I'm roughly (edit: very well) familiar with flight simulation, but recently I came across a new term. In this brochure (scroll to the second page) by Airbus about flight simulators, they talk about

Natural Flight Loop models:

GRM, Aerodynamics...

I've never heard that term before. What does "Natural Flight Loop" mean? Is it Airbus-specific?

(GRM is probably ground-reaction model, aerodynamics is obvious - but that doesn't really explain Natural flight loop, does it?)

EDIT: Ok, "roughly familiar" is a bit understated... I should have made clearer that I'm an aerospace engineer. Actually I have been working on flight dynamics models for simulators myself, so I understand very well, what it needs to develop an accurate flight simulator from a technical point of view (yup - natural flight loop seems to be what is required for FAA FTD Level 6 devices and FFS).

The issue that remains is that I'm curious what this natural flight loop contains in detail.

Is there someone out there who can tell me if this is...

  • executable code (like a .dll or whatsoever),
  • mathematical equations (with probably huge lookup-tables for the parameters),
  • something like Simulink models (or Modelica or ... )?
  • does it contain separate models for actuators, gear, aerodynamics, weight & balance,...?
  • does it contain just the open loop model or also the flight control system?

2 Answers 2


At Airbus, the Natural Flight Loop is the set of the models that simulate the Natural Aircraft behaviour: kinematics, mass, fuel, center of gravity, inertia, thrust, ground handling, ground reaction, slat/flap, aerodynamics.

Let me know if you need more info.

  • $\begingroup$ Ok - thank you for your answer. Can you provide more information, how these models are distributed (executables/mathematical equations/Simulink models/...)? Is this just one big model that contains all the parts or are the models separated and need to be integrated by the user? What about the FCS - is the natural flight loop open or closed loop? $\endgroup$
    – snowflake
    Commented Jan 3, 2019 at 18:04
  • $\begingroup$ It depends on the model, but they have to be integrated by the user. What are you thinking to build? $\endgroup$
    – Afe
    Commented Jan 4, 2019 at 12:29
  • $\begingroup$ I try to get some idea what it takes to develop the software for an FTD/FFS simulator. $\endgroup$
    – snowflake
    Commented Jan 4, 2019 at 18:08
  • $\begingroup$ I am building something similar. One thing not included in GO5 is the scnery which you have to integrate with the flight model. Send me your email if you wish to chat. $\endgroup$
    – Afe
    Commented Jan 5, 2019 at 2:02

It's saying that the the sim software uses mathematical models (input/computation/output loops) that are able to accurately replicate natural aerodynamic behaviour, providing a sim that behaves closer to the real thing. Some simulators are better feeling like the real thing than others.


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