Definitions for some of the terms relative to
only for personnel but also for equipment on
board. Similarities exist in the electronic
temperature control are as follows:
equipment controlling these systems and the
components within these systems.
Absolute temperature. Temperature measured
along a scale that has zero value at that point
The environmental systems on most aircraft
where there is no molecular motion (273.1C or
include cockpit/cabin air conditioning and
459.6F).
pressurization, equipment cooling, windshield
anti-icing and defogging, and equipment pressuri-
Adiabatic. A word meaning no transfer of
zation systems. Some aircraft accomplish equip-
heat. The adiabatic process is one in which no heat
ment cooling by teeing off with ducting from the
transfers between the working substance and any
cockpit/cabin system; other aircraft use a separate
outside source.
system. These systems are not the exclusive
responsibility of the AE, but rather are the
responsibility of other ratings with the AE
Ambient temperature. The temperature in the
assisting.
area immediately surrounding the object under
discussion.
TERMS AND DEFINITIONS
Ram air temperature rise. The increase in
temperature created by the ram compression on
The system that maintains cabin air tempera-
the surface of an object traveling at high speed
tures to meet the requirements for pilot efficiency
through the atmosphere. The rate of increase is
is the air-conditioning system. You must become
proportional to the square of the speed of the
familiar with some terms and definitions to
object.
understand the operating principles of air-
conditioning systems.
Temperature scales.
The following terms are self explanatory:
engine heat, solar heat, electrical heat, a n d
1. Celsius (C)--A scale on which 0 represents
body heat of personnel. These sources of
the freezing point of water, and 100 is the boiling
heat make cabin air conditioning necessary,
point of water at sea level.
and another source is ram air temperature.
Ram air temperature is the frictional tempera-
2. Fahrenheit (F)--A scale on which 32
ture increase created by ram compression on
represents the freezing point of water, and
the skin surface of an aircraft. This factor
212 is the boiling point of water at sea
becomes serious only at extreme airspeeds.
level.
For example, for an aircraft flying at 45,000
feet, at 1,200 MPH, the ram air temperature
would be about 2,000F on some parts of
CABIN SYSTEM
the aircraft. This extreme temperature, plus the
heat from other sources, would cause cabin
The primary function of the cabin air-
temperature to rise to about 190F. The maximum
conditioning and pressurization system is to
temperature that a crew member can endure and
maintain cockpit temperature and pressure within
still maintain top physical and mental efficiency
parameters for crew safety and comfort. To do
i s about 80F. Prolonged exposure to a
this, the system forces a mixture of dehumidified
temperature greater than 80F will seriously
refrigerated air and hot engine bleed air through
impair his/her mental and physical abilities.
cockpit diffusers. The temperature of the
Furthermore, under low-speed operating con-
mixture is automatically maintained through a
ditions at low temperature, cabin heating may be
continuously selective range by a temperature
necessary.
control system, consisting of temperature sensors
with associated flow control valves and an
NOTE: Some of the terms were discussed in
electronic controller. A pressure regulator and
chapter 1, "Elementary Physics." Although they
safety valve control cabin pressure. The manual
are briefly defined in this chapter, a review of
dump control is available if the safety valve
chapter 1 will be helpful.
malfunctions. A block diagram for the airflow of
