Sopwith Camel


The company directors and designers: Thomas Octave Sopwith, Fred Sigrist and Harry Hawker, soon saw that they would not benefit much from redesigning the Pup, so an entirely new aircraft needed to be built. The designers were to some degree influenced by the Triplane construction, especially in terms of its excellent maneuverability due to the low wing loading resulting from the concentration of the most of aircraft’s weight (i.e. engine, weapons, pilot and fuel tanks) near the gravity center. Applying this principle to a biplane wasn’t easy, but the resulting design came close to specification despite some predictable minor flaws. Herbert Smith and R. J. Ashfield, who then worked for the company, were responsible for taking care of the details of the design.
Today’s designers may be surprised, but at that time Sopwith as well its main competitor Fokker did not have any drawing boards for its designers. Prototype details were simply chalked on the floor. Manufacturing was done according to these drawings without any structural tests. Instead, the great experience of the whole team successfully worked instead of such tests.
Real detailed blueprints for mass production were prepared later. But these were also done the simplest way, without even the aid of drawing boards.

Sopwith F.I Camel, scale 1/24  [Drawings by Maciej Noszczak]

 

History of power plant
All inventions pass the stage when only their good side is to be seen. Later, time shows their flaws and imperfections. This was the case with aircraft rotary engines. Today rather no one writes poems about aircraft engines, attaching to them romantic features. But it was a fact that the rotary was at that time the hope of aviation and inspiration for engineers.
A rotary three-cylinder steam engine had been used by Hargrave in his aircraft model of 1889. Other concepts, of petrol-fueled rotaries, came in early 20th century in works by Marquis de Dion in France or Stephen Balzer in America (for Langley’s Aerodrome aircraft). The rotary engine was quite early tested on road vehicles (e.g. Adams-Farwell car engine of 1904). Eventually its aviation version was designed in 1908 by the Seguin brothers
(Laurent and Louis) as a development of 1900’s Oberursel Motoren Gesellschaft licensed small stationary engine. The result was a bigger unit of 5 air-cooled cylinders. Its 34 hp were initially to propel a fast motor boat via transmission gear.
It was named “Gnome” (dwarf) and was also stationary. Cooling deficiencies were soon discovered and in trying to find better cooling conditions a 7-cylinder rotary was developed, in which the bank of cylinders spinned with the propeller, while the shaft remained stationary. For those times the construction was perfect. It had a small weight of 75 kg, was rated at 50 hp (thus the name Gnome Fifty) at 1,200 rpm, and it easily fitted to an airplane.
It should be noted that most internal combustion engines were car-type – water-cooled, big and heavy. These features and their constant tendency to get overheated made them irrelevant for aircraft. There were air-cooled static aircraft engines at the time (e.g. By the famous V. Anzani company) but their cooling was insufficient for little knowledge of combustion physics and low-octane value of fuel at the time; they were not very reliable. Therefore various types of rotary engines soon dominated in aircraft, as the rotation of the bank of cylinders (20-25 rpm) seemed to promise no “undercooling”.
Soon aircraft began to be fitted with series-produced engines of the type. In 1909 the Gnome of 34 hp was the best known, weighing 55.5 kg, which gave an excellent index of 1.63 kg/hp. The power soon increased, first to 50 hp, then 60, and finally 80 – the 80-hp unit was the one to become “mobilized”. It turned out, however that a four-stroke rotary had a bad side coming along with the good one. The fact of its being driven by a hollow stationary camshaft which was at the same time the fixing point was a hard issue. The big rotating mass and problems with balancing it effected great centrifugal forces partly out of symmetry. These forces spoilt the reliability of the timing gear and fuel-feeding. In extreme cases cylinders would break off, which usually resulted in a crash. Therefore power could not be higher than approx. 200 hp, for that would have meant a greater cylinder capacity, which would have entailed a greater weight (and centrifugal forces).
The heavy bank of cylinders being settled on the camshaft was often the cause of engines breaking off due to shaft cracks, especially at those times of inconsistent quality wartime production. This was addressed by using light alloys for cylinder construction, but even then the loss of weight was not significant. Also, those engines usually worked at full throttle only, as they were controlled by ignition, which was hard to handle and unreliable, and not by dosing fuel.

Fuselage structure. [Kagero archive]