bleed air and pneumatic system

[seed]

hello

 

i have a question and a request

 

what is the difference between main air supply switch and bleed air switch in ESP??

 

and has anybody got a DIAGRAM of pneumatic system of a10c to post in here??

 

thanks

[mvsgas]

IIRC, Bleed air switch is to control... well bleed air while main air supply is for cabin pressure.

Hope this helps

5.0. Environmental Control System

The Environmental Control System (ECS) provides a life-sustaining comfortable

environment for the pilot when the canopy is closed during preflight, flight, and

postflight operations. Bleed air is extracted from the left and/or right engine compressor

tenth-stage bleed ports or from the Auxiliary Power Unit (APU), and is supplied to the

precooler. The precooler cools the hot engine bleed air which is then divided for cabin

air and service air usage. Precooled bleed air for cabin usage is supplied to the cabin air

conditioning and cabin pressurization systems. Precooled bleed air for service usage is

supplied to the anti-g suit system, canopy and windshield defog system, rain removal

system, and windshield wash system. Service air is also supplied to the inflight refueling

purge system and the external fuel tank pressurization system. Should a total electrical

failure occur, the ECS and its components are designed to provide fail-safe operation.

System control capability will be disabled while the components maintain the position

achieved prior to the electrical failure. The ESC consists of:

Bleed Air Supply System

Bleed Air Leak Detection System

Cabin Air Conditioning System

Cabin Pressurization System

Cabin Depressurization and Ventilation System

Anti-G Suit System

Canopy and Windshield Defog System

Rain Removal System

Windshield Wash System

Windshield Deice System

Compartment Cooling System

Embedded GPS/INU (EGI) Cooling System

Fire Extinguishing System

Liquid Oxygen (LOX) System

Emergency Oxygen System

5.1. Bleed Air Supply System

The bleed air supply system supplies tenth-stage engine bleed air from either engine or

from both engines simultaneously. An onboard APU is used as an auxiliary bleed air

source. An external ground air source can be applied through the ground start transition

duct to be used as a source for bleed air supply and/or engine starting power during

ground operation. Bleed air is applied through an engine bleed air shutoff valve in each

engine nacelle to the penta-manifold, which is a central location for the merging of bleed

air from either engine, APU, or ground support equipment. The bleed air is then applied

through the penta-manifold to the engine bleed air regulator and shutoff valve where it is

regulated to 65 psi and applied to the flow limiter. The Environmental Control Unit

(ECU) converts bleed air to conditioned cabin air which is then applied through insulated

ducting along the right side of the aircraft to the cabin. For purposes of maintenance, a

red poppet-type bleed air overpressure indicator button extends to indicate that a system

overpressure condition has occurred. The button must be manually reset (depressed)

when duct pressures subside.

5.3. Cabin Air Conditioning System

The cabin air conditioning system uses bleed air supplied by the left or right engine 10th

stage bleed ports or by the APU. External air from ground support equipment (applied

through the ground start transition duct) can also substitute for engine or APU bleed air

when ground operation of the cabin air conditioning system is desired. The bleed air is

routed through the precooler to the ECU pressure regulator, shutoff valve, and to the

temperature control valve. Bleed air from the ECU pressure regulator and shutoff valve

is then routed to the ECU, where it is converted from precooled bleed air to cooled

conditioned air for the cabin. Levers are installed on top of each ejector to regulate the

flow of air into the cabin. The conditioned air is then vented through the cabin pressure

regulator to the electronics and avionics compartments to further assist in cooling

equipment within these compartments. The cabin air conditioning system is controlled

by switches and controls on the environment control panel.

5.4. Cabin Pressurization System

The cabin pressurization system compensates for the difference between ambient air

pressure and cabin air pressure during flight from 10,000 feet to 40,000 feet. The cabin

pressure regulator valve provides cabin pressurization by automatically regulating the

discharge of conditioned cabin air. Below 10,000 feet, the cabin remains unpressurized.

