A cargo aircraft (also known as freighters or freight aircraft) is an fixed-wing aircraft designed or converted for the carriage of goods, rather than passengers. They are devoid of passenger amenities, and generally feature one or more large doors for the loading and unloading of cargo. Freighters may be operated by civil passenger or cargo airlines, by private individuals or by the armed forces of individual countries. However most air freight is carried in special ULD containers in the cargo holds of passenger aircraft.
Aircraft designed for cargo use have a number of features that distinguish them from conventional passenger aircraft: a "fat" looking fuselage, a high-wing to allow the cargo area to sit near the ground, a large number of wheels to allow it to land at unprepared locations, and a high-mounted tail to allow cargo to be driven directly into and off the aircraft.
Aircraft were put to use carrying cargo in the form of air mail as early as 1911. Although the earliest aircraft were not designed primarily as cargo carriers, by the mid 1920's airplane manufacturers were designing and building dedicated cargo aircraft.
The earliest "true" cargo aircraft is arguably the World War II German design, the Arado Ar 232. The Ar 232 was intended to supplant the earlier Junkers Ju 52 freighter conversions, but only small numbers were built. Most other forces used freighters in the cargo role as well, most notably the Douglas DC-3, which served with practically every allied nation. Post war Europe also served to play a major role in the development of the modern air cargo and air freight industry during what became known as the "Cold War." It is during the Berlin Airlift at the height of this "Cold War," when a massive mobilization of aircraft was undertaken by the "free world," to supply Germany's citizens with food and supplies, in a virtual around the clock air bridge; after the Soviet Union attempted to close and blockade Berlin's borders and land links to the west.
In the years following the war era a number of new custom-built cargo aircraft were introduced, often including some "experimental" features. For instance, the US's C-82 Packet featured a removable cargo area, while the C-123 Provider introduced the now-common upswept tail. But it was the introduction of the turboprop that allowed the class to mature, and even one of its earliest examples, the C-130 Hercules, is still the yardstick against which newer military transport aircraft designs are measured.
The Boeing 747 can be ordered in a freighter version with a large nose door which could be raised above the cockpit for loading. The bulged top deck housing the cockpit was originally designed to allow an unobstructed main deck, and to keep cargo from crushing the pilots in the case of an accident. The interior size of the fuselage is matched to the size of a standard cargo container, stacked two high and two wide.