Student CYPRES question

[ghost47 18]

So, I read in the incidents forum (and confirmed in the CYPRES manual) that a student CYPRES fires at: 750 feet if the jumper is falling at over 78 mph, but 1000 feet if the speed is between 29mph and 78 mph.

(CYPRES manual says the student CYPRES "activates the release unit when it detects a rate of descent higher than 29 mph (13 meters per second). The activation altitude is split. In the case of rate of descent being approx. that of free fall, the opening altitude is at approx. 750 feet (the same as with Expert CYPRES). However, should the rate of descent be lower than that of freefall but still above the limit of 29 mph (e.g. with partially opened canopy, or after a cutaway), then Student CYPRES activates the release unit when the altitude falls below approx. 1000 feet (approx. 300 meters) above ground level.")

I don't understand the logic behind that. It seems reversed. Could someone explain?

It would seem to me that there are these possible scenarios:

1. No pull. Jumper will be at over 78 mph at both 750 and 1000 feet. Seems better to fire at 1000 feet.

2. Low pull. Say at 1500 feet. Jumper slows down as the canopy snivels and opens. In that situation, it seems you would not want a CYPRES fire. But it seems more likely that you will be under 78 mph but over 29 mph at 1000 feet. So, seems better to have it set to fire at 750 feet if you're going over 29 mph at that point -- not 1000 feet.

3. Normal pull, but with mal and cutaway. In that situation, if the jumper has not slowed to under 78 mph by 1000 feet, it seems better to fire the CYPRES then.

4. Normal pull, but with a problem or mal and no cutaway. In that situation, if the jumper is falling at less than 78 mph but more than 29 mph, wouldn't you want to give the jumper the most time to work the problem out, or decide to cut away? So why have it set to fire at 1000 feet in that situation?

[NovaTTT 2]

The Student CYPRES will activate when the rate of descent exceeds 29mph.

Parameter I: In the case of rate of descent being equal to that of freefall the CYPRES activation altitude is at approx. 750 feet, the same as the Expert CYPRES.

Parameter II: Should the rate of descent be lower than that of freefall but still above 29mph (e.g. with partially opened canopy), the Student CYPRES activates at approx. 1000 feet above ground level. The student will then have some more time to prepare for landing (and presumably deal with a two-out situation).

Hope this helps.

(edited for colour)

ETA:

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4. Normal pull, but with a problem or mal and no cutaway. In that situation, if the jumper is falling at less than 78 mph but more than 29 mph, wouldn't you want to give the jumper the most time to work the problem out, or decide to cut away? So why have it set to fire at 1000 feet in that situation?

The student has used up his time to work the problem out - in fact, he's gone deep into the red. At 1000', the student is in a world of shit and he'd better hope the activation of the CYPRES results in a clean reserve deployment.

Despite the reality that one should act regardless of altitude (although the outcome might be nonetheless grim), the student's time to act is at or before 3000' - the minimum deployment altitude. I hope you recognize that the student, in this scenario, has failed to or is unable to act and the CYPRES is his last chance.

"Even in a world where perfection is unattainable, there's still a difference between excellence and mediocrity." Gary73

[riggerrob 563]

The Student Cypres is programmed to react in two different scenarios.
The first scenario is the same as all other AADs: no pull and freefalling through 750 feet rapidly.

The second scenario is more complex: hanging under a partially malfunctioned main canopy. If a main is partially deployed, it will slow you down partially. The landing may not kill you, but it will mangle you. So Student Cypres is programmed to get more nylon out if you are spinning under a partially-deployed main.
This feature is deleted from other AADs (and other versions of Cypres) because experienced jumpers routinely descend faster than this, under properly-functioning main canopies.
Heck! I am embarrassed to admit that I scared an FXC 12000 by spiralling through 1,000 feet under a student main!

That is why there is a SWOOP version of Cypres, to prevent unwanted reserve deployments, when when pro pond swoopers do aggressive spirals below 1000 feet.

[BIGUN 1,110]

You're one of them thar math majors, ainchya? Here's a little Oklahoma logic fur ya...
If ya always take the spoon outchyer coffee cup, you'll never get stuck in the eye.

Nobody has time to listen; because they're desperately chasing the need of being heard.

[ghost47 18]

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The second scenario is more complex: hanging under a partially malfunctioned main canopy. If a main is partially deployed, it will slow you down partially. The landing may not kill you, but it will mangle you. So Student Cypres is programmed to get more nylon out if you are spinning under a partially-deployed main.

It would seem to me that a CYPRES firing when you have a malfunctioning or partially malfunctioning canopy overhead could also potentially kill or maim you by causing an entanglement, or a bad two out situation. So, in this scenario, what I'm not getting is why you wouldn't want to have the CYPRES fire at 750 instead of 1000, to give the student slightly more time to work the problem out.

In the same vein, I don't understand why you wouldn't want the student CYPRES to fire a little higher if the student is in freefall. I would think that if the student is going over 78 mph at 1000 feet, chances are, (s)he hasn't pulled and isn't going to be pulling. So why not give the reserve that slightly extra chance to come out?

