engines.cfg - Additional Information

This page contains various notes related to some of the functionality derived from the engines.cfg sections and parameters.

Notes On Emergency Boost

The emergency boost system will work in two "modes" depending on whether the emergency_boost_mp_damage parameter has been set to anything other than 0 or not. When set to 0, boost calculations will be done using the legacy FSX time counter:

for water and methanol-water injection:

Elapsed_time = Elapsed_time + ( deltaT * current_rpm / max_rated_rpm )

for WEP:
```
Elapsed_time = Elapsed_time + deltaT
```

NOTE: deltaT here is the "Delta Time" value, which is the time that has elapsed between the last simulation frame and the current simulation frame. See here for a more in-depth explanation.

When setting emergency_boost_mp_damage to a value that is greater than 0, it will enable the Microsoft Flight Simulator 2024 time counter which works like this for methanol-water injection, water injection, and WEP:

Elapsed_time = Elapsed_time + (deltaT * (current_manifold_pressure / emergency_boost_mp_damage))

Considering that a manifold pressure above the damage threshold will accelerate the counter, one should take into account the desired upper limit for manifold pressure when setting the max_emergency_boost_time.

As an example: let's consider an aircraft where going above 61inHg of manifold pressure will start damaging the engine and emergency boost can allow for a maximum of 67inHg. If one wants to be able to spend 315 seconds at 67inHg then max_emergency_boost_time should be set to:

max_emergency_boost_time = 315 * (67/61) = 315 * 1.098 = 346

To get the current elapsed time since the emergency boost has been activated, you can use the SimVar RECIP_ENG_EMERGENCY_BOOST_ELAPSED_TIME.

Notes On Supercharger

In legacy FSX, the supercharger - activated using the supercharged parameter - used a calculation that was actually lacking an essential parameter:

boost = ( supercharger_boost_high_end - supercharger_boost_low_end ) * Throttle_position

In this formula, the supercharger_boost_low_end parameter is not used at all. In Microsoft Flight Simulator 2024 this has been rectified and you can enable the use of the correct formula by enabling the new_supercharged parameter in the engines.cfg file, using one of the following values:

1: This will make the simulation use a fixed formula to calculate the supercharger boost using the existing legacy supercharger parameters supercharger_boost_high_end and supercharger_boost_low_end. Boost will then be calculated using the following formula:
```
boost = ( supercharger_boost_high_end - supercharger_boost_low_end ) * Throttle_position + supercharger_boost_low_end
```

2: This will permit the simulation to have multi speed support for the supercharger using the following parameters: supercharger_altitude_gear.N, supercharger_boost_high_end_gear.N, supercharger_boost_low_end_gear.N. This system will allow for a maximum of 5 gears. As an example, if a two speed supercharger is needed then the CFG parameters would have this structure:
```
supercharger_altitude_gear.1 = [VALUE]
supercharger_boost_high_end_gear.1 = [VALUE]
supercharger_boost_low_end_gear.1 = [VALUE]
supercharger_altitude_gear.2 = [VALUE]
supercharger_boost_high_end_gear.2 = [VALUE]
supercharger_boost_low_end_gear.2 = [VALUE]
```
When using the multi-speed supercharger you can monitor which gear is engaged by monitoring the SimVar RECIP_ENG_SUPERCHARGER_ACTIVE_GEAR. The supercharger system will continuously check if the current Pressure Altitude is superior or equal to the altitude at which each gear should engage in order to automatically switch between the gears. If an altitude is set as -1.0 the gear is considered inactive and the engaging altitude for this gear will not be checked thus preventing the switch to this particular gear (which is why default altitude value is -1.0). When a gear is engaged the boost values corresponding to this gear will be used in the following calculation of boost:
```
boost = ( supercharger_current_gear_boost_high_end - supercharger_current_gear_boost_low_end ) * Throttle_position + supercharger_current_gear_boost_low_end
```

IMPORTANT! When using the "new_supercharged" param, the legacy "supercharged" parameter must be either set to 0 or removed from the CFG file.

Note On Autofeathering

If your aircraft is to support auto-feathering, then it is worth knowing the following information to enable you to set it up and use it correctly:

You must have created a dedicated electrical circuit.N of the type CIRCUIT_AUTO_FEATHER.
You will need to set up the min_n1_for_autofeather_armed parameter as this will be used to arm autofeathering (if the N1 goes above this value, it will be armed).
You will need to set up the max_n1_for_autofeather_actuated value, which is used to unfeather the propeller when the N1 goes above this value.
NOTE: Currently you will need to use the alias max_pct_torque_for_autofeather_actuated since there is a bug in the code.

Once those have been setup, in the simulation the SimVars CIRCUIT AUTO FEATHER ON and PANEL AUTO FEATHER SWITCH will need to be set to 1.

Note On Propeller Pitch And Throttle

The parameter min_flight_beta_throttle_pos enables the propeller pitch control algorithm in the BETA-range of throttle (power lever), while simultaneously defining a throttle position that forces the propeller to the minimum flight pitch, specified by the beta_min parameter. The way this works is that the min_flight_beta_throttle_pos value essentially divides the entire range of travel of the throttle into two ranges:

the normal position (ie: when the throttle position is greater than the min_flight_beta_throttle_pos), in which the propeller pitch is controlled by the governor, in accordance with the prop speed set by the throttle
the beta position (ie: when the throttle position is less than or equal to the min_flight_beta_throttle_pos), in which the throttle position sets the the propeller pitch using the following guidleines:
- When the throttle is less than or equal to min_flight_beta_throttle_pos then the propeller pitch is at beta_min.
- When the throttle is at 0 then the propeller pitch is at minimum_on_ground_beta.
- When the throttle is less than 0 and greater than or equal to the min_throttle_limit then the propeller pitch is at minimum_reverse_beta.

NOTE: Set tp_high_idle_throttle_pos to the min_flight_beta_throttle_pos if you want a turboprop engine to idle in the range of throttle positions between 0 and tp_high_idle_throttle_pos.

When min_flight_beta_throttle_pos is greater than 0 it will additionally have the following effect on the simulation:

If the throttle is in the thrust reverse range (ie, the throttle position is less than 0) and prop_reverse_available is enabled, then the minimum propeller pitch limitation no longer depends on the throttle position (this is the same as for Microsoft Flight Simulator 2020 aircraft). Thus, if a pilot sharply moves the throttle from the reverse position to position 0 and above, then the propeller blades will no longer exit the reverse mode instantly, but will increase pitch at a limited speed.
When the following conditions are met:
- the throttle is greater than 0 and:
- prop_reverse_available is enabled and:
- one or more landing gear is touching the ground and:
- the ground type is not water:
then the minimum propeller pitch limitation is no longer set to the minimum_on_ground_beta. Thus, it becomes possible to control the propeller pitch in the BETA-range, regardless of the interaction of the aircraft landing gear with the ground.

Note On Corrected Values

The various parameters that use corrected values have their calculations based on the following paper:

GAS TURBINE PARAMETER CORRECTIONS, by Allan J. Volponi
January 2020
DOI: 10.1007/978-3-030-41076-6
ISBN: 978-3-030-41075-9