PNEUMATIC SYSTEM SETUP INFORMATION
On this page you can find additional information and parameters that are related to correctly setting up the Pneumatic System for an aircraft.
Electrical Definitions
Some of the pneumatic system components need to be powered electrically, therefor definitions must be added to the the [ELECTRICAL] section of the systems.cfg file. When setting up the electrics, each component must be defined with a name, its power usage, the bus it's connected to, and a circuit type. There are three types corresponding to the pneumatic components that need power:
CIRCUIT_PNEUMATICS_PACK- for the Pack componentsCIRCUIT_PNEUMATICS_VALVE- for the Valve componentsCIRCUIT_PNEUMATICS_FAN- for the Fan components
A typical circuit definition would look like this:
circuit.56 = Type:CIRCUIT_PNEUMATICS_VALVE #ConsumerCfg:ConsumerPneumatics #Name:PneumaticsValveA #WearAndTearCollision:GlobalDamageYou can find further examples on the following page:
System Operation
This section outlines multiple concepts and principles used by the simulation to define the operation of the pneumatic system of an aircraft.
Update Loop
The pneumatic system will update each component depending on its role in the system. The airflow in the system is not simulated line by line but rather by air-processing component to air processing component, in order to greatly simplify the processing required by the system. This also mean that airflows aren't actually being mixed in the lines on their way to the different components, so it's in the components themselves that all the air is blended.
An air-processing component is a component that is either creating, transforming, or consuming the air flow, as listed below:
- Engine and RamAir: These gather airflow from engine bleed air or aircraft movement.
- Pack: These cool the received airflow from the engines to reach the desired temperature selected by the pilot in the connected areas.
- MixerUnit: This mixes the air received from the packs or the ram air with the air coming back from the areas via the loop
- Area: An area receives airflow from the mixer, mixing it with the existing air already present and sending some back into the loop.
- Line: Lines can become air processing components when they have been set with maximum flow permitted to go through them.
The list above gives an idea of the order in which each of the components is updated within the simulation (except for lines which can be checked multiple times), and the system will always assume this hierarchy is respected. At each air-processing step, the pressure, volume, and temperature of the airflow will be calculated using the pressure and temperature formulas listed below.
Pressure Formula
The simulation pressure formula is as follows:
$$\large P = \frac{nRT}{V}$$
Where:
- \(P\): Pressure in Pascals
- \(n\): Number of moles
- \(R\): Ideal gas constant (8.31446261815324 \(m^3 \times P_a \times K^{-1} \times mol^{-1}\))
- \(T\): Temperature in Kelvins
- \(V\): Volume in cubic meters
Temperature Formula
The simulation temperature formula is as follows:
$$V_1T_1 + V_2T_2 = V_3T_3$$
- \(V\): Volume of the air flow in cubic metres
- \(T\): Temperature of the air flow in °C
By using these formulas, the resulting temperature of two airflows mixing together (\(V_1T_1\) and \(V_2T_2\)) can be written like this:
$$\large T_3 = \frac{V_1T_1 + V_2T_2}{ V_3}$$
Where: \(V_3 = V_1 + V_2\).
Packs
In order to reach the target temperature in each Area, the Packs (via the pack controller) will cool the air received from the Engines on a range wider than the temperature selection knob in the cockpit. In this system, the pack controller will look for the largest temperature delta between the current temperature of an area and the target temperature, to determine how much over the minimum and maximum temperatures of the areas the packs need to go. It will also ensure that the largest delta found won't override the coldest temperature selected by the pilot.
Examples
In these examples, the packs output temperature range goes from 8°C to 50°C.
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Example 1
Area Current Temperature Targeted Temperature Cockpit 30°C 18°C Forward Cabin 24°C 24°C Aft Cabin 24°C 24°C
Here the targeted temperature of the cockpit has just been changed from 30°C to 18°C. This is the biggest temperature delta out of the three areas, but also the biggest temperature delta possible. To determine how much the packs will go under 18°C to cool the cockpit effectively, a ratio is calculated between the difference of temperatures in the area (current temperature to the targeted one) and the range the pack can go. Since the delta is maximum in this example, the pack will go all the way to its lowest temperature possible at 8°C.
