Ram Air - Pneumatics - Airframes & Aircraft Systems #37
Summary
TLDRThis lesson delves into the pneumatic systems of aircraft, highlighting how light aircraft utilize ram air and heating methods like exhaust gas or combustion heaters for cabin comfort. It explains the role of blowers in supplying air for pressurization and conditioning in larger aircraft, and the use of Roots blowers for creating a comfortable cabin environment. The importance of safety features in combustion heaters and the operation of various valves for temperature control are also discussed.
Takeaways
- 🛫 Most aircraft have a pneumatic system, with large modern airliners using a high-volume, low-pressure system that supplies air from engine compressors.
- 🚁 Light aircraft may use ram air, which is dynamic air pressure created by the aircraft's motion, to operate gyroscopic instruments.
- 🔥 Ram air can be heated by engine exhaust gases or a combustion heater to heat the cockpit and cabin, and to demist the windscreen.
- 🌬️ Aircraft without engine compressor air, like large pressurized piston engine aircraft, use blowers driven by the engine to supply air to air conditioning and pressurization systems.
- 🛬️ Older turboprop aircraft, such as the Fokker F27, use high-pressure pneumatic systems for operating landing gear and brakes.
- 🌡️ A typical light aircraft system using an exhaust gas heater includes hot windscreen misters and a fresh air blower for use on the ground.
- 🔧 Muff or exhaust muff allows ram air to come into close contact with the hot exhaust pipe to provide hot air for heating the cabin and demisting the windscreen.
- 🔥 Combustion heaters, which use the same fuel as the aircraft's engines, are standalone devices that burn a fuel-air mixture within a combustion chamber.
- 🌬️ Cabin air supply in some aircraft is provided by blowers driven through the engine accessory gearbox or by turbo compressors driven by bleed air.
- 🌡️ Roots blowers, a type of positive-displacement blower, are used in some systems to supply air, but they can cause a thumping noise in the air-conditioning ducts.
Q & A
What is the primary source of air for the pneumatic system in large modern airliners?
-The primary source of air for the pneumatic system in large modern airliners is from the engine compressors, supplying a bleed air manifold with high-volume low-pressure air.
How do light aircraft typically operate their gyroscopic instruments?
-Light aircraft typically operate their gyroscopic instruments using ram air, which is a dynamic air pressure created by the aircraft's motion.
What are the alternative sources of heating for the cockpit and cabin in light aircraft?
-Alternative sources of heating for the cockpit and cabin in light aircraft include ram air heated by engine exhaust gases or by a combustion heater.
What is a muff or exhaust muff, and how does it contribute to heating the cabin in aircraft?
-A muff or exhaust muff is a close-fitting cowl around the exhaust pipe that allows ram air to come into close contact with the hot exhaust pipe, providing hot air for heating the cabin and for misting the windscreen.
How does a combustion heater function in an aircraft?
-A combustion heater functions by burning a fuel-air mixture within its combustion chamber. Air for combustion is supplied by a combustion blower, and the fuel is supplied via a solenoid-operated fuel valve. The flame is lit by an ignition unit, controlled by duct temperature sensors.
What safety devices are typically included in a combustion heater system in aircraft?
-Safety devices in a combustion heater system include an automatic shutoff if the outlet air temperature becomes too hot, fire protection in case of combustion chamber failure, and an automatically operated fire extinguisher in some systems.
What type of blowers are used in aircraft to supply air to the air conditioning and pressurization systems when engine compressor air is not available?
-Blowers driven by the engine, such as those in the engine accessory gearbox or turbo compressors driven by bleed air, are used to supply air to the air conditioning and pressurization systems when engine compressor air is not available.
What is a roots blower, and how does it function in an aircraft's cabin conditioning system?
-A roots blower is a type of positive-displacement blower that consists of two lobes which mesh together and are rotated by the engine gearbox. It pulls in air through the inlet and expels it through the outlet, producing a small pressure increase but large flow rates.
Why is a silencer used in the cabin conditioning system with a roots blower?
-A silencer is used to smooth out the airflow and reduce noise caused by the pulsing effect of the roots blower, as the air comes out in short pulses due to its design.
How is the air temperature in the cabin maintained at a comfortable level in aircraft with a pneumatic system?
-The air temperature is maintained by mixing hot and cold air supplies in varying proportions. A variable restrictor, known as a choke valve, can be progressively closed to increase the pressure and temperature of the air leaving the blower.
What is the role of a mass flow controller in the pneumatic system of an aircraft?
