Pneumatic Systems
General
Pneumatic Systems are systems that use pressurized air for various purposes. Aircraft may use pressurized air in the following type of applications:
- Cabin Pressurization
- Hot Air De-Icing
- Air-Conditioning (Heating / Cooling)
- Water/Hydraulic Reservoir Pressurization
- Pneumatic actuators
- Engine Starting
Pressurized air in small recip powered aircraft generally come from turbochargers and on turbine powered aircraft, comes from bleed air, i.e. air that is bled off (tapped) from a compressor section as shown in the illustration at right. Because a turbine engine's power output is a function of the compressor output pressure, then bleeding air from the compressor section is akin to a leak and will lower the engine power output slightly. The amount of power drawn from the engine by pneumatic systems may be configured in Standard > Systems > General 2 Tab > Pressurization Panel.
Bleed air from a turbocharger or compressor stage is hot and for many applications needs to be cooled. For small turbocharged GA aircraft, the air is simply cooled through a radiator and then typically used for pressurization of the cabin. For transport category aircraft, the hot air flows into a manifold and from there is distributed and conditioned as required.
Pressurized air for the cabin needs to be conditioned, and by conditioned, we mean heated or cooled and humidified or dehumidified. This cabin air conditioning takes place in what is called a Pack for transport category aircraft. The Packs receive air from the manifolds, condition it, and then pass it along into the cabin to keep passengers happy and comfortable.
Bleed Air / Pneumatic Model
X-Plane's pneumatic model is built around a center manifold, which supports backward-compatibly for airplanes created prior to XP 11.35. This center manifold is the most basic configuration and provides bleed air and pressurization capabilities for all aircraft. Aircraft created for X-Plane 11.35 and later can further implement a left/right or left/center/right pneumatic confguration. This model is illustrated via the diagram below.
You can hover the mouse over the various components for more information about those components. The system is described in detail further below.
Pressurization
- Isobaric versus Constant Differential.
Cabin Pressurization Settings in PlaneMaker can be configured at Standard > Systems > General 2 Tab > Pressurization Panel
Cockpit Controls Datarefs
| Dataref | Type | Writable |
|---|---|---|
| sim/cockpit2/pressurization/actuators/air_cond_on | int y boolean | Electrical air conditioning compressor on, consuming all the amps of rel_HVAC - not needed on airplanes with air cycle machines that drive the air conditioner off the bleed air power itself. |
| sim/cockpit2/pressurization/actuators/heater_on | int y boolean | Electrical heater grid on, 0 = off, 1 = flight max (consumes rel_HVAC amps), 2 = ground max (consumes 2x rel_HVAC amps, turned off by weight-off-wheels) - not needed on airplanes that are using hot bleed air and have no heaters |
| sim/cockpit2/pressurization/actuators/fan_setting | int y enum | Electric fan (vent blower) setting, consuming 0.1 of rel_HVAVC amps when running. 0 = Auto (Runs whenever air_cond_on or heater_on is on), 1 = Low, 2 = High |
| sim/cockpit2/pressurization/actuators/bleed_air_mode | int y enum | 0 = off, 1 = left, 2 = both, 3 = right, 4 = apu, 5 = auto |
Valve Control Datarefs
| Dataref | Type | Writable |
|---|---|---|
| sim/cockpit2/bleedair/actuators/engine_bleed_sov[n] | int[8] y boolean | Engine bleed air shut off valve, close or open |
| sim/cockpit2/bleedair/actuators/apu_bleed | int y boolean | APU bleed air valve, close or open. APU must be running at 100%N1 to provide bleed air |
| sim/cockpit2/bleedair/actuators/gpu_bleed | int y boolean | GPU bleed air valve, close or open. A GPU is supposed to be always available. |
| sim/cockpit2/bleedair/actuators/isol_valve_left | int y boolean | Isolation Valve for left duct, close or open. This separates all engines on the left side of the plane, the left wing, and the left pack from the rest of the system |
