View source for General Aircraft Monospar

{{Short description|1930s British utility aircraft}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{Use dmy dates|date=August 2019}}
{{Use British English|date=March 2017}}
{|{{Infobox aircraft begin
 |name= Monospar series
 |image= GAL_Monospar_ST-10_G-ACTS_1934.jpg
 |caption= GAL Monospar ST-10 G-ACTS Hatfield 14 July 1934, winning the King's Cup Air Race
}}
{{Infobox aircraft type
 |type= Cabin monoplane
 |manufacturer= [[General Aircraft Ltd]]
 |designer=
 |first flight= [[1932 in aviation|1932]]
 |introduced=
 |retired=
 |status=
 |primary user=
 |more users=
 |produced=
 |number built= 45
 |variants with their own articles= [[Monospar ST-25]]
}}
|}

The '''General Aircraft Monospar''' was a family of touring and utility aircraft designed and built by the [[United Kingdom|British]] aviation company [[General Aircraft Ltd]] (GAL).

==Development==
In 1929, the Monospar Company Ltd was formed to pursue new techniques of designing [[cantilever#Aircraft|cantilever]] wings, based on the work of [[Switzerland|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.<ref name="Ord-Hume">{{cite book |last=Ord-Hume |title=The Monospar: From tailless gliders to vast transport: The story of General Aircraft Ltd. of Hanworth |year=2013 |page= |publisher=Stenlake Publishing |isbn=978-1-84033-636-8 }}</ref>

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.<ref name=jackson>Jackson 1973, pp. 208–214.</ref>

The first production design was the '''Monospar ST-4''', a twin-engined low-wing monoplane with a fixed tailwheel landing gear and [[folding wing]]s for ground storage.<ref>[https://books.google.com/books?id=qygDAAAAMBAJ&dq=Popular+Science+1932+plane&pg=PA31 "New British Plane Has Hinged Wings"] ''Popular Science'', November 1932, photos showing wings folded</ref> 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.<ref name=jackson/><ref>Sherwood (1999)</ref> The '''Monospar ST-11''' was developed from the ST-10, with retractable landing gear, and two were built for export to [[Australia]].<ref name="Ord-Hume"/><ref>{{cite web |last1=Goodall |first1=Geoff |title=General Aircraft Monospar in Australia |url=https://www.goodall.com.au/australian-aviation/gal-monospar/galmonospar.html |website=www.goodall.com.au |access-date=13 June 2022}}</ref><ref>Priest, Joan. ''Virtue in Flying'' 1975 Angus & Robertson {{ISBN|0-207-13230-5}}</ref> 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.<ref name="Ord-Hume"/>

The [[Croydon Aerodrome|Croydon]] factory closed down in 1934, and a larger factory was opened in 1935 at [[London Air Park|London Air Park, Hanworth]].<ref name=stroud>Stroud May 1988, {{page needed|date=May 2024}}.</ref>

==Design==
The General Aircraft Monospar was a family of unorthodox touring and utility aircraft.<ref name = "naca 1"/> In its original configuration, it was a three-seater aircraft, placing the pilot and one passenger side by side, albeit slightly staggered, while a second passenger could be seated directly behind them. The forward position of the pilot's seat and the absence of a nose-mounted engine meant that forward visibility was exceptionally good.<ref name = "naca 2"/> The cabin was furnished with sizable windows that also provided good external visibility, although the occupant of the rear seat has a less generous view, largely due to the low-mounted position of the wing obstructing visibility from that position. The engines were completely enclosed in [[cowling]]s, which were arranged so that the airflow (both over and under the wing) would freely cool the engine.<ref name = "naca 2"/> Fuel was housed within a single tank within the aircraft's nose, almost directly forwards of the instrumentation panel; it was supplied to the engine directly and was fed by [[gravity]].<ref name = "naca 2">NACA 1931, p. 2.</ref>

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.<ref name = "naca 12">NACA 1931, pp. 1-2.</ref> 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.<ref name = "naca 1"/> This increase was viewed as being commercially significant, particularly against other competing modes of transport. It was also judged to be valuable in boosting the [[factor of safety]] for such an aircraft.<ref name = "naca 1">NACA 1931, p. 1.</ref>

