The Turn Co-ordinatorNavigation — Instrumentation — DGCA CPL practice questions

All 3 questions — The Turn Co-ordinator

Navigation — Instrumentation · DGCA CPL. The correct option is marked on each.

1. Q1. The gimbal ring of a turn co-ordinator is inclined at about 30° with respect to the aircraft's longitudinal axis in order to:

   • A.make the rate of turn more accurate
   • B.make the gyro sensitive to banking of the aircraft as well as to turning✓
   • C.make the gyro more effective during inverted flight
   • D.have a higher rotor speed which will prolong the life of the instrument

   Why: The 30° inclination of the gyro axis with respect to the aircraft's longitudinal axis makes the rate gyroscope sensitive to both roll (banking) and yaw (turning), unlike the standard TBI which responds to yaw only. This allows the Turn Co-ordinator to anticipate the turn from the initial banking motion. See Section 2 . — The 30° inclination is the defining physical difference between the Turn Co-ordinator and the standard TBI. Everything else (ball, spring, rate gyro principle) is the same.

2. Q2. If an aircraft turns as indicated in Figure 1 [aircraft symbol aligned with left Rate 1 mark]:

   • A.the aircraft will turn through 180° in two minutes
   • B.it will take one minute to turn through 90°
   • C.the aircraft is turning left at less than 3°/second✓
   • D.the aircraft is turning left at 3°/second

   Why: The illustration shows the aircraft symbol aligned between the centre and the Rate 1 mark (left). This indicates a left turn at a rate less than Rate 1 (i.e., less than 3°/second). Rate 1 would place the symbol exactly on the Rate 1 graduation mark. See Section 3 . — On the Turn Co-ordinator, the Rate 1 graduation is the standard reference mark. Symbol on the mark = Rate 1 = 3°/sec. Symbol between centre and mark = less than Rate 1.

3. Q3. A turn co-ordinator has (i) ..... pivoted (ii) ........ in the case

   • A.(i) two gimbal rings — (ii) orthogonally
   • B.(i) a single gimbal ring — (ii) longitudinally✓
   • C.(i) one gimbal ring — (ii) laterally
   • D.(i) two gimbal rings — (ii) mutually perpendicular

   Why: The Turn Co-ordinator has a single gimbal ring (like the TBI) but pivoted longitudinally in the case (unlike the TBI which pivots laterally). This longitudinal pivot, combined with the 30° gyro axis inclination, gives sensitivity to both roll and yaw. See Section 2 and comparison table in Section 5 . — TBI = single gimbal, pivoted laterally. TC = single gimbal, pivoted longitudinally. Both have only one gimbal (one degree of freedom). This is the key exam fact about the TC.