General Aircraft Monospar ST 25

Design and development

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.

Operational history

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.

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.

Variants

Monospar ST-25 Jubilee

(1935-1936) Single fin and rudder. 30 built.

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.

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.

Monospar ST-25 Universal

(1936-1939) Twin fin and twin rudder. 29 built, including the conversion of the De Luxe.

Monospar ST-25 Freighter

A variant of the Monospar ST-25 Universal, with a large freight door but without the passenger seating.

GAL.26

One modified Monospar ST-25 Jubilee, fitted with two Cirrus Minor I engines in 1936.

GAL.41

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.

Operators

 Australia

Adelaide Airways

 Canada

Eastern Canada Air Lines (five ST-25 Freighters, delivered in 1936)

 Denmark

 France

Armée de l'Air (2 ST-25 in Indochine (Vietnam) in November 1945)

 Netherlands

Van Melle's Confectionery Works, Breskens (one Jubilee, PH-IPM "Dubbele Arend', delivered in 1935)

 New Zealand

New Zealand Aerial Mapping

Royal New Zealand Air Force

 Romania

Royal Romanian Air Force

 Spain

Spanish Republican Air Force

 Spain

Spanish Air Force

 Turkey

General Command of Mapping (Turkey)

Turkish Government (two ST-25 Freighters for parachute training delivered in 1937)

 United Kingdom

Crilly Airways

Royal Aircraft Establishment (two Jubilees used for radio development)

Royal Air Force (impressed civil aircraft used during the second world war)

Specifications (Monospar ST-25 Jubilee)

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

Performance

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)