The Heat Factor

Some aircraft, especially fast military aircraft, cannot be made from aluminum alloys. Airplanes heat up as they fly faster because they both compress the air they fly through and create friction as they rub against it. Planes flying faster than about two-and-a-half times the speed of sound heat up so much that an aluminum body would become danger­ously soft and weak. Aluminum melts at a temperature of about 1220°F (660°C).

О A worker at the Douglas Aircraft Company in California during World War II fastens the frame of an A-20 bomber with thousands of rivets.

An aircraft that flies faster than three times the speed of sound reaches nearly 1000°F (538°C). These planes are built from a metal called tita­nium. The Lockheed SR-71 Blackbird spy plane was the first to be built from titanium in the 1960s. It could fly at three-and-a-half times the speed of sound.

The first manned space capsules used in the Mercury and Gemini space proj­ects also were made from titanium. The Apollo command module was made of a lightweight aluminum honeycomb sand­wiched between aluminum sheets. It had a heat shield to protect it from the high temperatures of reentry. The Space Shuttle is made of aluminum protected by insulation material.