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

In FS2004, you cannot set an aircraft's real top speed with cruise_speed. Back up aircraft.cfg, then adjust engine output—static_thrust for jets or power_scalar for piston and turboprop aircraft—and, only when justified, parasite_drag_scalar. Make small changes and test at identical weight, altitude, throttle and weather because the AIR file also controls performance.

The file is normally under FS2004\Aircraft\AircraftFolder\aircraft.cfg. An edit affects every [fltsim.x] variation defined by that file, so changing one livery usually changes all the others as well. Keep an untouched copy and use our safe aircraft.cfg editing and recovery procedure if you are unfamiliar with FS9 configuration files.

Which aircraft.cfg settings change aircraft speed?

The correct setting depends on the engine type and on whether the performance error comes from insufficient power or incorrect aerodynamic drag.

Power and thrust settings are normally the better first choice when the aircraft is slow everywhere. Change parasite_drag_scalar only when there is evidence that the model has too much or too little drag. Avoid using induced_drag_scalar as a general speed control; it has its strongest effect at higher lift coefficients and can distort low-speed handling.

How should I edit and test the speed?

Change one setting at a time in small increments, then compare the aircraft under repeatable flight conditions.

1. Record a baseline. Note the aircraft's weight, altitude, power setting, indicated airspeed, true airspeed or Mach, rate of climb and fuel flow. Let the aircraft stabilise in straight-and-level flight before recording speed.
2. Identify the engine type. Use the section already present in the file. Do not add a piston or turboprop section to a jet merely because it contains a convenient scalar.
3. Make a small change. As an initial diagnostic adjustment, raise power_scalar from 1.000 to 1.030, or raise an existing static_thrust value by about 3%. To test excess drag, reduce parasite_drag_scalar from 1.000 to 0.980. These are test increments, not universal correct values.
4. Reload the aircraft. Save the file as plain text without adding a .txt extension. Restarting FS2004 is the safest way to ensure the configuration has been reloaded.
5. Repeat the same test. Use the same fuel, payload, altitude, weather and throttle setting. Compare like with like: IAS for an indicated-speed limit, or TAS and Mach for high-altitude cruise performance.
6. Refine or reverse the edit. If acceleration and climb become unrealistic before the desired speed is reached, restore the engine value and investigate drag or the AIR file instead.

Do not change thrust, power and drag together on the first test. If the result is wrong, you will not know which edit caused it. A 3% increase in thrust also does not guarantee a 3% increase in top speed because speed is reached where available thrust and aerodynamic drag balance.

Why doesn't cruise_speed make the aircraft faster?

The values under [Reference Speeds] describe reference figures and limits; they do not supply engine power or rewrite the aerodynamic model.

• cruise_speed records a nominal cruise figure used by parts of the simulator or aircraft information.
• 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 speeds rather than directly changing the wing's calculated lift.

Update those entries after correcting the flight model so the stated values and limits remain consistent. Raising max_indicated_speed can move a warning or gauge marking, but it does not give the aircraft more thrust or make the airframe aerodynamically capable of that speed. A custom gauge may also contain its own hard-coded limits.

What if aircraft.cfg changes are not enough?

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

FS2004 combines configuration values with aerodynamic and engine tables rather than treating speed as a single editable number. Our explanation of how flight-dynamics data becomes simulated performance covers that relationship in more detail.

The sim= entry in each [fltsim.x] block identifies the corresponding AIR filename without its extension. Renaming or replacing that file without keeping sim= consistent can cause an Aircraft Initialization Failure. For deeper work, Microsoft's FS2004 SDK package with FSEdit and supporting documentation provides the appropriate tools, but back up both files first.

Common failures after a speed edit

• Nothing changes: FS2004 may still have the old configuration loaded, the wrong aircraft folder was edited, or a custom gauge or AIR-file table is governing performance.
• Every repaint changes: this is expected when all liveries share one aircraft.cfg.
• The aircraft accelerates unrealistically: restore the original drag setting or reduce the power increment; excessive thrust and reduced drag compound each other.
• A propeller aircraft reaches maximum RPM but not the expected speed: propeller pitch, reduction gearing, governor limits or AIR-file data may be the constraint rather than engine power.
• The aircraft no longer loads: restore the backup and check section names, decimal formatting, the sim= entry and whether the editor created aircraft.cfg.txt.