So I guess I still don't get it. (I mean, I understand HOW it works. I just don't understand WHY the decisions were made the way they were.)

[NovaTTT 2]

Please re-read Post #2.

The activation altitudes are not arbitrary.

What you must understand is that the AAD is not there to save your life (that's your job). It is there to cut your closing loop under specific conditions at a predetermined (and low) altitude which hopefully will result in a lifesaving reserve deployment.

This is your last hope.

A student who is under 2000' with no parachute or a malfunctioning parachute has not done his job, for whatever reason, and is in real trouble. If that student is at or below 1000' feet, that student has FAILED. Failed to act, failed to respond, failed to clear - for whatever reason, be it incapacitation, fear, confusion, whatever. The student is in a world of shit and the time for "let's wait and see if he'll work this out" is gone, gone, gone.

In this case, the Cypres is designed to activate, to cut the loop. Airtec doesn't say their device deploys the reserve, and they don't say their device will save your life. They say their device will cut the closing loop.

There is no chance for a reserve deployment if the container is closed. There is a chance the reserve will deploy past a malfunctioning main. There is a chance that more fabric out will decelerate the student to a survivable rate of descent.

If you don't like their parameters, and you are using an Expert Cypres, change the firing altitude.

I wouldn't call it a good idea under normal conditions, but it can be done.

If you don't want to be bothered with this, then you can design your own AAD and encode it with what you consider to be better parameters.

But keep in mind Airtec (and the other AAD manufacturers) have a lot of research, testing and field use behind their designs. They know what they are doing.

"Even in a world where perfection is unattainable, there's still a difference between excellence and mediocrity." Gary73

[pilotdave 0]

I'm not sure, but my guess is that a big part of the reason why the low speed activation altitude is higher is the same reason an expert cypres can fire as high as 1200 feet. In the case of a low speed malfunction, the burble behind the jumper is gone. The cypres will fire at a higher altitude when a jumper is upright rather than belly-to-earth. The chances are pretty good that if a jumper is descending somewhere between 29 and 78 mph, they are probably not in a belly-to-earth body position. So the cypres will fire at a higher altitude.

So I wonder if the student cypres is really designed with dual activation altitudes, or if a 29 mph activation speed simply fires higher because the altitude calculation is calibrated for belly-to-earth freefall.

Dave

[NovaTTT 2]

According to page 10 of the User's Manual, the activation altitude is split on the Student CYPRES.

One presumes that's intentional.

"Even in a world where perfection is unattainable, there's still a difference between excellence and mediocrity." Gary73

[ghost47 18]

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Please re-read Post #2.

I did. You said that: (a) the student would have more time to prepare for landing and presumably deal with a two out; and (b) the student should have acted by then, and at that point, the CYPRES is the last hope.

While that makes sense to me, what I don't understand is why you would then wait until 750 feet if the student is going above 78 mph. I would have no question if the CYPRES went off at 1000 feet for students if the descent rate is above 29 mph, period.

But CYPRES has decided to split activation rates. So my question was, and is, if you're going to do that, it seems like it should be split the other way. Why isn't it?

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The activation altitudes are not arbitrary.

Thank you.

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What you must understand is that the AAD is not there to save your life (that's your job). It is there to cut your closing loop under specific conditions at a predetermined (and low) altitude which hopefully will result in a lifesaving reserve deployment.
This is your last hope.

Oh, is that how a CYPRES works.

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A student who is under 2000' with no parachute or a malfunctioning parachute has not done his job, for whatever reason, and is in real trouble. If that student is at or below 1000' feet, that student has FAILED. Failed to act, failed to respond, failed to clear - for whatever reason, be it incapacitation, fear, confusion, whatever. The student is in a world of shit and the time for "let's wait and see if he'll work this out" is gone, gone, gone.

If so, then what is the point of waiting until 750 feet to cut the loop if the student is going faster than 78 mph? I would think that, in that scenario, the student is in a deeper world of shit, and the time for waiting to see if the student will pull is gone, gone, gone. Why not cut the loop at 1000 feet in that scenario?

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In this case, the Cypres is designed to activate, to cut the loop. Airtec doesn't say their device deploys the reserve, and they don't say their device will save your life. They say their device will cut the closing loop.
There is no chance for a reserve deployment if the container is closed. There is a chance the reserve will deploy past a malfunctioning main. There is a chance that more fabric out will decelerate the student to a survivable rate of descent.

Right. But that doesn't answer the question -- if you're splitting the altitudes at which activation occurs, why 750 feet for 78+ mph and 1000 feet for 29 to 78 mph?

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If you don't like their parameters, and you are using an Expert Cypres, change the firing altitude.
I wouldn't call it a good idea under normal conditions, but it can be done.
If you don't want to be bothered with this, then you can design your own AAD and encode it with what you consider to be better parameters.
But keep in mind Airtec (and the other AAD manufacturers) have a lot of research, testing and field use behind their designs. They know what they are doing.

