Rotor wash is something mentioned by many entities in Hammer. Rotor wash is the effect of downward wind generated by a helicopter as the propellers spin. In Source, this effect is represented in multiples ways:
- Ropes being pushed up.
- Dust clouds.
- Physics objects being pushed away.
- Special ring-shaped water overlays.
All of the large flying NPCs in Half-Life 2 are capable of generating rotor wash.