| sim/cockpit2/bleedair/actuators/isol_valve_right | int y boolean | Isolation Valve for right duct, close or open. This separates all engines on the right side of the plane, the right wing, and the right pack from the rest of the system |
| sim/cockpit2/bleedair/actuators/pack_left | int y boolean | Left pressurization pack, off or on. The left pack is supplied from the left side of the plane or through the left isolation valve and only available for airplanes made for 11.35 or newer |
| sim/cockpit2/bleedair/actuators/pack_center | int y boolean | Center pressurization pack, off or on. The center pack is supplied from center duct, which can be supplied from a center engine, APU, GPU, or, via the isolation valves, the left and/or right ducts. This pack is the only pack available for airplanes made for X-Plane 11.33 or older |
| sim/cockpit2/bleedair/actuators/pack_right | int y boolean | Right pressurization pack, off or on. The right pack is supplied from the right side of the plane or through the right isolation valve and only available for airplanes made for 11.35 or newer |
| sim/cockpit2/bleedair/indicators/bleed_available_left | float n ratio | Bleed air available in the left duct, which can come from left engines or through the left isolation valve. |
| sim/cockpit2/bleedair/indicators/bleed_available_center | float n ratio | Bleed air available in the center duct, which can come from a center engine, APU, GPU, or, via the isolation valves, the left and/or right ducts. |
| sim/cockpit2/bleedair/indicators/bleed_available_right | float n ratio | Bleed air available in the right duct, which can come from right engines or through the right isolation valve. |
| sim/cockpit2/bleedair/indicators/engine_loss_from_bleed_air_ratio | float[8] y ratio | Bleed air being sapped from the engine, stealing efficiency from the compressor. Writeable only with override_pressurization set |
Bleed Air Commands
sim/bleed_air/engine_1_off
sim/bleed_air/engine_2_off
sim/bleed_air/engine_3_off
sim/bleed_air/engine_4_off
sim/bleed_air/engine_5_off
sim/bleed_air/engine_6_off
sim/bleed_air/engine_7_off
sim/bleed_air/engine_8_off
sim/bleed_air/engine_1_on
sim/bleed_air/engine_2_on
sim/bleed_air/engine_3_on
sim/bleed_air/engine_4_on
sim/bleed_air/engine_5_on
sim/bleed_air/engine_6_on
sim/bleed_air/engine_7_on
sim/bleed_air/engine_8_on
sim/bleed_air/engine_1_toggle
sim/bleed_air/engine_2_toggle
sim/bleed_air/engine_3_toggle
sim/bleed_air/engine_4_toggle
sim/bleed_air/engine_5_toggle
sim/bleed_air/engine_6_toggle
sim/bleed_air/engine_7_toggle
sim/bleed_air/engine_8_toggle
sim/bleed_air/gpu_off
sim/bleed_air/gpu_on
sim/bleed_air/gpu_toggle
sim/bleed_air/apu_off
sim/bleed_air/apu_on
sim/bleed_air/apu_toggle
sim/bleed_air/isolation_left_shut
sim/bleed_air/isolation_left_open
sim/bleed_air/isolation_left_toggle
sim/bleed_air/isolation_right_shut
sim/bleed_air/isolation_right_open
sim/bleed_air/isolation_right_toggle
sim/bleed_air/pack_left_off
sim/bleed_air/pack_left_on
sim/bleed_air/pack_left_toggle
sim/bleed_air/pack_center_off
sim/bleed_air/pack_center_on
sim/bleed_air/pack_center_toggle
sim/bleed_air/pack_right_off
sim/bleed_air/pack_right_on
sim/bleed_air/pack_right_toggle
Pressurization Comands
sim/pressurization/test Pressurization test.
sim/pressurization/dump_on Dump pressurization on.
sim/pressurization/dump_off Dump pressurization off.
sim/pressurization/vvi_down Cabin vertical speed down.
sim/pressurization/vvi_up Cabin vertical speed up.
sim/pressurization/cabin_alt_down Cabin altitude down.
sim/pressurization/cabin_alt_up Cabin altitude up.
sim/pressurization/aircond_on Air conditioning on.
sim/pressurization/aircond_off Air conditioning off.
sim/pressurization/heater_on Electric heater on.
sim/pressurization/heater_grd_max Electric heater on ground max.
sim/pressurization/heater_off Electric heater off.
sim/pressurization/heater_up Electric heater off->on->grd max.
sim/pressurization/heater_dn Electric heater grd max->on->off.
sim/pressurization/fan_auto Vent fan auto (on only with AC or heat).
sim/pressurization/fan_low Vent fan on low.
sim/pressurization/fan_high Vent fan high.
sim/pressurization/fan_up Vent fan setting up.
sim/pressurization/fan_down Vent fan setting down.