How do I change aircraft speed via aircraft.cfg in FS2004?

In FS2004 (FS9), an aircraft’s true performance cannot be set with cruise_speed or a speed.cfg file. Back up aircraft.cfg, then tune static_thrust for jets, power_scalar for piston or turboprop aircraft, and only if the drag model is wrong, parasite_drag_scalar. Test one small change at a time under identical conditions.

Where is aircraft.cfg, and is there a speed.cfg file?

Each FS2004 aircraft normally has an aircraft.cfg in FS2004\Aircraft\AircraftFolder\aircraft.cfg, with the first part depending on where Flight Simulator 2004 was installed. FS2004 itself has no standard per-aircraft speed.cfg; if an add-on includes that filename, it is a custom add-on file rather than an FS9 flight-model file.

Do not confuse aircraft.cfg with the simulator-wide FS9.cfg. An aircraft edit normally affects every [fltsim.x] livery defined in that aircraft’s file, because those variations share the same engine and flight-tuning sections.

Keep an untouched copy before changing anything. Our aircraft.cfg backup, editing and recovery procedure covers hidden file extensions, plain-text saving and the permissions problems commonly encountered when FS2004 is installed under a protected Windows folder.

Show me the config: which settings control aircraft speed?

There is no single top-speed value: choose the setting that matches the engine type and the part of the performance envelope that is wrong.

If take-off, climb and cruise are all weak, test the appropriate power or thrust setting first. If take-off and climb already match the aircraft’s expected performance but maximum level speed is wrong, investigate parasite drag or the AIR file rather than adding engine power.

Avoid treating induced_drag_scalar as a general speed control. Induced drag matters most when the wing is producing a high lift coefficient, so changing it can damage climb and low-speed handling without fixing high-speed cruise.

How do I make a turboprop faster in Flight Simulator 2004?

For a turboprop in Flight Simulator 2004, begin with the existing [turboprop_engine] power_scalar only when the aircraft is underpowered in both climb and cruise. A temporary change from 1.000 to 1.030 is a useful diagnostic increase of 3%, not a universal correct value.

If the engine already reaches its expected governed RPM or torque while the aircraft remains slow, more power_scalar may simply produce unrealistic torque, take-off and climb. Propeller efficiency, blade pitch, governor limits, reduction gearing or AIR-file tables are then more likely to be the constraint.

Compare the aircraft against the correct figure. Turboprop cruise specifications are normally true airspeed at a stated altitude, weight and power setting; indicated airspeed or wind-affected groundspeed is not an equivalent measurement.

How should I edit and test aircraft speed?

Use a controlled before-and-after test so that the configuration change is the only meaningful variable.

1. Record the baseline. Stabilise in straight-and-level flight, then note weight, altitude, throttle or power setting, indicated airspeed, true airspeed or Mach, climb performance and fuel flow. For propeller aircraft, also record RPM and any available torque or manifold-pressure indication.
2. Identify the existing engine section. Edit the section appropriate to the aircraft. Do not add a piston or turboprop section to a jet merely to obtain a convenient scalar.
3. Change one value. As a diagnostic test, increase an existing power_scalar from 1.000 to 1.030, multiply a jet’s existing static_thrust by 1.03, or reduce parasite_drag_scalar from 1.000 to 0.980. Pick one of these tests, not all three.
4. Save it as aircraft.cfg. Use plain text, retain the original section and key names, use a full stop for decimal values, and make sure the editor has not created aircraft.cfg.txt.
5. Reload the aircraft. Restarting FS2004 is the safest way to ensure the changed configuration has been read rather than retained from the previous aircraft session.
6. Repeat the same flight condition. Match fuel, payload, centre of gravity, altitude, weather, temperature and power setting. Use IAS for an indicated-speed limit and TAS or Mach for cruise performance; do not tune an aircraft using groundspeed.
7. Check the whole result. If acceleration and climb become excessive before the desired level speed is reached, restore the engine value and investigate drag, the propeller model or the AIR file instead.

A 3% thrust increase does not produce a 3% speed increase. Maximum level speed occurs where available thrust balances aerodynamic drag, and that relationship is not linear.

Why doesn’t cruise_speed make the aircraft faster?

The [Reference Speeds] entries describe nominal figures and limits; they do not add engine output or change the aircraft’s aerodynamic calculations.

• cruise_speed provides a reference cruise figure used by parts of FS9 or an add-on, but it is not a physical speed command.
• max_indicated_speed and max_mach define reference limits that gauges or overspeed logic may use.
• flaps_up_stall_speed and full_flaps_stall_speed record reference stall figures rather than directly rewriting the wing’s lift model.

Raising cruise_speed or max_indicated_speed may alter displayed information, a gauge marking or warning behaviour, but it will not make the aircraft accelerate to that value. Correct the flight model first, then update the reference entries so the displayed numbers and limits agree with the resulting performance.

What if aircraft.cfg changes are not enough?

If reasonable power and drag adjustments cannot reproduce the required performance, the limiting data is probably in the associated .air file, propeller model or custom gauge logic.

The sim= line in each [fltsim.x] block identifies the AIR filename without its extension. For example, sim=MyAircraft expects the corresponding MyAircraft.air file; breaking that relationship can produce an Aircraft Initialization Failure.

An AIR file is not a normal text configuration file. Back it up and use a suitable flight-dynamics editor rather than opening it in a text editor; our guide to deciding when aircraft.cfg is insufficient and the AIR file must be examined explains the division between the two.

Why did the edit do nothing or break the aircraft?

• No performance change: the wrong aircraft folder may have been edited, FS2004 may still have the old configuration loaded, the file may be read-only, or the relevant limit may reside in the AIR file or custom gauge code.
• Every repaint changed: this is expected when all [fltsim.x] entries share one aircraft.cfg and AIR file.
• Acceleration and climb became unrealistic: reduce or restore the power change. Do not combine extra thrust with reduced drag until each has been tested independently.
• A propeller aircraft reaches maximum RPM but remains slow: inspect propeller pitch, governor behaviour, gearing and AIR-file data rather than continuing to raise engine power.
• The aircraft no longer appears or loads: restore the backup and check the filename, section syntax, decimal formatting, sim= entry and whether Windows or the editor added a hidden .txt extension.