Which term describes the position of the two needles on the engine/rotor tachometer when they are not superimposed?

Which term describes the position of the two needles on the engine/rotor tachometer when they are not superimposed?

• A. Split Needles
• B. Dual Needle
• C. Separated Needles
• D. Twin Needles

Answer: (A)

The tachometer on a helicopter shows two values: engine RPM and rotor RPM. When those two needles are not sitting on the same line, the instrument is described as having split needles. This happens because engine speed and rotor speed respond differently to changes in power and load. The rotor has inertia and is connected through the drive system, so it can lag behind or move differently than the engine during acceleration or deceleration. When conditions settle and the speeds match, the needles overlap again. Although terms like dual needles or twin needles describe two indicators, split needles is the standard term for this situation.

The tachometer on a helicopter shows two values: engine RPM and rotor RPM. When those two needles are not sitting on the same line, the instrument is described as having split needles. This happens because engine speed and rotor speed respond differently to changes in power and load. The rotor has inertia and is connected through the drive system, so it can lag behind or move differently than the engine during acceleration or deceleration. When conditions settle and the speeds match, the needles overlap again. Although terms like dual needles or twin needles describe two indicators, split needles is the standard term for this situation.