Was: Recommended specs on reserve exit weight, do you go over max?

[phoenixlpr 0]

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Let's say that doubling the max weight causes the canopy to experience the peak load twice as long. I know that this might not be linear, I'm just giving an idea a shot. Wink

You have a really interesting definition of peak force.

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Are reserves also rated for how many terminal openings they can sustain?

AFAK some reserves have limitation of maximum number of deployment.

[labrys 0]

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You have a really interesting definition of peak force.

No I don't.. I never even made an attempt to define peak force.

Owned by Remi #?

[strop45 0]

Weight does affect terminal velocity. Imagine that you are lying in a wind tunnel as it starts. As the speed of the wind increases, so does the lift created by the wind hitting your body. When the lift created is equal to your WEIGHT you 'float'. If at this point if you add more weight than you 'sink' and either the wind speed needs to increase or you must generate more lift (e.g. de-arch).

For a heavier object with the same shape/size/surface roughness then the wind speed must be higher, i.e. when falling through the sky its terminal velocity will be higher.

The difference between stupidity and genius is that genius has its limits." -- Albert Einstein

[Ron 7]

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I wonder what makes you think that mine is bigger than yours ... or his is bigger than your ... is the right way to prove anything?

Well even though you seem unable to admit anytime you are wrong...It is pretty simple concept that a guy with 6 times more experience (Sparky) than you, who WAS A TEST JUMPER! Might know more than you.

But your ego will not let you admit you are out of your league. You can make "penis size" jokes all you want.

I am done here as well. Its clear you think you know more than everyone else, so why bother?

"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334

[JerryBaumchen 1,048]

Hi Roger RamJet

If you were witnessing TSO testing in the late '70's it would have been under C23(b)/NAS 804. Under C23(b) one could test per the Standard Type or the Low Speed Type. When I did my TSO testing in '79 I elected to test per the Standard Type. There is a table in NAS 804 which is a sliding scale; the more weight you use then you get to use less speed. We chose to use 400 lbs at a speed of 200 MPH. As an example, in using the table we could have also chose 275 lbs at 250 MPH; there are 10 options (weight & speed chart) for the Standard Type Strength Test.

Hi labrys

I served on the TSO committee for nearly 20 yrs. My first submittal (15 items submitted) had a req'ment that the sample being subjected to testing(canopy/harness/whatever) had to be the exact same sample for all three Strength Tests. In C23(b) there is no req'ment that the same sample be tested more than once. My concern was, as I think is yours, that a canopy once subjected to severe loading (I will not define 'severe' but I would consider a terminal opening to be somewhat severe) might not be airworthy and riggers in the field may not have the ability to determine incremental damage.

Sandy Reid once told me that when he was testing his Talon rig per C23(c) if he was using a C23(b) canopy for his Strength Tests he could almost predict that the canopy (which was not the test sample; the rig was the test sample) would be destroyed on the 2nd or 3rd test.

Hope that this helps,

Jerry
(A Happily Retired Mechanical Engineer)

[pchapman 261]

In reply to phoenixlpr who started all this, everything I've read about parachute testing suggests that weight does matter...although not as much as speed. Even without understanding all of the opening dynamics, this will be related to aerodynamic forces (e.g., dynamic pressure) increasing with the square of the speed.

>>> The rest of this post just looks at some numbers based on actual parachute testing. <<<

While phoenixlpr isn't inclined to believe anyone, let's look at the NAS 804 specs, which JerryBaumchen and mjosparky mentioned. To get to a 5000 lb peak force, one could have 150 mph and 660 lbs, or other combinations including 300 mph and 200 lbs.

The NAS 804 standard was based on a particular old round canopy, the C-9. It's not the same as a slider-reefed ram air, but some general trends should be similar.

Those numbers show that to keep the same load, when the speed was doubled, the weight didn't just get halved (a ratio of 1/2), which would be the case if weight and speed were equally weighted. Instead, the weight had to multiplied by a factor of 1/3.3 to compensate. So a change in speed has a substantially greater effect on peak opening force than does weight.

When comparing the rest of the NAS 804 tables for 3000lbs of force and 5000 lbs, it can be seen that forces nearly but don't quite rise as fast as the weight does. So doubling the weight won't quite double the force. (At least in some of the speed and weight range tested.)

As for speed, the tables show that forces rise much faster than does speed. But forces don't rise as quickly as the dynamic pressures (i.e., speed squared). So doubling the speed will increase force by much more than a factor of 2, but not by quite as much as a factor of 4. A canopy with a slider to control inflation should exhibit a smaller speed effect.

This is all based on one old type of parachute, but it still provides some feel for how opening forces can change with weight and speed.

