Aircraft STRUCTURES AND AIR CON

Airframe and Aircraft Systems

Jet Engine Mounting

• Jet engines are usually mounted using forged mounts and bolted to aircraft forged structure.

Pylon Structural Member

• A pylon structural member supports the engine.

Wing Mounted Podded Engines and Integral Fuel Tanks

• Wing mounted podded engines and integral fuel tanks provide wing bending relief.

Air Conditioning and Cabin Pressurisation

• As an aircraft descends from cruising altitude, the cabin altitude must decrease.
• A refrigerant is used in a vapour cycle.
• The control of ventilating and pressurising air released to atmosphere is achieved by a pressure controller/discharge valve combination.
• Rate of change of cabin pressure is most noticeably shown on a cabin V.S.I.
• Inwards relief valves usually open at a negative differential pressure not exceeding 0.5 p.s.i.
• Failure of the normal maximum pressure differential control is allowed for by fitting a safety relief valve.
• A cold air unit produces a drop in temperature by expanding hot air across a turbine which is driving a compressor.
• The function of spill valves is to control air supply to the cabin.
• Pressurisation control ensures that at operational altitude the cabin altitude is below 10,000 ft.
• Pitot and static lines during a cabin pressure test should be connected.
• If the cabin pressure fails to reach its maximum cabin pressure differential, the pressure controller should be adjusted.
• When the aircraft has reached its maximum cabin pressure differential, the discharge valve opens.

Cabin Pressure Control

• A cabin altitude is protected against reaching an altitude of 13,000 ft by an altitude sensor.
• The basic system of cabin pressurisation is to arrange a constant inlet and vary the outlet.
• The purpose of the differential capsule in a pressure controller is to control cabin differential pressure.
• Control of rate of change of cabin pressure is more important in descent.
• With a pressurised aircraft at maximum differential pressure and a cabin pressure increase occurs, the differential capsule in the pressure controller will let all pressurising air to be spilled overboard.
• If the cabin altitude increases above the normal maximum, a warning light comes on in the cockpit.

Air Conditioning and Cabin Pressurisation System Components

• A water separator is located downstream of the turbine.
• A comfortable rate of cabin altitude climb for passengers is 500 ft per min.
• Before carrying out a ground pressure check, all pitot and static lines should be fitted.
• On touch-down of aircraft, the outflow valve will be fully open.
• The velocity of air from the cabin ventilation system should not exceed 120 feet per second.

Inward Vent Valves and Cabin Rate of Climb

• Inward vent valves are fitted to limit negative differentials.
• Cabin rate of climb is shown by a double scale on the aircraft.
• During normal pressurized climb following take-off, the cabin R.O.C is less than ambient R.O.C.
• Inward vent valves will operate when cabin altitude exceeds aircraft altitude.
• Cabin differential pressure is the difference between cabin pressure and ambient pressure.
• Cabin altitude in pressurized flight is the altitude corresponding to cabin pressure irrespective of the altitude for the aircraft.

Temperature Conditioning and Pressure Cabins

• In pressurized aircraft, temperature conditioning is mainly achieved by extracting heat from the pressurising air.
• If pressurisation air supplies come from an engine compressor, an internal oil leak will contaminate the air.
• Heating for pressure cabins is obtained from air supply heated by the pressurising process.
• A cold air unit allows for cabin temperatures to be a little more than ambient air temperature.

Ditching Control and Ground Pressurisation Test

• Ditching control is used to close the outflow valves.
• Prior to conducting a ground pressurisation test, internal doors, cupboards, etc. must be all open.
• Before conducting a ground pressurisation test, the pressure controller must be reset/disabled.

Air Conditioning Systems

• An air conditioning system is used to decrease the temperature of air.
• In the flightdeck of a pressurised aircraft, there is a gauge that shows cabin differential pressure.
• Air exiting the compressor side of an ACM will have increased pressure and temperature.
• Cabin differential pressure is the pressure difference between the pressure inside the aircraft and the ambient air pressure.### Cabin Pressurisation and Air Conditioning
• During a pressurisation check at maximum differential with engines shut-down, the cabin ROC indicator gives indication of cabin seal efficiency.

Bootstrap Compressor

• The water trap is located at the inlet of the turbine in a bootstrap compressor.

Air Conditioning System

• In a 'blower' air conditioning system, the silencer is located at the outlet of the blower.
• The system produces the most air when not affected by altitude.
• Before distribution, the air goes through the Temperature Control Valve (TCV).

Air Mass Flow

• The minimum cabin air mass flow is 0.5 lbs per minute per person.
• The air mass flow control valve maintains a reasonably constant air mass flow into the cabin at all altitudes.

Cabin Air Recirculation System

• Recirculated air and fresh air are supplied in the proportions of 60% of fresh air and 40% of recirculated air.

Cabin Pressure

• Cabin pressure is maintained by controlling the amount of air discharged from the cabin.
• Control of rate of change of cabin pressure is most important in descent.

Air Supply

• Air supplied for pressurisation and conditioning is hottest from an engine compressor bleed.
• The mass flow delivery from engine-driven blowers is controlled by spill valves.

Heat Exchanger

• An air-to-air heat exchanger is provided to reduce the air supply temperature.

Temperature Control

• Temperature control of cabin air is achieved by [no information provided in the text].