Freeze Point
store, thermally stable, and has a high heat
content per gallon. JP-5 is a kerosene-type fuel
with a vapor pressure close to 0 psi. Its high flash
The freezing point of a fuel is the temperature
at which solid particles begin to form in the fuel.
point makes it safe for shipboard handling. In
fact, it is the only jet aircraft fuel used aboard
These particles are waxy crystals normally held
in suspension in the fuel. These particles can
ships. It has a lower tendency to vaporize than
readily block the filters in an aircraft fuel system.
the more volatile grades. The vapor-air mixture
in tanks or containers above its liquid surfaces will
The fuel almost always becomes cloudy before the
generally be too lean to be ignited until the surface
solid particles form. This cloud is caused by
of the liquid reaches a temperature of about
dissolved water coming out of the solution and
140F.
freezing.
JP-8. JP-8 (NATO Code F-34) is similar to
JP-5 in most characteristics, except flash point
TYPES OF JET FUEL
and freeze point. JP-8 is now available only in
Europe. JP-8 represents significant advantages
The U.S. Military grades of jet fuel are
over JP-4 in fuel handling and operational safety.
designated by the letters JP followed by a
Although, like JP-4, its flash point is lower than
number. The grade number merely shows the
shipboard safety standards. The disadvantages of
approximate sequence the fuel specifications
cost, availability y, and low temperature starting
were accepted by the military. NATO codes
problems prevent it from replacing JP-4.
show compatible fuel standards. When changing
to a different fuel, it is usually not necessary
Commercial Fuels. Common commercial fuels
t o drain out the old fuel. Some aircraft
used include types A, A-1, and B. Commercial
prohibit fuel mixing or require different settings
fuels are authorized for use in military aircraft
on some fuel components (fuel controls) when
when JP fuel is not available. The characteristics
switching fuel grades.
of commercial fuel are similar to military fuels.
A-1 is designated NATO code F-34, or equal to
JP-1. JP-1 was the original kerosene-type fuel
JP-8. Jet A is equal to JP-5, and Jet B is equal
used in turbine engines. Its characteristics were
to JP-4.
low vapor pressure and high energy content per
volume of fuel.
FUEL CONTAMINATION
JP-3. JP-3 was a mixture of 65 percent
gasoline and 35 percent kerosene. Because of its
The complex fuel systems of modern air-
high percentage of gasoline, its characteristics
craft do not function properly if the fuel is
were similar to gasoline. This included low flash
contaminated with dirt, rust, water, or other
point (40F), easy cold weather starting, and
foreign matter. Very small quantities of water may
poor lubricating qualities. There is also a high fuel
form into ice at altitude affecting small fuel
loss due to evaporation and a tendency to vapor
control orifices. Contaminated fuel has caused air-
lock.
craft accidents with a tragic loss of life and
valuable aircraft. This means clean fuel is a LIFE-
JP-4. JP-4 (NATO Code F-40) is an alternate
OR-DEATH matter with aviation personnel.
fuel to JP-5 for USN jet aircraft used at shore
stations only. It is never used on ships. Its low
vapor pressure reduces fuel tank losses and vapor
Besides being deadly, contaminants are also
sneaky. A certain type of emulsion resulting from
lock tendencies. Its fuel density is 6.5 pounds per
water and rust particles can adhere to the sides
gallon, and its flash point is below 0F. When
of aircraft's fuel cells and go undetected, even
switching to JP-4 from JP-5, engine operating
with fuel sampling. It will continue to build up
characteristics may change. Changes include easier
until parts of it wash off, blocking fuel filters,
starting, slower acceleration, lower operating
lines, or fuel control passages. Contamination
temperature, and shorter range.
causes unnecessary man-hours in troubleshooting
and fixing fuel problems and possible engine
JP-5. JP-5 (NATO Code F-44) is now the
failure.
Navy's primary jet fuel. It is relatively safe to
4-4