[phoenixlpr 0]

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Well even though you seem unable to admit anytime you are wrong...It is pretty simple concept that a guy with 6 times more experience (Sparky) than you, who WAS A TEST JUMPER! Might know more than you.

Notice that I do not question his experience. I'd rather question you way your way of measuring and comparing others experience.

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But your ego will not let you admit you are out of your league. You can make "penis size" jokes all you want.

You made it not me. I notice that I need much more jumps to challenge your ego.

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I am done here as well. Its clear you think you know more than everyone else, so why bother?

My opinion is base on a mathematical model. Why do you bother to prove my model is wrong or even more constructive way: give a better model.

[RogerRamjet 0]

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Hi Roger RamJet

If you were witnessing TSO testing in the late '70's it would have been under C23(b)/NAS 804. Under C23(b) one could test per the Standard Type or the Low Speed Type. When I did my TSO testing in '79 I elected to test per the Standard Type. There is a table in NAS 804 which is a sliding scale; the more weight you use then you get to use less speed. We chose to use 400 lbs at a speed of 200 MPH. As an example, in using the table we could have also chose 275 lbs at 250 MPH; there are 10 options (weight & speed chart) for the Standard Type Strength Test.

That is correct (C23(b)), it was around this time that manufacturers of the "modern" gear (Wonderhog, Eagle, SST, etc.) began to go for TSO certification as the FAA was begining to take notice that none of the sport gear on the market was carrying a TSO. Some of that testing was done at Z-Hills with our 196.

I don't know if everyone tested beyond the certification to see where their canopies or harnesses would fail, but Strong did in this case and it was pretty interesting. I hadn't really considered the repeated dropping of the same unit and the incremental destruction that might lead to, good food for thought for those that have used their reserve at terminal more than once...

-----------------------
Roger "Ramjet" Clark
FB# 271, SCR 3245, SCS 1519

[riggermick 6]

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Well even though you seem unable to admit anytime you are wrong...It is pretty simple concept that a guy with 6 times more experience (Sparky) than you, who WAS A TEST JUMPER! Might know more than you.

Notice that I do not question his experience. I'd rather question you way your way of measuring and comparing others experience.

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But your ego will not let you admit you are out of your league. You can make "penis size" jokes all you want.

You made it not me. I notice that I need much more jumps to challenge your ego.

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I am done here as well. Its clear you think you know more than everyone else, so why bother?

My opinion is base on a mathematical model. Why do you bother to prove my model is wrong or even more constructive way: give a better model.

Cut your losses, Move on! You are apprantly not as smart as you think you are.



Some people EVEN IN THE FACE OF OVERWHELMING EVIDENCE (and annicdotal evidence)TO THE CONTRARY will STILL maintain their (untenable) position. That is the precept of a religion, unswerveing faith, no matter what is presented to the contrary.

A whole lot more people with many more years of REAL WORLD experience than you currently have, have demonstrated that YOU are WRONG!! Admit it and come back to the "real world". We all have beliefs and pre-conceptions of how stuff happens/ works, but sometimes we find out that we are wrong, or at least a little mis-guided. It's OK to be wrong, that's how we (as a species) learn.

The people you are rubbing the wrong way today did the same thing ten, twenty, thirty, hell even fourty years ago. That's human nature.

It's good to question, but have your have arguement fully thought out before you bring out the "big dick".


Just words of advice from someone "that's been there done that".


Mick.

[mjosparky 3]

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I have my opinion as long as someone can prove me that my point is wrong.

One more try. If weight does not matter, how do you develope the velocity/speed to produce opening forces? Do you use FM?

My idea of a fair fight is clubbing baby seals

[LongWayToFall 0]

I think the reason weight has something to do with peak forces is that there is time between the initial opening shock, and the peak force shock. During the start of deceleration the slider is up, and slows you a certain amount before you feel the peak shock, which is right when the cells begin to inflate and right around the time the slider starts to come down. Because you were slowed, the peak forces are less than if the canopy began to inflate instantly, like a slider-less base canopy. If you are jumping a smaller canopy, you can argue that a longer deployment time might make your cell inflation/slider-drop speed close to the same as a larger canopy, it will not be the same because the smaller area of your canopy will make your slider up velocity faster. Imagine a slider that is tied so it will not decend down the lines, when it opens if you are a 250lb jumper you will be going faster than a 150lb jumper correct? It is this difference in speed apon cell inflation that could save your canopy from explosion. But who knows, Im a noob with hardly any experience in anything, these are just simple observations and I most likely am completely wrong.

[mjosparky 3]

Look up and study the difference between "snatch force" and "opening shock".

