Jadine, Samantha, Joshua, Talia and Nicky, of Corstorphine School, asks :-

Why are planes made from metal?

John Smaill, a mechanical engineer at the University of Canterbury who specialises in engineering materials, responded.

It does seem strange that, although there are lighter materials, most modern aircraft are made from metal. The use, size, the distance between refuelling stops, and the speed at which they fly determines the best material for an aircraft.

For the low speeds of early aircraft, a fabric covering over a wooden frame gave the lightest structure.As engine power increased, an economical solution was a fabric-covered, metal-tubular structure as used in modern micro-lights and some small single-engine aircraft.

Gliders or sailplanes are made from a plastic, which is strengthened by either glass or carbon fibres to give a smooth finish. This material is called a composite and is similar to the materials used in the yachts that recently raced for the America's Cup.

The largest aircraft ever built was a flying boat, nicknamed the Spruce Goose, which was made, in 1947, out of laminated wood. However, it only ever flew one flight reaching a height of approximately 1-2 metres.

A large airliner such as the Boeing B747 is designed to carry a load of 260,000 kgm over a distance of 12000 km, at a speed of 910 km/hr. The air flowing over the wings has to produce lift or an upward force equal to the weight of the aircraft, fuel, cargo and passengers. Therefore the structure of the wings and body of the aircraft must have sufficient strength to support this entire load. An aluminium alloy is the metal giving the best combination of a high strength and low weight for an aircraft of this size.

High-speed reconnaissance aircraft flying at three times the speed of sound use titanium, a light metal, which is less affected by the high temperatures caused by the fast airflow over the surface of the plane. The space shuttle has to use ceramic tiles on the exterior surface to keep the temperature of the metal craft to below the temperature at which the metal is still strong, and certainly below its melting temperature.