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

 


phoenixlpr  (D 3049)

Jul 11, 2006, 8:10 AM
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Was: Recommended specs on reserve exit weight, do you go over max? Can't Post

I had one ride on a GlidePath Crickett 147.

MSW is 160 lbs, I was around 200-220 lbs with gear.
I had a soft, stand up landing.

I was just testing that rig and none told me about the limit of the reserve. It was not fair from the seller.


(This post was edited by slotperfect on Jul 11, 2006, 2:53 PM)


Sky15  (D 14847)

Jul 11, 2006, 8:16 AM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Wow!

I had a friend that probably weighed 190ish with gear that had terminal opening on his 120 reserve, think he did have bit of landing issue if I remember right, but not hurt seriously.


phoenixlpr  (D 3049)

Jul 11, 2006, 8:20 AM
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Re: [Sky15] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

I was prepared for a hard landing, I got a soft one.

I don;t like, but thats the way it is now.


mjosparky  (D 5476)

Jul 11, 2006, 9:07 AM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
MSW is 160 lbs, I was around 200-220 lbs with gear.
I had a soft, stand up landing.

And if you deploy at terminal while tumbling and the canopy blows up how do you think your landing will be? There is an old saying that fits this situation.

“If you are going to be stupid you had better be tough.”

Overloading your last chance at staying alive is stupid. jmo


phoenixlpr  (D 3049)

Jul 11, 2006, 9:12 AM
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
And if you deploy at terminal while tumbling and the canopy blows up how do you think your landing will be? There is an old saying that fits this situation.

“If you are going to be stupid you had better be tough.”

Overloading your last chance at staying alive is stupid. jmo
A canopy does not "know" about the suspended weight on deployment, only the airspeed. So why would it blow up?

I'm aware that I might use it beyond its certification.


mjosparky  (D 5476)

Jul 11, 2006, 9:30 AM
Post #6 of 134 (3484 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
A canopy does not "know" about the suspended weight on deployment, only the airspeed. So why would it blow up?

And where did you learn this interesting "fact"? Why do you think canopies are tested to a given speed and weight? You can blow a canopy up at a lower airspeed if you use enough weight or you can blow it up at a lower weigh if you use enough airspeed.

To produce shock load of 5000 lbs. you can use 325 pounds at 225 mph or 200 pounds at 300 mph. But it takes a combination of both weight and speed.

Before you give advise you should know what you are talking about.
Mad


phoenixlpr  (D 3049)

Jul 11, 2006, 9:38 AM
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Notice: I have not given any advice.

In reply to:
To produce shock load of 5000 lbs. you can use 325 pounds at 225 mph or 200 pounds at 300 mph. But it takes a combination of both weight and speed.
???

Size of a canopy is constant. The air resistance of the canopy is constant on a given size. The system: jumper+gear has a given amount of kinetic energy before opening. So it might take longer time to reach, decelerate to new speed of the system. Applied force on the lines and canopy is depending on the area of the canopy, the factor of air resistance and the deployment speed only.


SethInMI  (A 47765)

Jul 11, 2006, 11:35 AM
Post #8 of 134 (3390 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
???
Applied force on the lines and canopy is depending on the area of the canopy, the factor of air resistance and the deployment speed only.

You are mistaken. I will try to explain giving an extreme example: The drag force at a given speed and canopy size is fixed, but it is may also be very high. To deploy a canopy through the air at a continous terminal speed (behind a large plane for instance) would destroy the canopy as the drag force would be so high it would overstress the lines and fabric.

In a normal deployment, this high drag force is quickly absorbed by slowing the jumper as the canopy deploys. A heavier jumper exposes the canopy lines to larger forces because the canopy cannot decelerate as fast.

Since the drag force at terminal on a canopy is so high, I would think that the time it takes to slow from 120-10mph over a deployment would be almost the same whether the jumper is 100lbs or 200lbs. The difference is the forces on the lines.

