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GATE 2019 ME (ME1) – Question 41

Theory of Machines · Gyroscope · 2 marks · Multiple choice

An aircraft turbojet rotor has mass 180 kg and polar moment 10 kg·m² about its axis. It spins at 1100 rad/s clockwise viewed from the aircraft front. At 800 km/h the aircraft turns left with radius 1.5 km. Find gyroscopic moment on the aircraft and resulting nose motion.

  1. 1629.6 N·m, nose goes up
  2. 1629.6 N·m, nose goes down
  3. 162.9 N·m, nose goes up
  4. 162.9 N·m, nose goes down

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Correct answer: (B) 1629.6 N·m, nose goes down

Explanation

Precession speed is $\Omega=(800/3.6)/1500=0.148148$ rad/s. Moment magnitude is $I\omega\Omega=10(1100)(0.148148)=1629.6$ N·m. The right-hand rule for the stated front-view spin and left turn gives a reaction pitching the nose down. **B**.