Aeroplane

III

Supersonic Flight

The supersonic age that aviation entered after World War II presented a number of new problems so revolutionary that aerodynamicists found themselves resorting to flight experimentation as dangerous and adventurous as any faced by early pilots. Neither complex mathematical analyses nor improvement of such research tools as the wind tunnel, in which models of planes are tested, could ensure completely satisfactory performance of an aircraft under the conditions encountered in supersonic flight.

A

The Sound Barrier

The first formidable problem confronted by aerodynamicists is known popularly as the sound barrier. It arose when planes attained the speed of sound (approximately 1,220 km/h, or about 760 mph, at sea level), scientifically termed Mach 1. An aeroplane about to break the sound barrier is on the verge of catching up with the pressure waves created by its own forward motion. The resulting distortion of the airflow at Mach 1 causes the formation of a shock wave, known as the compressibility shock, which greatly increases the drag of the plane. If the craft is not properly designed to cope with this abrupt change in the nature of the airflow, its control will be severely, if not disastrously, impaired.

B

Noise Pollution

A major problem associated with supersonic aircraft is noise. Engine noise of supersonic transports is louder and more high-pitched than that of subsonic jets, already a serious annoyance to airfield workers and residents of communities near airports. Medical concern, moreover, has been expressed about the effect of sonic booms, which are produced when the shock waves from an aircraft in supersonic flight pass over the listener. The shock front that travels with the aircraft extends over large vertical distances and reaches the ground with an impact that sounds like an explosion, even if a plane flies at maximum altitude. The shock wave may be so severe that it breaks windows on the ground far beneath the plane. Attempts are being made by designers and manufacturers to reduce both engine noise and sonic booms with aircraft such as the British Aerospace BAe 146, which entered service in 1983, and is one of the world’s quietest jet airliners. Regulations prevent supersonic flight over populated areas.

C

The Heat Barrier

Among other serious problems associated with supersonic flight is the high temperature caused by the friction of the air against the outer surfaces of the aeroplane. This problem is sometimes known as the heat barrier. To withstand the high temperatures and pressures generated at supersonic speed, the structural materials must be more resistant to heat than the materials used for subsonic aircraft. Titanium is an example of the type of heat-resistant, high-strength metal required in supersonic aircraft. The demands of the supersonic age for higher speeds, higher altitudes, and longer ranges have led not only to new aerodynamic designs, but also to research into new structural materials.

IV

Aeroplane Structure

The present-day conventional aeroplane may be divided into four components: fuselage, wings, tail assembly, and landing gear, or undercarriage.