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.<ref name = "naca 4">NACA 1931, p. 4.</ref> The wing structure consisted of a single main spar that was strong in its ability to bend but was braced against [[Torsion (mechanics)|torsion]] by two sets of spiral [[Bracing (aeronautics)|bracing]] wires, that ran around the wing in opposing directions.<ref name = "naca 2"/> The single spar was composed of [[duralumin]] and built up from several members to form an I-shaped beam. A supportive web, comprising a plain duralumin plate with triangular holes stamped out for lightness, used a series of lattice bars that functioned as braces between top and bottom [[flange]]s.<ref name = "naca 2"/> These spar flanges were built up of strips and consisted of angle sections that were [[rivet]]ed to the web with reinforcing cover plates added on the outside.<ref name = "naca 3"/> Curved angle sections were used instead of plain flat counterparts, which made them considerably stronger in [[Compression (physics)|compression]] as the curved members that composed it helped to brace one another. Where local reinforcement of the spar was necessary, this can be provided by additional [[lamination]] on the outer faces of the spar.<ref name = "naca 3"/> The flat spar web was stiffened in places by vertical V-section members.

The spiral bracing used tie rods that were anchored at their ends to the tubular [[rib]]s and to plate fittings on the spar flanges where the tie rods of a bay crossed each other; it did not extend out to the wing tips, instead finishing on the spar just beyond the inner end of the [[aileron]].<ref name = "naca 3"/> Instead, the false spar that carrying the aileron was used to brace the outer-most wing elements, such as the wing tips. This false spar was at a pronounced angle to that of the main spar, thus triangulating the structure; the former ran inwards from the wing tips, where they are attached to the main spars, to the final compression members of the monospar system via flanged duralumin plates.<ref name = "naca 3"/> Additional stiffening of the wing forwards of the aileron was achieved via a pair of hinge ribs. Prise-type ailerons were fitted, which had a fabric covering and a built-up spar on which were threaded diaphragms of duralumin spaced by a flattened tube of duralumin along their [[trailing edge]]s.<ref name = "naca 3"/> The spars are U-shaped and closed with a flanged plate with lightening holes. The wing was built entirely of duralumin, excluding some steel fittings and wiring plates.<ref name = "naca 3">NACA 1931, p. 3.</ref>

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.<ref name = "naca 45">NACA 1931, pp. 4-5.</ref> 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.<ref name = "naca 4"/> The four booms were kept apart, and resistant to collapse, via a series of tubular distance pieces, both vertically and horizontally placed, that ran between the corner booms. This approach was relatively un-standardised and thus not particularly cheap to manufacture.<ref name = "naca 45"/>

The shape of the fuselage was obtained via a series of hoops of trough-section duralumin and [[Longeron|stringer]]s (both fore and aft) of similar section.<ref name = "naca 5"/> Furthermore, spiral wiring was present to increase the fuselage's torsional strength and make it thoroughly rigid. The result was a fuselage that was free from torsional and [[Aeroelasticity#Flutter|flutter]]-related concerns.<ref name = "naca 5"/> The four booms were kept apart, and resistant to collapse, via a series of tubular distance pieces, both vertically and horizontally placed, that ran between the corner booms. The underside of the fuselage was rigidly-braced to the aircraft's tail unit, which was fairly conventional.<ref name = "naca 5"/> It had a cantilever [[fin]] while both the [[Elevator (aeronautics)|elevator]]s and [[rudder]] were balanced.<ref name = "naca 5"/> The stabiliser had a single spar along its trailing edge and triangularly-arranged flanged duralumin plates that ran forwards, along with five duralumin ribs, while the leading edge was formed from flattened tubing. Both the elevators and rudders had similar structures.<ref name = "naca 5">NACA 1931, p. 5.</ref>

The flight controls were duplicated and of the conventional stick and rudder-bar type.<ref name = "naca 6"/> The control columns were mounted in forks on the ends of compact fore-and-aft torque tubes that were mounted beneath the seats; these torque tubes were linked together as well as to a lever from which wires ran to the ailerons. The elevators were operated via a torque tube to which each control column was linked through a universally jointed push-pull tube.<ref name = "naca 6"/> Wires ran back to a lever on a lay-shaft in the tail unit from where the elevators actuated via a push-pull tube. Actuation of the rudder was via a series of cables that ran directly to the rudder from the rudder-bar.<ref name = "naca 6"/> 