Seth

I think I got that right!


phoenixlpr  (D 3049)

Jul 11, 2006, 11:42 AM
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
In a normal deployment, this high drag force is quickly absorbed by slowing the jumper as the canopy deploys. A heavier jumper exposes the canopy lines to larger forces because the canopy cannot decelerate as fast.

You'd rather start drawing. Forces are not larger just takes more time....

Force of deceleration is the air resistance of the canopy.
Air resistance is depending on the speed, surface and resistance quotient only.


(This post was edited by phoenixlpr on Jul 11, 2006, 11:45 AM)


bch7773  (C License)

Jul 11, 2006, 1:51 PM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

if you are so sure that weight doesn't matter to reserve sizes, why don't you ask every single canopy manufacturer about the weight limits.

or ask DZs why they have weight limits on tandems.


phoenixlpr  (D 3049)

Jul 11, 2006, 1:57 PM
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Re: [bch7773] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Deployment speed is the limit for opening.

Flight characteristic is depending on the suspended weight.

Think about basic physics. You may end up with similar conclusion.

IMHO the overloaded reserve blowing up on opening has no base, that's just a myth.


Premier slotperfect  (D 13014)

Jul 11, 2006, 2:55 PM
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Hey gang,

The original poster exercised their privilege of removing the original post. No need for me to know the reason, but since the conversation was so constructive, I clipped all of the replies and put them back in here in G&R with a new subject line.


JerryBaumchen  (D 1543)

Jul 11, 2006, 3:02 PM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Hi phoenixlpr,

About 40 yrs or so ago when I was in Physics it was
F=MA

F= force
M=mass
A=acceleration

A given mass at a certain acceleration equals the forces that will result.

In engineering & physics there is no deceleration, we called it negative acceleration, it is just delta v.

Now, of course, I might be wrong.

Jerry


mjosparky  (D 5476)

Jul 11, 2006, 3:27 PM
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
so apparently many go over the max.

The fact that many do it does not make it smart or legal. People have died deploying a reserve outside of the design envelope.


5. Reserve Sizing

There are several factors to consider when choosing the size of your reserve. The most important factor to consider is the maximum exit weight limit for a particular size. Many jumpers exceed the maximum weight limit for their main canopies. While this may be foolish, it is not illegal. The maximum exit weight for a reserve is a legal limit. In the United States, it is a violation of federal law to jump a reserve if your exit weight exceeds this limit, and other countries may enforce this limit as well. The maximum exit weight is published on the Warning Label sewn to the tail of every PD Reserve, in the PD Series Ram-Air Reserve Owner’s Manual, and in the product information on our web site at www.performancedesigns.com.



mjosparky  (D 5476)

Jul 11, 2006, 3:45 PM
Post #15 of 134 (3285 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Flight characteristic is depending on the suspended weight.

You are right, the suspended weight will affect how a canopy flies.

In reply to:
IMHO the overloaded reserve blowing up on opening has no base, that's just a myth.

Your opinion is wrong. I have been involved in testing for over 20 years and have seen many canopies that were tested beyond their design limits blow up. This can happen by the use of too much weight or by too much speed. Or it can be a combination of the 2 that create a force higher than the canopy was designed to take.

In reply to:
Notice: I have not given any advice.

You are giving advice on what will affect a canopy during deployment and you do not understand the basic physics involved.Unsure


SethInMI  (A 47765)

Jul 11, 2006, 5:13 PM
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Re: [JerryBaumchen] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
In Physics it's
F=MA

F= force
M=mass
A=acceleration

Jerry,

I think phoenix would agree (can't argue with Newton), but he is saying that F is basically constant, so a greater M results in a lower A. (Heavier people on a same size canopy just open more slowly).

I think drag forces at high speeds are so great that the canopy is going to decelerate at about the same speed regardless of the weight below it. Then if A is constant a bigger M will result in a bigger F.

