Gyros

[Nidalap]

I'm studying the AHRS system for a turboprop and learning about gyros at the moment.

The AHRS is described as a strapdown system and the gyros are described as rate gyros.
So to me this means that in each AHRS unit, there are 3 gyros, one mounted on each of lateral, longitudinal and vertical axis.
Each gyro doesn't move? So it just spins on its axis and the rates are calculated... somehow... I tried finding info on rate gyros, but there isn't a lot out there unfortunately, so could someone please give me a rundown on how rate gyros work exactly?
Also, how can rate gyros be subject to drift, acceleration and turn errors?

[Banana Joe]

Search Ring Laser Gyros.

A Ring Laser Gyro emits two laser beams of identical wavelength in opposite directions. The gas in the laser beams determines the frequency of the laser beam and rotation around its axis causes the apparent path of travel of the laser beams to increase or decrease. This causes a change in the frequency and the difference in frequency between the two laser beams is used to detect rotation around the axis of rotation.

[Nidalap]

I don't think the system I'm studying uses ring laser gyros.

[Banana Joe]

You've got nothing spinning in that system. It's a solid-state system.

[Nidalap]

In reduced performance mode, the manual states that the AHRS performs similar to:

Vertical Gyro with roll and pitch erection cutoffs and also with drift and acceleration errors for the attitude indication (I think the main factor contributing to reduced performance mode for this part of the system is the lack of air data) and

Directional Gyro with drift and turn errors for the directional gyro (I think the only factor determining reduced performance here is the flux valve failure)

I didn't think RLG behaved like this? But I'm not sure...

I have so far only been able to find the following errors for RLG:

Long-term errors result from instability of gyro compensation parameters and include the following terms:
• Bias error
• Scale factor error
• Input axes misalignment error

Short-term errors cannot be calibrated and include:
• Dither spillover
• Random walk
• Quantization noise

[Banana Joe]

What type is it? You might actually have more luck in finding a definite answer in the Tech Log forum.

Anyway, this reduced performance mode is similar to the IRS selector knob set to ATT on my type: it provides only attitude and heading information after IRS failure or loss of alignment.

[paco]

AHRS is more likely to have MEMS circuitry, similar to the stuff that rotates your phone screen.