S A F E T Y P R O P E R T I E S
Jet fuel can be hazardous if not handled properly. First, and foremost, it is
easy to ignite and it burns rapidly. Second, exposure to jet fuel liquid or
vapor should be limited. Anyone planning to handle jet fuel should obtain
and read the Material Safety Data Sheet (MSDS) issued by the supplier.
Liquid doesn’t burn; only vapor burns. And vapor doesn’t always burn – the
mixture of vapor and air must be within the flammable3 range. Mixtures with
insufficient vapor (below the lower flammability limit) or too much vapor
(above the upper flammability limit) will not burn. For kerosene-type jet fuel,
the lower and upper flammability limits4 are 0.6 volume percent vapor in air
and 4.7 volume percent vapor in air, respectively. For wide-cut jet fuel, the
lower and upper flammability limits are 1.3 volume percent vapor in air and
8.0 volume percent vapor in air, respectively.
In most circumstances, the hydrocarbon vapor-air mixture in an enclosed
space over kerosene-type jet fuel will not be in the flammable range; the
mixture will be below the lower flammability limit. However, high ambient
temperature can heat the fuel enough to bring the vapor space into the flammable
range. The flash point of a fuel is the lower flammability temperature
of the fuel under the specific test conditions. However, this is not necessarily
the lower flammability temperature under other conditions, such as in an
aircraft fuel tank.
For the more volatile wide-cut fuel, the hydrocarbon vapor-air mixture in an
enclosed space may be in the flammable range. The upper flammability temperature
limit depends on the vapor pressure of the fuel. A fuel with a vapor
pressure of 18 kPa (2.6 psi) will have an upper flammability temperature limit
of approximately 18°C (64°F).
However, in the absence of specific information to the contrary, any jet fuel
handling situation should be considered potentially hazardous and the appropriate
safety measures observed.
An airplane operates near the surface of the earth which moves about the
sun. Suppose that the equations of motion (F = ma and M = I) are
derived for an accurate inertial reference frame and that approximations
characteristic of airplane flight (altitude and speed) are introduced into
these equations. What results is a set of equations which can be obtained
by assuming that the earth is flat, nonrotating, and an approximate
inertial reference frame, that is, the flat earth model.
The equations of motion are composed of translational (force)
equations (F = ma) and rotational (moment) equations (M = I)
and are called the six degree of freedom (6DOF) equations of motion.
For trajectory analysis (performance), the translational equations are
uncoupled from the rotational equations by assuming that the airplane
rotational rates are small and that control surface deflections do not
affect forces. The translational equations are referred to as the three
degree of freedom (3DOF) equations of motion.
As discussed in Chap. 1, two important legs of the commercial
and military airplane missions are the climb and the cruise which occur
in a vertical plane (a plane perpendicular to the surface of the earth).
The purpose of this chapter is to derive the 3DOF equations of motion
for flight in a vertical plane over a flat earth. First, the physical model is
defined; several reference frames are defined; and the angular positions
and rates of these frames relative to each other are determined. Then,
the kinematic, dynamic, and weight equations are derived and discussed
for nonsteady and quasi-steady flight. Next, the equations of motion for
flight over a spherical earth are examined to find out how good the flat
2.1. Assumptions and Coordinate Systems 17
earth model really is. Finally, motivated by such problems as flight in
a headwind, flight in the downwash of a tanker, and flight through a
downburst, the equations of motion for flight in a moving atmosphere