Seth


To put some numbers on my point:
Fd=Cv^2
(Drag Force is proportional to square of the velocity)
This means that for a canopy that can lower 220lb person at 10mph would require a force of 32000lb to move it at 120mph.


kenneth21441  (B License)

Jul 11, 2006, 7:00 PM
Post #17 of 134 (3246 views)
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Exit weight has alot to do with the rated capatity of a parachute.
I first saw this back in 88 when we were test dropping over fifty thousand pounds for the C17 project. With 12 cargo parachutes: one of these parachutes opened two secounds before the other ones and needless to say it had totally blown its gores: (the other parachutes brought load down but harder then normal).

So with this it goes for cargo parachutes as well as personal parachutes that if you exceed the max limits things will go.

Plus added to this it is against the law to exit with a parachute that is overloaded to this point. Thats why they are published. While some compnaines will test there systems at a higher loading does not mean that you can jump them and be legal.

So anytime you are going to purchase a main/ reserve you should know the legal limit and if you fall witin that max exit weight then either go with another size larger or lay off that soda/ pop before the next jump... (Best answer super size on the canopy size then the drink)...


kelpdiver  (B 7)

Jul 11, 2006, 7:18 PM
Post #18 of 134 (3243 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Think about basic physics. You may end up with similar conclusion.

the equation for kinetic energy is of the most basic = .5 mass X velocity squared. Mass is a big part of total energy. (and a overloading jumper weighs more, so V is likely to be higher as well.

Reserves are certified to open within 3 seconds. I'd be surprised if that testing is done at a normal weight. Others here can say with certainty.


mjosparky  (D 5476)

Jul 11, 2006, 8:08 PM
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Re: [kelpdiver] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Under TSO-C23b they tested in 2 categories, standard and low speed. In the standard category they needed to produce a load of 5,000 lbs. In the low seed category they needed to produce a load of 3,000 lbs. The first attachment shows the various combinations of speed and weight that will produce the required loads.

The second attachment shows what is required under TSO-C23d.

In all cases the canopy is tested to a given weight and a given speed at deployment.

phoenixlpr

As I posted before, your opinion is wrong.
Attachments: NAS 804.jpg (94.4 KB)
  AS 8015B.doc (20.0 KB)


JerryBaumchen  (D 1543)

Jul 11, 2006, 8:16 PM
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Re: [kelpdiver] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Hi kelpdiver,

The various versions of the TSO req'ments vary somewhat in detail. But for the most part, the common two tests are what are called 'functional' and 'strength' (OK, some folks will argue with me on what is 'common').

Since I know TSO C23b the best; the functional test was to be performed with a 170 lb dummy and the strength test could vary (more weight & less speed; or less weight & more speed); we did ours with a 400 lb dummy at 200 MPH (BTW, we blew two harnesses apart until I redesigned things; out of necessity).

The later versions of the TSO are very similar; but that is it in a nutshell. For more detail, go to the PIA website and look up Technical Standard 135; this is the standard that the PIA committee developed.

Hope this helps,

Jerry


mjosparky  (D 5476)

Jul 11, 2006, 8:17 PM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Were you in the same geometry class as this blond?
Attachments: Blonde'sgeometrytestanswer.jpg (11.3 KB)


JerryBaumchen  (D 1543)

Jul 11, 2006, 8:20 PM
Post #22 of 134 (3225 views)
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Re: [kelpdiver] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Hi kelpdiver again,

I forgot to mention that in TSO C23b the functional tests have a req'ment to be open within 3 seconds. The strength tests do not have any opening time req'ment.


Sparky,

Will you quit getting ahead of me when I am trying to post?Smile

Jerry


mjosparky  (D 5476)

Jul 11, 2006, 8:25 PM
Post #23 of 134 (3223 views)
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Re: [JerryBaumchen] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Hi kelpdiver again,

I forgot to mention that in TSO C23b the functional tests have a req'ment to be open within 3 seconds. The strength tests do not have any opening time req'ment.


