Force effects reference

The force pipeline runs a stack of sub-models in parallel: a base centring spring, two airspeed-loaded constant forces, several sustained aero-drag pushes, and a catalogue of continuous and one-shot rumble / buffet / shudder channels. Everything sums into pitch and roll outputs, scaled by the master gain, gated by the master arm. This page documents each effect: what it simulates, what telemetry drives it, and what you should hear / feel when it fires correctly.

At a glance

1. Centring spring

Telemetry

G-load, airspeed, pitch/roll trim positions, control deflection

Output

Spring coefficient + centre offset, both axes

Key sliders

Base, low-speed floor, 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. The low-speed floor keeps the stick from going limp during taxi and after simulator disconnects, while still letting profiles soften the spring when airflow is low. 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.

Trim Trim authority determines how strongly telemetry relieves held aerodynamic force, and on aircraft whose controls are cable-linked to the trim system it also shifts where the control settles. Hydraulic and fly-by-wire types such as the 737 and A320 trim the stabilizer, so their control column stays neutral-centred while trim runs; force relief still works on every type. Elevator and aileron are independent; set either slider to 0% to disable that axis.

1a. Control-system feel

Telemetry

None — per-aircraft profile metadata

Output

Modulates the centring spring and airspeed-loaded forces

Key control

Control system selector (page-level card)

Not a separate effect — a per-aircraft setting on the Tuning page (saved in the profile) that reshapes how the centring spring and aero-load forces behave, to match the aircraft's flight-control architecture:

• Manual — mechanical / cable-driven controls. The controls load up with airspeed and stiffen under G, the classic direct-linkage feel. Built-in for the C172, TBM 930, and King Air 350i.
• Hydraulic-boosted — gentler, smoother boosted feel. Aerodynamic loading is still present but reduced. Built-in for the 747-8.
• Fly-by-wire — a constant side-stick spring that doesn't load with speed or G, the way an isolated side-stick feels. Engine rumble and the stall stick-shaker are also silenced on the side-stick (a real fly-by-wire side-stick is mechanically isolated and doesn't transmit them) — flight cues like stall buffet and ground / touchdown still come through. Built-in for the A320neo.

Rotorcraft

Rotorcraft control systems enable cyclic damping and force trim plus six dedicated cues: ETL shudder, VRS buffet, 2/rev vibration, retreating-blade-stall buffet, skid scrape, and rotor rumble. Each gain uses 0% as off. VRS buffet uses the simulator's own vortex-ring-state indication alongside the bridge's heuristic, whichever is stronger.

Rotation kick · Surface follow · Sideslip coupling

Rotation kicks (the plane being shaken sideways pushes the stick), surface back-drive (severe gusts and stall flutter come through the column), and sideslip cross-coupling so a yawed aircraft pushes its ailerons through the airflow.

Control friction

Telemetry

No simulator telemetry — reacts to physical stick or yoke motion.

Output

Native Friction condition on pitch and roll.

Key control

Strength slider; 0% is off, and 5–10% is a sensible starting point.

Control friction adds breakout and sliding resistance that stays roughly constant as you move the control. Rate damping instead follows the simulator's aircraft pitch and roll rates and opposes faster aircraft rotation more strongly; helicopter cyclic damping is the effect tied to physical stick velocity.

It is optional and off by default. Unsupported backends remain inert; FFB-Bridge never synthesizes friction with constant forces.

2. Airspeed-loaded pitch force

Telemetry

Indicated airspeed, elevator deflection, pitch trim

Output

Constant force on the pitch axis

Key sliders

Pitch gain (trim modulates the input)

Pushing or pulling the stick at cruise should feel like pushing against air. Force scales with airspeed squared. With trim disabled, the input is total elevator deflection. With trim enabled, the input is (elevator − trim) — so a trimmed aircraft with the stick at the trimmed position feels zero force. The control-system feel above scales this force: reduced under Hydraulic-boosted, removed under Fly-by-wire.

