Force effects reference

The force pipeline ships with fourteen effects. Each runs as a separate sub-model feeding into a summing stage, after which a master gain and the master arm gate decide what actually reaches the stick. This page documents each effect: what it simulates, what telemetry drives it, and what you should hear / feel when it fires correctly.

1. Centring spring

Telemetry: G-load, airspeed, pitch/roll trim positions, control deflection
Output: Spring coefficient + centre offset, both axes
Key sliders: Base, G-gain, min clamp, max clamp, deadband

The force pulling your stick toward neutral. Stiffness grows with load factor, matching how a real stick behaves under G. Deadband widens at low airspeeds so the stick doesn't feel sticky at dead-centre on the ramp. The centre offset is shifted by elevator and aileron trim so a trimmed aircraft feels neutral when the stick is at the trimmed position.

TrimRelief alt-trim mode changes the trim coupling. With TrimRelief off (the default), the centre relocates by the legacy partial amount — historical TrimFeel behaviour. With TrimRelief on, the centre tracks trim with full authority, and the airspeed-loaded forces (effects 2 and 3 below) reference (stick − trim) instead of total surface deflection. Net effect: at trimmed steady state with neutral stick, every force is zero and the stick holds at the trimmed position on release. Toggle on the Tuning page under Stick feel.

2. Airspeed-loaded pitch force

Telemetry: Indicated airspeed, elevator deflection, pitch trim
Output: Constant force on the pitch axis
Key sliders: Pitch gain (TrimRelief modulates the input)

Pushing or pulling the stick at cruise should feel like pushing against air. Force scales with airspeed squared. With TrimRelief off, the input is total elevator deflection. With TrimRelief on, the input is (elevator − trim) — so a trimmed aircraft with the stick at the trimmed position feels zero force.

3. Airspeed-loaded roll force

Telemetry: Indicated airspeed, aileron deflection
Output: Constant force on the roll axis
Key sliders: Roll gain

Same idea as the pitch force but on the roll axis. Tuned independently because most airframes have asymmetric pitch-vs-roll authority.

4. Rate damping

Telemetry: Body-axis rotation rates (p, q)
Output: Opposing constant force proportional to rate
Key sliders: Rate-damping gain

Subtracts from the commanded pitch and roll forces in proportion to the current angular rate. This is what makes a sharp stick input decay back toward the trim point instead of ringing around it. Think viscous damping.

5. Stick drop

Telemetry: Indicated airspeed
Output: Constant forward bias on the pitch axis at low airspeed
Key sliders: Force, Fade airspeed

In a non-power-assisted aircraft (most GA), the elevator is unloaded when there's no air flowing over it — gravity plus cable rigging pulls the surface down, which pulls the yoke forward. The pilot feels a constant forward pull while parked or taxiing, fading to nothing once airflow loads the elevator. Modeled as a linear fade from the configured Force at 0 kts to zero at the configured Fade airspeed.

Defaults — Force 0.25, Fade airspeed 30 kts — are tuned for a Cessna-class GA feel: the stick rests roughly halfway forward against the default centring spring, and the bias has decayed to nothing well before rotation. Drop the Force toward 0 to silence it on jet or fly-by-wire profiles where the elevator isn't free to droop. Setting Force to zero disables the effect without flipping the parent enable bit, which is convenient for A/B comparison.

6. Autopilot back-drive

Telemetry: Autopilot-on, AP commanded pitch/roll
Output: Spring centre shift toward AP command
Key sliders: Back-drive gain, rate limit

When the autopilot is engaged, the centring spring's centre tracks the AP's commanded deflection, rate-limited so it moves at a plausible speed. Grab the stick while AP is on and you'll feel it resist in the direction the AP is demanding.

7. Runway rumble

Telemetry: On-ground, ground speed, surface type enum
Output: Continuous periodic force
Key sliders: Rumble gain

Scales with ground speed and the surface-type enum. Grass and gravel are roughly 1.5–1.9× a paved runway; ice is about 0.3–0.5×. Fires only when on-ground is true.

8. Touchdown thump

Telemetry: On-ground (transition)
Output: Single impulse
Key sliders: Thump gain

A single, firm impulse the moment the on-ground flag flips to true. Tuned so a greaser feels softer than a firm arrival, but not by much — it's a fixed amplitude multiplied by the vertical speed at touchdown.

9. Brake shudder

Telemetry: Brake pedal deflection, on-ground
Output: Continuous low-frequency rumble
Key sliders: Brake-shudder gain

Amplitude scales with brake pedal pressure. Gated on-ground so airborne braking doesn't fire it.

