World War I: The Push for Performance

Workers manufacturing aircraft propellers for biplanes, July 1916. 

Photo Hampton & Sons Ltd, Lambeth, London

Aircraft design has never been an exact science. Even today, it is a process that blends proven scientific principles with engineering intuition, the performance requirements of the aircraft, as well as a dash of inventiveness and daring. During World War I, aircraft design was more inventive, intuitive and daring than ever.

 At the outbreak of the war in 1914, all the major powers saw the military potential for aircraft. Committing men and resources to realizing that potential took what had been the domain of mechanically inclined tinkerers and backyard inventors to create the beginnings of an aircraft industry. Still with the basic principles of aeronautics still a mystery, aircraft design consisted more of guesswork than engineering. Prototypes were frequently constructed from full-size chalk drawings laid out on the factory floor. Structural design was haphazard, and stress analysis did not become a standard part of the design process until midway through the war. While government laboratories such as Great Britain’s Royal Aeronautical Establishment would contribute greatly to the understanding of aeronautical engineering, it would take years for such knowledge to have an impact on aircraft design.

Nearly all planes of the period consisted a wooden framework braced with wire and covered externally with cloth, which was “doped” with glue to stretch it tight and to provide weatherproofing. Most wings were supported externally by a combination of wires and struts, although a few designers developed aircraft with internally braced cantilever wings. Some aircraft employed a mixture of metal and wood in their construction, but state of the art would not advance to the point to make an all-metal aircraft practical until after the war.

Literally hundreds of types of planes were built and flown from 1914-18, using an amazing variety of configurations, powerplants and control systems—from monoplanes to biplanes to triplanes, and even a few quadruplanes; from pusher-type planes with the engines mounted in the rear to forward, tractor-type installations. Some planes were powered with stationary, water-cooled engines. Others had rotary, radial-powered engines. A few planes used forward canard-style elevators, some used flexible, wing-warping to control lateral movement, while most consisted of the now-conventional wing ailerons with a vertical and horizontal tail assembly. While competition between the warring powers produced rapid advances in technology, the emphasis on greater performance—faster, higher, more maneuverable, greater payloads—meant factors such as flight handling, reliability and ease of use were often secondary considerations, at best.

            Even the most successful planes were often dangerously idiosyncratic to fly. Take the Eindecker, Anthony Fokker’s revolutionary fighter. Introduced in 1915, the monoplane was the first aircraft outfitted with a synchronized machine gun that could fire through a propeller arc, and was so successful for the Germans that the Allies called the plane the “Fokker Scourge.” The plane was powered with a 100 horsepower rotary engine and had a top speed of around 87 miles per hour. The plane was controlled through “wing-warping”, in which cables attached to a control stick physically changed the shape of the airfoil to force the plane into a turning bank. The vertical and horizontal tail units consisted of one-piece free-floating unit.

Fokker Eindecker, 1915. The first aircraft to have a synchronized machine-gun mounted behind the propeller.                                                  Photo from the Peter M Grosz collection

            In his 1973 book, Flying the Old Planes, the late Frank Tallman wrote of his experience flying a replica of an Eindecker. Tallman wrote that he had to constantly fight for control of the plane: “the major flight characteristic ever present is the feeling that if you took your hands off the stick or your feet off of the rudders, the Eindecker would turn itself inside out or literally swap ends.”

            Or, for example, the legendary Sopwith Camel, the most successful Allied plane of the war, with a total of 1,294 enemy aircraft downed from when it first entered operation in July 1917 to the end of the war in November 1918. Though the plane’s performance was only middling in terms of top-speed and altitude, the light-weight Camel was superbly maneuverable, particularly in the hands of a skilled pilot. But the plane was also tricky and unforgiving to fly.

The Sopwith Camel: Beloved but treacherous.

            The Camel was powered by a rotary engine, generally of 130 hp. The rotary engine had cylinders arranged radially around a crankshaft, but unlike the modern radial engine in which the fixed engine turns the crankshaft and propeller, a rotary engine turns with the crankshaft and propeller. The advantage of the rotary engine over stationary, water-cooled engines of the period is that they were lighter and usually more reliable, with the engine rotation cooling the cylinders. But the torque and gyroscopic forces caused by the spinning engine also affected the plane’s handling characteristics.

             In the case of the Camel, the plane’s heavy rotating engine gave the plane an incredibly fast turning capability (with a tendency to pull to the left), but it also made it difficult to handle. The gyroscopic action of the engine also caused a nose-up moment in a left turn and a nose-down moment in a right turn. To make a steep left bank, the pilot needed to apply left stick, left rudder and forward stick. To make a steep bank to the right, the pilot need to apply right stick, some left rudder and back stick to hold it up—but too much back stick caused the aircraft to stall and spin. Any confusion on these control movements could prove fatal, and often did in the case of inexperienced or student pilots. No wonder, the Camel has been called the most loved and the most hated aircraft of World War I: loved by those who mastered it and exploited its peculiarities; hated by those who did not. 



Video of pilot describing how to fly a Sopwith Pup with a 80hp Le Rhone rotary engine.

Courtesy San Diego Air & Space Museum