From 10,000 feet to 18,000 feet, the cabin pressure altitude is maintained at a level of

10,000 feet (±1000). From 18,000 feet to 40,000 feet, the cabin is pressurized to 2.75 psi

above ambient air pressure. Cabin pressure is monitored by the CABIN PRESS ALT

indicator located on the environment control panel. Overpressurization protection is

provided by a cabin pressure safety (dump) valve when the cabin pressure exceeds 3.25

(±0.15) psi above ambient air pressure.

5.5. Cabin Depressurization And Ventilation System

The cabin depressurization and ventilation system ventilates cabin air pressure in flight.

Should the cabin become overpressurized, the windshield crack, or the canopy jar loose,

depressurization should be used. If the cabin air conditioning system fails or the cabin

becomes smoke-filled, the ventilation system should be used. Depressurization occurs

when the MAIN AIR SUPPLY switch is set to MAIN AIR SUPPLY with the

TEMP/PRESS switch set to either DUMP or RAM. In this way the cabin safety valve

opens to exhaust the pressurized cabin air. Depressurization will also occur when the

MAIN AIR SUPPLY switch is set to OFF. Ventilation occurs when the TEMP/PRESS

switch is set to RAM.

[seed]

in what situation these switches should be off??

manual says if "service air hot" or "bleed air leak" cautions occurs turn the bleed air switch to off.

if i turn off bleed air switch EGI and other avionic systems would warm up and damage.

Edited November 26, 2012 by seed

[seed]

non of my business but any clarifications would be appreciated.

:smartass:

[mvsgas]

in what situation these switches should be off??

manual says if "service air hot" or "bleed air leak" cautions occurs turn the bleed air switch to off.

if i turn off bleed air switch EGI and other avionic systems would warm up and damage.

 

When should the be off? Follow the manual. Bleed air leaks can cause fires. EGI overheating may damage the equipment but not the aircraft. Which one will you prefer, aircraft fire due to bleed air or damaged EGI or other avionics?

[seed]

ok

thank you mvsgas

[StrongHarm]

From a previous thread:

I was an Aviation Environmental Systems Technician for a while in the military.

 

Oxygen

Positive pressure is the key. The o2 regulators in our military aircraft are super expensive. They have the best available components and redundancies. The mask is sealed against your face so the o2 system can fill your lungs for you. Sometimes in a highG or stressful situation, breathing isn't on the top of your priority list. As stated earlier, having an oxygen rich environment in the cockpit can be bad if there's a fire. o2 isn't flammable, but remember the flame triangle... heat, fuel, o2.. increase any one of those and your flame increases. I used to soak cigarettes in liquid oxygen, light them, and watch them go off like rockets.

 

 

Cooling

There are two cooling systems we use; Air Cycle Turbines (ram air) and Chemical Condenser (liquid chemical).

 

The liquid chemical system is similar to what you'd see in a car, but the military uses chemicals that make freon seem drinkable in your morning coffee. In some heat exchange systems they use liquid nitrogen when necessary, but that is super inefficient and dangerous due to the high expansion rate (800:1) of a chemical that is -321F. Liquid nitrogen is just super compressed gas. It's much more efficient to compress a gas or liquid in a closed system where it doesn't have to bleed off.

 

The Air Cycle system is interesting and super efficient: There's a scoop that takes in ambient high speed air from the outside of the aircraft. It flows through a turbine fan that is connected to a shaft to another turbine fan that turns fast enough to pull clean air from around the outside of the compression section of the jet engine(bleed air). The hot air is forced by that turbine system (ram air), through a small orifice. The physical impact of the super heated air being rammed with such force through a small orifice super cools the air to around -30F. This system also inherently pulls any moisture out of the air. Other valves provide pure hot bleed air to increase the temp of that air if it drops too low, depending on the system or area being cooled. On most weapons systems there are elaborate heat exchangers made of classified materials that this air runs through. A good example of this physical reaction of Ram Air is to blow on your hand with your mouth open (like steaming glasses to be cleaned), then blow on your hand like you're cooling it (small orifice in lips).

[bradleyjs]

Love the diagrams guys -- very educational - thanks!

 

Used to be an aircraft mechanic (USAF) back in the early 80's ...