Did I ever say students shouldn't use CYPRESes because the logic didn't make sense? Did I say I wanted to change my CYPRES (which is an expert CYPRES, so no, I don't have a problem with the logic behind it)? No. I'm asking a question about why things are done a certain way. I'm perfectly willing to believe that CYPRES has a good reason to make student CYPRESes do what they do. But since I couldn't figure out what that reason was, I thought I'd ask the online skydiving community.

[pilotdave 0]

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According to page 10 of the User's Manual, the activation altitude is split on the Student CYPRES.

One presumes that's intentional.

Not me. I mean it may very well be intentional. But we also know that under a snivelling main, a cypres will tend to fire high. If the activation speed is just 29 mph with an activation altitude of 750', it would likely fire at ~1000 feet if the jumper was doing say 50 mph.

So I'm just suggesting that it's possible that the cypres logic doesn't really have split activation altitudes... maybe it would work the same with an activation altitude of 750' and 29 mph. I don't know that airtec ever shares their actual activation logic, so I don't know if it can be confirmed one way or the other.

But you could just as easily say that an expert cypres has split firing altitudes. It'll fire at ~1000 feet if the jumper is under a sniveling canopy at greater than 78 mph, or at 750' if in freefall.

The fact that they use two different activation speeds for the student cypres may be meaningless... it fires above 29 mph. If I understand it correctly, there's no need to reach 78 mph to fire at 750 feet. If you are going through 750 feet at 31 mph, it'll fire, right? I wonder if the split activation altitude is more of a warning in the manual that the student cypres can fire high, under a malfunctioning main or a spiralling student.

Dave

[NovaTTT 2]

If you just want to know why the CYPRES freefall activation altitude is ~4.5 sec to impact (750'), it is my understanding that it is so because: (1) they decided to make it high enough to allow the reserve to deploy and stabilize but (2) low enough that the jumper is separated (vertically) from other jumpers in the sky and deploys in clean air.

A quick email to Airtec will get you the best answer to that question. [email protected]

The second parameter, which is most likely a malfunctioning main, is higher so the skydiver can have additional time to deal with a likely two-out situation.

Again, a quick email to Airtec will get you the best answer to that question. [email protected]


ETA:

Dave -

Airtec is very tight with their software so we may never know if it is intentional or by-product. I'm not a technical writer, but if I were I would rather clearly spell out a risk than to clothe it as a separate feature. But as I said, I'm not a technical writer so what do I know???

"Even in a world where perfection is unattainable, there's still a difference between excellence and mediocrity." Gary73

[davelepka 4]

The Cypres is aware when a deployment, and the subsequent reduction in speed has taken place.

If a student has deployed, and not taken action to keep his speed below 29 mph by 1000ft, the assumption is that he will never take any action, and the Cypres will activate.

In the case of no deployemnt, the Cypres will wait until the perscribed firing altitude of 750ft to activate. This altitude was chosen as the last reasonable moment that you could initiate a reserve deployment and expect an open canopy before impact without interfering with the skydive.

If a Cypres were to fire in the absence of a deployment any higher than 750ft, you start to get into the area where a PC hesitation, or slow deployment which was jumper initiated at 2000ft may snivel down into the firing altitude, and give the jumper a two-out when it is not needed.

Even in the case of a student, we all know that AFF Is can and will chase a student down to 2k if they get loose in freefall. Again, in these cases, if the Cypres were to fire higher than 705ft, you are risking a two-out following what was otheriwse a clean deployment, albeit at a lower than intended altitude.

Of course, it is possible to suck it way down, and snivel into the 750ft firing altitude, again resulting in a two out when the main was opening fine, but that's 100% jumper error. The Cypres waited as long as it could to intervene, but the jumper got so low it had to fire.

This is what's meant when people say that it's your 'last chance'. It is intentionally programmed to wait until the last second in order to avoid interfering with the jumpers intended actions. This is true for both the expert and student models.

[danielcroft 2]

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This is what's meant when people say that it's your 'last chance'. It is intentionally programmed to wait until the last second in order to avoid interfering with the jumpers intended actions. This is true for both the expert and student models.

There was a discussion about this a few weeks ago - why wouldn't you just set the student AAD to activate at 3000ft? was the question and the answer is what Dave wrote.

A reserve is meant to open in 3 seconds, if you have 4.5 seconds to impact at 750ft, you have 1.5 seconds of leeway in the algorithm. A reserve is more likely (I believe) to hesitate when you're under a malfunctioning canopy or at least take longer to open. My guess would be that the 29 mph to 78 mph mode in the Student cypress is in order to give the reserve the best chance of opening (which may take longer than 3 seconds based on the configuration of the main and why the Student is falling at >29 <78 mph). Expert AADs don't do this (or at least, they're not supposed to!) or you'd have a lot of broken/unhappy swoopers.

So, the general answer is the quote from Dave above.