-A mass flow controller signals a spill valve to vent excess airflow to the atmosphere when too much air is supplied, especially at high engine speeds and low altitudes, ensuring the required mass flow of air under all operating conditions.
Outlines
🛫 Pneumatic Systems and Cabin Heating in Aircraft
This paragraph delves into the various sources of air for an aircraft's pneumatic system and the basics of cabin heating. It explains that large modern airliners typically use a high-volume, low-pressure system that draws air from engine compressors, while light aircraft may rely on ram air, which is dynamic air pressure created by the aircraft's motion. The paragraph also covers the use of exhaust gas heaters or combustion heaters to warm the cockpit and cabin, and the role of blowers in supplying air to air conditioning and pressurization systems in aircraft where engine compressor air is not available. The Fokker F27 is highlighted as a unique case still using high-pressure pneumatic systems for landing gear and brakes. The paragraph concludes with a look at ram air systems in light aircraft, including the use of exhaust muffs for heating and the importance of regular inspections to prevent toxic exhaust gases from entering the cabin.
🔧 Auxiliary Systems for Aircraft Air Conditioning
The second paragraph focuses on auxiliary systems used for air conditioning in aircraft, particularly in piston-engined aircraft and some turbojet aircraft where compressor air is deemed unsuitable. It discusses the role of blowers, which can be driven by the engine accessory gearbox or turbo compressors, and the necessity of these systems in maintaining cabin comfort. The paragraph describes the function of different types of blowers, including centrifugal and positive displacement types, with a specific mention of the Roots blower, which is known for producing large flow rates despite a small pressure increase. It also explains the process of air heating through choke valves and the mixing of hot and cold air supplies to achieve a comfortable temperature. The importance of a mass flow controller and spill valve in managing excess airflow is highlighted, along with the operation of the pack valve, hot air bypass valve, cooling pack, and water separator, which are covered in a separate air conditioning lesson.
Mindmap
Keywords
💡Pneumatic System
💡Bleed Air
💡Ram Air
💡Exhaust Gas Heater
💡Combustion Heater
💡Blower
💡Pressurization System
💡Cabin Supercharger
💡Roots Blower
💡Choke Valve
💡Safety Devices
Highlights
Various sources of air are available to an aircraft's pneumatic system.
Large modern airliners use a high-volume low-pressure system supplying air from engine compressors.
Light aircraft may use ram air, a dynamic air pressure created by the aircraft's motion, to operate gyroscopic instruments.
Ram air can be heated by the engine exhaust gases or a combustion heater to heat the cockpit and cabin.
Crafts without engine compressor air use blowers driven by the engine for air conditioning and pressurization systems.
Older turboprop aircraft use high-pressure pneumatic systems for operating landing gear and brakes.
Fokker F27 is an example of an aircraft still using high-pressure pneumatic systems.
Light aircraft use forward-facing air intakes to introduce ram air into the cabin.
Exhaust gas heaters or combustion heaters can be used to heat ram air for cabin heating.
A muff or exhaust muff allows ram air to come into close contact with the hot exhaust pipe for heating.
Regular inspections are required to ensure toxic exhaust gases do not enter manned areas.
Some aircraft use a combustion heater, which burns fuel-air mixture in a combustion chamber.
Combustion heaters have safety devices like automatic shutoff and fire protection systems.
Cabin air supply can be provided by blowers driven through the engine accessory gearbox or by turbo compressors.
Roots blowers, a type of positive-displacement blower, can produce large flow rates with a small pressure increase.
A silencer is used to smooth out airflow and reduce noise in cabin conditioning systems.
A mass flow controller and spill valve are used to regulate air supply under different operating conditions.
Air can be heated by restricting flow with a variable restrictor, known as a choke valve.
Hot and cold air supplies are mixed to maintain a comfortable delivery temperature for passengers and crew.
