Turn and slip indicator vs. a turn coordinator

[Rowdy Burns]

What is the difference?

[Shiny Side Up]

Wikipedia is awesome.

The turn coordinator (T/C) is a further development of the turn and balance (T/B) indicator with the major difference being the display and the axis upon which the gimbal is mounted. The display is that of a miniature airplane as seen from behind. This looks similar to that of an attitude indicator. "NO PITCH INFORMATION" is usually written on the instrument to avoid confusion regarding the aircraft's pitch, which can be obtained from the vertical horizon instrument.

In contrast to the T/B, the T/C's gimbal is pitched up 30 degrees from from the lateral axis. This causes the instrument to respond to roll as well as yaw. This allows the instrument to display a balance change more quickly as it will react to the change in roll before the aircraft has even begun to yaw. Although this instrument reacts to changes in the aircraft's roll, it does not display the roll attitude.

The turn coordinator should be used as a performance instrument when the attitude indicator has failed. This is called "partial panel" operations. It can be unnecessarily difficult or even impossible if the pilot does not understand that the instrument is showing roll rates at as well as turn rates. The usefulness is also impaired if the internal dashpot is worn out. In the latter case, the instrument is said to be underdamped and in turbulence will indicate large full-scale deflections to the left and right, all of which are actually roll rate responses. In this condition it may not be possible for the pilot to maintain control of the aircraft in partial-panel operations in instrument meteorological conditions. For this and other reasons, many highly experienced pilots prefer the "older" turn and bank indicator design.

[FlyGy]

Wikipedia is awesome.

The turn coordinator (T/C) is a further development of the turn and balance (T/B) indicator with the major difference being the display and the axis upon which the gimbal is mounted.

Okay smarty pants, what's the difference between a Turn and Slip Indicator and a Turn and Bank Indicator. Your Wiki quote says nothing about a Turn and Slip Indicator.

[Rowdy Burns]

Thanks! My question now is specifically geared towards slipping. I understand that in a side-slip (or fwd slip) the wings would be level in both instruments with the ball off center. The entry has me perplexed.

If I were to roll the wings but use my feet to keep the nose straight (whether or not this is the correct way to enter is unnecessary for this thought experiment) what would these instruments show?

I imagine in both instruments the ball would slide off to the side. Since the turn and slip reacts only to yaw, I would expect it to remain level the whole way through. However, would the TC react to the roll in this case(ie initially show a turn and then go wings level)?

A ground school instructor once posed this question to me but I could not answer it, and now I forget after all these years.

[FlyGy]

The wings aren't level, but the instrument indicates that they are. During entry into the slip there is some motion from the turn indicator until the inputs are properly counteracting one another and the aircraft is flying straight.

At the risk of ridicule, I'm gonna use Microsoft Flight Sim to illustrate this for ya.

Here an exterior view of the control inputs...



Here is the corrosponding TBI...



And the corrosponding TCI...



Hope this is helpful.

[Rowdy Burns]

Nice illustration, thank you.

I (think) I understand the mechanical differences, but it would seem as though the only practical difference is that the TC responds quicker to a banked turn (since it detects the roll in) than the TBI (since it has to wait for the ensuing turn rate) but as a result may be more sensitive in turbulence (especially if it isn't properly dampened).

Someone once told me that the AI will tumble sooner than the TC because the TC spin axis was cantered, hence why most emergency spin w/o visual cues has you look at the TC.

Would the TC's gyro be less likely to tumble than the TBI's gyro?

[tester]

An interesting thread here that should help to clear up confusion over "Turn Co-ordinator, Turn and Bank, Turn and Slip" etc. I've heard some very uninformed and occasionally completely incorrect explanations about the various types of cockpit instruments that display turn, yaw, bank, slip, roll, roll-rate and other lateral and directional indications.

My early aviation background was as a RAF pilot in the UK, initially flying the Jet Provost trainer and then onto operational aircraft. In the JP, we had the classic 6-pack IFR Panel display, which included what we called a "Turn and Slip" indicator. Basically, the turn part was a display of yaw rate, which was taken from the output of a simple yaw-rate gyro. The slip part was simply a gravity-sensing ball, which naturally "fell" towards the lowest part of a gently curved, clear-liquid filled tube on the lower part of the instrument, as illustrated on some of the pictures in the posts above. When I learnt to fly, we didn't have and I had never heard of Turn Co-ordinators.

With our Turn and Slip indicator we could tell what our yaw rate was and, although this didn't give us our angle of bank directly, it did give a good approximation of rate of turn (depending on the "g" being experienced) from which we could calculate bank angle if we wanted to do the arithmetic. More importantly though, following appropriate training, the instrument could be used in instrument flying should the Attitude Indicator fail.

