Preview Release

This is an early preview release intended to gather community feedback while development continues. Additional flight-control laws, systems, avionics improvements, and performance refinements are planned for future updates.

JAS39E Advanced Flight Control & Systems Mod is a comprehensive overhaul of the Deimos G39/JAS39E (all variants now included), replacing much of the aircraft's default flight-control logic, aerodynamic modeling, and systems behavior with a custom implementation developed specifically for Microsoft Flight Simulator 2020.

Unlike conventional flight model modifications that primarily tune configuration values, this project replaces significant portions of the aircraft's control architecture with custom logic that drives control-surface scheduling, stability augmentation, and aircraft systems. The goal is to provide a more believable and engaging representation of the JAS39E's handling characteristics while remaining within the capabilities of the MSFS simulation engine.

This project is not intended to be a perfect or certified simulation of the JAS39E.

Features:

Custom Fly-By-Wire Flight Control System

• Completely replaces the default Asobo Fly-By-Wire implementation
• Custom WASM-driven flight-control logic
• Independent control-surface actuator logic
• Realistic control-surface rate limiting
• Custom control scheduling
• Native RPN integration through ModelBehavior variables

Flight Control System

• Custom pitch command system
• G limiter
• AoA limiter
• Roll-rate limiter
• Automatic trim
• Yaw damper
• Surface rate limiting
• Flap scheduling
• FBW on/off
• Pilot-selectable limiter disable
• G-Limit Toggle Switch ( 9G - 12G)

Aircraft Systems Improvements

Numerous cockpit systems have been redesigned to provide more logical and independent operation.

Includes:

• Independent cockpit flood, FMC, and console lighting controls
• Improved switch functionality
• Revised Nose Wheel Steering logic
• Water Rudder command repurposed as an NWS DISC switch
• Complete steering disconnect functionality
• Redesigned AP system functionality
• Custom HUD implementation
• Custom MFD/DDI panel implementation driven by stock Super Hornet logic
• Redesigned multiplayer animations and spawn logic
• Custom model files for improved local and multiplayer animations

Landing Gear & Ground Handling

The landing gear has been revised to better represent the geometry and ground handling characteristics of the JAS39E.

Includes:

• Corrected landing gear track width
• Revised landing gear geometry
• Improved taxi handling
• Updated landing gear dynamics
• Improved takeoff and landing behavior

Aerodynamics

The aircraft's aerodynamic model has been substantially revised using publicly available references.

Includes:

• Reworked aerodynamic geometry
• Updated lift and drag characteristics
• Revised control-surface effectiveness
• Improved pitch and roll response
• Drag tuning based on available Energy-Maneuverability (EM) chart data
• Improved high-speed and high-G handling

Engine Performance

Engine performance has been revised to provide more representative thrust throughout the low and medium altitude envelope.

Includes improvements to:

• Static thrust
• Military power
• Afterburner performance
• Low altitude acceleration
• Tuned performance from sea level through approximately 20,000 feet

Aircraft Animations

Aircraft animations have been refined to better represent control surface motion and mechanical behavior.

Includes:

• Reworked primary flight control animations
• Updated leading and trailing edge flap animations
• Improved stabilator movement
• Refined rudder animation
• Improved engine nozzle animation
• Revised canopy operation
• Improved light positioning

Stores & Weight Distribution

External stores have been revised to better represent publicly available weight and station data.

Includes:

• Revised store weight L/R balances
• Updated center-of-gravity effects
• Corrected geometric placement of external stores
• Improved wing and fuselage station positioning
• More representative aircraft handling as stores are added or removed

Compatibility

Designed for:

Deimos Inc v12.5.25 only!

Do NOT use the Deimos weapons patch. That conflicts with my model file, and will break this mod. Custom weapons are already built-in to the updated base plane.

This mod is designed specifically for Deimos Inc v12.5.25. Because several core aircraft files are replaced, compatibility with future aircraft updates cannot be guaranteed until the mod is updated.

Disclaimer

This project is an independent community modification and is not affiliated with or endorsed by Deimos Inc.

While extensive effort has been made to produce realistic aircraft behavior, the simulation is ultimately limited by the capabilities of Microsoft Flight Simulator and the availability of publicly accessible technical information.

This modification should be considered a research-informed interpretation of the JAS39E rather than a certified or authoritative simulation.

Acknowledgements

This project would not have been possible without the work of several people and teams in the flight simulation community.

• Thanks to Deimos Inc. for creating the G39/JAS39E that made this project possible.
• The FlyByWire Simulations Team for publishing their open-source work and comprehensive WASM architecture. Their documentation and source code provided valuable insight into implementing custom flight-control logic within Microsoft Flight Simulator.
• Thanks to TouchingCloud for their excellent Super Warrior mod, integrating radar into the Super Hornet DDI pages.

All flight-control logic, systems implementation, aerodynamic tuning, avionics modifications, and other features included in this mod were independently developed specifically for this project.