My idea of a fair fight is clubbing baby seals

[LongWayToFall 0]

Snatch force is the force you feel when your decelerated bag/canopy reaches line stretch and begins your rotation. Opening shock being the force you feel after this, caused by drag of the airstream on your slider/canopy. The time period I am talking about is after line stretch, before maximum force being applied to the risers. check out this diagram:

http://www.pcprg.com/should03.gif

The time that there is a registered amount of force on the risers untill maximum force, is about 1.5 seconds. During this time there has to be some sort of deceleration, but to what speed? I am just saying that when the peak of force hits, you want to be going as slow as possible, because this will hopefully reduce it. If you are jumping a higher wing loading you will almost HAVE to be going faster at that time, because drag during that 1.5 seconds will be less than a larger slider/canopy above your head. But again, i have no experience in this stuff.

[mjosparky 3]

Snatch Force: The force imposed on the suspended load by the decelerator from it velocity at line extension (not line stretch) to the velocity of the suspended load.
PPM Vol. I

In other words the PC slows the bag and canopy down and just before line stretch you, as the load accelerate the bag and canopy back to you speed.

Opening Shock: The opening shock is the deceleration force exerted on the load following the snatch force. It is caused by the acceleration of the open canopy and the air associated with it.
PPM Vol.I

In other words this is the force imposed when the open canopy slows you down to the speed of the open canopy.

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The time that there is a registered amount of force on the risers until maximum force, is about 1.5

There is no set time as to when or for how long peak forces will take place although time is a critical factor. But a good rule of thumb is that the more time between snatch and opening force the less total force will be produced.

The variables are many; a smaller PC will produce less snatch force but may increase opening shock. A larger canopy may increase snatch force but reduce opening force and on and on.

I hope this helps.

My idea of a fair fight is clubbing baby seals

[imstu 0]

The variables are many; a smaller PC will produce less snatch force but may increase opening shock. A larger canopy may increase snatch force but reduce opening force and on and on.
I hope this helps.

[bob.dino 0]

Jumping canopies that are seriously out of trim can result in funky openings. Why not get the canopies relined if they're out of trim?

As to the pilot chute question, I'm afraid I don't have enough knowledge to comment.

[mjosparky 3]

With out knowing more about you (fill in your profile) I would not attempt to offer any advice.

But just from reading your post I would guess that a 150 anything is too small for you to be on.

My idea of a fair fight is clubbing baby seals

[imstu 0]

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Jumping canopies that are seriously out of trim can result in funky openings.

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That's for sure! I found that out the hard way. I didn't know how far out of trim they were until after the two bad openings.
***Why not get the canopies relined if they're out of trim?

I will not jump those two canopies again until they are relined (I have a few canopies). I'm stupid, but not suicidal. The Stiletto 170 I'm jumping now is a newer one. It has less than 200 jumps on it and my rigger is checking the lines on it just to be sure. The older Stiletto 170 and 150 are going back to PD to be relined.
Thank you for the input, Bob.
Stuart

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[imstu 0]

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With out knowing more about you (fill in your profile) I would not attempt to offer any advice.

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I'm sorry about that Sparky. I filled in my Profile.

But just from reading your post I would guess that a 150 anything is too small for you to be on.

Admittedly, the 150 was too small for me. I was jumping alot at the time and thought I could handle it. I didn't have any problems with it, but I can see where it was a bit much for me. I would like to stay with the 170 for a while and learn to fly it to it's potential. I really like how it flies! I'm going to get the older 170 relined so I will have two rigs with the same canopies in them like I did with the Sabre 190s. I still jump a 190 when I first get to a new dropzone or it's been a while since I last jumped. Then I jump the 170. I stand up my landings and land where I set out to land. I did ask my old instructor about jumping the 170 and he OK'd it before I started on it. I haven't had any trouble flying or landing the canopies, just surviving the openings. I would like to learn as much as possible about opening sequence and what affects it. Thank you for any input you can give me.
Stuart

[br0k3n 0]

The sabre is easy to fix, get a rigger to make you larger slider. I would suggest a slider the same size as one you would get on a sabre 210.... problem solved......