10. Gear bumps

Telemetry: Ground speed, on-ground
Output: Repeated short impulses
Key sliders: Bump gain, frequency

Separate from the continuous runway rumble — these are discrete “taxiway seams and paint” bumps. Tuned to feel natural under 40 kt; above that, the continuous rumble dominates.

11. Aero buffets (stall / overspeed / Mach / spoiler / turbulence)

Telemetry: AoA, stall warning, overspeed warning, spoiler handle, airspeed, G-load rolling stddev
Output: Periodic force with a randomised envelope
Key sliders: One gain per sub-effect

This is really five sub-effects sharing a buffet generator.

Stall buffet. Builds progressively as AoA crosses a low threshold and saturates at the sim's stall warning.
Overspeed buffet. Triggers on the sim's overspeed flag. Sharper frequency than stall.
Mach buffet. Fires at high altitude + high Mach; useful on jets.
Spoiler buffet. Scales with spoiler handle position times airspeed.
Turbulence overlay. Uses rolling standard deviation of G-load as a turbulence proxy, feeding a low-amplitude broadband jitter.

12. Engine rumble

Telemetry: Per-engine RPM percent, combustion flag
Output: Continuous periodic force
Key sliders: Engine-rumble gain

Scales with per-engine RPM percent — a four-engine aircraft with one engine dead produces 75% the rumble of one with all four running. Gated by the engine's combustion flag so shutting an engine down silences its share.

13. Reverse-thrust rumble

Telemetry: Reverse-thrust engaged flag, ground speed
Output: Continuous low-frequency rumble, scaled by ground speed
Key sliders: Reverse-rumble gain

Rollout feel after touchdown with reversers deployed. Tapers off below ~30 kt.

14. Mechanical one-shots

Telemetry: Gear handle position (transitions), flap handle index (transitions)
Output: Single impulse per transition
Key sliders: Gear-deploy gain, flap-step gain

A gear-deploy shudder fires on any gear-handle move. A flap-step shudder fires on any non-zero step — both extension and retraction. (Early v1 fired only on extension; a bug that we fixed on the port.)

Safety gate: stale-telemetry watchdog

Not a user-tunable effect but important to know: if telemetry stops flowing, MSFS opens the pause menu, or MSFS Active Pause freezes the aircraft, every dynamic force fades or drops to a safe state and stays there until the stream resumes. Beta.11 also keeps a neutral default spring while paused, so the stick should not go limp simply because the sim is paused.

Combined output

All fourteen effects sum into two outputs — a pitch force and a roll force — plus the spring parameters. Master gain is applied last. The Dashboard separates the always-present baseline spring from dynamic channels like axis load, engine rumble, ground roll, buffets, and mechanical one-shots, so you can see why the stick feels alive even when the signed pitch / roll force is near zero.

Hardware effects vs software-blended periodics

The bridge has two dispatch modes, switchable from Doctor → Hardware compatibility:

Hardware mode (the fresh-install default). On Windows beta.11 uses a compact DirectInput topology: one vector constant, one two-axis spring, and a lazy three-slot periodic pool (Sine, Triangle, Triangle). The firmware still drives the periodic waveforms at native rate, but the bridge reuses a few physical slots instead of retaining one hardware effect per logical cue. The dispatcher reuploads spring parameters after pause / quiesce paths so both axes recover after stutters. Crisp, low-latency, and much safer on old pid.dll stacks.
Software-blended periodics. The bridge keeps only the continuous force / centering hardware path, then synthesises every periodic, one-shot, and buffet in C# at 200 Hz, folding the result into the constant-force outputs. It is the compatibility fallback if a specific Windows driver stack still crashes in hardware mode. Tradeoff: high-frequency effects (engine rumble, gear bumps) feel a touch less crisp because they're rate-limited by the bridge's tick rate.

Either mode is fully tuned — the same fourteen effects, the same sliders, the same Dashboard contribution display. The mode is a dispatch choice, not a feature toggle. Fresh installs prefer hardware mode; software blending is for explicit user choice, failed probe, or classified hardware-effect crash recovery. Restart-required when you flip it because the dispatcher reads the mode at startup. See Doctor for the toggle.

Install-level pitch / roll polarity

Different production runs of the Sidewinder Force Feedback 2 interpret force polarity differently. The bridge applies an install-level polarity flip at the device-output edge, controlled by the Invert axis polarity toggle on the Doctor page's hardware compatibility card. When invert is on, both pitch and roll forces are negated together as the very last step before the device API call. None of the per-effect tuning is involved; the math above stays the same regardless of which way your hardware reads polarity.