AIRCRAFT PNEUMATIC SYSTEMS

AIRCRAFT PNEUMATIC SYSTEMS• Pneumatic is also called vacuum pressure systems• Similar to hydraulic system. • Advantages of pneumatic systems – Simple and inexpensive components. – Reliable and Unaffected by atmospheric changes – Light weight and small. – Safe and no fire hazard. – Clean system and environments friendly. – No requirement for reservoir or return lines as air will be vented overboard.• Disadvantage of pneumatic systems – Air is compressible so pressure variability might lead to inaccurate movement and control.

AIRCRAFT PNEUMATIC SYSTEMS

• Pneumatic system on the aircraft is used to, Powers engine Suction System for – Heading indicators. – Attitude indicators. Actuates Landing Gear (some aircraft) Emergency Brakes (some aircraft) Cabin Pressure (for pressurized aircraft). Engine start. Ice protection / De-icing.

ELEMENTS OF BASIC COMPRESSED AIR PNEUMATIC SYSTEM

• A) Air Compressor.• B) Check Valve.• C) Accumulator.• D) Directional Valve.• E) Actuator.

ELEMENTS OF BASIC COMPRESSED AIR PNEUMATIC SYSTEM

• AIR COMPRESSOR: Raising the air pressure to above ambient pressure and pump that

compressed air to be used in pneumatic systems.

• CHECK VALVE: One-way valve allows pressurized air to enter the pneumatic system, but prevents backflow of air toward the Compressor when Compressor is stopped (prevent loss of pressure).

• ACCUMULATOR: Stores compressed air. Prevents surges in pressure. Prevents constant Compressor operation

ELEMENTS OF BASIC COMPRESSED AIR PNEUMATIC SYSTEM

• DIRECTIONAL VALVE:

To start, stop, and change the direction of flow in compressed air applications.

The moving part in the valve will connect and disconnect internal flow passages within the valve body and this action results in a control of airflow direction.

ELEMENTS OF BASIC COMPRESSED AIR PNEUMATIC SYSTEM

• ACTUATORS:

Converts energy stored in compressed air into mechanical motion

Example is a linear piston (piston limited to moving in two opposing directions).

PNEUMATIC SYSTEM OPERATION IN SMALL AIRCRAFT

• Filtered Air is pulled through system by vacuum in pump.• Evacuated air passes through instrument case causes gyro to spin.• Spinning gyros provide “rigidity in space” for instrument ref.• Air is exhausted overboard.• Gauge measures sys. press.• Failure warning systems.

PNEUMATIC SYSTEM COMPONENTS IN SMALL A/C• Pneumatic Air Filter: Prevent sys. contamination and remove air particulates.

• Pneumatic pressure regulator: Prevent system over pressurization.

• Air Pump: Heart of pneumatic system is pressure or vacuum air pump

(usually engine driven). - Wet / Dry Air Pump.

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PNEUMATIC SYSTEM COMPONENTS IN SMALL A/C• Aircraft Instrument Panel (Alt., Heading, ..etc).

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PNEUMATIC SYSTEM DESIGN

• Pneumatic symbols.• Pneumatic Calculations.• Pneumatic Symbols

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PNEUMATIC CALCULATIONS

• Sizing a Cylinder

• P = F / A

• Velocity of pneumatic cylinder• s = 28.8 * q/A

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PNEUMATIC CALCULATIONS

• Ideal Gas Law• The change in density is directly related to the change of temperature

and pressure as expressed by the Ideal Gas Law.• The Ideal Gas Law and the Individual Gas Constant- R• P V = m R T         (1)• P = ρ R T         (2)• The Ideal Gas Law and the Universal Gas Constant- R• P V = n R T         • The True Gas Law, or the Non-Ideal Gas Law,:• P V = Z n R T 

• Example: A tank with volume of 1 ft3 is filled with air compressed to a gauge pressure of 50 psi. The temperature in tank is 70 oF.

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PNEUMATIC SYSTEM DESIGN• Pneumatic Circuit

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PNEUMATIC SYSTEM FAILURE SIGNS

• Pneumatic system failure signs:• Inaccurate/conflicting Instrument information.• Suction/pressure gauge indicates outside normal operating (green

range).

• Causes of Pneumatic System Failure:• Contamination: Solid particles in pneumatic system damage pump and plug valve openings. Liquids from oil, water, or engine cleaning solvents.• A loose fittings or damaged hoses.• Worn out, misused, or incorrectly routed hoses.• Sudden engine deceleration or stoppage.

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QUESTIONS THANK YOU

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REFERENCES• http://www.tpub.com/content/aviation/14014/img/14014_93_1.jpg• http://

www.robotstoreuk.com/ACTUATORS/AIR-MUSCLE/AIR-Muscle-IMAGES/Basic-air-system-350.jpg

• http://www.airportbusiness.com/images/article/1154550280769_DOW.jpg• http://greggordon.org/images/pitotStaticSystem.jpg• http://

books.google.com/books?id=A0buKXqCcUMC&pg=PA287&lpg=PA287&dq=pneumatic+system+aircraft&source=web&ots=YwVrW63vnu&sig=ayKt1S2YoCQ689T9yg4NUhIudYw#PPA283,M1

• http://ranier.oact.hq.nasa.gov/team116/2003/lessons/Lesson7-Pneumatics.pdf• http://www.aopa.org/asf/publications/SB06.pdf• http://www.nfpa.com/Education/

Edu_LearningOpps_SelfPacedFundamentalsPneumatic.asp

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