Post-war aviation
The period between 1945 and 1979 is sometimes called the post-war era or the period of the post-war political consensus. During this period, aviation was dominated by the arrival of the Jet Age. In civil aviation the jet engine allowed a huge expansion of commercial air travel, while in military aviation it led to the widespread introduction of supersonic aircraft.
By the end of the Second World War Germany and Britain already had operational jet aircraft in military service. The next few years saw jet engines being developed by all the major powers and military jet aircraft entering service with their air forces. The Soviets' most important design bureau for future jet fighter development in the decades to come, Mikoyan-Gurevich, started preparing for building swept-winged jet aircraft with the small, experimental piston-engined MiG-8 Utka pusher, which flew with slightly swept-back wings only months after V-E Day.
Supersonic flight was achieved in 1947 by the American Bell X-1 rocket plane, however the use of rocket engines would prove short lived. The development of the afterburner soon allowed jet engines to provide similar levels of thrust and longer range, while needing no oxidant and being safer to handle. The first supersonic jet to enter service was the North American F-100 Super Sabre, in 1954.
Meanwhile, commercial jetliners were being developed with the first of these, the British de Havilland Comet, first flying in 1949 and entering service in 1952. The Comet suffered from a new and unexpected problem now known as metal fatigue, several examples crashed and by the time a new version was introduced, American types such as the Boeing 707 had overtaken its design and it was not a commercial success. These types and their descendants contributed to an era of great social change, typified by popular phrases such as "the jet set" and introducing new medical syndromes such as jet lag.
The propulsive efficiency of jet engines is inversely related to the exhaust velocity. The turbofan engine improves on the propulsive efficiency of the turbojet by accelerating a larger amount of air to a lower velocity. The overall gain in efficiency increases the range and lowers the cost of operation for a given aircraft. Development had begun in both Britain and Germany during the war but the first production version, the Rolls-Royce Conway did not come into use until around 1960.
Attempts were made to develop a supersonic airliner, with the Anglo-French Concorde and Soviet Tupolev Tu-144 entering service during the 1970s, but they proved uneconomic in practice due to the high fuel consumption at supersonic speeds. The associated pollution and sonic boom from these aircraft also raised awareness of the Environmental impact of aviation, making it difficult to find countries prepared to tolerate them.
Many other advances took place during this period, such as the introduction of the helicopter, development of the fabric Rogallo wing for sport flying and the reintroduction of the canard or "tail-first" configuration by the Swedish Saab Viggen jet fighter.
Aircraft
Supersonic flight
Designers already knew that as an aircraft approaches the speed of sound, in the transonic region, shock waves begin forming, causing a large increase in drag. Wings, already thin, had to become thinner and finer. Fineness is a measure of how thin the wing is compared to its front-to-back chord. A small, highly loaded wing has less drag and so some early types used this type, including the Bell X-1 rocket plane and the Lockheed F-104 Starfighter. But these craft had high takeoff speeds, the Starfighter causing significant pilot deaths during takeoff, and small wings fell out of use. An approach pioneered by German designers during the war was to sweep the wing at an angle, delaying the buildup of shock waves. But this made the wing structure longer and more flexible, making the aircraft more likely to suffer from bending or aeroelasticity and even causing a reversal in the action of the flight controls. Stall behaviour of the swept wing was also poorly understood and could be extremely sharp. Other problems included divergent oscillations which could build up lethal forces. In researching these effects, many pilots lost their lives, for example all three examples of the de Havilland DH.108 Swallow broke up in the air, killing their pilots. while another survived only because he lowered the seat so that, when violent oscillations developed, he did not bang his head on the canopy and break his neck.The triangular delta wing has a swept leading edge while maintaining a sufficiently deep wing root for structural stiffness, and from the introduction of the French Dassault Mirage fighter it became a popular choice, with or without a tailplane.
But the plain delta wing proved less manoeuvrable in combat than a more conventional tapered wing, and as time progressed became more heavily modified, with tailed, cropped, double-delta, canard and other forms appearing.
As speed increases and becomes fully supersonic, the wing centre of lift moves backwards, causing a change in longitudinal trim and a pitching-down tendency known as Mach tuck. Supersonic aircraft had to be made capable of adjusting sufficiently, in order to maintain adequate control at all stages of flight.
