Sopwiths had been working at full capacity since 1914 with the Tabloid and its successors the Schneider and Baby, but these aircraft were scouts, not fighter planes. You could say that the Tabloid had been a failure because, despite its early success as the Schneider Trophy winner, it was never developed into a weapons platform, and by late 1914 there wasn't a single Sopwith aircraft on the Western Front. In early 1915 Sigrist, Sopwith's chief designer, had saved the company by producing the 11/2 Strutter as a fighter and bomber, but there was still an urgent requirement for a single-seat fighter.
In late 1915 legend
has it that Hawker (the Chief Test Pilot), Sigrist and Sopwith
chalked out, on the floor of the Sopwith Experimental Works, a
single-seater to be powered by a 50 hp Gnome radial engine. When
built, this became "Hawker's Runabout" or the SLTBP
(Sopwith Land Tractor Biplane, pictured above) and became the
development airframe for the Pup, having the same dimensions and
general arrangement. By early February 1916 the prototype Pup
was flying, so the SLTBP has an important but generally unacknowledged
place in the history of fighter aircraft.
Despite the success of the Pup, working drawings were prepared in late 1916 for four more "Small Scouts" to the SLTBP design. These were called the Sparrow and were produced with the same 50hp Gnome power plant in mind. They were not well documented and nothing seems to be known of their use during the War, but one was modified to take the ABC Gnat 35 hp horizontally-opposed twin cylinder engine and another, still with a Gnome engine, was still flying in 1925. One was apparently converted to a 2-seater with ailerons on its lower wing. Serial numbers A8970-8973 were allocated but there is no evidence of their being marked on the aircraft: in fact they were not recommended for purchase by the RFC, being "very old machines" in 1917.
Sopwith was also involved in work on a radio controlled drone in 1916 and it seems likely that one of the Sparrows was cannibalised to make this airframe, which was built by apprentices and fitted with a Gnat engine (and also called the Sparrow!). The AT (Aerial Target) project was unsuccessful and perhaps the Gnat engine was used to power one of the other Sparrow Scouts on an experimental basis.
Finally, a Sparrow was built in Australia between June and November 1916, by Basil Watson, an ex-Sopwith assistant test pilot, who flew it regularly until in March 1917 a wing folded during an aerobatic display and he was killed.
It is extraordinary (but not unusual for Sopwiths) that such an undistinguished little aircraft could have produced so many variations. I am drawing plans of all of them for a future article, although the details of the AT Sparrow are somewhat sketchy. In the one photograph I have found it seems to have PC10 upper wings and fuselage, which is why I believe it may have been made from one of the Sparrows, which were painted to match a 1916 operational aircraft. However it is that rarest of model aircraft, the one that can properly flown without a model pilot. The plan of the 2-seater will just be conjecture: it must have been a very marginal aeroplane!
Building the Models
Both are Pink Foam lightweights sprayed with car body or Tamiya
acrylics, designed for flying in calm conditions or indoors, using
the Pico Stick GWS hardware. The SLTBP is 29" span (1:11)
and the Sparrow 31" (1:10), weighing in at 7 oz and 8 oz
respectively. The former flew at Waltham Chase and Calshot last
year and is now looking very tired, but the Sparrow has been up
and about early in the calm sunny mornings and flies well. I was
a bit disappointed with its weight, so have been experimenting
with carbon fibre spars and good old 1/16" square balsa.
The next Sopwith will be 23" span and weigh about 4 oz, with
a couple of Lithium cells and a Falcon motor. Now that really
is a lightweight!