What does the pilot control by placing his hand on the collective?

Placing a hand on the collective allows the pilot to control the angle of the main rotor blades, which is crucial for adjusting the helicopter's lift. The collective pitch control changes the pitch of all the rotor blades simultaneously, enabling the pilot to raise or lower the helicopter’s altitude. When the collective is pulled up, the pitch angle of the rotor blades increases, resulting in more lift and allowing the helicopter to ascend. Conversely, pushing the collective down decreases lift, enabling the helicopter to descend. This function is vital for maintaining altitude and controlling the flight path during maneuvers.

Understanding this concept is essential for any pilot, as it directly impacts the helicopter's ability to navigate, land, or take off safely.