) made its first flight at Hanworth Air Park. It was designated Monospar ST-25 Jubilee, to honour the 25th anniversary of the reign of King George V.[2]

Operational history[edit]

  • The last flying Monospar ST-25 (ZK-AFF), of Piet Van Asch, the owner of New Zealand Aerial Mapping Ltd, was lost in 1986 in a hangar fire.[3]
  • The last surviving Monospar ST-25 (OY-DAZ), an ST-25 Ambulance, was fully restored during 1989–1999, and is now displayed in Egeskov Veteranmuseum at Egeskov Castle, Denmark.[4]


Monospar ST-25 Universal, after conversion from ST-25 De Luxe
Monospar ST-25 Universal
Monospar ST-25 Jubilee
(1935-1936) Single fin and rudder. 30 built.[2]
Monospar ST-25 De Luxe
One Monospar ST-25 Jubilee with a large single fin and two Niagara II engines, later converted to the prototype Monospar ST-25 Universal, with twin fins.[2]
Monospar ST-25 Ambulance
Variants of both Monospar ST-25 Jubilee and ST-25 Universal, with a large door on the starboard side to allow a stretcher to be loaded.[2]
Monospar ST-25 Universal
(1936-1939) Twin fin and twin rudder. 29 built, including the conversion of the De Luxe.[2]
Monospar ST-25 Freighter
A variant of the Monospar ST-25 Universal, with a large freight door but without the passenger seating.[2]
One modified Monospar ST-25 Jubilee, fitted with two Cirrus Minor I engines in 1936.[2]
One experimental aircraft based on the Monospar ST-25 Universal. A new fuselage was built containing a pressurized section with two seats. Its purpose was to test possible pressurization systems for a proposed airliner, the GAL.40. The GAL.41 flew for the first time 11 May 1939, and was grounded in 1941.[5]


  • Adelaide Airways
  • Eastern Canada Air Lines (five ST-25 Freighters, delivered in 1936)
  • Armée de l'Air (2 ST-25 in Indochine (Vietnam) in November 1945)[6]
  • Van Melle's Confectionery Works, Breskens (one Jubilee, PH-IPM "Dubbele Arend", delivered in 1935)[7]
 New Zealand
 United Kingdom

Specifications (Monospar ST-25 Jubilee)[edit]

Data from Jackson, 1973

General characteristics

  • Crew: one
  • Length: 26 ft 4 in (8.03 m)
  • Wingspan: 40 ft 2 in (12.24 m)
  • Height: 7 ft 10 in (2.39 m)
  • Wing area: 217 sq ft (20.2 m2)
  • Empty weight: 1,680 lb (762 kg)
  • Gross weight: 2,875 lb (1,304 kg)
  • Powerplant: 2 × Pobjoy Niagara II 7-cyl. air-cooled radial piston engine, 90 hp (67 kW) each


  • Maximum speed: 142 mph (229 km/h; 123 kn)
  • Range: 585 mi (508 nmi; 941 km)
  • Service ceiling: 16,000 ft (4,900 m)
  • Rate of climb: 800 ft/min (4.1 m/s)

See also[edit]



  1. ^ Howson, 1990
  2. ^ a b c d e f g Jackson 1973, pp. 215–220
  3. ^ PIET VAN ASCH – New Zealand's Aerial Mapping Pioneer at Archived 9 February 2013 at the Wayback Machine
  4. ^ Ogden (2009)
  5. ^ General Aircraft Monopar ST-25 – British Aircraft of World War II accessed 1 July 2017]
  6. ^ "Les Nakajima Ki-43 « Oscar » dans l'Armée de l'Air, une fausse bonne idée" (in French). 21 February 2016.
  7. ^ "Rond vliegveld" (in Dutch). Archived from the original on 25 February 2014.


  • Howson, Gerald. 1990. Aircraft of the Spanish Civil War 1936–39. Putnam ISBN 978-0-85177-842-6
  • Jackson, A.J. (1973). British Civil Aircraft since 1919, Volume 2. Putnam. pp. 215–220, 519–521 ISBN 0-370-10010-7
  • Lumsden, Alec; Heffernan, Terry. Probe Probare, Aeroplane Monthly, February 1984
  • Ogden, Bob (2009). Aviation Museums and Collections of Mainland Europe. Air-Britain. ISBN 978-0-85130-418-2
  • Stroud, John. Wings of Peace, Aeroplane Monthly, April 1988