The correct function of the swashplate, which is located below, is that it controls the angle of attack of the rotor blades individually.
To confirm this answer, we can break down the functions mentioned and eliminate the incorrect ones:
1. "It acts as a transmission between the shaft and the rotor." - This is not the primary function of the swashplate. Typically, the transmission system in a rotorcraft is responsible for transmitting engine power to the rotor system. The swashplate is not directly involved in this power transfer.
2. "It controls the angle of attack of the rotor blades collectively." - This function is not accurate either. The collective pitch control system, typically through a collective pitch lever or control system, is responsible for controlling the angle of attack of all rotor blades collectively. The swashplate works in combination with the collective pitch control system but does not directly control the collective pitch.
3. "It controls the angle of attack of the rotor blades individually." - This statement is correct and aligned with the primary function of the swashplate. The swashplate is a key component of the cyclic pitch control system, allowing for independent adjustment of the angle of attack for each rotor blade. By controlling the angle of attack individually, the swashplate contributes to adjusting lift and controlling the movement and stability of the rotorcraft.
4. "It controls the velocity distribution over the blades." - This function is not directly performed by the swashplate. The velocity distribution over the rotor blades is primarily influenced by the overall aerodynamic design of the blades and the rotor system as a whole, rather than the swashplate specifically.
In conclusion, the correct function of the swashplate, from the options provided, is that it controls the angle of attack of the rotor blades individually.