npc_helicopter is a point entity available in 
Half-Life 2 series, 
Portal, and 
Alien Swarm.
A Combine helicopter, (also called a "Hunter-Chopper") armed with a machine gun and capable of dropping mines. The mines are buoyant, and their timer only activates when they collide with the environment. Upon touching an NPC they detonate instantly. They can be dropped one at a time, or when triggered the helicopter can rush a target dropping a massive amount of mines.
This NPC only uses path_track for navigation: When the helicopter finds an enemy, it moves along a chain of path_tracks to the closest one to its target.
Related Entities:
Placement Tip:Hunter-Choppers are used mainly in the Half-Life 2 series as chase vehicles, hence the name.Placement Tip:Helicopter battles require the player to be very mobile, and have some cover available to them. Just one can present a great challenge, so like striders use them sparingly.
Bug:When npc_helicopter that's waiting for Activate input is killed, game crashes! [todo tested in?]Destruction
When helicopter is destroyed 3 helicopter_chunks are created at it's crash location alongs with random number of smaller gibs.
Keyvalues
- Name
(targetname) <string>
- The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g.
parentname or target).
Also displayed in Hammer's 2D views and Entity Report.
- Initial Speed
(InitialSpeed) <float>
- Grace Period
(GracePeriod) <float>
- Time in seconds the helicopter has to see the player before he starts shooting.
- Patrol Speed
(PatrolSpeed) <float>
- Speed at which the helicopter moves if he has no enemy.
BaseHelicopter:
- Initial Speed
(InitialSpeed) <string>
- The speed that the entity should try to reach as soon as it spawns
- Target path_track
(target) <targetname>
- The name of a path_track that this NPC will fly to after spawning.
BaseNPC keyvalues
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CBaseCombatCharacter:
- Relationship
(Relationship) <string> !FGD
- <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this entity likes or dislikes certain other things. Used like the
ai_relationship entity, with this entity as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- Physics Impact Damage Scale
(physdamagescale) <float>
- Multiplier for damage amount when this entity is hit by a physics object. With a value of 0 the entity will take no damage from physics.
CAI_BaseNPC:
- Target Path Corner
(target) <targetname>
- The
path_corner that this NPC will move to after spawning.
- Squad Name
(squadname) <string>
- NPCs that are in the same squad (i.e., have matching squad names) will share information about enemies and will take turns attacking and covering each other.
- Hint Group
(hintgroup) <string>
- Hint groups are used by NPCs to restrict their hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hint group names will be considered by this NPC.
- Hint Limit Nav
(hintlimiting) <boolean>
- Limits NPC to using specified hint group for navigation requests. Does not limit local navigation.
- Sleep State
(sleepstate) <choices>
- Holds the NPC in stasis until specified condition. See also Wake Radius and Wake Squad.
- 0: None
- 1: Waiting for threat
- 2: Waiting for PVS
- 3: Waiting for input, ignore PVS
- 4: Auto PVS
- 5: Auto PVS after PVS
- Wake Radius
(wakeradius) <float>
- Auto-wake if player comes within this distance.
- Wake Squad
(wakesquad) <boolean>
- Wake all of the NPCs squadmates if the NPC is woken.
- Enemy Filter
(enemyfilter) <targetname>
- Filter entity to test targets against.
- Ignore unseen enemies
(ignoreunseenenemies) <boolean>
- Prefers visible enemies, regardless of distance or relationship priority.
DamageFilter:
- Damage Filter
(damagefilter) <targetname>
- Name of the
filter_damage_type entity that controls which entities can damage us.
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Flags
- Wait Till Seen : [
1]
- Gag (No IDLE sounds until angry) : [
2]
- Fall to ground (unchecked means *teleport* to ground) : [
4]
- Drop Healthkit : [
8]
- Efficient - Don't acquire enemies or avoid obstacles : [
16]
- No Rotorwash : [
32]
- Await Input : [
64]
- Wait For Script : [
128]
- Long Visibility/Shoot : [
256]
- Fade Corpse : [
512]
- Think outside PVS : [
1024]
- Template NPC (used by npc_maker, will not spawn) : [
2048]
- Do Alternate collision for this NPC (player avoidance) : [
4096]
- Don't drop weapons : [
8192]
- Loud rotor wash sound : [
65536]
- Electrical drone : [
131072]
- Helicopter lights : [
262144]
- Ignore avoid spheres+boxes : [
524288]
- More aggressive attacks : [
1048576]
Inputs
StartBombingVehicle- Starts the chopper leading enemy vehicles and dropping bombs on them.
StartTrailingVehicle- Starts the chopper trailing enemy vehicles and shooting at them.
StartDefaultBehavior- Starts the chopper in the mode where he always stops at nav points instead of stopping anywhere in between nav points.
StartAlwaysLeadingVehicle- Starts the chopper *always* leading enemy vehicles (regardless of how they are moving w/respect to the path) and dropping bombs on them. This mode is different from StartBombingVehicle in that it never uses the machine gun.
StartSprinkleBehavior- Starts the chopper dropping bombs randomly + shooting at the player.
