I am surprised indeed.
The turn coordinator is only accurate at 1g. The more G the less accurate the indication.
The higher the airspeed, the more bank is required in order to complete a rate 1 turn.
The more bank in a balanced turn the higher the g loading.
In general this is only theoretical since standard turns are at rate 1 or 25 deg angle of bank whichever requires the less bank.
The reason why we use the simple calculation of (airspeed (in knots)/10 ) +7 to obtain an angle of bank for rate 1 rather than simply select rate 1 on the turn coordinator (when using full pannel) is becuase of the inaccuracies of the turn coordinator.
Use the simple equation and the figures measured by contacttower and you will see the errors.
I would laso like to warn anyone about following the advice of "
Enter and exit the turn with a rapid roll to/from wings level, to minimise errors. from IO540
Firstly, the turn coordinator shows roll as well as turn and that is why it is used in basic aircraft for a limited panel back-up i.e. you do not have to wait for a rate of turn to develop before discovering that your wings are not level i.e. any roll will cause movement of the indicator. Now please imaging what the turn coordinator does when you apply a large rolling moment.......how easy is it to smoothly find wings level then? Remember also what your instrument instructor taught you when doing unusual attitude recoveries - nose low and banked.
The timed turn will work well enough no matter how slowly you enter the turn provided that you enter and exit the turn
at the same rate
Start the watch, start the roll to acheive rate 1. Let's say that you acheive a steady rate 1 at oh 5 seconds. When the time is up you roll out at the same rate and thus you will be back wings level 5 seconds after the required time. The turn lost while making the entry is compensated for by the extra time at the end.
Finally the single speed is the one where you can turn rate 1 in balanced flight with zero roll moment i.e. ailerons perfectly neutral (think about climbing and descending turns here) and only 1g load factor.
Don't think that I have come across that speed often.
Regards,
DFC