Recommended Operating Procedures

These procedures have been developed around the custom flight-control laws and aerodynamic model implemented by this mod. They should be considered recommended starting points and may vary with aircraft weight, environmental conditions, and fuel state.

Takeoff

Typical configuration (approximately 24,000–26,000 lb, full internal fuel):

• Trailing Edge Flaps: DOWN
• Pitch Trim: 10% Nose Up
• Rotate: ~125 KCAS
• Liftoff: 140–150 KCAS
• Pitch Attitude: 9-11° Nose-High

Heavier gross weights will require higher rotation and liftoff speeds.

Landing

The aircraft is intended to be flown using Angle of Attack rather than a fixed approach speed.

Recommended technique:

• Target 11° - 14° AoA on final, (15 - 20% Nose up trim)
• Typical approach speeds:

  • Light: ~130 KCAS

  • Heavy: ~150 KCAS
• Maintain approximately 75–85% RPM depending on weight, field elevation, and wind conditions.

  Start of the N1 ramp should be around 70-75% and end should be around 80-85%. In mild/moderate gusty conditions active throttle management is necessary. Use sink rate to gauge throttle requirement (target -650 to -750 FPM).

• Use Speedbrakes greater than 50% as required to improve glidepath control.

Because the aircraft uses a custom fly-by-wire system and revised aerodynamic model, approach speeds will vary naturally with aircraft weight.

Recommended Control Setup

The flight-control system has been developed and tested using linear flight control curves with only small hardware deadbands.

| Axis | Recommendation |

| -------| -------------------------|

| Pitch | Linear (0% sensitivity) |

| Roll | Linear (0% sensitivity) |

| Rudder | Linear (0% sensitivity) |

| Deadzone | Small, only enough to eliminate hardware noise |

| Setting | Recommendation |

| ---------------------------| -----------------------------------------------------------------|

| Atmospheric Turbulence | Low |

| Framerate | Prioritize stable frame pacing over maximum average FPS |

The custom flight-control system and aerodynamic model were tuned using these settings.

While the aircraft remains flyable with other simulator configurations, increased turbulence levels and aggressive control sensitivity curves will produce handling characteristics different from those intended. It is strongly recommended to tune these settings prior to flying. Additionally, using 3rd party weather mods or tools that amplify gust or wind-shear effects will produce handling characteristics outside those intended by this mod.

Maintaining consistent frame times generally provides smoother flight-control response than simply maximizing average frame rate. Users with hardware supporting technologies such as Frame Generation may find that these improve perceived control smoothness by reducing presentation jitter, although they do not increase the simulator's underlying physics update rate.

New Flight Control Switches:

Several existing cockpit switches have been repurposed to control custom flight-control functions.

Because MSFS does not expose every real-world cockpit switch, existing controls have been reassigned to provide access to the custom FCS features.

| Switch | Function |

| FBW ON/OFF| Toggled through "FCS On/Off" switch. Disables the custom fly-by-wire schedulers, allowing evaluation of the aircraft without the custom FCS logic.

| DDI SIDE SELECT | Toggled through "DDI Side Select" switch. Functions as a shift key to allow for pressing buttons on the opposite side of the MFD/DDI panel. This is a workaround for lack of modeled buttons in the stock aircraft.

| GPS / NAV | Toggled through "ENG CTRL" switch. Functions as a toggle between NAV or VOR setting the desired heading. Use to get GPS/NAV locks set on the compass.

|HSI RANGE| Toggled through "GAIN" knob. Sets the desired zoom level for the central MFD display.

| NWS DISC | Toggled through "TOGGLE WATER RUDDER" command. Disconnects nose wheel steering, preventing steering inputs from reaching the nose wheel.

Cockpit Lights:

| Switch | Function |

| HUD BRIGHTNESS | Set through the "Flood Lights" knob. Allows for custom control over the HUD brightness.

| HMD BRIGHTNESS | Set through the "CONT" knob. Allows for custom control over the HMD brightness.

Known Limitations

This is a preview release and several flight-control systems continue to be refined as development progresses. The aircraft is fully flyable, but the following behaviors are currently known:

• Aircraft Sounds: I am using a custom sound pack offline, and therefore sound edits are not included in this release. If sounds have problems, please let me know.
• Aircraft Animations: This modification uses an entirely different system and custom model files to drive animations. Due to this, people flying the stock aircraft won't spawn properly for you in MP mode, and vis versa. Everyone you fly with needs this mod for animations to properly spawn and sync. That is not something I can fix. For problems with MP animations where both users have this mod installed, please let me know. MP animation debugging is difficult.

Feedback & Suggestions

This project is still under active development, and community feedback is greatly appreciated.

If you encounter an issue, have suggestions for improvements, or notice behavior that differs from publicly available references, please leave a comment below. Constructive feedback helps guide future updates.

When reporting flight dynamics or systems behavior, it is especially helpful to include:

• Aircraft weight or fuel state
• External stores configuration
• Flight condition (airspeed, altitude, G loading, etc.)
• Control hardware and sensitivity settings
• Any supporting reference material, if available

Thank you to everyone who takes the time to test the mod and share their experiences.