Propulsion for Aviator File Format (*.prop)

A propulsion file is an ASCII text file that is formatted for compatibility with STK and ends in a .prop extension. In STK's Aviator capability, It defines the rate at which the aircraft will speed up or slow down and provides a method for computing the fuel flow for an Aviator aircraft.

Aero and prop files may be used in several different performance model representations with Aviator (standard aircraft, Advanced Fixed Wing, Missiles, and potential plugin representations) and it is important to understand that ultimate aircraft performance is not only a function of the underlying data, but also the code and algorithms that apply that data. An example of this involves computing the effect of thrust on lift. Each of the performance models make use of slightly different methods for performing that function based on the needs of the different representations. Some are more efficient but offer less accuracy, while others are more robust to highly nonlinear data. Each makes use of the data for its own purposes that may differ from the other representations. It is generally not possible to fly a complex high performance maneuver in one representation and achieve the exact same numbers for AOA or ThrustRequired or Ps as another representation. They should be very close, but because the different representations were established to meet specific requirements and apply to different use cases, they may differ slightly.

Keywords

A propulsion file contains some common elements called keywords, defined in the following table. Keywords and their associated values must precede the specification of the actual data points. Keywords used in propulsion files are not case-sensitive.

Keyword	Required	Description
Version: <major release number>.<minor release number>	Yes	The version of STK software for which the file is formatted. Files can be created in, and imported to, STK software versions either consistent with the file version stamp or a later version. Example: Version: 9.0 You can import a file created in and stamped with version 9.0 into STK software version 9.0 or later.
AccelerationG:	See Note	Defines how quickly the aircraft speeds up at maximum throttle. If DecelerationG is included, this keyword must also be included. If this keyword is omitted, you will be able to specify the parameter in the Aviator user interface.
DecelerationG:	See Note	Defines how quickly the aircraft slows down when the thrust setting is at a minimum. If AccelerationG is included, this keyword must also be included. If this keyword is omitted, you will be able to specify the parameter in the Aviator user interface.
DensityExponent:	No	Defines the relative impact of atmospheric density on the aircraft's acceleration/deceleration performance. A supercharged/turbocharged engine with a variable pitch propeller may have an exponent close to zero, while a non-turbo/supercharged engine may have an exponent closer to 1; 0.7 is a common setting for turbine powered aircraft. If this keyword is omitted, you will be able to specify the parameter in the Aviator user interface.
DensityScale:	No	Scale acceleration/deceleration performance by the ratio of density at altitude to sea level density raised to the Density Ratio Exponent. Give a value of 1 turn this keyword on or a value of 0 to turn it off. If this keyword is omitted, you will be able to specify the parameter in the Aviator user interface.
NormalizeThrottle:	No	For n thrust and fuel flow tuples specified, an internal throttle value is linearly interpolated between the two bounding data points with the fraction being added to the 0-based index of the lower bound. This results in a range of throttle values from 0 to n-1. The default behavior is to normalize this internal value. This generates a throttle value between 0 and 1. The normalized value is computed by dividing the internal value by n-1. When dealing with unevenly spaced data, the un-normalized mode may be preferable as it explicitly indicates the interval used to generate the throttle value. Give a value of 1 turn this keyword on or a value of 0 to turn it off.
NThrottleTuples:	Yes	Indicates the number of tuples of paired thrust and fuel flow values contained in each data row.

Data Column Formats

Propulsion data is grouped into rows of numerical values. Each row must contain values for altitude (in meters) and airspeed (in Mach number) and at least two tuples of paired thrust and fuel flow values (in newtons and kg/s, respectively). There is no maximum number of tuples that can be specified in a single file. The data need not be in any consistent order or formatting; the data is triangulated and interpolated across triangle faces.

Data units in propulsion files are STK default units and cannot be changed. Each number is converted inside the application to the user-specified scenario units.

Click here to view a sample .prop file.