Why were Rate 4 Turn and balance indicators phased out in favour of Turn coordinators

[Centaurus]

Pre-war and early post war aeroplanes usually were equipped with Turn and Balance Indicators with the Turn needle calibrated with instrument markings to Rate 4 turns. In common parlance then, an instructor would ask his student for a Rate 4 Turn - not just a steep turn. The "skid" or "balance" needle part of the instrument was also calibrated to show the number of degrees the aircraft was out of balance. Tiger Moth instrumentation for example. When the pilot flew on instruments it was called "Primary panel" flying or sometimes "Limited Panel" flying. Now for modern airliners it is called flight on standby electrical power.

These early T&B indicators were gradually phased out to be replaced with Bat and Ball turn indicators for which the turn needle (the bat) was only calibrated to one marking and that represented Rate One. The ball was just that and sometimes called the skid ball. Finally the ubiquitous Turn Coordinator appeared in early Cessnas and nothing else has replaced them so far.

Would appreciate any comments as to why the old Turn and Balance instrument which was very good for instrument flying skills was phased out over the years for the now largely current Turn Coordinator in light aircraft?

[Birthday Boy]

The turn and bank instrument has the gyro mounted so that it reacts to yaw only and not to roll.
The turn co-ordinator has the gyro mounted at a 35 degree angle therefore it reacts to roll and yaw.
If you think about it when we turn an aeroplane we roll it into a banked attitude but this would not be seen on the turn and bank indicator until the aircraft starts to yaw around the turn.
In a nutshell think of the turn and bank indicator as a yaw instrument and the turn co-ordinator as a yaw and roll instrument.

[Jhieminga]

Next to the comment above, I would guess that the fact that all instrument procedures are based on rate one turns has something to do with it. If the only situation where a rate two and above turn is needed is during training, then the addition of these markings to a TC or T&B is a bit of a luxury. Admittedly training a steep turn on a AI is slightly different from training this on a T&B as you're aiming for an angle of bank on the AI while it is a constant yaw rate on the T&B, but I wouldn't be bothered by the difference. Actually, now that I'm thinking about it, at rate four the vertical axis of the airplane and the axis about which the aircraft is turning are so misaligned in roll that you could argue that it wouldn't be accurate anyway.

[megan]

Turn Coordinator appeared in early CessnasFlew Cessnas up until 66 Centaurus and never saw a turn coordinator. When did they start to appear?