M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)
Deleted by request of (c)Schiffer Publishing
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.