A divided-type [[landing gear|undercarriage]] with a relatively wide track was fitted.<ref name = "naca 5"/> It was highly maneouverable while on the ground, in part due to the use of a [[Caster|castor]]ing tail skid and [[Bendix Corporation|Bendix]] brakes; the aircraft could reportedly be kept straight even with only a single engine running even though each wheel was directly under an engine. At least one aircraft had an arrangement in which the brakes were coupled to the control column so that the brakes would activate whenever the pilot pulled back on the stick during a three-point landing; the interconnection could be released whenever the brakes were conventionally operated via a centrally-placed lever.<ref name = "naca 5"/> The [[axle]]s were hinged to the wing girder or main spar on the underside of the fuselage. Each vertical leg, which incorporated a [[Vickers]]-supplied [[Oleo strut|oleo]] [[shock absorber]], were connected to a sturdy point within the engine mounting. A streamline radius rod braced each spring-leg to the wing girder.<ref name = "naca 6">NACA 1931, p. 6.</ref> 

==Operational history==
{{expand section|date=May 2024}}
The Monospar ST-10 prototype (''G-ACTS'') won the 1934 [[King's Cup Air Race]] with an average speed of 134.16&nbsp;mph.<ref>Lewis 1971, p. 262.</ref> Only one other ST-10 was built.<ref name="Ord-Hume"/><ref>Priest, Joan. ''Virtue in Flying''. 1975, Angus & Robertson. {{ISBN|0-207-13230-5}}.</ref>

==Variants==

[[File:GA ST.4.jpg|thumb|right|GAL Monospar ST-4]]   
;Monospar ST-3
:Experimental cantilever monoplane, powered by two {{cvt|45|hp}} [[British Salmson AD.9]] engines; one built.<ref name=JAWA1931>{{cite book |title=Jane's all the World's Aircraft 1931 |editor1-last=Grey |editor1-first=C.G. |year=1931 |publisher=Sampson Low, Marston & company, ltd |location=London, UK |pages=35c–36c}}</ref>
;Monospar ST-4
:Cantilever touring monoplane, powered by two {{cvt|85|hp}} [[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.
[[File:General Aircraft Monospar c. 1935 SLNSW.jpg|thumb|GAL Monospar ST-11 (VH-USN) with pilots Collins and Wylie, after flight from UK to Australia, February 1935]]
;Monospar ST-10
:Improved variant with two {{cvt|90|hp}} [[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 Croydon|General Aircraft ST-18 Croydon]]
:Ten-seat transport with two [[Pratt and Whitney Wasp Junior]] engines, one built.
;[[Monospar ST-25|Monospar ST-25 series]]
:Development of Monospar ST-10

==Operators==
;{{POR}}
* [[Portuguese Navy]]
;{{flag|South Africa|1928}}
* [[South African Air Force]]
;{{flag|Spanish Republic|1928}}
* [[Spanish Republican Air Force]], 1936 from [[LAPE]]
;{{ESP}}
* [[Spanish Air Force]]
;{{TUR}}
* [[Turkish Air Force]]

===Civil operators===
;{{AUS}}
* [[Australian Transcontinental Airways]] (ATA), 1935–1936{{efn|ATA was a short-lived airline registered in [[Melbourne]] in 1935 by Harold Berryman, of [[Ballarat]], and four other directors. Its three aeroplanes did the mail run from [[Darwin, Northern Territory|Darwin]] to [[Adelaide]], Melbourne and [[Sydney]], until it ceased operations in 1936 owing to the impossibility of importing more planes from Germany at that time.<ref>{{cite web |title=Major Harold John Thomas Berryman |first=Amanda |last=Bentley |publisher=Ballarat & District in the Great War |date=10 September 2019 |url=https://greatwarballarat.wordpress.com/2019/09/10/major-harold-john-thomas-berryman/ |access-date=31 October 2022}}</ref>}}
;{{BRA}}
* [[VASP]], 1933–1938
;{{UK}}
* [[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,<ref name=baa>{{cite web |title=Woodgreen Station |publisher=Bureau of Aircraft Accidents Archives  |url=https://www.baaa-acro.com/city/woodgreen-station |access-date=31 October 2022}}</ref> 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]].{{efn|One later report says the destination was [[Melbourne Zoo]].<ref name=baa/>}} Renfrey walked for two days towards [[Ryan Well Historical Reserve|Ryan's Well]], a watering hole on the [[Overland Telegraph Line]] around {{cvt|40|mi}}, to seek assistance. Three men (one of several search parties sent out to look for the men<ref>{{cite news |url=http://nla.gov.au/nla.news-article61097674 |title=Mishap to Monospar 'plane |newspaper=[[Western Argus]] |volume=41 |issue=2361 |location=Western Australia |date=17 September 1935 |accessdate=31 October 2022 |page=2 |via=National Library of Australia}}</ref>) motoring across the desert found him, and took him to [[Anmatjere, Northern Territory|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.<ref name=macleay>{{cite news |url=http://nla.gov.au/nla.news-article173225376 |title=A Monospar down. |newspaper=[[The Macleay Chronicle]] |issue=2951 |location=New South Wales, Australia |date=11 September 1935 |access-date=31 October 2022 |page=4 |via=National Library of Australia}}</ref>

