Page 109 - Planning and Design of Airports

Air craft Characteristics Related to Airport Design 79

useful in airport planning for determining the most probable weight
characteristics of aircraft flying particular stage lengths between
airports.
The distribution of the load between the main gears and the nose
gear depends on the type of aircraft and the location of the center of
gravity of the aircraft. For any gross weight there is a maximum aft
and forward center of gravity position to which the aircraft can be
loaded for flight in order to maintain stability. Thus the distribution
of weight between the nose and main gears is not a constant. For the
design of pavements it is normally assumed that 5 percent of the weight
is supported on the nose gear and the remainder on the main gears.
Thus if there are two main gears, each gear supports 47.5 percent of
the total weight. For example, if the takeoff weight of an aircraft is
300,000 lb, each main gear is assumed to support 135,000 lb. If the
main gear has four tires, it is assumed that each tire supports an equal
fraction of the weight on the gear, in this example, 33,750 lb. As will
be discussed in Chap. 7, pavement strengths are designed based on
the maximum structural takeoff weights, as well as the landing gear
and loading configurations, of the aircraft of intended use.
Runway Performance
One of the most critical elements of aircraft performance is how such
characteristics, along with local atmospheric conditions, affect the
runway length for an aircraft to safely takeoff and land.
For any given operation, whether it be a takeoff or landing, an
aircraft will require a certain amount of runway. Required runway
length may vary widely for a specific aircraft, as a result of the air-
craft’s weight at the time of the operation, as well as the local atmos-
pheric conditions. For the airport planner and designer, such varia-
tions have less direct impact on the design length of runways, and
more to aircraft operators who must determine whether the length of
a runway at a given time is safe for a particular operation. Neverthe-
less, the airport planner and designer should be aware of how an
aircraft’s performance characteristics specifically affect its runway
length requirements.
The factors which have a bearing on and aircraft’s runway length
requirements for a given operations may be grouped into two general
categories:

1. The physical capabilities of the aircraft under given environ-
mental conditions
2. Requirements set by the government to protect for safe
operations

An aircraft’s performance capabilities and hence runway length
requirements are often significantly affected by certain natural envi-
ronmental conditions at the airport. The more important of these