Page 91 - Planning and Design of Airports

Air craft Characteristics Related to Airport Design 63

weight less than the maximum structural takeoff weight. This is so
because an aircraft loses weight en route by burning fuel. This loss in
weight is considerable if the journey is long, being in excess of 80,000 lb
for large jet transports. It is therefore not economical to design the
main gear of an aircraft to support the maximum structural takeoff
weight during landing, since this situation will rarely occur. If it does
occur, as in the case of aircraft malfunction just after takeoff, the pilot
must jettison or burn off sufficient fuel prior to returning to the air-
port so as not to exceed the maximum landing weight. For short range
aircraft, the main gear is designed to support, in a landing operation,
a weight nearly equal to the maximum structural takeoff weight. This
is so because the distances between stops are short, and therefore a
large amount of fuel is not consumed between stops.
On landing, the weight of an aircraft is the sum of the operating
weight empty, the payload, and the fuel reserve, assuming that the
aircraft lands at its destination and is not diverted to an alternate air-
port. This landing weight cannot exceed the maximum structural
landing weight of the aircraft. The takeoff weight is the sum of the
landing weight and the trip fuel. This weight cannot exceed the max-
imum structural takeoff weight of the aircraft.

Engine Types
Perhaps the most significant contributor to increased aircraft per-
formance has historically come from improvements in aircraft engine
technology, from early twentieth-century piston engines to twenty-
first-century high-performance jet engine technology.
While there are many makes and models of aircraft engines pro-
duced by a number of engine manufacturers, aircraft engine types
can generally be placed into three categories, piston engines, turbo-
props, and turbofan (or jet) engines.
The term piston engine applies to all propeller-driven aircraft pow-
ered by high-octane gasoline-fed reciprocating engines. Most small
general aviation aircraft are powered by piston engines. The term tur-
boprop refers to propeller-driven aircraft powered by turbine engines.
The term turbofan or jet has reference to those aircraft which are not
dependent on propellers for thrust, but which obtain the thrust
directly from a turbine engine. Jet engines are typically powered
using a form of diesel fuel, known as Jet-A. While historically jet
engines have been used to power larger general aviation and com-
mercial service aircraft, jet engines recently have been increasingly
produced for smaller “regional jet” commercial service aircraft, and
even smaller “very light jet” general aviation aircraft.
In the early part of the twenty-first century, most of the transport
category aircraft in service are equipped with jet engines, and as such,
much of the planning and design of airports serving commercial serv-
ice and business general aviation are based around jet engine aircraft.