vsi zero error
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vsi zero error
dear friends ,
i am not an professional engineer , but am facinated by aviation. recently i acquired a VSI that belonged to a b 747 and was made by aerosonic. the problem is that when it is at rest on my level table it shows a small climb. i wonder why it has this zero error. i have seen photgraphs of vsi s , many of which seem to show a small climb error. is this some design error or is it simply somehting wrong with the unit that i had. furthermore , why don't they have a knob that can correct for the error located outside of the instrument ?
loads of questions ....and merry christmas to all !
i am not an professional engineer , but am facinated by aviation. recently i acquired a VSI that belonged to a b 747 and was made by aerosonic. the problem is that when it is at rest on my level table it shows a small climb. i wonder why it has this zero error. i have seen photgraphs of vsi s , many of which seem to show a small climb error. is this some design error or is it simply somehting wrong with the unit that i had. furthermore , why don't they have a knob that can correct for the error located outside of the instrument ?
loads of questions ....and merry christmas to all !
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there should be a small adjusting screw on the back of the instrument or maybe on the face to adjust the cam to centre the needle.
If the instrument is on a desk, there will be the same atmospheric pressure outside the capsule as inside it, so the needle should be at zero.
The instrument works on the principle that a change in altitude will cause a change in pressure. The pressure around the capsule is allowed to leak into it at a controlled rate to show as a change in barometric pressure, hence a change in altitude.
If the instrument is on a desk, there will be the same atmospheric pressure outside the capsule as inside it, so the needle should be at zero.
The instrument works on the principle that a change in altitude will cause a change in pressure. The pressure around the capsule is allowed to leak into it at a controlled rate to show as a change in barometric pressure, hence a change in altitude.
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I forgot to add, there is also compensation internally for temperature, using bi-metallic springs, so this could cause a slight error outside of the aircraft. I would guess that there is a small adjuster though.
[This message has been edited by CONES R US (edited 26 December 2000).]
[This message has been edited by CONES R US (edited 26 December 2000).]
