Flight Model

Every helicopter in the pack flies on real forces rather than on a scripted “move forward” push. Lift, drag and the turning forces are worked out and applied to the aircraft many times a second, so the aircraft behaves like an object with weight rather than a vehicle on rails. No two aircraft handle the same way. Each one is tuned around its own weight, drag and control strength, so a nimble MD500 and a heavy AW101 Merlin need very different technique.

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How It Works

The pilot’s own machine works out its flight forces locally, so the controls answer instantly — there is no delay while the server replies, no rubber-banding, and no stepping while you hold a turn. Everyone else — co-pilot, passengers, people on the ground — sees the aircraft move smoothly from the server’s updates, whether or not anyone is flying it.

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Flight Modes (Simple / Advanced)

The server’s flight.flightMode picks one of two flying personalities on top of the same physics:

• Simple (default) — assisted. Let go of the collective and the aircraft tries to hold its height, turns are helped along, and the controls are smoothed. Attitude still holds when you let go of the stick, and full aerobatics still work.
• Advanced — manual. No height hold, far less help through a turn, and crisper controls. Let go of the collective in a climb or a descent and the aircraft keeps going until you stop it yourself. The collective gauge on the HUD shows where your vertical power sits in both modes.

Each mode also has its own set of options (simple / advanced) covering Autohover, wind and the Advanced-only behaviours below — see Flight Mode Profiles.

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Wind

With windPhysicsEnabled switched on in the mode you are running, the world’s live weather wind actually pushes the aircraft — mostly as gusts that shove and lean you rather than one steady push. It only starts to bite a couple of metres off the ground and is at full strength by about 15 m up, so it is a flying problem, not a parking problem. Off by default; strength set by windStrength.

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Thin Air At Altitude

Air gets thinner as you climb, and the rotor feels it. Lift is scaled down with height above sea level:

• About 9% of your lift is gone by 1,000 m above sea level, and about 18% by 2,000 m
• The scaling never falls below 20% — height alone will never take your lift to nothing
• It works alongside the service ceiling below, which is a separate limit

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Advanced-Only Flying Behaviours

Three extra behaviours only exist in the Advanced profile:

• Vortex ring state (vrsEnabled / vrsSeverity / vrsOnsetDescent) — drop too fast into your own downwash and the rotor loses its grip on the air. It can only happen when you are descending faster than vrsOnsetDescent (default 6.0 m/s), slower than the ETL speed, and more than 2 m above the ground-effect height. It counts your speed in any direction, so sideways or backwards speed gets you out of it just as forward speed does. Fly out into clean air or ease the collective to get out of it. A fast descent with speed on, or one close to the ground, never triggers it.
• Anti-torque (antiTorque, default 0.04) — pulling collective kicks the nose sideways like a real single-rotor helicopter. Catch it on the pedals. It never happens on the Chinooks or the Ospreys.
• Blowback (blowback, default 0.08) — the nose wants to rise as you gain speed. Trim against it.

Blowback and anti-torque can never take more than a quarter of the pilot’s own control strength, whatever value you set, so neither can overpower you. vrsSeverity defaults to 0.22.

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Control Feel (Tau Smoothing)

Each control has two timing values under control.response: how quickly it winds up when you press a key, and how quickly it settles back when you let go. Smaller numbers feel sharper, larger numbers feel heavier. Advanced mode runs all six about a third quicker than the numbers in the file, which is most of what makes it feel crisper. A time of 0 or less cannot work, so it is replaced with that helicopter’s default and reported in the server log.

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Ground Effect

Close to the ground the rotor gets extra lift from its own downwash:

• aerodynamics.groundEffectBonus sets how much — 0.10 (+10%) on the MD500, MH-6 and SA342M, 0.12 on the UH-1H, Blackhawk, Merlin, Mi-24 and Osprey, 0.13 on both Chinooks, and 0.16 on the Barrel Helicopter
• aerodynamics.groundEffectAlt sets the height below which it applies — between 5 m and 17 m depending on the aircraft. A small value is used as you set it, and 0 effectively switches ground effect off; a negative one is replaced with that helicopter’s default and reported in the server log
• The bonus fades away evenly as you climb: full at ground level, nothing at that height
• Low hovering feels a little steadier because of it

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Translational Lift (ETL)

Moving through the air makes the rotor more efficient, so you need less collective to hold height than you do in a hover. It counts your speed in any direction, so flying sideways or backwards earns it as well as flying forward:

