Forums: Skydiving: Gear and Rigging:
different altimeter readings in tracking

 


danielskydiver  (B License)

Sep 11, 2012, 10:35 AM
Post #1 of 6 (916 views)
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different altimeter readings in tracking Can't Post

Hey everyone,

Since one season i'm using the neptune N3 digital altimeter, a really improvement from the analog rentals (IMO) because it's much more accurate.

However, when i'm tracking away after a FS-jump and look at my altimeter, it tells me al lower altitude than actual, I see this because when i'm returning in bellyfly to pitch, my altimeter goes up about 100-200 feet.

So to make it clear;

Track-away > reading altimeter in tracking until 3500ft > returning to belly > altimeter says 3600/3700ft and then drops as usual.


I think it has something to do with the higher air pressure in tracking.
Has anyone experienced a similar situation? maybe with other digital alti's?


theonlyski  (D License)

Sep 11, 2012, 4:35 PM
Post #2 of 6 (832 views)
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Re: [danielskydiver] different altimeter readings in tracking [In reply to] Can't Post

In reply to:
Hey everyone,

Since one season i'm using the neptune N3 digital altimeter, a really improvement from the analog rentals (IMO) because it's much more accurate.

However, when i'm tracking away after a FS-jump and look at my altimeter, it tells me al lower altitude than actual, I see this because when i'm returning in bellyfly to pitch, my altimeter goes up about 100-200 feet.

So to make it clear;

Track-away > reading altimeter in tracking until 3500ft > returning to belly > altimeter says 3600/3700ft and then drops as usual.


I think it has something to do with the higher air pressure in tracking.
Has anyone experienced a similar situation? maybe with other digital alti's?

If you're tilting your altimeter down (into the relative wind) it will show a difference than one that is on top of your hand. Think about the air pressure where the altimeter is.


hcsvader  (E 2952)

Sep 11, 2012, 6:54 PM
Post #3 of 6 (792 views)
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Re: [danielskydiver] different altimeter readings in tracking [In reply to] Can't Post

I've also noticed that I sometimes get a negative reading after landing. Sometime show -20 or something like that.


phoenixlpr  (D 3049)

Sep 11, 2012, 11:43 PM
Post #4 of 6 (750 views)
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Re: [hcsvader] different altimeter readings in tracking [In reply to] Can't Post

In reply to:
I've also noticed that I sometimes get a negative reading after landing. Sometime show -20 or something like that.

I sometimes got 20m difference between Neptune and Optima altituda indicated.


fcajump  (D 15598)

Sep 12, 2012, 10:02 AM
Post #5 of 6 (677 views)
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Re: [danielskydiver] different altimeter readings in tracking [In reply to] Can't Post

Altimaster III on my chest
Altitrack on my wrist

They are matched all the way up in the plane.
They are matched once settled down under canopy.

The Altimaster reads ~500-1000' lower in freefall and tracking.
Altitrack matches the alerts in my ear from a Protrack.

My _theory_ on why the analog chest mount shows a lower altitude is that it is in the relatively higher air pressure area (bow wave effect).

Where do you have your Alt with respect to the relative wind during your track??

JW


danielskydiver  (B License)

Sep 26, 2012, 6:28 AM
Post #6 of 6 (588 views)
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Re: [fcajump] different altimeter readings in tracking [In reply to] Can't Post

yeah that's also what I think, the relative wind is in tracking right at my altimeter (hand mount, faced down) so the pressure will be higher.
As long as you aware of the difference it isn't dangerous, but when I saw my altimeter 'tripping' I was curious if it was an error in the alti itself, luckily it's not Smile



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