Ram Air - Pneumatics - Airframes & Aircraft Systems #37

Aero & Air

14 Jun 202008:41

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

00:00

🛫 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.

05:01

🔧 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

A pneumatic system in the context of the video refers to the network of components that use pressurized air to perform various functions within an aircraft. It is integral to the operation of the aircraft, supplying air for a variety of purposes including instrument operation and cabin heating. The script mentions that most aircraft have some form of pneumatic system, with large modern airliners having a high-volume, low-pressure system that supplies air from the engine compressors.

💡Bleed Air

Bleed air is the hot, compressed air taken from the engine compressors and used in aircraft for various purposes, including cabin heating and pressurization. The script explains that in large modern airliners, this air is supplied to a bleed air manifold, highlighting its importance in the pneumatic systems of these aircraft.

💡Ram Air

Ram air is the dynamic air pressure created by the aircraft's motion through the air. In the script, it is mentioned that light aircraft may use ram air to operate gyroscopic instruments and to heat the cockpit and cabin. The term is central to understanding the basic pneumatic systems used in smaller aircraft where engine compressor air may not be available.

💡Exhaust Gas Heater

An exhaust gas heater is a device that uses the heat from the aircraft's engine exhaust to warm the air that is then supplied to the cabin. The script describes how ram air can be heated by an exhaust gas heater or a combustion heater, indicating its role in providing a comfortable cabin temperature in light aircraft.

💡Combustion Heater

A combustion heater is a standalone heating device that burns fuel to generate heat. The script explains that it typically uses the same fuel as the aircraft's engines and is an alternative to an exhaust gas heater for heating the cabin air in some aircraft.

💡Blower

A blower is a device that moves air or other gases through a system. In the context of the video, blowers are used to supply air to the air conditioning and pressurization systems in aircraft where engine compressor air is not available. The script also mentions roots blowers, a specific type of positive-displacement blower, which are used in some aircraft's cabin conditioning systems.

💡Pressurization System

A pressurization system is used in aircraft to maintain a certain air pressure inside the cabin, which is higher than the pressure outside the aircraft, especially at high altitudes. The script discusses how air from the engine compressor or a cabin supercharger is used to supply these systems in larger aircraft.

💡Cabin Supercharger

A cabin supercharger is a device that increases the air pressure inside the aircraft cabin. The script explains that in some turbojet aircraft, a cabin supercharger may be used if the air supply from the compressor is considered too dirty or contaminated for use in the air conditioning system.

💡Roots Blower

A Roots blower is a type of positive-displacement blower that consists of two lobes which mesh together and are rotated to pull in air and expel it through an outlet. The script provides an example of how a Roots blower is used in a cabin conditioning system, noting that it can produce large flow rates despite a small pressure increase.

💡Choke Valve

A choke valve is a variable restrictor used to control the flow of air in a system. In the script, it is mentioned that the choke valve can be progressively closed to increase the pressure and temperature of the air leaving the blower, which is crucial for maintaining a comfortable cabin temperature.

💡Safety Devices

Safety devices are mechanisms incorporated into systems to prevent accidents or mitigate their effects. The script describes various safety devices used in combustion heaters, such as automatic shutoff in case of overheating and fire protection measures, which are essential for ensuring the safe operation of aircraft heating systems.

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.