Wrist alti suffers wrist burble?

[FrogNog 1]

I'm pretty sure my wrist alti reads 500 feet high in totally stable bellyflying (like I do on hop-and-pops). I figured this out by noticing 5 seconds out the door it sometimes looked like I was _higher_ than before I left, and between pull and slider-down was a lot higher than I could account for time-wise, and finally I looked at my alti, didn't believe it, rotated my hand 90 degrees so the alti was off to the side, and noticing it immediately read 500 feet lower.

OK, this makes sense. It also handily explains the "+/- 500 feet" accuracy statement the altimeter comes with.
So my question is, what should I do if I want to be pulling on time? Should I pull 500 feet higher according to my alti? Should I get into the habit of rotating my wrist to deburble? Should I stop flying on my belly? (I'm actually quite fond of flying on my belly at deployment altitude. )

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Pull.

[Jumpmunki 0]

i'd go head down before pulling to allow a clean airflow over your alti...

it'd be safer than pulling low ...

[bch7773 0]

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So my question is, what should I do if I want to be pulling on time? Should I pull 500 feet higher according to my alti? Should I get into the habit of rotating my wrist to deburble?

I would say no to both of those. first of all, how do you know that alti3 didn't make the mechinism so that it accounts for the wrist burble. so when you turn your wrist, you are actually giving an incorrect altitude reading? you may wanna email alti3 and ask.

and i wouldn't pull 500 feet higher... because then you would screw up the vast majority of the people who read their altimeter "as-is". just my zwei pfennig

MB 3528, RB 1182

[Harksaw 0]

I'd see if you can send the altimiter to the manufacturer and find out if they can fix the problem.

__________________________________________________
I started skydiving for the money and the chicks. Oh, wait.

[councilman24 37]

Wear a chest mount.

+/- 500 ft depends on altitude. At 0 they all pretty much return to zero, so the inaccuaracy isn't over their whole range.

I've never heard of one being affected by "wrist burble", but I suppose it's possible. If it's on the back of your hand most people turn their hand to look at it anyway. If you wear it on the side it may not be affected.

Of course the torso is big enough to make a difference to chest mounts and back mounted AAD's.

Hmmm, stop looking at your altimeter and start having fun? Just kidding, kinda.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[koz2000 1]

what type of altimeter is it? I had a brand that never read accurate in freefall. (I don't use it anymore)

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- Does this small canopy make my balls look big? - J. Hayes -

[FrogNog 1]

To answer some common questions:
* it's an alti-2 Altimaster Galaxy. I think it's a great altimeter and I have plenty of confidence in it, as long as the needle keeps moving and I don't drop it too many more times.
* In the plane it tends to read correct or as much as 500 low, from sea level to 14k. The effect of door open vs. door closed seems to be about 100 feet - not much.

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Pull.

[FrogNog 1]

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If it's on the back of your hand most people turn their hand to look at it anyway.

I think this is the key. When I bellyfly solo I have a tendency to lay head-high with my arms pushed in front of me (looks goofy on video, but it works) and that's why I can read my alti when it's perfectly in my wrist burble. I'll just work on flying with my arms up so I have to turn it to see it. (When I bellyfly with others, I think I do better with my arms.)

Kinda makes me go "Durr, I shoulda figured that out."

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Pull.

[Chrisky 0]

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OK, this makes sense. It also handily explains the "+/- 500 feet" accuracy statement the altimeter comes with.

Barometric Altimeters for skydiving are not super-prezise. Any altimeter shows "off" somewhere on it's scale, and if you get a good alti, they will send you a report from calibration showing how much it shows off at which standard atmospheric altitude. This is due to tolerances in the manufacture of the pressure pill. Mine reads correctly at 1000 m, shows -100m off at 0m (ground) and 200m at 4000m.
So if i zero it at the DZ, i know it reads my precise altitude at 1100m. And i know i don't really get 4200m even though my alti makes me believe.

The mind is like a parachute - it only works once it's open.
From the edge you just see more.
... Not every Swooper hooks & not every Hooker swoops ...

[kelpdiver 2]

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Barometric Altimeters for skydiving are not super-prezise.

Is this an argument for digitals?

500ft, or 100m, is a huge variance. 100ft I can understand, but now we're talking about 10% of the min pull altitude (for A)

[sundevil777 102]

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Barometric Altimeters for skydiving are not super-prezise.

As opposed to radar altimeters?

I like to wear my wrist mount with only the index finger through the loop (it is small), so that the dial is more toward the thumb, not so much in the burble, and easier to see without turning your wrist.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[Chrisky 0]

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Is this an argument for digitals?

No.

It was simply to state that on a barometric altimeter indicated altitude does not equal factual altitude (equal meaning exactly matching). They still are very useful low-tech mechanical devices.
As i have no clue how exactly the digitals work, i assume that they are actively measuring surrounding air pressure. In some countries (UK?) it is not officially allowed to use sensitive (active) devices as your only skydiving altimeter (like the Suunto watches etc.).
Motto: Why rely on something thats' battery can fail if a no-battery mechanical device does the job?

The mind is like a parachute - it only works once it's open.
From the edge you just see more.
... Not every Swooper hooks & not every Hooker swoops ...

[sundevil777 102]

Digital altimeters are still barometric.

Digital alti's measure pressure with a transducer, that is why they are more accurate.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[quade 4]

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Digital alti's measure pressure with a transducer, that is why they are more accurate.

That and some software. In and of themselves, the baro sensors are pretty unintelligent devices.

quade -
The World's Most Boring Skydiver

[kelpdiver 2]

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Digital altimeters are still barometric.

Digital alti's measure pressure with a transducer, that is why they are more accurate.

Digitals have the advantage of being able to do a non linear transformation. I didn't think air pressure was directly porportional (ie, going from 29.92 inches to 28.92 isn't the same as going from 20 to 19.

Mechanicals need to act on a lever, so the only way to reflect such a difference is in the markings on the dial. Or you have it accurate near the ground, less so up high. Hopefully that would be the choice made! 500ft strikes me as excessively inaccurate for the usage.

The fact that altimeters are based on barometric pressure is not an explanation for the error since you zero it out at departure and pressure systems don't change things that quickly.