• aerodynamics.etlBonus sets how much extra lift you get — Barrel 0.18, MD500 0.12, MH-6 0.13, SA342M 0.11, UH-1H 0.09, Blackhawk 0.08, Merlin 0.07, MH-47G 0.06, CH-47D 0.06, Mi-24 0.08, Osprey 0.06
• aerodynamics.etlSpeed sets the speed (in knots) at which the full bonus is in — 24 · 24 · 24 · 26 · 28 · 30 · 32 · 35 · 35 · 32 · 35 in that same order
• The bonus starts building at half that speed and is fully in at the speed itself, so an MD500 begins to feel it around 12 knots and has all of it by 24
• Light scouts get the biggest boost and reach it soonest; the heavies get less of it, later
• An etlSpeed of 0 or less cannot work, so it is replaced with that helicopter’s default and reported in the server log

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Tilt And Inverted Flight

Lift pushes out of the top of the rotor, so the more the aircraft tilts, the less of that push is holding you up. Tilt past vertical and the rotor cannot hold you at all — you fall under your own weight, exactly as you should. It is fully recoverable: roll or pitch back towards upright and the lift comes back as the rotor comes back over you.

• There is no artificial tilt limit in manual flight. Loops, rolls and inverted passes all work, in both modes. The one exception is Autohover, which holds pitch and roll inside 40° while it is engaged
• At 90° of tilt the rotor is pushing sideways: no lift at all, all of it turning into speed, and gravity does the rest until you right the aircraft
• This is honest in Simple mode too. The Simple height assist is at full strength up to about 30° of tilt and has faded to nothing by about 63°, so dives and inverted flight genuinely cost you height. Everyday flying under about 30° is unaffected

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Autorotation

If the engine stops — fuel gone, engine destroyed, or shut down on purpose — the rotor keeps turning under its own momentum:

• The aircraft settles into a controlled glide instead of dropping like a stone
• Tilting the cyclic moves you along, so you can glide forward and steer to a landing spot rather than just spinning on the spot
• autorotation.gravityFactor sets how much of gravity the turning rotor cancels — tuned per aircraft (see below)
• autorotation.descentCap sets the fastest you will sink, in knots — also tuned per aircraft
• autorotation.flareStrength (default 6.0) sets how much lift a collective flare buys you at the bottom
• autorotation.coastMinutes (default 4.0) sets how long the rotor keeps turning and making noise after the engine dies in the air — it winds down gradually instead of stopping dead, and the engine and rotor sounds fade together over that time
• A careful pilot can walk away from it

The glide is tuned per aircraft — light scouts sink gently, heavies drop fast:

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Service Ceiling

Each aircraft has a height above which the rotor simply cannot lift it any further: The fall-off is gradual, so performance starts to sag before you reach the ceiling rather than stopping dead at it.

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Top Speed (VNE)

Each aircraft has a never-exceed speed, set per variant with flight.maxAirspeed (in knots) and shown on each helicopter’s page. Fly close to it and drag builds up sharply and holds you there. There is no shared hard cap — every aircraft has its own — and how firm that wall feels is tunable: See Per-Helicopter Settings for the full list of tunable values.

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Tilt-Rotor Flight (Ospreys)

The CV-22B and MV-22B Ospreys are tilt-rotors, and they fly the same way. Each one’s two proprotors sit on engine pods — the nacelles — at the tips of its wing, and the nacelles turn. Pointing straight up, it flies as a helicopter and everything above on this page applies. Tilt them forward and the proprotors pull it along like propellers while the wing carries its weight, like an aeroplane. In between it is a little of both, and the change from one to the other has to be flown.

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Tilting the nacelles

• In the pilot seat, hold B and roll the mouse wheel — the hold key can be changed in Options → Controls (Nacelles: Tilt (hold + scroll)). Wheel up tilts them toward helicopter (straight up), wheel down toward aeroplane (forward). Each click is a tenth of the way
• They turn at tiltRotor.conversionRate degrees a second — 7.5 by default, about 12 seconds end to end, like the real aircraft
• They move smoothly, for the pilot and for everyone watching, and in aeroplane mode they line up with the wing
• The HUD shows the angle on a line above the dials: NAC 90 is straight up, NAC 0 is fully forward, and while they move it shows where they are going, for example NAC 45 > 0

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Near the ground, and taking off