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--+ There are 10 types of people in the world: Those who understand binary, and those who don't.. --+

[AceJack 0]

Hi all,
I am new to this forum and this is my first post. I've been reading this thread and can't help but to chime in. Although I am a layman to this subject and new to the sport I actually agree with Phoenix and think what he have to say have merit. I totally believe that airspeed have more affect on peak loads than weight. I don't have any fancy mathematical formula but if you look at this problem from another perspective, you may see that what he says might be true. Example: You take a heavy guy and he deploys his large 'chute at a certain speed. You will get a X number of force as he decelerate. Now you take the same guy and have him deploy a much smaller (overloaded) 'chute at the same airspeed you should not get more force. In fact, you should get less force due to less drag from the smaller 'chute. Yes, the smaller canopy will fall somewhat faster for a longer period of time, this should not cause the canopy to blow up because you are well within the design parameter (airspeed) of that canopy. Remember, the forces generated here is not the same as if you tie a weight to a fixed object and drop it. With that said, I am assuming that the smaller 'chute is made with the same construction techniques and material as the bigger chute and of the same strength. I am also assuming the two 'chutes have similar opening speed as each other. I know that is a lot to assume but I am keeping those two factors the same for the sake of argument. And as for the max recommended weight on the canopy, I think that has more to do with the sink rate and the speed it would fly when you try to land it.
I know I'm going to catch a lot flak by going against the grain here but I'm here to learn and so far I've learned a lot by reading different opinions.

[mjosparky 3]

You forgot about "fill time" speed of load at "snatch force" and maybe time between "snatch force" and "opening shock". You can take the same load with the same canopy at the same speed and change the "overall force" by changing the size of the PC.

Me thinks you assume too much.

My idea of a fair fight is clubbing baby seals

[980 0]

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Hi all,
I am new to this forum and this is my first post.

way to go on an awesome first post!

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Although BECAUSE I am a layman to this subject and new to the sport I actually agree with Phoenix and think what he have to say have merit.

there, I fixed it for you

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I don't have any fancy mathematical formula

you also have almost no real experience in this matter, so why would you be willing to contradict people that do?

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I am also assuming the two 'chutes have similar opening speed as each other.

wrong

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as for the max recommended weight on the canopy, I think that has more to do with the sink rate and the speed it would fly when you try to land it.

wrong again

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I know I'm going to catch a lot flak by going against the grain here but I'm here to learn and so far I've learned a lot by reading different opinions.

you're not catching flak for going against the grain, you're catching flak for making ridiculous statements with no practical experience or reasonable theory to back them up

if you think you have learned from reading phoenixlpr's (and such, but he's the prime example) opinions, you have a lot to learn about learning

[billvon 2,400]

>Example: You take a heavy guy and he deploys his large 'chute at
>a certain speed. You will get a X number of force as he decelerate.
>Now you take the same guy and have him deploy a much smaller
> (overloaded) 'chute at the same airspeed you should not get more
> force.

Some things you are overlooking:

1) A heavier guy falls faster.

2) A given force will decelerate a small mass quickly, and on a partly elastic system (which a parachute is) the forces peak at a low value. A given force will decelerate a large mass more slowly, and on a partly elastic syste, the forces will peak at a higher value.

>In fact, you should get less force due to less drag from the smaller 'chute.

Parachutes don't work that way. If you open almost any parachute instantaneously at terminal, it will be destroyed, no matter what its size. Reefing (the process of slowing the opening) is required for survivable openings. Some parachutes (like rounds) have some inherent reefing; some require external devices like sliders.

A slider-controlled reefing system is dependent on many things, like jumper weight, deployment airspeed, density altitude etc. So the statement "a smaller parachute gives you less drag during opening" just doesn't make any sense. It's like saying "a smaller car stops faster." The power of the brakes make a much bigger difference than the size of the car.

[AceJack 0]

Ah, I see so parachutes are not normally designed to handle the load if they are opened fully at terminal speed and it's the reefing system not the overall drag of the parachute that is more important in keeping the parachute from blowing up upon deployment.

I agree that when you apply a force to an object to slow it down. A more massive object would take longer to slow. But, if you were to measure the force to slow an object down, wouldn't the measurement be equivalent to the force opposing the movement not the weight of the object?

Quote: "A heavier guy falls faster." That's why I mentioned that it is the same guy falling at the same speed. Only the size of the canopy is changed. Are the smaller canopy built weaker than the larger ones? I'm still trying to figure that one out.

Like I said before I am inexperienced in this sport. The statement I made before is just a conclusion from I've read from certain posts. It is more of a hypothesis or rather a question to this subject, not facts. Thanks to those who were able to answer some of the questions. To those who just like to say that I'm wrong, maybe it is just easier to pick on the guy who has different opinion and don't have the backing of the general consensus. You still have not provided any explanation to why I'm wrong. You ridicule me on my lack of experience and lack of things to back up what I say, well what real knowledge do you have and what do you have to back up what you say. Like I said, I'm here to learn I'm all ears. BTW why do I go against what everyone has to say? Maybe because at one time everyone thought the world is flat and someone was not afraid to question it.