With the temperature in the cockpit going lower, the output temperature of the pack will go higher to finally reach a value closer to 18°C. It will, however, not truly reach it, since the air coming back to the mixer from the loop will be warmer because of the other areas being at 24°C.
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Example 2
Area Current Temperature Targeted Temperature Cockpit 18°C 30°C Forward Cabin 18°C 30°C Aft Cabin 18°C 30°C
The targeted temperature of all the areas has been changed from 18°C to 30°C - this is once again the biggest temperature delta possible - so the packs will deliver their highest output available: 50°C. This case is interesting because the cockpit, being smaller than the other areas, will reach its target temperature much quicker, therefore limiting the packs output temperature.
To prevent blowing warmer air than necessary, and heating an area over its target temperature or at the highest possible temperature, the packs will output less warm air and let the hot air valves of each area do the rest. In this case, when the cockpit reaches 30°C, the packs will limit their output to this temperature, even if the other areas still have a bigger delta to cover. This is simply because it is not possible to lower the temperature going out of the mixer into the areas, so if the mixer outputs 50°C, this is the temperature the cockpit will receive and it will go over 30°C while other areas are heating, then go down when they reach their target.
However, it is possible to heat the air going out of the mixer with the hot air valves. So blowing colder air than necessary won't be a problem for the other areas, as their valve will cover the rest of the heating.
NOTE: The hot air valves heat the air coming from the mixer into the areas, but won't go over the temperature threshold set in the CFG files (see AreasMaxTemperature) so the people inside the areas aren't burnt by receiving air at 200°C on them.
Activation / Deactivation Of Areas Temperature
In some aircraft, the knob selecting the temperature of a given area can be turn off, meaning that no temperature is selected. If all the areas temperature selection are not turned off as well, then the deactivated ones will tend to the lowest selected temperature among the other areas. If all the temperatures selection are disabled, the target temperature will be the default one.
Default Temperature
On multiple occasions, a default temperature is used by the system, and it simply corresponds to the middle value between the AreasMinTemperature and AreasMaxTemperature settings from the CFG file. In an aircraft with 18°C minimum and 30°C maximum temperatures, the default would be approximately 24°C.
Valve Modes
When the pneumatic system runs, there are several modes that can be selected for the valves assigned to the system lines. However, these are not fixed modes that are only set once when the aircraft system is initiated, but instead they are changeable during the flight according to what the pilot does on the overhead cockpit controls. As such they are not defined within the CFG files by any parameter (although you can set them using the FLT file [PNEUMATIC_SYSTEM_EX1.N] section for specific flights or missions).
The possible valve modes available are as follows:
- Auto: The system manages the target status of the valve on its own.
- Manual: The target status of the valve is set by the pilot on the overhead.
- Open: The valve is forced open.
- Closed: The valve is forced closed.
When the valve is forced open or closed, it will ignore any target status change from the system.
Notes For Creating A Pneumatic System
In this section we'll outline a few things that should be considered when creating the pneumatic system for an aircraft, starting with the mandatory components that should be included for both pressurization and temperature management:
- Engine: At least one to create the bleed air used in the system.
- Pack: At least one, but you would normally have as many as there are engines.
- MixerUnit
- Hot air regulation valves: These are connected to the line linking the mixer unit and the area.
- Area: At least one.
You can find examples of both simple and complex systems on the following page:
Index Order Between Packs And Engines
When using packs, the system will assume there is an equal number of engines and packs and that they are indexed in the same order. Usually, the first engine (and so the first pack) will be the left one.
Hot Air Regulation Valve Placement
When regulating the temperature of a zone, the valve needs to be included in the Line that connects to the Junction where the air coming from the MixerUnit goes through. Otherwise the valve will not find the mixer unit and won't be able to do its job and the temperature will not be regulated.
Key Events
The table below shows the different key event IDs that can be used to modify things within the electrical system of an aircraft. These are often used along with the Pneumatics SimVars to control the pneumatics systems within the aircraft. For more details on how to use these events, please see here: Event ID's As Key Events.
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