ST.1 - Monospar test wing (for British Air Ministry)
ST.2 - Monospar wing for Fokker F.VII 3m (for Air Ministry)
ST.3 - Three-seat enclosed cabin monoplane, 2 x 45 hp Salmsons (aka Gloster S.S.1).
ST.4 - Monospar cabin twin, 2 x 85hp Pobjoy R.
ST.5 - Monospar wing built under subcontract (for "Spartan monoplane"))
ST.6 - Retractable undercarriage version of ST.4.
ST.7 - Monospar wing built under subcontract (for Saro Cloud))
ST.8 - (Monospar wing, test flown on Caproni Ca 97, delivered in 1933).
ST.9 - [project] wing ordered for Italian Romeo Ro.35 sailplane. Designed but not built.
--
http://www.secretprojects.co.uk/forum/index.php/topic,18738.msg211881.html#msg211881
ST.10 - Improved ST.4 variant, 2 x 100hp Pobjoy Niagara.
ST.11 - Retractable undercarriage version of ST-10.
ST.12 - ST.10 variant with 2 x DH Gipsy Major
ST.13 - [not used - jumped to ST.25 to celebrate Silver Jubilee of King George V]
ST.14 - [not used]
ST.15 - [not used]
ST.16 - [not used]
ST.17 - [project]
ST.18 - Croydon, 10-seat light transport, 2 x 450hp P&W SB-9 Wasp Junior.
ST.19 - [not used]
ST.20 - [not used]
ST.21 - [not used]
ST.22 - [not used]
ST.23 - [not used - 'GAL 23a' / 'GAL 23b' probably typos for GAL.32a / 32b/ to Spec T1/37.]
ST.24 - [not used] (Note "GAL 24 Cygnet" is a typo for GAL 42 Cygnet II)
ST.25 - Monospar ST.25 Jubilee, De Luxe, and Universal, 2 x Pobjoy.
GAL 26 - ST.25 development, 4/5 seat light transport, 2 x Cirrus Minor I engines.
GAL 27 - [project] twin-engined, high/mid-wing transport, 2 x Menasco B6-S or DH Gipsy pushers.
GAL 28 - [project] single-seat fighter for Spec. F35/35, 1 x Hercules, variable area wings.
GAL 29 - [project] four-engined, high-wing, 12 seat transport aircraft. (GAL 29A 4 x AS Cheetah X, GAL 29B 4 x Menasco B6-S, GAL 29C 2 x Bristol Pegasus XC)
GAL 30 - 5/8 seat transport, 2 x De Havilland Gipsy Six II engines.
GAL 31 - [project] high-wing monoplane freighter, 1 x 300 hp Wasp Junior engine.
GAL 32 - two-seat trainer for Specification T1/37, 1 x 205 hp DH Gipsy Six II engine.
GAL 33 - Cagnet, twin-boom trainer/F.O.P aircraft, 1 x 90hp Cirrus Minor engine.
GAL 34 - [project] high-wing, 14 seat transport with retractable u/c.
GAL 34A was twin-engined, GA -34B was four-engined aircraft.
GAL 35 -[project] radio-controlled target seaplane, mid-wing monoplane with single float and pylon mounted engine, for Specification Q8/37 (Queen Bee replacement).
http://www.secretprojects.co.uk/forum/index.php/topic,3655.0/
GAL 36 - [project] communications aircraft, 2 x 280 hp Gipsy Six II, to Spec. T7/37.
GAL 37 - [project] twin engined transport, 2 x 600 hp Jacobs L.5 engines.
GAL 38 - Fleet Shadower, 4 x 130hp Pobjoy Niagara IIIs.
GAL 39 - [project] carrier-borne general purpose aircraft, 2 x 1000 hp Aquila, to Spec. S30/37. GAL-39A (50' span) and GAL-39B (44' 9" span).
GAL 40 - [project] four-engined, pressurized transport with tricycle u/c. GAL-40a 4 x RR Merlins (4200 hp), GAL-40b or 4 x Bristol Hercules (4700 hp). To Spec. 15/38. (along with Fairey F.C.1).
GAL 41 - research aircraft (first British aeroplane to fly with pressurized cabin), based on Monospar ST-25 Universal, 2 x 95hp Pobjoy Niagara IIIs.
GAL 42 - Cygnet (Cygnet II, nose-gear variant), 1 x 150hp Cirrus Major II.
GAL 43 - [project] engine test-bed aircraft for Spec. 43/37. GAL 43A (Centarus) and GAL 43B (Sabre). [Won by Folland Fo.108 'Frightful']
GAL-44 - [project] transport, 2 x 890 hp Alvis Leonides Major.
GAL 45 - Owlet (DP420), open-cockpit Cygnet II training variant, 1 x 150hp Cirrus Major I.
GAL-46 - [project] single-seat high-altitude pressurized fighter, for Specification F4/40.
GAL 47 - Flying Observations Post (FOP), twin-boom pusher, 1 x 90hp Cirrus Minor.
GAL 48 - Hotspur glider, GAL 48B was Twin Hotspur glider prototype (MP486).
GAL 49 - Hamilcar Mk I heavy tank-carrying glider, to Specification X.27/40.
GAL 50 - half-scale flying model of GAL 49 Hamilcar transport glider.
GAL 51 - synthetic day landing trainer to give landing and take-off training, one built
GAL 52 - wing-fold design for the Supermarine Seafire
GAL 53 - [project] single-seat naval jet fighter, 4 x 20 mm cannons in nose.
GAL 54 - [project] light transport glider (led to GAL 55 glider trainer). GAL 54 designation may have been re-used for an auto-trimmer device design.
GAL 55 - side-by-side seating, two-seat, mid-wing training glider to Specification TX3/43.
GAL 56 - tailless research glider (3 a/c, three different planforms.
http://www.flightglobal.com/pdfarchive/view/1948/1948%20-%200018.html?search=tailless+glider
http://www.secretprojects.co.uk/forum/index.php/topic,4498.0/
GAL 57 - [project] powered variant of GAL 56 glider.
GAL 58 - Hamilcar Mk.X tank-carrying heavy glider (assited by 2 x Bristol Mercury)
GAL 59 - naval target tug/plotter aircraft, modified DH Mosquito for Specification Q19/45.
GAL 60 - Universal Freighter Mk I (led to GAL 65/Blackburn B-100 Beverly), 4 x Bristol Hercules.
GAL 61 - Research glider (4th GAL 56 with retractable u/c and endplate fins eliminated).
GAL 62 - [?]
GAL 63 - aka Handley Page HP.88 (contracted out to GAL)
GAL 64 - [?]
GAL 65 - Universal Mk II (GAL 60 development, B-100 Beverly prototype), 4 x Bristol Centaurus
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Also: GAL's unnumbered (?) 'New Medium Glider' Horsa replacement concept http://www.secretprojects.co.uk/forum/index.php/topic,3564.45.html
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Sources (via Lark)
"General Aircraft Ltd.: Potted History - IV", The Aeroplane Spotter, 26 June 1948
"In General Terms: Pictorial History of the UK's General Aircraft" by Daniel Ford, Air Enthusiast, No.93 (May/June 2001)