Turn coordinator/indicator?

[tsw77]

I have asked a few different people now and still no answer, just what they think. Here goes...

 

The rate of turn is the speed in which you change direction. That being said, what if you were to do a very slow, steady, pedal turn that took 2 minutes to complete, would the turn coordinator display a standard rate turn?

[apiaguy]

No, it wouldn't unless you had a "coordinated turn" if you're skidding the helicopter thru the turn with the pedal, the indicator would show the ball out of center opposite the direction you're turning and the little airplane wings would show anywhere from no bank to a little depending on how much you force the turn with the pedal.

[Pogue]

No, it wouldn't unless you had a "coordinated turn" if you're skidding the helicopter thru the turn with the pedal, the indicator would show the ball out of center opposite the direction you're turning and the little airplane wings would show anywhere from no bank to a little depending on how much you force the turn with the pedal.

Uhh... If you are in a hover and do the two minute pedal turn, yes it would show a standard rate turn. I thought that was what he was asking.

[tsw77]

I'm talking about a hovering turn. I notice when I do a clearing turn before take off, the airplane wings on the TC are as far banked as they are going to get. I understand the characteristics of the inclinometer, I guess I was just curious how slow of a "hovering pedal turn" would it take to indicate a standard rate turn.

[tsw77]

Thank you Pogue.

[Gomer Pylot]

I've never even seen a turn coordinator in a helicopter. All I've ever seen are 'turn and slip', or ball and needle indicators. The turn coordinators with wings on them are designed for airplanes, and I can't see the point of putting them in helicopters.

[tsw77]

I've never even seen a turn coordinator in a helicopter. All I've ever seen are 'turn and slip', or ball and needle indicators. The turn coordinators with wings on them are designed for airplanes, and I can't see the point of putting them in helicopters.

 

 

The only point any of the gyros in our r22s is for training only. They are good enough to get your rating with, but you are not allowed to fly into imc with them. Very expensive simulator if you ask me.

 

So Gomer, do you agree with Pogue of the fact that if you were to do a hovering turn, twice as slow as the second hand on a clock, your turn indicator or 'turn and slip' would indicate a standard rate?

[joker]

As there is no rate of roll, all the turn coordinator movements are based on the rate of turn. Therefore, for a 2 minute turn at 0kts speed, I suspect TC will show the little aircraft at '2 min' bank, but ball to right.I.e., the turn rate is standard. Note, this is NOT coordinated.Coordinated is only achieved when TC shows the little aircraft banked to the 3 min mark AND the ball in centre.It should be impossible to achieve coordinated turn at 0kts! (Unless negative G exists!)Gomer, if it helps, I'll design a TC with a picture of a helicopter instead of a airplane!Joker

Edited February 19, 2008 by joker

[Gomer Pylot]

The turn needle should show a turn in a hover, and the ball should be more or less centered, depending on how much the pedals are being rocked. In a hover, a turn is actually a 'coordinated turn', because the g force, and lift, are straight up and down, more or less. I don't recall ever looking at the turn needle in a hover, though, there are more important things to be looking at. I can say that if you start a turn using cyclic only, and no pedal input, the turn needle will initially show a turn in the opposite direction, because of the adverse yaw you induce. It quickly moves back in the direction of the turn, though, and most people never notice it.

[AngelFire_91]

I think it important here to get some common wording down since we all seem to be confusiong different words for different meanings.

 

A Turn Cordinator (the one with the little airplane and wings), is an instrument that will show Rate of Turn AND Rate of Roll, because the gyro that is inside is canted at an angle of around 30*.

 

A Turn and Slip indicator (Most helicopters have one), will show Rate of Turn only due to the fact that the gyro is mounted at 90* or level which ever way you want to look at it and will only sense movement around the vertical axis.

 

The inclinometer (the little ball) is an instrument that essentally uses inertia and gravitational force to push or pull the ball.

 

Now with that being said, a Coordinated turn can be maintained with either instrument. Coordinated would indicated that the Helicopters tail is following the same path as it's nose irrespective of the rate of turn or roll due to the fact that the amount of ineritia equals the amount of gravity at the current bank angle.

 

So if you were to be in a hover and start a pedel turn to the left faster then 3* per second (2 min standard rate turn) the Turn coordinator or Turn and Slip would show a turn to the left and stay that way, inclinometer would be to the right due to inertia (but probably not all the way to the right, unless it's really fast.)

 

Now if you did that same turn to the left at exactly 3*/sec the Turn coordinator and Turn and slip would indicated a Standard rate turn, and the inclinometer would also swing to the right, but the force would be almost negligable so it won't move very much. This is of course assuming a perfect pedel turn without any change in rate at all.

Edited February 19, 2008 by AngelFire_91

[joker]

In a hover, a turn is actually a 'coordinated turn', because the g force, and lift, are straight up and down, more or less.

 

Goto disagree.

 

Theoretically, your statement is only true for the pivot point above the yaw axis.

 

At any arm (fwd or aft) of this point, any rate of turn will require a yaw action which will offset the ball. Thus, the turn is not strictly coordinated.

 

OK, pactically speaking there might be no perceivable deflection of the ball if the pedal turn is slow enough.

 

Theoretically however, there cannot be a coordinated turn at 0kts airspeed.

 

(Explained quicky because I am still on holiday!)

 

Joker

[Gomer Pylot]

The ball will be out of center in a hover whether there is a turn or not, because no helicopter I know of hovers completely level. Translating tendency and wind prevent it. I think the whole subject of the ball and needle in a hover is moot.

[relyon]

The ball will be out of center in a hover whether there is a turn or not, because no helicopter I know of hovers completely level. Translating tendency and wind prevent it. ...

I've seen installations where the longitudinal mounting of the entire instrument could be adjusted for this. Any A/C (including fixed wing) are subject to inclinometer centering errors under certain conditions.

 

The ball will be offset in a hover turn (however small) unless the yaw axis passes directly through the vertical axis of the instrument. Also, it is possible to offset the ball by simply translating left or right with no turn whatsoever.

 

I've seen many helicopters with a turn coordinator (as opposed to a turn and slip indicator). Because of the dual nature of the information displayed by the gyro (rate of turn and rate of roll), I've always felt if I had only one gyro instrument it would be a turn coordinator.

 

... I think the whole subject of the ball and needle in a hover is moot.

Very much agreed.

 

Bob

[Gomer Pylot]

Why would you want to adjust to put the ball in the center for hover? You don't spend much time there, and never IMC. If the ball is centered on the ground, on a level surface, it should be centered in coordinated level flight. It is affected only by gravity and mementum. Momentum is why it moves at the start of a turn. It's in a horizontal tube, and if you move the tube quickly the contents also move, but later, due to inertia. The race is adjustable so you can put the ball in the center on the ground, to correct for gear anomalies.

Edited February 21, 2008 by Gomer Pylot

[nsdqjr]

I'm still trying to figure out why you would care??

[BOATFIXERGUY]

I'm still trying to figure out why you would care??

 

I have to agree. When you're in a hover, your attention should be outside. Sure, you glance inside to monitor gages, but needing to glance at the turn coordinator is not practical. A 2 minute hover turn seems like an eternity.