# Half-Standard Rate Turns and Turn Coordinator

What does a half-standard rate turn look like on a typical turn coordinator? Is the wing tip exactly between the "wings level" mark and the standard rate mark? I am not asking about turn-and-slip indicators, just turn coordinators.

Thank you

• Interesting question actually. I couldn't find any info on whether the gyro's displacement is linear or not when it's canted 30 degrees. I assume so, and imagine banking to the middle of the range gives you a 1.5 deg/sec turn rate, more or less. Ballpark is all you need, since precision isn't possible anyway. Commented Dec 14, 2023 at 18:07

If you are asked to do a half-standard rate turn by ATC, then you should indeed do a turn where the wing tip is halfway between the wings level marking and the standard rate marking, unless your turn coordinator has a specific mark for half-standard rate turns.

This will probably not be exactly half a standard rate turn. Turn coordinators are calibrated to show a standard rate turn during a coordinated level turn of standard rate at a specific true airspeed. There is no such calibration requirement for half-standard rate turns, and even if there were it would only be exactly correct at one specific true airspeed.

But this really doesn't matter. If you're asked to do a half-standard rate turn, ATC really isn't expecting you to successfully do exactly 360 degrees of turn in 240 seconds. If you're doing timed turns they don't expect you to roll out on the exact heading they would like. That level of precision simply isn't possible or expected.

You can experimentally test it on your own equipment using the formula:

rate of turn is proportional to tan bank angle/Velocity

and see how your turn indicator displays

Most applications for turn indicators are to "do a 180" course reversal to get out of a bad (weather) situation.

But if you wish to try 1/2 standard rate, use the attitude indicator to set the proper bank angle for your speed based on the bank angle for a standard rate turn at the same velocity.

With the tangent function, the comparison of bank angle to tangent angle is not quite linear, but close:

10 degrees. 0.176
15 degrees. 0.268
20 degrees. 0.364
30 degrees. 0.577
40 degrees. 0.839

The bank angle for a "1/2 rate turn" will be approximately 1/2 that of a standard rate turn. Velocity can also be adjusted a bit if you want to "fine tune" it.