• On the ground the nacelles tilt no further forward than the proprotors can clear it — about 53° forward of straight up on flat ground (about NAC 38), and less when the aircraft is banked or nose-down. Climbing away, the limit eases and is gone about 2 m up. While the ground is holding them the NAC line shows GND in amber
• Coming down with the nacelles forward and the landing gear down, the aircraft tilts them up by itself in good time for the proprotors to clear the ground, only as far as it needs to, and holds them up while you keep coming down. Level off instead of landing and, about 2 seconds after you stop sinking, it lets go and the nacelles ease back to where you set them. It looks ahead at how fast it is sinking and allows for pitch and bank, so on a descent the limit starts earlier than on a climb, and a short message tells the pilot when it takes over. With the gear up it never moves them for you: the HUD shows a red PROP and a message tells you to climb or tilt them up
• The pilot chooses how to take off: straight up with the nacelles up, or a rolling take-off — nacelles at the ground limit, add power, and it rolls and lifts off on its wing and rotor thrust together as speed builds. Raising the nose helps. Once it reaches flying speed — a little above the wing’s stall speed — with the collective up, it lifts its own nose to about 7°, the rotation a pilot makes, so the wing takes it off the runway; hold the nose down if you want to stop it (new in v0.4.7). On the wheels the collective is a straight thrust lever: at the bottom the proprotors idle, at the top they give take-off power, and the roll builds up steadily. You can set the nacelles further forward before you go; they hold at the ground limit and carry on down once you lift off

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Converting to the wing

• Tilt the nacelles forward as speed builds. Tilt them all the way forward from a hover with no speed and the aircraft sinks — the wing is not flying yet
• With the nacelles forward the wing stalls below tiltRotor.wingStallSpeed — about 110 knots by default. It stalls like an aeroplane: the nose drops, a lowered wing drops further, and pulling back does little until it has picked up speed again. The proprotors cannot hold its weight with the nacelles forward, so a climb straight up runs out of speed and falls away. Lower the nose and add power to recover
• Stall warning: with the nacelles more than about 58° forward (below about NAC 32), more than 3 m up and below 1.1 times the wing stall speed, the NAC line turns red with STALL and a pulsing stall horn sounds in the cockpit. Only the people inside hear it
• On the wing the controls are the aeroplane’s surfaces: they need airspeed, and the pull is limited to about 2.5 g. The control surfaces move with the controls: the rudders follow Q/E, the elevator follows pitch, and the flaperons follow roll and droop down in helicopter mode, like the real V-22
• tiltRotor.propellerPull sets how well the proprotors keep pulling as speed builds: 1 is stock, higher is faster on the wing

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Power, speed and height on the wing

• Once the nacelles are forward, the collective is the throttle, like the real V-22’s thrust lever. The climb and descend keys move a lever that stays where you leave it — for every pilot, whatever their Collective Hold setting — and the needle on the collective dial shows where it sits. Centred is cruise power, up is full power, down is idle. Tilt the nacelles back up and it hands back to the normal collective
• With the collective centred it cruises at about 246 knots. Full power takes it to just under its airspeed limit flight.maxAirspeed: about 275 knots on both Ospreys (limit 288). That is roughly 2.3 times its top speed as a helicopter. Below the middle the thrust lever turns the proprotors into an airbrake, slowing you hard at high speed — that is how you get down to landing speed
• Simple flight mode holds the height for you on the wing: pitch (W/S) to climb or dive, let go with the nose near level and it levels off at the new height. Leave the nose set well up or down — more than about 10° up or 5° down — and it lets you keep climbing or diving instead of fighting you. The hold fades out below about 1.3 times the wing stall speed, so a slow aeroplane still stalls, and pulling the thrust lever back lets go of it, so you can come down on low power. Advanced mode has no height hold — you fly it
• Q/E keeps working with the nacelles part-way forward at low speed. In full aeroplane mode the yaw is weaker, like a rudder, so turn by banking. Bank with A/D and pull S for a tighter turn — about 11° a second at 250 knots — and when you roll level the nose lines up with the way you are travelling

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Converting back

• Slow down first. The nacelles only come up as far as the airspeed allows, and are fully up at tiltRotor.helicopterTopSpeed — 120 knots by default — or less
• While they wait, the NAC line shows SLOW in amber: the aircraft is too fast for the rotors to take the weight back. Slow down and they carry on
• With the nacelles up, tiltRotor.helicopterTopSpeed is the airspeed limit and the speed below which they can come fully up. Level flight with them straight up tops out a little below it, nose well down; tilting them a few degrees forward flies faster and flatter, which is what the autopilot does
• Or land rolling, like the real aircraft: thrust lever back, approach at around 115–130 knots on small pitch inputs, gear down, and let the nacelles come up by themselves near the ground so you touch down part-converted, then brake with S. Once the wheels are down, the wing stops lifting unless the thrust lever is pushed well up, so it stays on the runway even after a fast touchdown. At rolling speed the nose can’t be pushed down into the runway, and S still lifts the nose right down to touchdown. See Rolling Landings

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The speed dial

On both Ospreys the speed dial reads double range — to about 324 knots — so the needle does not sit pinned in a cruise. The number in the middle is the real speed.

