By 1917 trial and error during the first World War had established the wire braced biplane with aft-tailed surfaces as the normal configuration. Diagonal brace wires between the wing struts and fuselage and within the wing frames made a torsionally rigid structure that resisted twisting and instability failure in high-speed dives. The heavy engine in front and the generous tail surfaces behind tended to keep the fuselage and wings aligned with the velocity of flight. The pilot could apply roll control by aileron deflection, yaw control by rudder deflection, and pitch control by elevator deflection – all independently. Aerodynamic hinge moments tended to center the controls. By ground adjustment of wing, fin, and tailplane rigging the airplane could be made to maintain level flight with cruising power in calm air for a minute or so.
Violent maneuvering in combat was provided mainly by the elevator, which had sufficient authority to bring the airplane to a full stall. Horizontal turning flight required rolling the airplane about its longitudinal axis quickly, which was most often accomplished by combined rudder and aileron deflection. The rudder-induced sideslip produced an unsymmetric stall and a snap or flick roll that could be checked at the desired angle by relieving stick back pressure and centering the rudder and ailerons.
The ailerons were difficult to deflect at combat speeds but could be used to produce a slow or barrel roll. An important use of the ailerons was to produce a cross-controlled (e. g., right rudder and left stick) nonrolling sideslip for glide path control while landing. The glide angle could be steepened appreciably by sideslipping in a steep bank, incidentally giving the pilot a good view of the touchdown point.
A dangerous aspect of stability and control of the otherwise benign World War I airplanes was inadvertent stalling and spinning at low altitudes, the so-called arrival and departure stalls (and spins). Moderate sideslip at stall would provoke a snap roll, which rapidly developed into the dreaded tail spin, or spinning nose dive. Generally there was insufficient room for recovery before ground contact.
Arrival stalls are still produced in modern airplanes by attempting to rudder the airplane around to the proper heading on final approach at a low speed without banking. The inner wing stalls and drops. The pilot attempts to pick it up with aileron deflection, which aggravates the situation. The airplane stalls and spins into the intended turn. The pilot who survives complains that the ailerons did not work.
Departure stalls are more spectacular. The pilot takes off from a small field. As the obstacles at the end of the field get near, with the engine at full power, the pilot rolls with the ailerons to a steep bank angle and turns away. The airplane has insufficient power to climb in steeply turning flight, so the pilot applies top rudder to hold up the nose. The resulting sideslip stalls the top wing, and the airplane performs an over-the-top snap roll and spin entry, followed by a fiery crash at full power.
Because of the stall-spin propensity of World War I airplanes, student pilots were given flight instruction on spin entry and recovery in airplanes with generally docile behavior. However, some airplanes, notably the Sopwith Camel, killed many student pilots because of its particularly vicious stalling characteristics. The Camel’s main fuel tank was behind the pilot, and the fully loaded center of gravity was so far aft that the airplane was unstable in pitch just after takeoff. Constant pilot attention was required to keep it from stalling.
Not only that, but, like many other World War I airplanes, the Camel’s vertical tail was too small. Any stall automatically became a snap roll spin entry, even without intentional rudder deflection. Finally, once spinning, the Camel required vigorous rudder deflection against the spin to stop the motion. A well-behaved airplane, on the other hand, has to be held in a spin; letting the controls go free should result in automatic recovery. Directional instability was so common among World War I airplanes that the Royal Air Force (R. A.F.) resisted closed cockpits for years so that pilots could use wind on one cheek as a sideslip cue.
Another dangerous feature of World War I airplanes was the gyroscopic effect of rotary engines. According to Gibson (2000), engine gyroscopic effect in the Sopwith Camel required left rudder for both left and right turns and caused a departure if full power was used over the top of a loop at too low an airspeed. Pilots were warned to attempt their first hard right turns only above 1,000 feet.