StartBullrushBehavior- Starts the chopper bullrushing the player.
SetHealthFraction <float>- Sets the chopper health as a percentage of max health.
EnableDeadlyShooting- Starts the chopper being deadly to on-foot players.
DisableDeadlyShooting- Stops the chopper being deadly to on-foot players.
StartNormalShooting- The chopper will fire in short bursts. Good for on-foot experiences.
StartLongCycleShooting- The chopper fires in long bursts.
StartContinuousShooting- The chopper fires continuously.
ResetIdleTime- Allows the helicopter to fire immediately if he's not in the middle of charging or firing.
SetAngles <angles>- Instantly snaps the orientation of the helicopter.
DropBomb- Immediately drops a bomb based on normal bomb dropping rules.
DropBombStraightDown- Immediately drops a bomb directly downwards.
DropBombAtTarget <targetname>- Immediately drops a bomb directly at the target destination, but only if the player isn't right there.
DropBombAtTargetAlways <targetname>- Immediately drops a bomb directly at the target destination, no matter whether it's fair or not.
DropBombDelay <float>- Add a delay before the next bomb is dropped.
BecomeIndestructible- Makes the helicopter take no more damage.
DisablePathVisibilityTests- When the helicopter moves, he will not check for visibility from the path_track to the enemy to cull out path_tracks.
EnablePathVisibilityTests- When the helicopter moves, he will only move to path_tracks that have line-of-sight to the enemy.
BaseHelicopter
MoveTopSpeed- The helicopter will immediately move at top speed toward its current goal, or in its current orientation if it's on top of its goal.
MoveSpecifiedSpeed <float>- The helicopter will immediately move at the specified speed (you provide this as parameter override in units per second) towards its current goal.
ChangePathCorner <targetname>- Tell the helicopter to move to a path corner on a new path.
SelfDestruct- Self Destruct.
Activate- Activate. Use to wake up a helicopter that spawned with the 'Await Input' spawnflag on.
SetTrack <targetname>- Set a track for the helicopter to adhere to. The helicopter will do nothing if it's on the same path, and will move to the closest point on the specified track if it's on a different path.
FlyToSpecificTrackViaPath <targetname>- The helicopter will first fly to the closest point on the path if it's on a different path. Then it'll fly along the path to the specified track point.
FlyToPathTrack <targetname>- The helicopter will fly to the given
path_track.
StartPatrol- Start patrolling back and forth along the current track.
StopPatrol- Stop patrolling back and forth along the track. This will cause the helicopter to come to rest at the track which he's currently flying toward.
ChooseFarthestPathPoint- When tracking an enemy, choose the point on the path furthest from the enemy, but still in firing range.
ChooseNearestPathPoint- When tracking an enemy, choose the point on the path nearest from the enemy.
StartBreakableMovement- The helicopter is now allowed to disobey direct commands to go to particular points if it senses an enemy. It will move to the closest point (or farthest point, if ChooseFarthestPathPoint is used), on the path if it senses an enemy.
StopBreakableMovement- The helicopter can no longer disobey direct commands. It will continue to fly along it's patrol path or to it's specified target even if it senses an enemy.
EnableRotorSound- Starts the chopper's rotors making noise (normal behaviour)
DisableRotorSound- Stops the noise made by the rotors
EnableRotorWash- Makes the chopper exert a force on physics objects underneath its rotor, and produce a wind pattern on any water (normal behaviour)
DisableRotorWash- Turns off the forces and wind pattern
SetAngles !FGD
InputStartLeading !FGD
InputStopLeading !FGDGunOn- Allows the chopper to use its gun (normal behaviour)
GunOff- Prevents the chopper from using its gun
MissileOn- Starts the chopper firing rockets
Bug:Non-functional. [todo tested in?]
MissileOff- Stops the chopper firing rockets
Bug:Non-functional. [todo tested in?]
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BaseNPC inputs
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CAI_BaseNPC:
ActivateSpeedModifier !FGD
DisableSpeedModifier !FGD
Break- Smash into pieces. If this is not possible, disappear.
BecomeRagdoll (in all games since  )- Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. outputs will NOT be fired.
ForceInteractionWithNPC <string> <string> (in all games since  )- Force the NPC to use a dynamic interaction with another NPC. Syntax is <targetname> <dynamic interaction>.
ForgetEntity <targetname>- Clears out the NPC's knowledge of a named entity.
UpdateEnemyMemory (in all games since )- Update (or create) this NPC's memory of of the given entity.
GagEnable
GagDisable- Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.
HolsterWeapon (in all games since )
UnholsterWeapon (in all games since )- Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.
HolsterAndDestroyWeapon (in all games since )- Same as
HolsterWeapon, except the weapon is destroyed once it has been concealed.
IgnoreDangerSounds <float>- Ignore danger sounds for the specified number of seconds.
InsideTransition !FGD
OutsideTransition !FGD
SetBodyGroup <integer>- HACK: Sets this NPC's body group (from 0–n).
SetEnemyFilter <string>
SetHealth <integer>- Set the NPC's health.
SetMaxLookDistance <float> (only in  )- Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.
