Gyros
 

Hie,

I'm new to this website therefore not sure where to search for my answers so for the meantime here it is..

I'm currently sitting for a local engineer's exams and there's this question which i'm not sure of

Which of this/these are earth gyroscopes?
1) Directional Gyro
2) Artificial Horizon
3) Both


Really appreciate you guys to shed some light on it

Hello Shah, from Wikipedia about the Direction Gyro, or Heading Indicator (HI):
<The HI works using a gyroscope to establish an inertial platform, which will remain fixed in space.>

The DG will remain fixed on an axis in space, so will pick up errors requiring regular adjustment to a compass heading as the earth rotates. The Artificial Horizon simply hangs in the local gravity field wherever you are as it rotates to show movement about your local vertical. Therefore the Artificial Horizon is an 'earth gyroscope' while the DG is referenced to a point in space.

thanks for the info.

To help clarify,

A basic DG is indeed free. However DG's used on aircraft are not they are earth tied. That is to say there is a leveling system on the gyro which ensures the gyro spin axis remains level with the local horizon otherwise after a few hrs the gyro would be useless as a directional aid.

There. Clear as mud eh??!!

I don't have easy access to my old notes. As I understand it, an AH only has to hang with its access on the local vertical at all times. A DG must spin with its axis horizontal, but the important thing is the DG axis is referenced to a point in space, so are they both 'earth gyros' then? 36 years is a bit long to stretch the memory (which is still referenced to Inertial Navigation Systems!)