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decaff42 edited this page Dec 21, 2025 · 8 revisions

Editor's Note: This page is still under development.

YSFlight Community Edition (YSCE) retains much of YSFlight's physics engine, however there are some tweaks which clean up some bugs and issues in particular situations.

Atmosphere

The YSCE atmosphere extends from ground level (0 meters) to 32,000 meters.

Air Density

The YSCE Atmospheric Density largely follows the Standard Atmospheric Model below 16,000 meters, but deviates at higher altitudes due to the way performance is calculated.

YSCE Atmospheric Density

Altitude (m) Air Density ($kg/m^3$)
0 1.224991
4000 0.819122
8000 0.529999
12000 0.299988
16000 0.153000
20000 0.084991
31999 0.084991
32000 0

Gravity

YSCE gravity is a constant value at all altitudes:

$$g = 9.807 m/s^2$$

Indicated Air Speed

An aircraft's Indicated airspeed is a function of its altitude and True Air Speed.

$$IAS = TAS \times \sqrt\frac{\rho_{alt}}{\rho_{sea}}$$

Where:

  • $IAS$ is the Indicated Airspeed
  • $TAS$ is the True Airspeed
  • $\rho_{alt}$ is the Air Density at the aircraft's altitude.
  • $\rho_{sea}$ is the Air Density at sea level (0 meters altitude).

Jet Engines

The Jet Engine performance calculations are relatively straight forward and a function of DATVARs and Altitude.

Jet Engine Thrust

The thrust of the jet engine is calculated based on two DAT Variables (THRMILIT and THRAFTBN), throttle setting and altitude (in the form of the jet engine thrust efficiency). This equation does not account for thrust reversers or thrust vectoring.

For non-afterburning operations:

$$T = \eta \times Thr \times THRMILIT$$

For afterburning operations:

$$T = \eta \times \left[ THRMILIT + (THRAFTBN - THRMILIT) \times Thr \right]$$

Where:


Jet Engine Thrust Efficiency

The Jet Engine Thrust Effiency $\eta$ is a function of altitude. For all altitudes between 0 and 32000m, $\eta$ is a one-dimensional linear interpolation of the table. For all values outside the table, the value of the closest is used.

Altitude (m) $\eta$
0 1
4000 1
12000 0.6
16000 0.3
20000 0.084991
31999 0.084991
32000 0

YSCE Jet Engine Thrust Efficiency

Jet Engine Fuel Consumption

The DAT file defines the sea-level fuel consumption at maximum afterburning and non-afterburning throttle settings (FUELABRN and FUELMILI). YSCE does not account for altitude in fuel consumption rates.

For Afterburning operations:

$$\dot{F} = dt \times FUELABRN$$

For non-Afterburning operations:

$$\dot{F} = dt \times FUELMILI \times Thr$$

Where:

  • $\dot{F}$ is the change in fuel weight
  • $dt$ is the change in time
  • $Thr$ is the throttle setting

Lift Coefficient

In YSCE, the Lift Cofficient is a function of a number of DATVARs and the Lift Coefficient curve as a function of angle of attack. The magnitude of the Lift Coefficient, is primarily calculated at two reference conditions: Cruise and Landing. The YSCE Lift Coefficient "curve" is defined by 6 reference angles of attack:

YSCE Lift Coefficient Curve

Stall Regions

If an aircraft is flying at an angle of attack greater than CRITAOAP, it will be in the positive stall region. If an aircraft is flying at an angle of attack less than CRITAOAM, it will be in the negative stall region. If an aircraft DAT File contains post-stall maneuverability specifications, then the player will have various levels of control of their aircraft's attitude as a function of throttle setting. This is mostly designed to simulate the F-22's thrust vectoring capabilities, but can be used in other ways.

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