134 lines
4.8 KiB
Text
134 lines
4.8 KiB
Text
By Default systems are initialized by the Aircraft/generic/generic-system.xml
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This initializes the following:
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- The generic electrical system
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- 1 pitot system, index [0]
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- 1 static system index [0]
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- 2 vacuum systems [0] and [1], depending on engine rpm of engine[0] and
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engine[1] respectfully
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If you want to define more systems, copy the generic-system file to your
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aircraft-name/Systems folder and rename it systems.xml
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In your aircraft -set file add the path to the system.xml file:
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<sim>
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....
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<systems>
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....
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<path>Aircraft/aircraft-name/Systems/systems.xml</path>
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....
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</systems>
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....
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</sim>
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** Adding a second pitot system.
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In your systems.xml, you should already have
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<pitot>
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<name>pitot</name>
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<number>0</number>
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<stall-deg>60</stall-deg> # optionnal, default to 60 degrees
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</pitot>
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and you need to add for a pitot system with index 1:
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<pitot>
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<name>pitot</name>
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<number>1</number>
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<stall-deg>60</stall-deg> #optionnal
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</pitot>
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For the any pitot system except for the first (with index 0)
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add in the aircraft -set file (below for index 1):
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<systems>
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<pitot n="1">
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<serviceable>1</serviceable>
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</pitot>
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</systems>
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Of course you can add a third or fourth etc.
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** Adding a second static system
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Absolutely analog with the pitot system. So add in systems.xml:
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<static>
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<name>static</name>
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<number>1</number>
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<tau>1</tau>
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<type>0</type> #optionnal: 0,1 or 2 default is 0
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<error-factor>0.5</error-factor> #optionnal see below default = 0
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</static>
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and in the aircraft -set file:
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<systems>
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<static n="1">
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<serviceable>1</serviceable>
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</static>
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</systems>
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Now you can source your instrumentation relying on static and pitot
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pressure (airspeed, altimeter, vertical speed indicator) from different
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and independent systems
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** The PITOT System
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The pitot system measures impact pressure and is basically a tube pointing forward.
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Small aircraft have one, small IFR aircraft have one or two (of which at least
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one is heated) and larger commercial aircraft have three or even more. In those large
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aircraft the left pitot serves the pilot instruments, the right the co-pilot and
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the third system the back-up instruments. This might be different for each type
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of aircraft of course.
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In Flightgear the pitot system outputs the total pressure to the following property:
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/systems/pitot[n]/total-pressure-inhg and
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/systems/pitot[n]/measured-total-pressure-inhg
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which are the same except at supersonic speeds. For supersonic aircraft use the "measured"
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property. See also the README.airspeed-indicator.
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However it is advised for every aircraft to use the measured property. In future
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this will be the property where all the measurement faults are reflected.
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the following "measurement failures" are currently applied:
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1) decrease of total and measured pressure due to side-slip and angle of attack
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2) at 60 deg the pitot tube will stall and the value will fall back to static pressure
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3) for the "measured" property only: at Mach>1, a shock wave is assumed in front of the
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pitot tube, decreasing the total pressure.
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The stall angle may be (optionally) set to any angle between 0 and 90 deg
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(default = 60 deg) like so:
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<pitot>
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<name>pitot</name>
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<number>0</number>
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<stall-deg>45</stall-deg>
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</pitot>
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Both the decrease of the pitot pressure and the default stall angle are based on a measurement
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on an AN5812 pitot tube.
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** The STATIC system
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The static system measures the static pressure. So all influences of airspeed are eliminated.
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In real life this is however not always easy. Effects from angle of attack, side-slip, flap defection,
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gear extension, engine power setting and airspeed are present and for the aircraft
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designer it is not alway easy to find a good position for the static port.
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Usually the number of static systems are equal to the number of pitot systems.
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In Flightgear there are 3 types of static systems modelled.
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Type 0 (default): the perfect sensor. No measurement failures.
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Type 1: Dual static ports on the fuselage sides. Side-slip angle influence only. this model the whole pair.
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Type 2: Static port on the pitot tube. Both angle of attack and side-slip influence.
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If you want to use type 1 or 2:
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<static>
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<name>static</name>
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<number>0</number>
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<tau>0.1</tau>
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<type>1</type>
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<error-factor>0.5</error-factor>
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</static>
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The output property /systems/static[n]/pressure-inhg is filtered. Therefore, if you want to see
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the effect of the measurement failure, "tau" should be 0.1 or smaller.
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The "error-factor" should be between 0.2 and 0.7. Setting it to 0 equals a "perfect sensor".
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A setting of 1 means the whole (projected on static port face) impact pressure is applied.
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This is not realistic as usually there are more than one static pick-up points
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and so the pressure increase gets "flattened".
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