M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)
Deleted by request of (c)Schiffer Publishing
SOPWITH tractor biplane 'The Sigrist Bus'
An entry on 7 December 1914, in the Order Book, authorized a 80hp two-seater tractor to Mr. Sigrist's instructions, to be built for stock. The machine was built by the Experimental Dept in the Rink at Kingston incorporating Fred Sigrist's ideas to aid production, as well as advancing performance. Sigrist was basically responsible for the Works, but was sufficiently powerful to influence design, backed by Hawker's experience and with Sopwith's approval.
The Type 807 Folder, itself derived from the 'Circuit' and 'Spinning Jenny' biplanes, was the basis for the new aircraft. The fuselage displayed little difference, but it was to the wing structure and tail unit that changes were made.
The top wing was built in halves, meeting on the aircraft centerline and was rigged with dihedral. The mounting was by two sets of W-form struts, the outer arms of which were widely splayed to support the wing well outboard, and enabling the use of a single bay. Ailerons were fitted to all wings, with the control cables running externally across the span of the lower wing, which was slightly shorter than the upper wing. To help to overcome the spinning problem of the earlier type a taller fin and rudder, of greater area, were fitted. The configuration of the top wing support structure was used in the very successful 1 1/2 strutter.
The aircraft was flown at Brooklands for the first time on 5 June 1915 and the following day Hawker flew it to Hendon in thirteen minutes and then proceeded to set a British Altitude Record, by flying to a height in excess of the recorded 20,000ft, although this was later adjusted down to 18,293 ft due to the inaccuracy of the barograph.
Power: 80hp Gnome Monosoupape nine-cylinder air-cooled rotary, Lang propeller.
Data (From unnumbered drawing by R.J. Ashfield countersigned H. Smith 15 December 14)
Span top 31ft 6in
Span bottom 29ft 9 3/4in
Chord 5ft 2in
Area 298 sq. ft inc. ailerons
Area fin 4.4 sq. ft
Area tailplane 25 sq. ft
Area rudder 8 sq. ft
Area ailerons 10.2 sq. ft each
Area elevators 16 sq. ft
Length 25ft 6in
Height 9ft 9in
Dihedral top 7 deg bottom 2 deg
Weight 920 lb.
Weight allup 1,5801b.
H.King Sopwith Aircraft 1912-1920 (Putnam)
With his usual professional touch Harald Penrose thus summarised the salient facts: 'At Kingston, Tom Sopwith's great factotum, the dour determined Fred Sigrist, as a result of discussion with Hawker on the possible form of a replacement two-seater with enhanced performance and safer characteristics, modelled a new fuselage on the 807 [see 'Folder Seaplane'] using a bigger fin having a rounded nose of bent tube, and stiffened the main wing spars in order to employ a single bay with outward-raking struts, shortening the lower wing proportionately [N.B. The 'Sigrist Bus', unlike the 'definitive' 1 1/2 Strutter, had wings of unequal span]. To reduce bending moments of the upper wing he used steel centre-section struts steeply sloping from the top longeron to a point well out in the spar bay, and then braced the centre-line juncture of port and starboard spars within inverted V-struts arranged like a trestle, resulting in a widespread transverse W. The machine had been growing slowly in a corner of the old Kingston Skating Rink, for Sigrist was preoccupied with production matters, and it would be another month or more before the framework was ready for covering. Meanwhile it was jocularly referred to by the workmen as 'Sigrist's Bus’.
J.Bruce British Aeroplanes 1914-1918 (Putnam)
Sopwith Two-seat Biplane (The “Sigrist Bus"’)
KNOWN in the Sopwith company’s shops as the “Sigrist Bus”, after its designer, F. Sigrist, this biplane was built in 1915. It bore a certain resemblance to the Tabloid, for its 80 h.p. Gnome engine had a bull-nose form of cowling over a fore-and-aft mounting; and the provision of head fairings in front of, between and behind the cockpits recalled the similar fittings on the seaplane Type 807 and on the Spinning Jenny.
The wings of the Sigrist Bus were of unequal span, and the interplane struts had a slight outwards rake. But of the greatest interest and significance was the bracing of the upper wings at their centre point: there was no centre-section, and the two halves of the upper wing were supported by a trestle-shaped cabane structure, whilst additional support was provided by two further struts on each side which ran from the upper longerons to the main spars of the upper wing. The resulting structure resembled a letter W when seen in end elevation, and was to earn a later Sopwith biplane the curious name of “1 1/2-Strutter”.
The Sigrist Bus was a considerable time building, for Sopwith endeavours were concentrated on the Schneider seaplane scout, but the machine was flown in the early summer of 1915. Many experiments were made in attempts to vary the position of the aircraft’s centre of gravity: these included the fitting of a central skid-like projection to the undercarriage with a container holding several pounds of lead.
In June, 1915, Harry Hawker set up a new British altitude record when he flew the Sigrist Bus to a height of 18,393 feet.
The machine played no active part in the war, but is of historical interest as the precursor of the famous Sopwith 1 1/2-Strutter.
