Turn Indicator
There are Turn Indicators and Turn Coordinators. They both do essentially the same thing, they show you what direction you are turning and how fast, up to 3 degrees per second and they also have a skid indicator built into them.
The older style, Turn Indicator, has a vertical needle that stayed centered if no turn is present. On either side of the needle are markings called “dog houses”, if you are turning and have the needle under a dog house then you are turning at 3 degrees per second. Three degrees per second represents a rate at which your inner ear can detect a turning motion. Actually, your inner ear senses a turning motion at 2 ˝ degrees per second. Most of these instruments have a placard on them stating “2 MIN”. This means that it takes 2 minutes or 120 seconds to turn the aircraft through 360 degrees of heading change, this is how they get the 3 degrees per second.
The new type is called a Turn Coordinator, it looks like a miniature airplane as viewed from the rear. It shows the same information, turns up to a rate of 3 degrees per second.
This is a more advanced instrument as it uses both roll and yaw information for the display. It displays rate of roll and rate of turn, not bank angle.
I have flown with both instruments and I prefer the Turn Coordinator. It seems the Turn Indicator was always wobbly and oscillating whereas the Turn Coordinator’s miniature airplane was rock solid.
In the States and electric Turn Coordinator can be purchased for about $500, this is cheap insurance if you do night flying or fly on hazy days. With some training you could keep a helicopter upright if you inadvertently entered IMC or lost the horizon.