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 follow cue

Telemetry

Autopilot-on, AP commanded pitch/roll

Output

Physical back-drive of the linked axis toward the AP command; a bounded spring-centre cue on the MSFS coupled path

Key sliders

AP authority, AP strength

When enabled, AP follow physically moves the stick toward the autopilot's command. On X-Plane, when the aircraft does not drive its own controls, the bridge takes per-axis ownership of the control datarefs while the AP is engaged and back-drives the stick with the full saved 0–100% authority on every device; the pilot residual is written back to the sim, so grabbing the yoke still reaches X-Plane. Ownership is released at disarm, disconnect, and shutdown, and the Zibo 737-800X is detected through its own autopilot and its datarefs are never written. On MSFS no axis ownership is possible, so the coupled path renders a bounded cue from a washed flight-director/surface reference, with live authority capped at a validated 20%. On MOZA AB6, AB9, and AY210, follow runs in the base's own firmware.

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. An undercarriage-type multiplier set per profile (wheels / skis / floats) further scales the continuous ground-roll rumbles (runway rumble, gear bumps, nosewheel shimmy) — skis run a touch stronger, floats softer.

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: a fixed amplitude multiplied by the impact speed the simulator latches at contact, which stays correct on sloped ground.

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.

10a. Nosewheel shimmy

Telemetry

On-ground, ground speed

Output

Continuous lateral (roll-axis) vibration

Key sliders

Shimmy gain

A rapid side-to-side wobble on the roll axis at and above taxi-rotation speed — the classic nosegear shimmy. Ramps in from a low ground speed and holds. Tuned per profile: strongest on the free-castoring GA nosewheel, weaker on steered and damped airliner gear.

10b. Ground-acceleration pitch cue

Telemetry

On-ground, longitudinal body acceleration

Output

Signed pitch-axis force

Key sliders

Ground-accel gain

On the ground, fore/aft acceleration is felt as a pitch-axis cue: the takeoff surge throws you back (stick aft), braking pushes you forward (stick forward). Scales with the longitudinal acceleration, with a small deadband so taxi jitter doesn't trip it, and never fires airborne. Tuned per profile by mass and braking authority.

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

Telemetry

AoA, stall warning, overspeed warning, Mach, spoiler handle, flap handle, gear handle, airspeed, ambient turbulence, detrended G-load variation

Output

Periodic force with a randomised envelope

Key sliders

One gain per sub-effect

Several sub-effects share the buffet generator.

• Stall buffet. Builds progressively as AoA crosses a low threshold and saturates at the sim's stall warning. Both the AoA envelope and the stall-warning flag are gated while on the ground, so it stays silent during taxi and the takeoff roll.
• Stall stick-shaker. A sharp, fixed-frequency buzz gated directly on the simulator's stall-warning flag, distinct from the AoA-ramped stall buffet. It stays silent on the ground, and its airspeed floor comes from the aircraft's design stall speed where the simulator publishes one, with a fixed 40 kt fallback. Its profile-backed amplitude uses 0% as off; raise it only for an aircraft with a real mechanical shaker. It remains silent for Fly-by-wire control systems, whose isolated side-sticks have no shaker.
• Overspeed buffet. Triggers on the sim's overspeed flag. Sharper frequency than stall.
• Mach buffet. Fires at high Mach on swept-wing aircraft. Where the aircraft publishes its own barber-pole Mach limit, the buffet is graded against that limit in the same relative window the overspeed cue uses; the profile's fixed Mach window remains the fallback. Silent on GA props.
• Spoiler buffet. Begins at the first crack of deployment at about a quarter of the selected strength, stays on continuously while the spoilers are deployed and held at any flying speed, and grows with both deployment and airspeed to the configured strength. Deployment movement additionally renders a travel cue.
• Flap buffet. Sustained low-frequency vibration whenever flaps are extended at speed. This comes from real-world pilot accounts of elevator oscillation with >20° flap extension. Set to 0% on profiles whose POH doesn't note this.
• Gear buffet. Drumming from gear-down drag in the air. Ships at 0% on fixed-gear profiles (C172); the per-effect slider on Tuning lets retractable-gear profiles dial it up.
• Turbulence overlay. Random shake scaled by how much the aircraft is being knocked around. On X-Plane the sim's ambient-turbulence signal feeds in directly; on MSFS the bridge derives it from the variation of recent G readings around the current G trend, so the pilot's own smooth maneuver produces nothing while genuine choppy air feels the same as before at the same setting.

