Friday, July 31, 2009

Interwar period (1919-1938)

Fighter development slowed between the wars, with the most significant change coming late in the period, when the classic WWI type machines started to give way to metal monocoque or semi-monocoque monoplanes, with cantilever wing structures. Given limited defense budgets, air forces tended to be conservative in their aircraft purchases, and biplanes remained popular with pilots because of their agility. Designs such as the Gloster Gladiator, Fiat CR.42, and Polikarpov I-15 were common even in the late 1930s, and many were still in service as late as 1942. Up until the mid-1930s, the vast majority of fighter aircraft remained fabric-covered biplanes.

An early monoplane fighter: the Boeing P-26 Peashooter which first flew in 1932

Fighter armament eventually began to be mounted inside the wings, outside the arc of the propeller, though most designs retained two synchronized machine-guns above the engine (which were considered more accurate). Rifle-caliber guns were the norm, with .50 caliber (12.7 mm) machine guns and 20 mm cannons deemed "overkill." Considering that many aircraft were constructed similarly to WWI designs (albeit with aluminum frames), it was not considered unreasonable to use WWI-style armament to counter them. There was insufficient aerial combat during most of the period to disprove this notion.

The rotary engine, popular during WWI, quickly disappeared, replaced chiefly by the stationary radial engine. Aircraft engines increased in power several-fold over the period, going from a typical 180 hp (130 kW) in the 1918 Fokker D.VII to 900 hp (670 kW) in the 1938 Curtiss P-36. The debate between the sleek in-line engines versus the more reliable radial models continued, with naval air forces preferring the radial engines, and land-based forces often choosing in-line units. Radial designs did not require a separate (and vulnerable) cooling system, but had increased drag. In-line engines often had a better power-to-weight ratio, but there were radial engines that kept working even after having suffered significant battle damage.

Messerschmitt Bf 110 Zerstörer "heavy fighter"

Some air forces experimented with "heavy fighters" (called "destroyers" by the Germans). These were larger, usually two-engined aircraft, sometimes adaptations of light or medium bomber types. Such designs typically had greater internal fuel capacity (thus longer range) and heavier armament than their single-engine counterparts. In combat, they proved ungainly and vulnerable to more nimble single-engine fighters.

The primary driver of fighter innovation, right up to the period of rapid rearmament in the late thirties, were not military budgets, but civilian aircraft races. Aircraft designed for these races pioneered innovations like streamlining and more powerful engines that would find their way into the fighters of World War II.

At the very end of the inter-war period came the Spanish Civil War. This was just the opportunity the German Luftwaffe, Italian Regia Aeronautica, and the Soviet Union's Red Air Force needed to test their latest aircraft designs. Each party sent several aircraft to back their side in the conflict. In the dogfights over Spain, the latest Messerschmitt fighters (Bf 109) did well, as did the Soviet Polikarpov I-16. The German design, however, had considerable room for development and the lessons learned in Spain led to greatly improved models in World War II. The Russians, whose side lost in the conflict, nonetheless determined that their planes were sufficient for their immediate needs. I-16s were later slaughtered en masse by these improved German models in World War II, although they remained the most common Soviet front-line fighter until well into 1942. For their part, the Italians were satisfied with the performance of their Fiat CR.42 biplanes, and being short on funds, continued with this design even though it was obsolescent.

The Spanish Civil War also provided an opportunity for updating fighter tactics. One of the innovations to result from the aerial warfare experience this conflict provided was the development of the "finger-four" formation by the German pilot Werner Mölders. Each fighter squadron (German: Staffel) was divided into several flights (Schwärme) of four aircraft. Each Schwarm was divided into two Rotten which was a pair of aircraft. Each Rotte was composed of a leader and a wingman. This flexible formation allowed the pilots to maintain greater situational awareness, and the two Rotten could split up at any time and attack on their own. The finger-four would become widely adopted as the fundamental tactical formation over the course of World War II.

[edit] Notable aircraft of the interwar period


No comments: