Refer to figure.
Ram air intake systems are widely employed in helicopters, to provide ventilation and cooling.

They are straightforward and efficient. They utilize the forward motion of the helicopter to force air into the intake. This design doesn't require additional components like fans or blowers, making it simple and reliable, which is crucial for small helicopters where complexity and weight are concerns.

As long as the helicopter is in motion, there will be a constant supply of fresh air entering the cockpit. This is especially important for ventilation purposes, ensuring a continuous flow of fresh air for the crew inside the confined space of the cockpit.

Therefore, the correct answer is “ram air entering via an air intake at the front of the helicopter” .

NOTE:

• Helicopters are designed with aerodynamics in mind, and incorporating an intake at the front allows the helicopter's forward motion to naturally channel air into the cockpit. This design integrates seamlessly with the overall aerodynamic profile of the helicopter.
• While some helicopters have separate air intakes for cooling various components like the engine or gearbox, the question specifies a small piston-engined helicopter. In such helicopters, the primary source of air for cooling is often separate from the cockpit ventilation system. Therefore, the main concern for cockpit ventilation is to provide fresh air for the crew, which can be efficiently achieved through a ram air intake at the front of the helicopter.