The simplest way to dampen a helicopter's noise is to increase the Angle of the rotor's blades, also called the pitch, and slow them down.

要降低噪音，最简单的方法是增大旋翼桨叶的夹角，也叫“节距”，或是降低转速。

youdao

The main blades pitch Angle is controlled by the up and down movements of the swashplate.

大桨的螺距角度是由倾斜盘的上升和下降动作控制的。

youdao

The amount of blade twist is called the pitch angle .

叶片扭曲的量被称之螺旋上升角。

youdao

Previously we were able to sit comfortably in seats that could recline at an angle of 45 degrees, with a pitch of something like 3 feet between seats.

BBC: News Online

When the device first launched in 2002, Angle brought a box of Cheerios to retailer pitch meetings.

FORBES: Invasion Of The Machines: iRobot Hunts Bombs, Cleans Floors, Now Wants To Heal You