X-Plane has two vacuum systems per airplane, one for the pilot side instruments and one for the copilot side instruments. By default, the suction is generated by pumps driven by the engine, so it is dependent on your engine RPM.
Two additional sources of vacuum are available in X-Plane 11.30:
- an aircraft can be equipped with a venturi tube instead, a very simple system found on vintage aircraft, where the suction is generated by the air going through a venturi tube placed on the fuselage, so it is effected by airspeed and propeller slipstream
- an electric backup pump that can be switched on and provide suction when the engine pumps fail
Engine-driven vacuum pumps – single engine
X-Plane simulates the vacuum system for physical vacuum-driven gyros as follows:
- There are two vacuum systems: One for the pilot instruments, one for the copilot instruments.
- If you have no copilot instruments, then no problem: The second vacuum system goes unused, like it is not even there.
- Each vacuum system has exactly one vacuum pump, which may be failed by the instructor.
- For a single-engine airplane, that one engine turns both pumps… and if your plane has only one system, no problem! Just don’t specify any instruments as “Copilot”, which would have them use the second system.
- The low-vacuum annunciator goes off if EITHER vacuum system runs low, but if you want to make an instrument that tracks WHICH system has run low on pressure, the simply use these datarefs
- For airplanes that have TWO vacuum pumps on ONE system, we just don’t simulate that, just like we don’t simulate both the tire and innertube inside it… we only simulate the actual outgoing force that you see. So, for the dual-vacuum pump planes that have two pumps on one system, simply fail the vacuum pump in the failure list to take out BOTH pumps, since that will remove the pumping pressure from the system.
Engine-driven vacuum pumps – twin engine
- For a multi-engine airplane, engine one turns the pump on system 1, engine 2 turns the pump on system 2… and if your plane has only one system, no problem! Just don’t specify any instruments as “Copilot”, which would have them use the second system.
- If the vacuum system is set up in a way that both engine pumps pull from a common vacuum manifold, check the “vacuum systems cross-tied” in Plane Maker on the Systems page. In this case, with both engines running you will have plenty of suction, and in case of an engine failure, the one remaining pump will be enough to sustain suction at most power settings, but maybe not at idle RPM.
Electric backup
If your aircraft is equipped with an electric backup pump, you can use the dataref
sim/cockpit2/switches/standby_vacuum_pump
to turn on the electric pump in case the engine-driven pump has failed.
Venturi for Vintage aircraft
If you check the “venturi vacuum system” in the Systems page of Plane Maker, X-Plane will not run the engine driven vacuum pumps and instead place a venturi tube on the fuselage, like you’d see in an old a straight-tail 172. That venturi tube will be affected by the airspeed and the propeller slip stream, so you will first see it generating suction during the engine runup, when there is plenty of airflow from the propeller.