Achid090

Hi guys,

although the question might seem stupid at first glance, I think there is something very unclear (and never mentioned anywhere) about the functioning of the turn indicator.

My question is: Why doesn't the TI indicate roll?
https://www.youtube.com/watch?v=0sRrSkSJc7w

Now I know how a gyroscope works, and I understand the way a TI is supposed to be working, i.e. how it indicates the amount of yaw. But it just doesn't make any sense to me.

I'll try to explain what I mean:
As turning gyros try to remain rigid in space, and because the axis of the TI-Gyro is parallel to the transversal axis of the plane (and parallel to the ground), whenever the plane rolls, the rotor should remain rigid and keep its axis parallel to the ground. So there should actually be an angle between the rotor axis and the wings. In fact it should pretty much the same way an artificial horizon does... Especially since thats the only axis the gimbal can turn on... But none of this occurs....
So how comes this motion is not present in the TI for rolling?


Thanks a lot!
Achy

rickair7777

I can't recall how everything lines up well enough to explain in an internet forum but the fundamental difference...

AI is a free-floating gyro which simply remains rigid in space.

TI is locked in two axis', and is activated by precession. In a turn, the precession translates the force to a locked axis so nothing happens. In yaw (turn) the precession translates the force to the free axis so the gyro (and the needle) can move. Pitch is the axis of rotation of the gyro, so that has no effect.

trent890

Try referencing the Instrument Flying Handbook, pages 5-20 through 5-22.

Good explanations there with pictures and diagrams to elaborate on what the text is attempting to explain.

Available here: http://www.faa.gov/regulations_polic...H-8083-15B.pdf

If you're still a bit puzzled, maybe you should ask a CFII?

WesternSkies

Specifically the TC measures a standard rate of turn (SRT) by reference of the white markings. The bank angle required to achieve a SRT has a variable of speed while the white markings of the TC are fixed. Think of the time, distance, speed variables.

JamesNoBrakes

Because a roll is not a turn. You can get a standard rate turn with just rudder, if you want. A good way to figure this out is set a jail-breaked turn coordinator out on the desk on a flat surface, align it facing you, and push the end of the case in the direction you want to "turn" (so the case twists), then, from where you pushed to achieve this, follow the gyro 90 degrees in it's plane along the direction of rotation and push there (where the force is felt). You'll see the gyro tilts and causes the indication.

blastoff

You'd be surprised how many pilots I've met that think that their Boeing is doing standard rate turns in a holding pattern. Above about 230 KTAS (slight variations depending on aircraft model), the bank angle required to maintain a standard rate turn exceeds 30 degrees.

joepilot

In most piston aircraft the index marks standard rate, in most jets the index marks 1/2 standard rate.

Joe

joepilot

There are two distinct instruments that are commonly referred to as turn indicators. The first is the pure turn indicator, which is the standard upright needle, and indicates only rate of heading change.

The other is the Turn Coordinator, which is sometimes miscalled a turn indicator. This instrument became popular during the 1970s on light aircraft. It looks like a little airplane, with index marks for a standard rate turn. This is a hybrid instrument. Upon initiating a bank it responds to BANK ANGLE CHANGE. Then, with a constant bank angle, it reverts to heading change rate. I have no idea about the internal workings of this device, but I will say that it makes flying with an inop attitude indicator much easier.

Joe

SoggyMcPancakes

By having the gyro canted, the readings from the TC indicate the X, Y, and Z axis all at once. It's a very simple concept to understand. The gyro rolls in one direction, and rotates in another which give X and Y axis indications. Tilting the gyro to a degree upward creates a Z axis reading.