Our instrument Rating Test included two areas where we had to show competence in these "limited panel" exercises: the first was Recovery from Unusual Attitudes (we would call that "Upset Recovery" now, I suppose) and the other was to make an IFR Approach down to non-precision minima. I won't pretend that it was easy, but it was a practical way to get the home following an electrical failure, for example, or any other failure of the Attitude Indicator, and I know of a number of occasions where this happened. Also, I know from personal experience during routine training and IR Tests that IFR Approaches could reliably be flown to non-pricision minima, but it does require training. Trying to do it safely without training would almost certainly lead to disaster!

I'm not so sure I would have the same confidence in the Turn Co-ordinator to produce the same results, so I still very much prefer the old Turn and Slip, no matter what we might actually call it these days.

As a matter of interest, we had exactly the same set-up of 6-pack instruments in the RAF's more advanced combat types up to the mid-1960s, (e.g. the Hunter fighter and Canberra bomber) with pretty much the same requirements on the Instrument RatingTest, e.g. UPs followed by Approaches on limited panel down to 400 ft a.g.l.

Finally, most of us had little idea what to do with the slip part of the display until we started flying aircraft with more than one engine!!

[Beefitarian]

Hi I'm here to ruin what up to know has been an excellent thread but I need to prepare better. Stand by.

[trey kule]

IIRC correctly from my early flying days, we were taught when things were not as they should be to step on the ball. Get it centered, and the needle would then tell us how we were banked...though we called it the needle and ball and not the turn something or other. I do remember using it to recover from a spin on instruments was occassionally a bit exciting. When I first saw a turn co-ordinator we used it to give us a rate one turn....something the needle would do only in the ball was centered..Is that correct, or is my old memory faulty?
As to slipping with them. Ｗｈｙ？Ｉｎｔｅｎｔｉｏｎａｌ　ｓｌｉｐｐｉｎｇ　ｉｓ　ｄｏｎｅ　ｉｎ　ＶＭＣ，　ａｎｄ　ｙｏｕ　ｄｏｎｔ　ｎｅｅｄ　ａｎ　ｉｎｓｔｒｕｍｅｔ．　Ｏｒ　ａｍ　Ｉ　ｍｉｓｓｉｎｇ　ｓｏｍｅｔｈｉｎｇ　ａｇａｉｎ　ｉｎ　ｔｈｉｓ　ｎｅｗ　ｗｏｒｌｄ．

[KK7]

If I recall correctly, the ball must not be centered for the needle to indicate the rate or turn. The needle acts from a yawing force on the gyro, so a non-centred needle would indicate heading change and the needle on the line would indicate rate one, whether coordinated or not. I recall for partial panel this was used to determine the direction of rotation in a spin, regardless of the ball. The difference with the turn and bank is that it also reacts to rate of roll as well as rate of turn.

As for the ball, in either instrument it's simply an inclinometer. When coordinated the total force acting on the ball should be straight down to the floor of the aircraft, where the bank angle should essentially match the rate of turn. Slipping in a turn will cause the rate of turn to decrease from "normal" and more force will be acting down towards the earth, causing the ball to go towards the low wing. Skidding a turn will increase your rate of turn causing a force to pull it to the outside of a turn, much like a car going around a curve, causing the ball to move towards the outside of the turn, or the upwards wing.

[iflyforpie]

What's the difference? If you are an aircraft owner you will be replacing the turn coordinator about four times as much as the turn and bank indicator. Even in a light chop, the rapidly oscillating turn coordinator is destroying most useful yaw rate information.

Old Indian trick: Use the turn coordinator like you use the compass. Set rate one in relatively smooth air then use the AI to maintain bank angle... only occasionally glancing at the TC for fine tuning in smooth patches.

The inclinometer works the same in each and is completely independent of the gyro. Make sure it is mounted straight or you will be cross controlling to keep it centered.

[Rowdy Burns]

When I first saw a turn co-ordinator we used it to give us a rate one turn....something the needle would do only in the ball was centered..Is that correct, or is my old memory faulty?
As to slipping with them. Ｗｈｙ？Ｉｎｔｅｎｔｉｏｎａｌ　ｓｌｉｐｐｉｎｇ　ｉｓ　ｄｏｎｅ　ｉｎ　ＶＭＣ，　ａｎｄ　ｙｏｕ　ｄｏｎｔ　ｎｅｅｄ　ａｎ　ｉｎｓｔｒｕｍｅｔ．　Ｏｒ　ａｍ　Ｉ　ｍｉｓｓｉｎｇ　ｓｏｍｅｔｈｉｎｇ　ａｇａｉｎ　ｉｎ　ｔｈｉｓ　ｎｅｗ　ｗｏｒｌｄ．

I think it can show a ROT without the ball centered, but this would be rediculously impractical.

This whole slipping thing is simply an experiment to help understand and distinguish the differences between the instruments.

[Rowdy Burns]

Hi I'm here to ruin what up to know has been an excellent thread but I need to prepare better. Stand by.

what'd'ya got?

[Beefitarian]

I didn't come up with much.