A question about computers and airplanes

[dannobee]

While I don't have the answer for your particular computer, I do remember when my daughter was playing with hers on a flight, once it was turned on, it knew what the altitude was and upon descent, it "thought" we were doing an altitude dive.

We don't turn computers on anymore during flights.

 

[ishmaelcat]

Hey dannobee:

Interesting point. I forgot when I posted the original question that most people turn their computers on and off; this might be why most people never see the apparent anomoly that has me so puzzled. My computer, howvere, like some other models, is always on -- if nothing else displaying the time of day and date.

 

[LaurenW]

My computer does the same thing, and this is my guess as to why:

The behavior at altitude (on a plane) is correct, it should, and does show some Nitrogen loading. My guess is that the rate of nitrogen buildup and offgassing is caculated relative to altitude, but the actual load you have (number of bars/pixels/whatever) doesn't get adjusted when altitude decreases. Computers tend to be conservative, so they would have to account for the loading gained by increasing altitude, but ignoring the positive effects of reducing altitude is conservative, and the difference is probably pretty negligible anyway. I think it's easier for the manufacturer to simply not include any model for giving you "credit" for reducing altitude.

If you really want to check it, go diving, then put the computer (dry) into some sort of pressurized container and see if it credits you for the increased air pressure. I would be willing to bet it won't.

 

[sschlesi]

If you really want to check it, go diving, then put the computer (dry) into some sort of pressurized container and see if it credits you for the increased air pressure. I would be willing to bet it won't.

I'd expect the computer to act as though it were on a dive. If the moisture sensor says dry, but the depth sensor says pressure is greater than sea level the safest assumption is to assume a dive is occurring and ignore the moisture sensor.

 

[LaurenW]

I'd expect the computer to act as though it were on a dive. If the moisture sensor says dry, but the depth sensor says pressure is greater than sea level the safest assumption is to assume a dive is occurring and ignore the moisture sensor.

It'd be an interesting experiment.

I'd bet you a beer the computer either breaks or does nothing at all rather than assume it's diving. Anybody have a chamber and a computer they're willing to sacrifice? For science?

 

[rstofer]

So, you've been on a long flight and your body (and computer) are now acclimated to 8000 feet. Essentially, you have offgassed all the excess nitrogen. Then you descend to sea level and the computer thinks you are accumulating nitrogen, which you are. Like a dive at altitude. Since you have only changed a fraction of an atmosphere (maybe a few feet of water) you aren't taking on nitrogen very fast. But, until the computer accounts for all the changes you are getting compressed.

On some computers, you can disable the water contacts. The computer starts when you push a button or when the pressure sensor detects a dive. The Aladin Prime works this way. But it still measures altitude every 60 seconds even when switched off.

Richard

 

[LaurenW]

So, you've been on a long flight and your body (and computer) are now acclimated to 8000 feet. Essentially, you have offgassed all the excess nitrogen. Then you descend to sea level and the computer thinks you are accumulating nitrogen, which you are. Like a dive at altitude. Since you have only changed a fraction of an atmosphere (maybe a few feet of water) you aren't taking on nitrogen very fast. But, until the computer accounts for all the changes you are getting compressed.
Richard

I don't think this is correct. If this was how the computer treated it (continuing to use altitude as the baseline) then the nitrogen would continue to rise, rather than either disappearing, which it should, or doing what it currently does and start counting down.

edit to clarify: What the computer should do is reestablish the baseline. What I think actually happens is the computer has a formula for calculating loading, and that formula depends on altitude. Returning to sea level doesn't change how it sees the nitrogen you've already "accumulated" by being at altitude, so it counts down like you're still decompressing.

 

[sschlesi]

It'd be an interesting experiment.

I'd bet you a beer the computer either breaks or does nothing at all rather than assume it's diving. Anybody have a chamber and a computer they're willing to sacrifice? For science?

That sounded like a challenge so here is what I did.

Not having my own personal deco chamber, I needed a DIY pressure vessel. A paint pot would have been ideal, but I don't have one of those either. Instead I took an empty costco sized peanut butter container, drilled a hole in the lid and inserted a valve stem that I cut out of a bicycle tire. I then switched on my Oceanic VEO 250 and dropped it in. A liberal application of duct tape around the valve stem and threads of the jar, and I had a container that would leak at a moderate pace.

I then spent about a minute slowly pumping air into the container using a bicycle pump. Trying not to pump so fast that the tape would unseal, and trying to squeeze shut any leaks that opened up. A quick peek at my computer showed that the dive counter had incremented from 0 to 1. A review of the dive log shows a dive with a max depth of 8ft. for less than 1 minute.

That was fun, I wonder if I can get a job on Mythbusters, all I'd need to do is wrap up by exploding the peanut butter container with an excessive amount of C4. With all that duct tape I'm likely better qualified for the Red Green show.

It will probably be a pain to ship the beer across the Canadian border, so I won't hold my breath while waiting.

 

[emoreira]

Computers tend to do what they are told, and no more.

The computer was probably programmed with some sort of an off-gassing clock. When you land, the clock is still running.

My computer does things that I do not tell to do, for example the blue screens

 

[sphillips3]

Are the departure and destination airports are the same elevation? Is the atmospheric pressure (barometer) exactly the same in both places?

If you land at a higher elevation and the flight is less than 24 hrs long you will in fact have N2 loading relative to the new elevation.