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When things go wrong

• One proprotor lost: the other still flies it, lopsided and on half the thrust. In a hover it rolls hard toward the dead side; at speed it rolls and yaws toward it
• Engines out on the wing: it glides, with the proprotors windmilling and dragging
• Both proprotors gone: it still glides on the wing if it has speed. Lose both in a hover and it falls
• Vortex ring state: coming down fast and slow as a helicopter can put one rotor into its own downwash before the other — a violent roll toward the lower wing that more power cannot fix
• Damage you can feel: lift comes off whichever proprotor is in worse shape and pedal follows the average of the two, and on the wing the rudder keeps the yaw

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Autopilot and Autohover

The autopilot flies a trip longer than 5 km as an aeroplane. Once it is at least 50 m up it tilts the nacelles forward and cruises on the wing, flying higher than it would as a helicopter — about 110 m above the ground ahead — then holds its cruise speed until it is a few kilometres out and slows firmly, so it is back in helicopter mode by about 2.5 km from the destination. A shorter trip is flown as a helicopter. Pressing Auto Hover or the landing itself brings it back to helicopter mode. Losing a proprotor switches the autopilot and Auto Hover off and leaves the nacelles where they are, so tilt them up yourself. Autohover, and auto-land away from a marked runway, fly an Osprey only as a helicopter. Engaging either one swings the nacelles up, and the pilot keeps control until they are nearly there — a notification says so. If they stop on the way, slow down. Auto-land waits until the nacelles are back in helicopter mode before it starts the landing approach. Range on this fuel. The autopilot map’s range figure allows for the aeroplane cruise. For a destination more than 5 km away — where the autopilot converts — it is worked out at aeroplane cruise speed, 85% of flight.maxAirspeed, with the last 2.5 km flown as a helicopter and about a minute allowed for climbing, converting and slowing down. For a destination 5 km or closer it uses helicopter speed, about 93% of tiltRotor.helicopterTopSpeed, because the autopilot stays a helicopter on short trips. With no destination set, the map shows the long-trip figure. Fuel burns at the same rate per hour in both modes, so on the wing an Osprey goes roughly 2.2 times as far on the same fuel.

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Tilt-rotor settings

Only the two Ospreys’ files have this section. See Per-Helicopter Settings for the ranges each one allows.

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Flying With A Sling Load

A load on the hook changes what the aircraft can do for as long as it is there, scaled by how heavy the load is against the aircraft’s lift class:

• Top speed drops by up to 35%
• Climb and descent rates drop by up to 40%
• Forward drag rises by up to 80% — you accelerate slowly and slow down quickly
• Some of the load’s weight is carried for you by extra rotor thrust — 85% in Simple mode, 55% in Advanced, so Advanced pilots genuinely feel the mass swinging underneath

See Sling Loading for hooking up, the lift classes and the winch.

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Ground Flip Recovery

If a helicopter ends up on its side or upside down, pressing X will roll it back upright.

• Off by default — switch it on with groundFlipRecovery set to 1 in the mode you are running (simple / advanced) in mod_config.json. Turn it on when players keep losing aircraft to rollovers on rough ground
• Works from any attitude tipped past roughly 70°. An upright helicopter can never trigger it, even parked on the steepest usable slope
• Only works with the lowest part of the aircraft on or within 3 m of the ground and all but stopped — never in flight. Tall aircraft lying on their backs, such as the Ospreys and Chinooks, can be stood up too. It won’t stand up a destroyed wreck
• A tipped helicopter whose pilot seat cannot be reached can be stood up from outside with the Flip Wrench, which works whether or not this setting is on

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When The Pilot Leaves Or Dies

• If the pilot gets out in the air, uses Move to Cabin or switches to the co-pilot seat — which cannot fly the aircraft — Autohover switches itself on and holds the aircraft in place (autoHoverOnExit, on by default in both modes). It needs the engine and rotor both above half power, and the aircraft at least 3.5 m above solid ground
• If the pilot is killed in their seat the aircraft counts as having nobody flying it. It is caught by the abandoned-aircraft handling — held steady, then landed by itself after autoPilot.abandonedLandingDelay (see Thresholds & Toggles). It no longer flies on until it crashes. Someone walking about in the cabin still counts as crew, so that does not trigger it. If the server has autoShutdownOnExitGroundOnly set to 0 the engine is cut the moment the last living pilot is gone and the aircraft autorotates down rather than being flown down