12. Engine rumble

Telemetry

Sim per-engine vibration (MSFS ENG VIBRATION, XP12 engine_vibration) when reported; otherwise RPM percent + combustion flag

Output

Continuous periodic force

Key sliders

Engine-rumble gain

Preferred source is the sim's per-engine vibration value, which carries aircraft-specific texture (mag drop on runup, rough engine, turbine spool, prop imbalance) the bridge can't model from RPM alone. When the sim reports it, the bridge uses it as the authoritative magnitude, scaled by the gain slider.

If the sim doesn't report engine vibration (some freeware MSFS models and legacy X-Plane aircraft don't), the bridge falls back to a synthesised RPM ramp + combustion gate. The fallback is smooth-by-construction but lacks the texture of the sim signal.

The gain slider scales the chosen source either way, so dropping it to 0% silences engine rumble regardless of aircraft. Under the Fly-by-wire control-system feel, engine rumble is silenced on the stick automatically — an isolated side-stick doesn't transmit it.

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, both retraction and extension. A flap-step shudder fires on any non-zero step — both extension and retraction. A sustained gear-transit vibration runs while the landing gear is actually travelling, driven by the gear motor circuit where the simulator reports one (MSFS 2024) and by actual gear movement elsewhere; the Gear travel control silences it at zero.

Flap movement combines the actuator circuit and actual surface travel as independent evidence, so the cue runs when either shows the flaps moving, and it follows failures. The short flap-step detent cue is a separate event tied to the handle.

15. Sustained aero-drag pitch forces

Telemetry

Flap handle, spoiler handle, gear handle, engine thrust, airspeed

Output

Sustained backwards pitch bias

Key sliders

Flap drag, Spoiler drag, Gear drag, Propwash pitch

Sustained pitch forces that mirror the trim-out you feel in the real aircraft when configuration changes:

• Flap drag. Backwards pitch force any time flaps are extended at speed.
• Spoiler drag. Same idea for spoilers / speedbrake.
• Gear drag. Same for gear-down drag at speed. Set to 0% for fixed-gear aircraft.
• Propwash pitch. Constant pitch-up bias modelling propwash over the elevator on a prop aircraft. Turboprops follow engine torque; piston aircraft follow propeller RPM.

Safety gate: pause + stale-telemetry watchdog

Most safety gates are automatic; watchdog timing is the one advanced setting in this section:

• Sim pause is instant. The moment MSFS reports paused (pause menu, Active Pause, frozen frame) or X-Plane reports paused, every dynamic force drops to zero on the same tick. The stick holds a neutral default spring (50% coefficient, 5% deadband) so it stays centred and never goes limp.
• Menu and time compression. Forces stop in the MSFS 2024 main menu, which publishes an incoherent flight frame that used to render overspeed and Mach buffet on an armed stick. Forces also stop above 2× time compression, because rate-derived forces arrive already multiplied by the simulation rate; only centering remains. Forces stop immediately on the change and return through the normal arm ramp.
• Device-reset recovery. While armed, FFB-Bridge verifies once a second that its effects still exist on the device and rebuilds them when another program (for example SteamVR) has reset the device. A bounded retry latches with an explanatory message rather than looping.
• Telemetry stall. If the sim keeps reporting "unpaused" but the values stop changing for ~2 seconds (the frozen-frame watchdog catches MSFS / Proton silent pauses that don't set the pause flag), the bridge enters the same neutral-spring safe state.
• Watchdog fade. If the sim stops sending packets entirely, the user-tunable Settings → Advanced → Watchdog sliders control how long before forces fade to zero and over what window. Defaults are conservative — five seconds of silence before fade-out begins, half a second to fade.

Combined output

Every effect sums into two outputs — a pitch force and a roll force — plus the spring parameters. Master gain is applied at the device-output edge to everything the bridge sends, including the spring coefficient; 0% is silent, 100% is the tuned design level. The Dashboard separates the always-present baseline spring from dynamic channels like axis load, engine rumble, ground roll, buffets, sustained aero-drag, and mechanical one-shots, so you can see why the stick feels alive even when the signed pitch / roll force is near zero.

Hardware-aware rendering

FFB-Bridge selects the validated effect path for known hardware and uses compatibility fallback only when needed. The normal workflow no longer asks users to choose between duplicate hardware and software effect modes. Open the hardware guide.

Install-level pitch / roll polarity

Different devices can report physical direction differently. Correct axis and force polarity once under Hardware.