Sparky,

Will you quit getting ahead of me when I am trying to post?Smile

Jerry

Opps! What an old grouch.Tongue


phoenixlpr  (D 3049)

Jul 11, 2006, 10:53 PM
Post #24 of 134 (3200 views)
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Re: [JerryBaumchen] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
About 40 yrs or so ago when I was in Physics it was
F=MA

F= force
M=mass
A=acceleration

Drag (physics)


F=m * a is one side of the equation.

Here is the other side:

F = c * A * v^2

where A is the area of the canopy
V is the speed
c is a coefficient

m * a = c * A * v ^ 2

As you see lager acceleration/deceleration belongs to bigger mass,because forces in this system does not depend on the mass of the system.

c is deppending on the shape, air desity....
A the area of the canopy is constant
V is the deployment speed


(This post was edited by phoenixlpr on Jul 11, 2006, 11:00 PM)


phoenixlpr  (D 3049)

Jul 11, 2006, 10:57 PM
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Were you in the same geometry class as this blond?

Your insult is not a proof or not even an argument.
It could be a sign showing you are incapable to describe the your point using the tools of physics.


(This post was edited by phoenixlpr on Jul 11, 2006, 11:05 PM)


mjosparky  (D 5476)

Jul 12, 2006, 1:00 AM
Post #26 of 134 (1450 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
In reply to:
Were you in the same geometry class as this blond?

Your insult is not a proof or not even an argument.
It could be a sign showing you are incapable to describe the your point using the tools of physics.

That was not meant as an insult but as an observation.

You are right; I do not know the finer points of applied physics. But I do know there are 3 things that affect the forces generated during the deployment of a canopy. They would be load, deployment speed and fill time.

I can not for the life of me understand how you can believe that weight is not a factor in deployment loads. How many test drops have you made using load links to come up with this concept?Crazy

Can you explain why all TSO testing requires that a canopy be tested using a minimum weight and a minimum airspeed if weight is not a factor.

As I posted before your opinion is wrong.


riggermick  (D 17071)

Jul 12, 2006, 1:57 AM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

 
A canopy does not "know" about the suspended weight on deployment, only the airspeed. So why would it blow up?

I'm aware that I might use it beyond its certification.


You haven't been included on many drop test progams have you?

In the "real world" Stuff like this happens all the time. That's how the "industry" works stuff out. What you are currently using is a DIRECT result of the drop testing done within that industry. Basic physics (in the real world) will hold true and theoretical science is still the underlying foundation to what happens during deploment, but in "real world " situations things become a little bit messier. In this realm nothing is going to be "text book" That's how it is, like it or not! Get used to it.



Mick.


980  (D 980)

Jul 12, 2006, 5:53 AM
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Re: [slotperfect] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Hey gang,

The original poster exercised their privilege of removing the original post. No need for me to know the reason, but since the conversation was so constructive, I clipped all of the replies and put them back in here in G&R with a new subject line.

except my reply? what gives?





From slotperfect: Clipping the original content is not an easy process, nor is it perfect. Here is your reply resurrected from the original thread . . .

Quote:
Why would you want to get a reserve that you will load above the manufacturer's recommended maximum?

When you can get a reserve that will fit the same size container that is within the manufacturer's recommended maximum loading?

and by all accounts has better flight characteristics and landings??


(This post was edited by slotperfect on Jul 12, 2006, 8:11 AM)


fcajump  (D 15598)

Jul 12, 2006, 7:02 AM
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
In reply to:
F=MA

F= force
M=mass
A=acceleration

---------------------------------------
F=m * a is one side of the equation.

Here is the other side:

F = c * A * v^2

where A is the area of the canopy
V is the speed
c is a coefficient

m * a = c * A * v ^ 2

As you see lager acceleration/deceleration belongs to bigger mass,because forces in this system does not depend on the mass of the system.

c is deppending on the shape, air desity....
A the area of the canopy is constant
V is the deployment speed

---------------------------------

I will agree with your initial equations, however...