==Surviving aircraft==
* One Monospar ST-12 (registration VH-UTH) is on display at the [[Newark Air Museum]], [[England]]

==Specifications (Monospar ST-12)==
[[File:Monospar 3 view L'Aerophile January 1933.png|thumb|Monospar ST-10 3 view from l'Aerophile magazine, January 1933]]
{{Aircraft specs
|ref=''The Illustrated Encyclopedia of Aircraft'',<ref>''The Illustrated Encyclopedia of Aircraft'' 1985, p. 1938.</ref> ''[[National Advisory Committee for Aeronautics]]''<ref name = "naca 710">NACA 1930, pp. 7-10.</ref>
|prime units?= imp
|capacity= four
|length m= 8.03
|length ft= 26
|length in= 4
|span m= 12.24
|span ft= 40
|span in= 2
|height m= 2.30
|height ft= 7
|height in= 10
|wing area sqm= 20.16
|wing area sqft= 217
|empty weight kg= 835
|empty weight lb= 1,840
|gross weight kg= 1,304
|gross weight lb= 2,875
|eng1 number= 2
|eng1 name= [[de Havilland Gipsy Major]] four-cylinder inverted inline piston engine
|eng1 kw=<!-- prop engines --> 97
|eng1 hp=<!-- prop engines --> 130
|max speed kmh= 254
|max speed mph= 158
|range km= 660
|range miles= 410
|ceiling m= 6,400
|ceiling ft= 21,000
}}

==See also==
{{aircontent
|see also=
* [[General Aircraft ST-18 Croydon]]
|related=<!-- related developments -->
|sequence=
|similar aircraft=<!-- similar or comparable aircraft -->
|lists=<!-- related lists -->
* [[List of Interwar military aircraft]]
* [[List of aircraft of the Spanish Republican Air Force]]
}}

==Footnotes==
{{notelist}}

==References==
{{commons category|General Aircraft Monospar}}

===Citations===
{{reflist}}

===Bibliography===
{{refbegin}}
* ''The Illustrated Encyclopedia of Aircraft'' (Part Work 1982–1985). Orbis Publishing, 1985, p.&nbsp;2158.
* Jackson, A.J. 1973. ''British Civil Aircraft since 1919, Volume 2''. Putnam {{ISBN|0-370-10010-7}}.
* Lewis, Peter. 1971. ''British Racing and Record-Breaking Aircraft''. Putnam {{ISBN|0-370-00067-6}}.
* Ord-Hume, Arthur W. J. G. (2013) ''The Monospar, from tailless gliders to vast transport: the story of General Aircraft Ltd of Hanworth''. Catrine, Ayrshire: Stenlake Publishing. {{ISBN|9781840336368}} 
* Sherwood, Tim. 1999. ''Coming in to Land: A Short History of Hounslow, Hanworth and Heston Aerodromes 1911–1946''. [http://www.hounslowlibraries.org Heritage Publications (Hounslow Library)] {{ISBN|1-899144-30-7}}.
* Stroud, John. ''Wings of Peace'', Aeroplane Monthly, April 1988.
* [https://ntrs.nasa.gov/citations/19930090449 "The Mono-Spar light airplane (British) : a twin-engined low-wing cabin monoplane"] ''[[National Advisory Committee for Aeronautics]]'', 1 July 1931. NACA-AC-148, 93R19739.
{{refend}}

<!-- ==External links== -->

{{GAL aircraft}}

[[Category:1930s British civil utility aircraft]]
[[Category:General Aircraft Limited aircraft|Monospar]]
[[Category:Low-wing aircraft]]
[[Category:Aircraft first flown in 1932]]
[[Category:Twin piston-engined tractor aircraft]]