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Turbofan Engine System

Implement first-order representation of turbofan engine with controller




The Turbofan Engine System block computes the thrust and the weight of fuel flow of a turbofan engine and controller at a specific throttle position, Mach number, and altitude.

This system is represented by a first-order system with unitless heuristic lookup tables for thrust, thrust specific fuel consumption (TSFC), and engine time constant. For the lookup table data, thrust is a function of throttle position and Mach number, TSFC is a function of thrust and Mach number, and engine time constant is a function of thrust. The unitless lookup table outputs are corrected for altitude using the relative pressure ratio δ and relative temperature ratio θ, and scaled by maximum sea level static thrust, fastest engine time constant at sea level static, sea level static thrust specific fuel consumption, and ratio of installed thrust to uninstalled thrust.

The Turbofan Engine System block icon displays the input and output units selected from the Units list.

Dialog Box


Specifies the input and output units:

UnitsAltitudeThrustFuel Flow
Metric (MKS)MetersNewtonsKilograms per second
EnglishFeetPound forcePound mass per second

Initial thrust source

Specifies the source of initial thrust:


Use initial thrust value from mask dialog.


Use external input for initial thrust value.

Initial thrust

Initial value for thrust.

Maximum sea-level static thrust

Maximum thrust at sea-level and at Mach = 0.

Fastest engine time constant at sea-level static

Fastest engine time at sea level.

Sea-level static thrust specific fuel consumption

Thrust specific fuel consumption at sea level, at Mach = 0, and at maximum thrust, in specified mass units per hour per specified thrust units.

Ratio of installed thrust to uninstalled thrust

Coefficient representing the loss in thrust due to engine installation.

Inputs and Outputs

InputDimension TypeDescription


 Contains the throttle position, which can vary from zero to one, corresponding to no and full throttle.


 Contains the Mach number.


 Contains the altitude in specified length units.

OutputDimension TypeDescription


 Contains the thrust in specified force units.


 Contains the fuel flow in specified mass units per second.

Assumptions and Limitations

The atmosphere is at standard day conditions and an ideal gas.

The Mach number is limited to less than 1.0.

This engine system is for indication purposes only. It is not meant to be used as a reference model.

This engine system is assumed to have a high bypass ratio.


Aeronautical Vestpocket Handbook, United Technologies Pratt & Whitney, August, 1986.

Raymer, D. P., Aircraft Design: A Conceptual Approach, AIAA Education Series, Washington, DC, 1989.

Hill, P. G., and C. R. Peterson, Mechanics and Thermodynamics of Propulsion, Addison-Wesley Publishing Company, Reading, Massachusetts, 1970.

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