1. c and A will be constantly changing during the deployment
2. v (velocity at deployment) is a function of:
m (mass)
c2 (shape, air density of freefalling body prior to deployment), and
A2 (the freefalling body's area)

Finally, it is common practice in modern science to take the theoretical equations and place them in the lab for validation. As we have both test results and actual experiences that seem to show that (in some combinations) overloaded and/or overspeeded canopes (and harnesses) have/will fail due to excessive stress, it seems that the mathmatical model is itself flawed.

As a heavier jumpers, who is a self-proclaimed chicken-sh!t, I will heed the warnings of the manufacturers and testers who have more practical experience with this stuff than I. (Matter of fact, this is why I retired a reserve...) To me, failure of a reserve system (including harness) because someone wanted to second guess the test results is unacceptable. If you want to be a test jumper or designer, go for it, but understand that is what you are doing when you go outside the placarded limits.

Just my rant.
Jim


phoenixlpr  (D 3049)

Jul 12, 2006, 7:19 AM
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Re: [fcajump] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
1. c and A will be constantly changing during the deployment
In any case, but that is not depending on the mass
In reply to:
2. v (velocity at deployment) is a function of:
m (mass)
We assumed that we don't exceed maximum deployment speed.
In reply to:
c2 (shape, air density of freefalling body prior to deployment), and
A2 (the freefalling body's area)

In reply to:
If you want to be a test jumper or designer, go for it, but understand that is what you are doing when you go outside the placarded limits.
That was not a question.


SethInMI  (A 47765)

Jul 12, 2006, 11:06 AM
Post #31 of 134 (1375 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

[SEE LATER POST FOR BETTER DATA]

I did some more thinking about this, and ran some spread sheet numbers to try and make some sense of it.

In my spreadsheet I assumed a parachute was completely open (a round) and checked to see how fast it would stop with different weights.

I believe what happens is the heavier jumper does cause the parachute to open more slowly, but this subjects the lines and canopy to the high opening drag forces for a longer period of time which is what will cause the failure.

Now a slower opening will change this, as has been pointed out, but the fact remains, a heavier load causes a longer deceleration which subjects the canopy to high drag forces for a longer period of time, which is tougher on the lines and fabric.

Seth


(This post was edited by SethInMI on Jul 12, 2006, 2:03 PM)


phoenixlpr  (D 3049)

Jul 12, 2006, 11:47 AM
Post #32 of 134 (1360 views)
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Where has your data set coming from?

As you see the peak forces are the same.
AFAIK textiles are rate by the peak break force.


Premier billvon  (D 16479)
Moderator
Jul 12, 2006, 12:18 PM
Post #33 of 134 (1343 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

You're using ideal physics; the real world is not ideal.

Here's one effect:

A light test object is dropped at a high speed. The reserve opens. Due to the high speed, elements of the parachute begin to overstress and elongate. Meanwhile, the force on the test object (caused by drag) decelerates it very quickly. Lower speed = less force on the elements of the parachute under load; the parachute does not ultimately fail (although some parts of elongated/saw a lot of stress during the opening.)

A heavy test object is dropped at a high speed. The reserve opens. Due to the high speed, elements of the parachute begin to overstress and elongate. Meanwhile, the force on the test object (caused by drag) decelerates it more slowly, since the mass is higher. Higher speed = more force on the elements of the parachute under load; the parachute fails.


SethInMI  (A 47765)

Jul 12, 2006, 12:29 PM
Post #34 of 134 (1338 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

I got the data from my own calculations. (Warning: Math!)

As you know, Fd=Cv^2 (where C is area and drag coefficent and some other things). If a parachute is allowing a 220 lb person to descend at a constant rate of 10mph then 220 = C (10mph)^2. So C = 49 in SI units. Knowing C means that one can solve Fd=Cv^2 for any velocity (assuming the parachute has the same shape), and find the drag force for a given velocity (say 120mph).

