One can then turn off or on the per-engine SOVs as per the supply switches and fire handles. Pack L and pack R are turned on as per the Air Cond Cockpit and Air Cond Shutoff switches. The center pack is turned off (by script or plugin) and never turned on again. Twin engine plane (McDonnell-Douglas)įor a plane like the MD-80, which has two isolation valves, operation becomes very simple: In that case, the system operates as GPU-fed until the GPU is off. If theAPU valve was commanded to open while the system is pressurized from the GPU, it simply wouldn’t open. Note that GPU and APU can never feed together – in real planes, the APU load control valve is also a one-way check valve. This way, the left engine is to the left of the isolation, and GPU and right engine are to the right of the isolation. To the right of the isolation valve is the right engine.įor operation on GPU, the isolation happens to the left of the GPU! That is, the isolation valve of the 737 in GPU feed is now the ISOL L valve in the X-Plane system (and ISOL R is always open). This way, center and left duct belong together, and are fed by left engine and APU. That is, the isolation valve of the 737 with APU feed is the ISOL R valve in the X-Plane system (and ISOL L is always open). For the sake of explanation, let’s assume we are looking at the 737, where the APU feeds into the left duct and GPU feeds into the right duct.įor operation with the APU, the isolation happens to the right of the APU. This is where it gets airplane specific and one needs to look at a diagram for the specific airplane: Look up whether the APU and GPU feed into the left or the right from the single isolation valve. Now the only remaining switch is the (single) isolation valve found in such aircraft. One can turn off or on the per-engine SOVs as per the engine switches. One can then turn on pack L and pack R as per the pack switches. The plugin can turn pack C off and pretend it doesn’t exist. That must be done actively by script or plugin, since X-Plane will never turn off the center pack – that would break existing aircraft! For correct operation, one must turn off the legacy center pack and never turn it on again. Twin engine plane (737, A320, CRJ, ERJ, etc.): The system operates exactly like a 747 would: Three packs are available, per-engine SOVs, APU SOV and GPU SOV and two isolation valves work exactly like you’d expect when comparing the above graphic to the schematic of a 747. If an APU was installed, it would feed into the center duct regardless of the isolation valve settings, controlled by the APU valve, just like the GPU. The bleed air mode thus maps to the isolation valves: left bleed air means left isol valve open, right bleed means right isol valve open, bleed both or auto mean both isolation valves open. The pack can be fed from the left engine, the right engine, or both. The center duct supplies the one center pack that provides air to the cabin. Two-engine plane with single pressurization (old King Air or similar) There’s only one duct, and only one available pressurization pack, center. Bleed “auto” adds APU valve on (the single engine plane most likely doesn’t have an APU, but if it has, it would work), GPU adds GPU off or on. The bleed selector doesn’t care for left or right or both, the isolation valves have no function, the only available settings are: Bleed “off” meaning engine shut-off valve off and Bleed “on” (any of L, R or BOTH) meaning engine shut-off valve on. Packs L and R are always off because they don’t exist. The center pack is the single source of cabin pressure. Single-engine plane (Lancair Evolution or similar) New to X-Plane 11.35 are: GPU bleed, left pack, right pack, wing-anti ice supply, and per-engine shut-off valves.Īnother way to understand the system is as a Lancair (legacy X-Plane) overlaid with a King Air overlaid with a 747 – you will then understand how to design many more aircraft types with it: 1. Both APU and the center engine in a one- or three-engined plane are considered to be providing air from the center of the aircraft. X-Plane legacy aircraft know only one pressurization pack, and one selector that selects the sources for this pack: left hand side of the aircraft, right hand side of the aircraft, and APU. The center components provided for compatibility are clearly marked. The system design is best understood with this diagram: X-Plane 11.35’s bleed air system is an extension of the earlier X-Plane bleed air system, designed both for versatility and compatibility.Īt the center of the new bleed air system is the center manifold which serves as the backward-compatible portion that is used by all airplanes, designed to provide basic bleed air and pressurization capabilities for existing aircraft.Īircraft modernized for X-Plane 11.35 and later can make use of the left and right extensions of the bleed air system, and opt to use 1, 2 or 3 air conditioning and pressurization packs.
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