Transcripts
in this lesson we will discuss the
various sources of air available to an
aircraft's pneumatic system
we will also look at some basic cabin
heating systems
most aircraft have a pneumatic system of
some sort large modern airliners have a
high-volume low-pressure system
supplying a bleed air manifold with air
from the engine compressors these
systems are covered in a separate lesson
light aircraft may use ram air a dynamic
air pressure created by the aircraft's
motion to operate gyroscopic instruments
they can also use ram-air heated by the
engine exhaust gases or by a combustion
heater to heat the cockpit and cabin and
to de mis the windscreen
crafts where air from the engine
compressor is not available such as on
large pressurized piston engine aircraft
and some turbo propeller types blowers
driven by the engine are used to supply
air to the air conditioning and
pressurization systems
some older turboprop aircraft use
high-pressure pneumatic systems to
operate the landing gear and brakes the
only example of this still in common use
is in the Fokker f27
the operation of this type of pneumatic
system is covered in the hydraulic
series of lessons
first we will look at the RAM air
systems used in light aircraft
is introduced to the cabin through
forward-facing air intakes some of this
ram air can be heated by an exhaust gas
heater or a combustion heater and then
mixed with the cold ambient air in
varying proportions to give a
comfortable cabin temperature
a typical system for a light aircraft
using an exhaust gas heater is shown
here
it also features hot windscreen -
misters and a fresh air blower for use
on the ground when there is no ram air
a muff or exhaust muff is a
close-fitting cowl around the exhaust
pipe which allows ram air to come into
close contact with the hot exhaust pipe
to provide hot air for heating the cabin
and a misting the windscreen
fresh cold air is allowed into the cabin
through the ram air inlets
on the wing leading-edge
after use the air is dumped overboard
through a vent on the underside of the
aircraft
this type of heater requires regular
inspections to ensure that toxic exhaust
gases do not enter the manned areas
some aircraft have a blower which can be
used on the ground to blow fresh air
into the cabin giving some cooling on
hot days
some aircraft use a combustion heater
rather than an exhaust gas heater
the combustion heater is a standalone
device
it normally uses the same fuel as the
aircraft's engines
it burns about half a gallon an hour
this needs to be taken into account when
calculating the fuel required for a
particular flight
it works by burning a fuel-air mixture
within its combustion chamber
air for combustion is supplied by a fan
or blower known as the combustion blower
and the fuel is supplied via a solenoid
operated fuel valve
the flame is lit by an ignition unit
controlling an igniter
the fuel valve and the igniter are
controlled by duck temperature sensors
but can be manually overridden
the system is designed with the fan
pushing the air into the cabin being
much more powerful than the combustion
blower fan this means that the clean air
is at a higher pressure than that in the
combustion chamber so there is no
possibility of leaks from inside the
chamber contaminating the cabin air
the combustion heater is provided with a
number of safety devices which will
include
an automatic shutoff if the outlet air
temperature becomes too hot
and adequate fire protection in the
event of failure of the structural
integrity of the combustion chamber this
will normally be a system for shutting
off the fuel and sealing the air ducts
if flames enter them
and automatically operated fire
extinguisher is also incorporated in
some systems
a cabin air supply may be provided by
blowers driven through the engine
accessory gearbox or by turbo
compressors driven by bleed air
such systems are necessary for
piston-engined aircraft and are used for
some turbojet aircraft where the air
supply from the compressor is considered
to be too dirty or contaminated for use
in the air conditioning system
these blowers operate in a similar
manner to the super charges fitted to
some piston engines they may either have
a centrifugal or a positive displacement
type blower fitted
one type of positive-displacement blower
is known as the roots blower it is named
after the roots brothers who first
painted the basic design in 1860 it
consists of two lobes which mesh
together and are rotated by the engine
gearbox
air is pulled in through the inlet and
expelled through the outlet the pressure
increase across the blower is small
however this type of blower can produce
large flow rates
shown here is a simple schematic diagram
of a cabin conditioning system using a
roots blower
because of the design of the blower the
air comes out of it in short pulses
this can cause a thumping noise in the
air-conditioning ducts
the silencer helps to smooth out the
airflow reducing the noise
the blower must be capable of supplying
the required mass flow of air under all
operating conditions which means that at
high engine speed and low altitude too
much air is supplied
a mass flow controller signals a spill
valve to vent the excess airflow to
atmosphere
the air can be heated by restricting the
flow by means of a variable restrictor
known as a choke valve which can be
progressively closed to increase the
pressure and thus the temperature of the
air leaving the blower
the hot and cold air supplies are mixed
in varying proportions to maintain the
delivery temperature at a comfortable
level for both passengers and crew
selection and control may be automatic
or manual
the operation of the pack valve hot air
bypass valve cooling pack and water
separator is explained in the air
conditioning lesson
in this lesson you should have learned
that most aircraft have a pneumatic
system of some sort on light aircraft it
usually consists simply of ram air
heated by either the exhaust gases or by
a combustion heater being used to warm
the cabin
larger aircraft where the air is
required to supply a pressurization
system it may be supplied by a cabin
supercharger or engine bleed air may be
used
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