Designed by Ernest Schweizer, the SGS 1-23 all-metal high performance single-seater was first flown at the 1948 US National Soaring Contest at Elmira, NY, and was based on the 1-21.
The 1-23 has mid-set single-spar cantilever wings and is of truly all-metal construction with flush riveting, there being no fabric covering at all; 75ST alloy was used in the spar ends and fuselage centre-section, and the remainder of the structure was of 24ST Alclad. In its initial form the 1 -23 had a wing span of 43ft 10in, and an aspect ratio of 12.88, and there were two sets of spoilers in the wing upper surfaces. The outside spoilers were double ones and could be locked in four positions, fully open as dive brakes or intermediately for the landing approach; the inner spoilers were single for glide control on the approach, and were coupled to the monowheel brake. There was a rubber-mounted skid forward of the non-retractable unsprung monowheel, and a small tail wheel.
The 1-23B & C were built for the 1952 World Championships held at Madrid Cuatro Vientos, Spain flown by Paul MacCready and Paul Schweizer. They both had the wing spars spliced and stretched to 15.24 m / 50 ft, and the C had thicker wing skins, a heavier spar and weighed 41 kg./ 90 lb more.
The SGS 1-23D production version of the B (Air Transport Certified), like the 1-23B and 1-23C featured a wing increased in span to 50ft 0in, with an aspect ratio of 15.58, for improved performance, and production of this version started in July 1953; the wing tips were now square-cut instead of pointed as on the 1-23, and the fin and rudder were slightly larger.
One flown by Paul MacCready won the 1953 Nationals, and another was flown 733 km / 455.5 miles by Joe Lincoln to earn the Barringer Trophy for 1960. An example belongs to the National Soaring Museum.
The single 1-23E was built for Paul MacCready to fly in the 1954 World Championships where it finished 4th. It has balanced airbrakes and originally no wheel, using the skid for takeoff and landing. The 1-23E had a wing span of 16.1 m / 52ft 9.5 in and a thicker wing skin. Paul Bikle won two world altitude records with the 1-23E (14.102 m / 46.267 ft absolute 12.894 m / 42.303 ft gain).
The one 1-23F built was an E which featured butt joints in the structure instead of lap joints. A larger fin and rudder with squared-off top distinguished the 1-23G (Air Transport Certified). The 1-23G was a 1954 production model with the longer wing of the E and F, standard spoilers and a larger vertical tail of slightly different shape.
One 1-23G was developed into the experimental 1-29, which was basically a 1-23G fitted with a new constant-chord laminar flow wing, the first Schweizer design to be so fitted; this was used to flight test new design features as well as for competition flying.
Final production versions, also with the larger vertical tail surfaces, were the 1-23H and 1-23H-15, the H, of which 8 were built, having a span of 52ft 8in and limiting speed DFS-type air brakes which replaced the double spoilers of earlier versions, as well as detachable wing tips enabling it to be converted to a Standard Class 15m span, in which form it was known as the 1-23H-15. The pilot sits over the leading edge under a blown one-piece sideways-opening Perspex canopy, and there is room behind him for a radio, barograph and oxygen equipment. The 1-23H and H-15 has a squared-off top to the fin and rudder. The more numerous H-15 version has a wingspan reduced to 15.0 m / 49.2 ft qualifying it for the FAI-OSTIC Standard Class. It was also produced with removable tips increasing the span to 16.1 m / 52.8 ft. 39 of this model were built.
On 30 December 1950, a 1-23 flown by William Ivans set a new World height record of 42,100ft above sea level at Bishop, California, gaining 30,100ft from his aero-tow release height, and on 25 February 1961 a 1-23E flown by Paul Bikle set the world height record of 46,266ft.
A total of 69 SGS l-23s of all versions have been produced.
One, which also belongs to the National Soaring Museum, was substantially modified by Sterling Starr by the fitting of a new NACA 65 (3)-618 section 16.5 m / 54 ft wing.
Wing span: 15 m / 49.2 ft
Wing area: 14.81 sq.m / 159.4 sq.ft
Aspect ratio: 15.12
Airfoil: NACA 43012A
Empty Weight: 213 kg / 470 lb
Payload: 127 kg / 280 lb
Gross Weight: 340 kg / 750 lb
Wing Load: 22.96 kg/sq.m / 4.7 lb/sq.ft
L/DMax: 29 80 kph / 43 kt / 50 mph
MinSink: 0.67 m/s / 2.2 fps / 1.30 kt
Seats: 1
No. Built: 74
SGS 1-23D
Wing span: 15.24 m / 50.0 ft
Length: 6.25 m / 20 ft 4 in
Height 1.52 m / 5 ft 0 in
Wing area 14.9 sq.m / 160 sq ft
Wing section: NACA 43012A/23009
Aspect ratio: 15.6
Empty weight: 190 kg / 420 lb
Max weight 340 kg / 750 lb
Water ballast: None
Max wing loading: 22.8 kg/sq.m / 4.6 lb/sq ft
Max speed: 114 kt / 212 km/h
Stalling speed: 28 kt / 52 km/h
Min sinking speed at 30 kt / 55 km/h: 0.61 m/sec / 1.86 ft/sec
Best glide ratio at 41.5 kt / 77 km/h: 30
SGS 1-23H
Span: 52 ft 8 in
Length: 20 ft 10 in
Wing area: 164.9 sq ft
Aspect ratio: 16.9
Empty weight: 480 lb
Max weight: 750 lb
Max speed: 140 mph
Min sinking speed: 2.05 ft/sec at 37 mph
Best glide ratio: 30.8:1 at 50 mph
SGS 1-23H-15
Span: 49 ft2.5 in
Length: 20 ft 10 in
Wing area: 159.4 sq ft
Aspect ratio: 15.12
Empty weight: 474 lb
Max weight: 750 lb
Max speed: 140 mph
Min sinking speed: 2.15 ft/sec at 38 mph
Best glide ratio: 29.2:1 at 50 mph
All Aero 