Then I used A = Fd/M for the 220lb weight and got deceleration A, which slows the parachute to a new velocity, which creates a lower drag force, which creates a smaller A, etc. (Someone better at math please provide a formula, I just iterated a spreadsheet).

Now it takes time for the parachute to deploy, so C is changing during deployment, but I think the basic math is ok. My calculated deployment took less that 0.1 sec, and travelled a distance of about 8 feet, but that is fully open at terminal. If my math (excluding assumptions) is off, let me know.

Seth


SethInMI  (A 47765)

Jul 12, 2006, 2:01 PM
Post #35 of 134 (1321 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

OK. I feel much better about this spreadsheet. I even attached a picture. The distortion I got was from assuming a constant C in Fd=Cv^2. I knew C varied as the parachute opened, but I did not think how dramatically that would affect the opening. This spreadsheet contains a crude means for ramping up C over time to simulate the opening.

The difference is dramatic. There are two main mechanisms "fighting" eachother. As the parachute opens Drag increases, but that causes Speed to decrease which decreases Drag.

Now it is easy to see that increased weight causes increased peak forces on the canopy lines. If you download the sheet, change the values in:
J23 for exit weight
L23 for opening speed
Q20 for opening time in seconds

Watching the results on the chart, it is very evident that larger masses cause higher peak loads. Try a very large mass like 20000 lbs. The force just keeps ramping up, enough to blowup the chute like that cargo parachute that opened early.

Seth


(This post was edited by SethInMI on Jul 12, 2006, 2:25 PM)
Attachments: OpenForce1.JPG (30.7 KB)
  Parachute Drag3.xls (67.5 KB)


mjosparky  (D 5476)

Jul 12, 2006, 3:52 PM
Post #36 of 134 (1304 views)
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Re: [riggermick] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
A canopy does not "know" about the suspended weight on deployment, only the airspeed. So why would it blow up?

I'm aware that I might use it beyond its certification.



You haven't been included on many drop test progams have you?

In the "real world" Stuff like this happens all the time. That's how the "industry" works stuff out. What you are currently using is a DIRECT result of the drop testing done within that industry. Basic physics (in the real world) will hold true and theoretical science is still the underlying foundation to what happens during deploment, but in "real world " situations things become a little bit messier. In this realm nothing is going to be "text book" That's how it is, like it or not! Get used to it.



Mick.
Mick,

Looks like a lot of time was wasted. All those tests could have been done with just a couple of 10 pound shot bags.Tongue


SethInMI  (A 47765)

Jul 12, 2006, 5:04 PM
Post #37 of 134 (1290 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

OK!! I feel even better about this spreadsheet.

The only difference between this and previous one is how I ramped up C in Fd=Cv^2. In the previous spreadsheet, I increased C linearly. In this one, C increases at a quadratic rate. Since C is proportional to the area of the canopy, and area proportional to the square of the radius (for a round), I figured the radius of the canopy increases linearly during inflation (or close to it, and this would roughly apply to squares as well), so C increases quadratically.

The interesting thing is with this spreadsheet, the values in the NAB test that Sparky posted make sense. I can plug in the combinations and see peak forces in the 5000 and 3000 lb range for the various tests with a 2 second opening time. This gives me some confidence that I am in the neighborhood of reality with the model that I have come up with.

Now obviously this is just an approximation of the actual forces involved, but it further demonstrates the basic point I want to make: Heavier people cause higher forces on the canopy during opening.

Seth
Attachments: ParachuteDrag4.xls (97.5 KB)


sprtdth  (D 4730)

Jul 12, 2006, 6:05 PM
Post #38 of 134 (1279 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

 
You haven't been included on many drop test progams have you?

