The Turn Co-ordinator — Page 200, Lesson 236

Let’s pick up with the Turn Co-ordinator. I want you to see it as a development of the Turn and Bank indicators — that’s the starting point. The primary difference between the two instruments comes down to two things: the setting of the precession axis of the rate gyroscope, and the method of display. Here’s what that means. The gyroscope in the Turn Co-ordinator is spring restrained, and it’s mounted so that its axis sits at about 30 degrees with respect to the aircraft’s longitudinal axis. That 30-degree tilt is the key. Because the axis is angled, the gyroscope becomes sensitive not just to turning, but also to banking of the aircraft. So it senses both. Now, think about how a turn actually begins. A turn is normally initiated by banking the aircraft. When you bank, the gyroscope will precess — that’s the gyroscopic reaction to the applied force — and this precession moves the aircraft symbol on the instrument. The symbol indicates the direction of bank, and that lets you, the pilot, anticipate the resulting turn before it fully develops. So the instrument isn’t just telling you you’re turning; it’s showing you the bank that will produce the turn. Once the turn is established, you control the turn at the required rate by aligning the aircraft symbol with the graduations on the instrument dial. Those graduations are the reference marks for rate of turn. The actual rate of turn will depend on the instrument in use — it could be a rate one turn, which is 3 degrees per second, or any other rate dependent on the instrument’s design. So the dial is calibrated to a specific rate, and you fly the symbol to match it. There’s one more critical element: the ball. The ball still has to remain central for a balanced rate of turn. That’s the same principle as in the older instruments — the ball tells you whether the turn is co-ordinated, meaning no slip and no skid. If the ball is off centre, the turn isn’t balanced, regardless of what the aircraft symbol shows. Now, there’s an important annotation on the indicator scale: “No Pitch Information.” That’s printed there deliberately. The reason is to avoid any confusion in pitch control. The presentation of the Turn Co-ordinator can look similar to the gyro horizon — the artificial horizon instrument — and a pilot might mistakenly read pitch information from it. The annotation is a warning that this instrument gives you no pitch information at all. It only shows bank and rate of turn. So, to tie it together: the Turn Co-ordinator is a spring-restrained rate gyroscope mounted at about 30 degrees to the longitudinal axis, making it sensitive to both bank and turn. It shows bank direction through the aircraft symbol, lets you fly a specific rate of turn against the graduations — rate one being 3 degrees per second — and the ball must stay central for a balanced turn. And the “No Pitch Information” marking keeps you from misreading it as a horizon. That figure shows the instrument presentation. Take a moment to look at the aircraft symbol, the graduations, and the ball — that’s the whole picture in one view.