FM Part 1 – Explaining the Original Falcon 4.0 FM Code

The original MicroProse (MPS) FM code has been extensively criticized since the very beginning of the simulator. The time has come to give a fair vision of the quality of the flight model proposed.

First, we must admit that the level of flight simulation was kind of unique for a simulator of 1997. Specific behaviors of the real F-16, like deep stalls or the CAT 1 limiter were evidence that real pilots were involved somehow in the development of Falcon 4 (F4, for short).

Second, thanks to some independent data coders, the accuracy of the two-dimensional (2D) performances (longitudinal accels/decels, turn rates & flight envelope) of the F-16 improved a lot as different patches were released over time. The prime and latest example of this were the “HFFM” series from October of 2004. Even with the Falcon source code, almost no work was ever done to improve the MPS FM as patches were released.

However despite all the improvements possible, the F-16 FM even equipped with the best data could not match the real aircraft and suffered heavily from the comparison with more recent simulators. The following are some examples of major problems with this FM:

  • No sensations were transmitted to the virtual pilot. “Aircraft on rails” was a common expression used to describe F4 flight models. Despite the FLCS of the F-16, anyone who has seen a real F-16 flight path marker (FPM) in flight (from a HUD tape for example) could tell that the Falcon 4.0 stability was exaggerated,
  • Some specific maneuvers were impossible to perform in F4, like knife edge pass, very low speed loop…
  • Many FLCS features were very poorly simulated or even worse compared to the real A/C: CAT 3, Cruise Gains, Landing Gear (LG) Gains. This lead sometimes the virtual pilot to do the exact opposite than the real pilot to perform the same action. Forward pressure on the stick to maintain landing glide slope while the real A/C demands a constant back pressure is an example,
  • Some FLCS features were not even simulated: Aileron Rudder Interconnection (ARI), roll rate control module, the FLCS trying to maintain 1G flight, etc…,
  • Total absence of aerodynamics or inertial coupling whereas this is one of the main subjects of the F-16 and 80% of the FLCS is dedicated to manage those couplings,
  • Stall behaviors and recovery were entirely scripted, reflecting very poorly all the departures possible for the real F-16 (roll departures for instance),
  • Very poor modeling of the rudder and more generally of the yaw problems,
  • Basic mechanics concepts like inertia were poorly implemented,
  • Ground behavior and continuity between air and ground was completely faked making any landing completely unrealistic,
  • No convincing interaction with the Air mass: wind & turbulence effects.

Additionally the whole MPS FM code was built around an F-16 basis making the classic aircraft (Non Fly-By-Wire (NFBW)) aircraft completely unrealistic to fly. Remember that the original Falcon 4.0 code was not supposed to give the player the opportunity to fly anything else but the F-16.

To enter more deeply in the heart of the subject, let’s try to give a general simplified overview of the original MPS FM code.

The MPS FM code is basically built around four main modules:

1) A module that interpolates from the data files the global lift/drag and thrust at a given speed, AOA and altitude.

2) A module that takes as input the global lift/drag/thrust and calculates the motion of the center of gravity (CG) (trajectory) (Euler dot calculation)

3) A pure computerized module based on the FLCS rules of the data files (the limiters) that generates the pitch/yaw/roll rates taking into account the pilots inputs and the flight conditions (AOA is derived from that module and injected in 1)).

4) A ground module that emulates ground behavior when the A/C is on ground by giving some turn rates/radius on ground. This module impacts directly on trajectory and supersedes partially the module number 2) here above (this leads to a major discontinuity between Air and Ground)

The major problem of this code is that the pitch/yaw/roll were not directly linked with the CG trajectory. To summarize, that means that the computed trajectory of the A/C may not be coherent with the attitude of the aircraft. This can be noticed at low speed where pitch rates were not physically possible compared to the trajectory.

Additionally as the module that rules the pitch/yaw/roll rate was purely mathematical and struggled into rules, this ended with the “A/C on rails” sensation, because nothing was dynamically computed but followed math rules rather than physics ones.

From this analysis, in August 2006 we decided to develop completely new FM code that could not only handle a far more realistic F-16 but also general NFBW aircraft.