Above speeds of around Mach 2.2 the airframe starts to heat up with the friction of the air, causing both thermal expansion and loss of strength in the cheap, easily workable light alloys used for lower speeds. Also, jet engines begin to reach their limits. The Lockheed SR-71 Blackbird was constructed of titanium alloy, had a special corrugated skin to absorb thermal expansion and dual-cycle turbofan-ramjet engines which ran on a special temperature-tolerant fuel. Mach tuck was reduced through the use of long "chine" extensions of the wing along the fuselage, which contributed greater lift at supersonic speeds.
Another problem with supersonic flight proved to be its environmental impact. A large aircraft creates a loud shock wave or "sonic boom," which can disturb or damage anything it passes over, while the high drag results in high fuel consumption and consequent pollution. These issues became highlighted with the introduction of the Concorde supersonic transport.
Engines
The propeller powered by a piston engine, in radial or inline form, still dominated aviation at the close of World War Two, and its simplicity and low cost mean it is still in use today for less demanding applications.Some early attempts to achieve high speeds, such as the Bell X-1, used rocket engines. However a rocket engine requires an oxidant as well as a fuel, making these aircraft dangerous to handle and short-ranged. Hybrid dual-motor types such as the Saunders-Roe SR.53 used the rocket to boost speed for a "supersonic dash." In the event the development of the afterburner allowed jet engines to provide similar levels of thrust and rocket power became confined to missiles.
As the jet turbine developed, distinct types emerged. The basic jet turbine appeared in two forms, with axial or centrifugal compressors. Axial flow is theoretically more efficient and physically slimmer but requires higher technology to achieve. Consequently, early jets were of the centrifugal type. It was not long before axial-flow types came to dominate.
A variation on the turbine theme is the turbo-prop. Here, the turbine drives not only the compressor but also the main propeller. At lower speeds and altitudes this design is more efficient and economical than the jet turbine, while having greater power for less weight than a piston engine. It therefore found a niche between the low-cost piston engine and the high-performance jet engine. The Rolls-Royce Dart powered the Vickers Viscount airliner, which first flew in 1948, and turboprops remain in production today.
The next development of the jet engine was the afterburner. Pure turbojets were found to fly little faster than the speed of sound. In order to increase speed for supersonic flight, fuel was injected into the engine exhaust, upstream of a divergent nozzle similar to that seen on a rocket engine. As the fuel burned it expanded, reacting against the nozzle to drive the exhaust backwards and the engine forwards.
Turbojet engines have a high fuel consumption, and afterburning even more so. One way to make an engine more efficient is to make it pass a larger mass of air at slower speed. This led to the development of the bypass turbofan, in which a larger-diameter fan at the front passes some air into the compressor and the rest around a bypass, where it flows past the engine at slower speed than the jet exhaust. The fan and compressor need to spin at different speeds, leading to the two-spool turbofan, in which two sets of turbines are mounted on concentric shafts spinning at different speeds to drive the fan and the high-pressure compressor respectively. Taking the principle a step further, the high-bypass turbofan is even more efficient, having typically three spools each spinning at a different speed.
Another way to improve efficiency is to increase the combustion temperature. This requires improved materials able to retain their strength at high temperature, and the development of engine cores has largely followed advances in the materials available, for example through the development of precision-made ceramic parts and single-crystal metal turbine blades. Rolls-Royce developed a carbon composite fan for the Rolls-Royce RB211 turbofan but in the event found the material did not have sufficient damage tolerance and they reverted to the more conventional titanium metal.
Avionics
The advent of reliable electronics led to a progressive development of avionic systems for flight control, navigation, communication, engine control and military purposes such as target identification and weapons aiming.New radio location systems provided navigation information which could be used to control an autopilot pre-set to fly a specific course rather than to simply maintain the present altitude and heading. Radio communications became more sophisticated, in large part to cope with increasing use as the skies became increasingly crowded.
In the military arena, Identification Friend or Foe systems were developed, enabling military aircraft to identify each other when within firing range of their missiles but beyond visual range. Weapons aiming systems developed into fire-control systems capable of arming, launching, tracking and controlling multiple missiles at different targets. The Head-Up Display was developed from the wartime reflector gunsight to provide key flight information to the pilot without needing to lower the eyes to the instrument panel. The increasing capability - and vulnerability - of avionics led to the development of airborne Early Warning and Electronic Countermeasures systems.