Gyroscope Platform AS-339, Gyroscopic System TARSYN 333, and the HSI.

[Xoho]

Flying the C-101CC, I noticed that my HSI indicated heading differed from my actual heading by up to 30 degrees or more in the Caucuses with failures disabled. As a result, I've been trying to look into what could affect this and how to correct it. The manual briefly describes these systems, but doesn't cover what the switches/knobs do and how to properly use them. The tutorials do not cover these either. If anyone has the information on these I would be extremely grateful if you wouldn't mind sharing.

 

Gyroscope Platform AS-339 Control Panel:

1.) Fast Erect Pushbutton - What does it do and when would it be used?

2.) Magnetic Variation Control - What does it do and when would it be used? (E.g. What position when flying in NTTR vs Caucuses, or PG, and why?)

3.) Latitude Correction Control - What does it do, and how do I tell what's selected? Default position has "0" at the top, but the caret indicator on the bottom is pegged out at 48 degrees, and requires you to rotate fully around, but can only reach 38 degrees, leaving 39-47 degrees completely unselectable. In either position it appears to have no effect, but as I do not know it's exact function I cannot say for sure.

4.) Hemisphere switch - What does it do, and is it any more complex to use than simply selecting the hemisphere?

5.) Synchronization Indicator - When would I use it instead of the indicator on the HSI, why would I do so, and is it modeled at the moment? If not, any plans to do so? When trying to test it here is my result: https://imgur.com/a/i8mocYW

6.) Malfunction Warning Lamp - What does it indicate, if something is malfunctioning can it be corrected, and will initiating a repair work to fix it?

7.) Synchronizer and Heading Set knob - What does it do, how do I use it, and is it supposed to be extremely sensitive near center? (i.e. one click of the knob does very little until near the correct position, at which point it often makes a massive change in relation to the HSI indicator of the + and o, as well as the indicated heading, which often changes by over 30 degrees with just one click when near center)

8.) Function Selector Switch - What do the various modes mean and when would they be used?

 

Gyroscopic System TARSYN 333:

1.) Vertical Gyro Fast Erection - What does this switch do, when would I use it?

2.) TARSYN Operation Selector - What does selecting the directional gyro accomplish compared to selecting the compass? What must be done to use either of these options correctly?

 

Again, neither the manual nor tutorials cover these beyond mentioning the names of the switches and what the overlying system does. They do not cover the switch function or use. If you have any information you can share, I'd be extremely appreciative. Thanks!

Edited November 17, 2019 by Xoho

[kontiuka]

^

I'll try to answer a few of these ...

 

Gyroscope Platform AS-339 Control Panel:

1.) Fast Erect Pushbutton - What does it do and when would it be used?

 

- Even slight G forces cause the gyroscope-driven ADI to become misaligned. The Fast Erect function just places the ADI straight and level. So, you should be flying straight and level while performing this operation so that the ADI and your aircraft's attitude are in synch.

 

7.) Synchronizer and Heading Set knob - What does it do, how do I use it, and is it supposed to be extremely sensitive near center? (i.e. one click of the knob does very little until near the correct position, at which point it often makes a massive change in relation to the HSI indicator of the + and o, as well as the indicated heading, which often changes by over 30 degrees with just one click when near center)

 

- Like the ADI, the HSI gets misaligned under G-forces. When the HSI is showing "O", turn the knob toward "O" until the "O" on the HSI moves off to the side and then recentre the knob. Do the reverse for "+". When you see equal parts "O" and "+" on the HSI, you have the correct magnetic reading. The HSI will actualy self correct after a while when in slaved mode (see below) but it takes a long time. Using the knob is a fast way to align it.

 

8.) Function Selector Switch - What do the various modes mean and when would they be used?

 

- DG stands for "degaussed" meaning your HSI is not slaved to the earth's magnetic field surrounding your aircraft. This would be useful if you want the HSI to read true heading instead of magnetic. Slaved means that the HSI is slaved to the magnetic field and, so, it will read magnetic heading once it's aligned properly.

 

Gyroscopic System TARSYN 333:

1.) Vertical Gyro Fast Erection - What does this switch do, when would I use it?

 

- Same idea as for Fast Erect Pushbutton on AS-339.

 

2.) TARSYN Operation Selector - What does selecting the directional gyro accomplish compared to selecting the compass? What must be done to use either of these options correctly?

 

-When it's set to compass, it means the HSI is slaved to the magnetic field. So, when the HSI is aligned, it should be reading magnetic heading and should be pretty close to your backup magnetic compass reading. When it is set to gyro, it is no longer slaved to the magnetic field. This would be useful if you want the HSI to read true heading instead of magnetic. Keep in mind that it can easily get misaligned under even mild G-forces.

 

I think the rest of the functions you mentioned aren't modelled.

Edited November 17, 2019 by kontiuka

[Xoho]

Thank you very much! Makes a lot more sense now.

[Willie Nelson]

Can anyone explain to me why the HSI drifts sometimes by up to 20 degrees in as many seconds?

 

When I used to fly Piper Warriors at the start of my career more than twenty years ago I had a DG only which we would reset every ten minutes or so adjusting it by no more than maybe five degrees. This thing has a flux gate slave mode and swings wildly all over the place.

 

I have also noticed on tracking from Laughlin to mesquite on the NTTR map (i.e. more or less North) that the standby compass sometimes gets locked on to 360 and then intanteneously flicks back to what I am guessing might be the correct heading. So you can be in a position where you have no reference point for heading from either the stanby compass or HSI

Edited April 2, 2020 by Willie Nelson
My beautiful five year old daughter pressed "enter' a little prematurely....bless!