TC is the only Instrument that is electrically driven. - Why? In case you will experience a Vacuum Pump failure, it is the only instrument that is going to remain usable and reliable for turn indications; The Turn Coordinator has a Gyro which is spinning on a horizontal Gimbal. Compared to the other Gyro Instruments (HI & AI), the case holding the Gyro is canted/angled at 30° (degrees), making it possible to indicate both, Rate of Turn and Rate of Bank.
Airplane: Represents airplane's Rate of Bank (Std. Rate of Turn = 3° (degrees)/sec));
Inclinometer: Tube filled with a fluid (kerosin) and a ball.
The ball reflects the movement of the airplane's tale around its vertical axis.
If your tail were to move to the right > ball moves to the right. > Push right rudder to get the ball centered again (coordinated flight).
If your tail were to move to the left > ball moves the left > Push left rudder to get the ball centered again (coordinated flight).
The goal should be to keep your airplane coordinated (ball between the thin black lubber lines).
2 Min: This depiction should remind you that a full 360° (degree) turn will take 2 minutes to complete. This information is based on a standard rate turn (3 deg/sec). - Why could this be important to you? - Read below!
Situations where uncoordinated Flight can be an issue ...
- during high pitch (nose high) attitudes due to P-Factor *, such as 'Slow Flight' (ball will be to the right of center);
- if True Airspeed (KTAS) is too high in relation to your bank angle or rate of turn. > your tail skids to the right during a left turn (ball will be to the right of center).
- if True Airspeed (KTAS) is too low in relation to your bank angle or rate of turn. > your tail slips to the inside of the turn (ball will be to the right of center).
In both turnning scenarios, you have to counteract this problem, by either using the rudder paddels and/or adjusting the airspeed/power setting in combination with your bank angle accordingly to get coordinated.
* P-Factor is a tendency of the airplane's nose to yaw to the left, because the descending (right blade from the pilots perspective)
propeller blade is producing more thrust.
If you want to find your apprx. Standard Rate of Bank Angle,
you can use the following formula:
Actual TAS / 10 + 7
act. TAS = 100kts
100kts / 10 = 10
10 + 7 = 17
→ about 17 degrees of Bank on the Attitude Indicator will be equal to a Std. Rate Turn
The 2 Min. depiction on your TC ...
For instance: Your HDG indicator would fail due to a Vacuum Pump failure.
The only directional instrument left in that case is the Magnetic Compass, which is subject to certain errors at all times. The following example is shows how we would still be able to make very exact turns. This is also known as 'Timed Turns' and a small part of your IR-Training.
To complete a 30° (degree) turn at STD rate, it would take us about how much time ?
30deg/3 = 10 sec.
'10 sec after we have initiated the turn'
Alternatively, we can also use the Undershoot North/Overshoot South (UNOS) rule.
TIP: If you have long turns, initiate your turn first, then do the math afterwards
while turning. This will save some time. For very small turns or corrections, you may as well just use ½ Std. Rate turns. This way, the Magnetic Compass Reading will be rather true during your entire turn.
How to use the table:
Objective = Turn to Hdg of 360°/0° deg (North) | Current Hdg = 270° deg (West)
Picture says Turn Past & 30 (for North), so ...
1. Start Std. Rate right turn and keep it.
2. The number 30 means you add 30 to 0 > 30° deg (030° deg) ... so,
3. We keep the Std. Rate (right) Turn until we reach our desired Hdg of 030° on the Magnetic Compass (start taking your bank out before reaching 030°)
4. The MC compass should tumblr back and stablelize close to North.
5. If not, you can put in very small & small correction to get there. MC is sensitive.