SetRelationship <string|targetname or classname> <string|disposition> <int|rank>- Changes whether this NPC likes or dislikes certain others. Used like the
ai_relationship entity, with this NPC as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
SetSquad <string>- Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.
StartScripting
StopScripting- Enter/exit scripting state, where NPCs ignore a variety of stimulus that would make them break out of their scripts. They ignore danger sounds, ignore
+Use, don't idle speak or respond to other NPCs' idle speech, and so on.
Wake- Wakes up the NPC if it is sleeping.
CBaseCombatCharacter:
KilledNPC !FGD- Tells the entity it killed something. Despite the name, this can include a player. This input will be automatically sent by the victim when they die.
physdamagescale <float>- Scales damage energy when this character is hit by a physics object. With a value of 0 the NPC will take no damage from physics.
DamageFilter:
SetDamageFilter <string>- Sets the entity to use as damage filter. Pass in an empty string (no parameter) to clear the damage filter.
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Outputs
OnHealthChanged <integer>- Fires when the helicopter health changes. The integer is the percentage of health the chopper has from 0-100.
OnShotDown- Fires when the helicopter is killed. When an info_target_helicopter_crash entity is present, this output should be used instead of
OnDeath.
BaseNPC Outputs
OnDamaged- Fired when this NPC takes damage (
!activator is the damage inflictor).
OnDamagedByPlayer- Fired when this NPC is hurt by a player (
!activator is the attacker or vehicle driver [if friendly fire]).
OnDamagedByPlayerSquad- Fired when this NPC is hurt by a player OR by one of the player's squadmates (
!activator is the attacker or vehicle driver [if friendly fire]).
OnDeath- Fired when this NPC is killed (
!activator is the killer).
OnDenyCommanderUse- Fired when this NPC has refused to join the player's squad.
OnForcedInteractionAborted- Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc.).
OnForcedInteractionStarted- Fired when the NPC starts a forced interaction.
OnForcedInteractionFinished- "NPCs in actbusies can no longer perform dynamic interactions."
Todo: What does this mean?
OnHalfHealth- Fired when this NPC reaches half of its maximum health.
OnHearCombat- Fired when this NPC hears combat sounds.
OnHearPlayer- Fired when this NPC hears the player.
OnHearWorld- Fired when this NPC hears a sound (other than combat or the player).
OnFoundEnemy <targetname>- Fired when this NPC establishes line of sight to its enemy.
OnLostEnemy- Fired when this NPC loses its enemy. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
OnLostEnemyLOS- Fired when this NPC loses line of sight to its enemy.
OnFoundPlayer <targetname>- Fired when this NPC establishes line of sight to its enemy, and that enemy is a player.
OnLostPlayer- Fired when this NPC loses its enemy, and that enemy was a player. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
OnLostPlayerLOS- Fired when this NPC loses line of sight to its enemy, and that enemy is a player.
OnSleep- Fired when this NPC enters a sleep state.
OnWake- Fired when this NPC comes out of a sleep state.
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Dedicated Console Variables
| Cvar/Command | Parameters or default value | Descriptor | Effect |
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sk_helicopter_health | 5600 | int | Helicopter Spawn Health. |
sk_helicopter_firingcone | | float | The angle in degrees of the cone in which the shots will be fired. |
sk_helicopter_burstcount | | int | How many shot bursts to fire after charging up. Bigger number = longer firing. |
sk_helicopter_roundsperburst | | int | How many shots to fire in a single burst. |
sk_helicopter_grenadedamage | | float | The amount of damage the helicopter grenade deals. |
sk_helicopter_grenaderadius | | float | The damage radius of the helicopter grenade. |
sk_helicopter_grenadeforce | | float | The physics force that the helicopter grenade exerts. |
sk_npc_dmg_helicopter_to_plr | | float | Damage helicopter shots deal to the player. Used in ammotype "HelicopterGun". |
sk_npc_dmg_helicopter | | float | Damage helicopter shots deal to everything but the player.Used in ammotype "HelicopterGun". |
sk_helicopter_drone_speed | | float | How fast does the zapper drone move? |
g_helicopter_chargetime | | float | How much time we have to wait (on average) between the time we start hearing the charging sound + the chopper fires. |
g_helicopter_bullrush_distance | | float | Todo: Effect description. |
g_helicopter_bullrush_bomb_enemy_distance | | float | Todo: Effect description. |
g_helicopter_bullrush_bomb_time | | float | Todo: Effect description. |
g_helicopter_idletime | | float | Todo: Effect description. |
g_helicopter_maxfiringdist | | float | Todo: Effect description. |
g_helicopter_bullrush_bomb_speed | | float | Todo: Effect description. |
g_helicopter_bullrush_shoot_height | | float | Todo: Effect description. |
g_helicopter_bullrush_mega_bomb_health | | float | Todo: Effect description. |
Class hierarchy
Tip:Use info_target_helicopter_crash entities to suggest spectacular crashing points for defeated helicopters.
Note:Some keyvalues, spawnflags, effect flags, inputs, or outputs might not affect an NPC, based on the functionality and coding of the NPC.