HDG Info on A320
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Joined: Feb 2002
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From: South America
HDG Info on A320
Wonder all A320 and Airbus drivers in general if someone could tell me where the IRU's get the heading info to be displayed on PFD and ND. I know how it gets its position, but how does it know which way its pointing??? <img src="confused.gif" border="0">
Joined: Jun 2000
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From: underground
When you first switch on the units they go into automatic 'Align' phase don't they...... .Well, that's exactly what they are doing, aligning with the earths 'North-South' axis i.e.Longitude.. .They also remember in which hemisphere they were shut down.. .All earth accelerations about the 3 axes (x,y,z) are then sensed,and from the relative proportions of each, the heading can be calculated.
This is the 'simple' pilots explanation.If you want the full 'Avionics Engineers' version,just wait, someone will be bound to put finger to keyboard!! <img src="wink.gif" border="0">
[ 25 February 2002: Message edited by: moleslayer ]</p>
This is the 'simple' pilots explanation.If you want the full 'Avionics Engineers' version,just wait, someone will be bound to put finger to keyboard!! <img src="wink.gif" border="0">
[ 25 February 2002: Message edited by: moleslayer ]</p>
Joined: Aug 1998
Aviation Qualifications: ATPL
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From: Ex-pat Aussie in the UK
Here's an easy way to think of it:
If I draw a quarter of a circle on a piece of paper, you could look at that quarter arc, complete the rest of the circle, and point out the centre pretty easily.
When you turn on the IRS, and the aircraft is stationary on the ground, then the only movenment the aircraft senses is the rotation of the earth. So as the IRS's plot their position, they start to "draw" a cirlce. Once they have drawn enough of a circle, the computer can complete the rest.
The size of the circle tells the computer the latitude of the aircraft, while the centre of the circle is true north.
If I draw a quarter of a circle on a piece of paper, you could look at that quarter arc, complete the rest of the circle, and point out the centre pretty easily.
When you turn on the IRS, and the aircraft is stationary on the ground, then the only movenment the aircraft senses is the rotation of the earth. So as the IRS's plot their position, they start to "draw" a cirlce. Once they have drawn enough of a circle, the computer can complete the rest.
The size of the circle tells the computer the latitude of the aircraft, while the centre of the circle is true north.
Joined: Mar 2001
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From: Toronto, Ont, Canada
An interesting link about the earth's rotation.
<a href="http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html" target="_blank">http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html</a>
This link says that to calc the speed of rotation at a specific latitude, mult cos(latitude) * equator rotation speed (approx 1040 mph).
How is that formula derived ? I assume there is a relation between the cos(latitude) and the decreasing radius of the earth as the latitude increases.
Mike
<a href="http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html" target="_blank">http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html</a>
This link says that to calc the speed of rotation at a specific latitude, mult cos(latitude) * equator rotation speed (approx 1040 mph).
How is that formula derived ? I assume there is a relation between the cos(latitude) and the decreasing radius of the earth as the latitude increases.
Mike
