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# CYPRES question?

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I'm curious as to how AADs know where the ground is. As a student pilot I'm rather familiar with the inner workings of an altimeter, and so far as I know they measure MSL altitude, not AGL... So how does your CYPRES know your AGL height to prevent you from doing the big splat if you pass out or for whatever reason need emergency deployment of the reserve?

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Remember the cypres is a computer, as such, it's got some built in logic. My guess, and this is only a guess...
The Cypres knows the ground is lower than exit altitude or anything on the ride to altitude. It probably knows that once it's started climbing it's left the ground. Therefore, whatever is below the beginning of the climb must be the ground. When it starts decending again, quickly, it realizes it's left the plane. Repeat cycle.
I'm just guessing.

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Quote

So how does your CYPRES know your AGL height

The Cypress calibrates itself when you turn it on. It can also be re-set: If the DZ is higher or lower than the airport it needs to be re-set to take this into consideration. This is the same principle as applied to your altimeter.
Cheers,
NewGuy

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I could be a little off on this (its been known to happen, hehe), but from what i know the Cypres somehow senses fall rate and altitude. When it reaches a certain altitude (700-1000ft.?) and the fall rate is still a certain value (obviously fast enough to not be under a canopy) it "fires", deploying the reserve. Again, I could be wrong, but from what I remember from the FJC of AFF thats the basics of it. Hopefully I'm at least a little bit on the right track with that answer ;-)

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Someone please correct me if I'm wrong.... thanks!
-Marshall

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Durning the start up sequence of the CYPRES, it takes rapid measurements of the air pressure and takes the average of these measurements as the "Baseline" pressure at ground level. The entire time the unit is on it keeps checking the air pressure. If the unit notices a slight increase or decrease in pressure but not that much of a change (approaching storm) it will reset the "Baseline" figures to read the new average. If it notices a rapid increase in pressure, it assumes you are climbing to altitude. You need to climb above 1500 feet in order for the unit to switch into "Jump" mode. In order to figure activaction altitude, the unit adds a set figure to the ground pressue to determine the pressure at that altitude. Once in jump mode it keeps looking to see if you break one of the conditions that is set forth in its programming (too low, too fast). Once it detects this, it "releases" the cutter, the cutter cuts the closing loop and the reserve deploys. The cutter is traveling with enough speed and force, SSK has pictures of it cutting steel braided wire. Cutting the closing loop is done in the blink of an eye. Thats a brief overview of the unit as it was explainded to me by SSK last year.
A rainy day at the DZ is better then a Sunny day at work

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Thanks everyone -- I've got it well enough. Once I get to my new home DZ I'll ask my instructor for a more thorough briefing. :)

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Instead of your instructor, talk to a rigger. Most times instructors only know enough about the gear to teach the operation to students.
Riggers know the in and outs of the equipment. A rigger can tell you the proper stitch count needed on different seams and how to do stuff like french seams that an instructor probally won't know.
A rainy day at the DZ is better then a Sunny day at work

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Even better than asking a rigger is to read the Cypres owners manual.

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> Instead of your instructor, talk to a rigger. Most times instructors only know enough about the gear to teach the
> operation to students. Riggers know the in and outs of the equipment.
Well, no, riggers know how to maintain equipment, whereas instructors know how to teach their operation to students. I've heard more bizarre explanations on cypres inner workings, canopy aerodynamics, wind effects and even aircraft performance from riggers than from instructors - not because one knows more than the other, but because I find instructors say "I don't know" more often than riggers.
-bill von

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