In the "real world" Stuff like this happens all the time. That's how the "industry" works stuff out. What you are currently using is a DIRECT result of the drop testing done within that industry. Basic physics (in the real world) will hold true and theoretical science is still the underlying foundation to what happens during deploment, but in "real world " situations things become a little bit messier. In this realm nothing is going to be "text book" That's how it is, like it or not! Get used to it.
__________________________________________________

Sparky, Mick
Obviously these guys have never had to cutaway an "experimental" only to hear (after landing) " But it worked on paper!".


mjosparky  (D 5476)

Jul 13, 2006, 1:05 AM
Post #39 of 134 (1251 views)
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

I just reviewed you last spreadsheet and it seems your model is pretty close. It also seems that you have way to much free time. I am going to lay down my head hurts.Smile

And yes, heavier loads create higher forces.Wink A very basic concept.


phoenixlpr  (D 3049)

Jul 13, 2006, 1:46 AM
Post #40 of 134 (1246 views)
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Your calculations are incorrect opening time is depending on the deployment speed and suspended weight.

In reply to:
Now obviously this is just an approximation of the actual forces involved, but it further demonstrates the basic point I want to make: Heavier people cause higher forces on the canopy during opening.
It shows what you want to see.


riggermick  (D 17071)

Jul 13, 2006, 2:01 AM
Post #41 of 134 (1238 views)
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In reply to:
Your calculations are incorrect opening time is depending on the deployment speed and suspended weight.

In reply to:
Now obviously this is just an approximation of the actual forces involved, but it further demonstrates the basic point I want to make: Heavier people cause higher forces on the canopy during opening.
It shows what you want to see.



Basicly, small parachutes HATE fat people and (for the most part) vise versa. Not aholelota math in that one!!Sly


Mick.


phoenixlpr  (D 3049)

Jul 13, 2006, 2:25 AM
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In reply to:
Basicly, small parachutes HATE fat people and (for the most part) vise versa. Not aholelota math in that one!!Sly
I'm sorry but I don't have love and hate relationship with my reserve canopy. Cool


riggermick  (D 17071)

Jul 13, 2006, 2:32 AM
Post #43 of 134 (1231 views)
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In reply to:
In reply to:
Basicly, small parachutes HATE fat people and (for the most part) vise versa. Not aholelota math in that one!!Sly
I'm sorry but I don't have love and hate relationship with my reserve canopy. Cool



What do you care? Youv'e already hung it up!! OR HAVE YOU?.............?


I'm betting NOT!!!! @ least for a while.Cool


MickLaugh


phoenixlpr  (D 3049)

Jul 13, 2006, 2:46 AM
Post #44 of 134 (1228 views)
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I really don't know what you mean.

I've jumped it, check first post.


SethInMI  (A 47765)

Jul 13, 2006, 5:46 AM
Post #45 of 134 (1209 views)
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In reply to:
Your calculations are incorrect opening time is depending on the deployment speed and suspended weight.

...

It shows what you want to see.

Phoenix:

It is true I don't have a good way to model opening time, and that will affect the calculations. However, if increasing suspended weight makes the parachute open faster, as I think it would, then this would only increase the peak forces on the heavier jumper.

I think you are only seeing what you want to see.


Sparky:

I did take way too much time to build that spreadsheet. I am glad I got something out of it that seemed to make sense, but I wish it didn't take me so long.CrazySmile Stupid Math!


(This post was edited by SethInMI on Jul 13, 2006, 5:46 AM)


phoenixlpr  (D 3049)

Jul 13, 2006, 5:59 AM
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In reply to:
It is true I don't have a good way to model opening time, and that will affect the calculations. However, if increasing suspended weight makes the parachute open faster, as I think it would, then this would only increase the peak forces on the heavier jumper.

Heavier load had longer opening time and high average opening forces, but peak forces were the same in your previous simulation.


bch7773  (C License)

Jul 13, 2006, 6:28 AM
Post #47 of 134 (1199 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

even IF what you are saying is true, that heavier loads cause slower openings....
then a reserve that is supposed to open in 500 ft and save your life might take 1000 ft and you go splat.


phoenixlpr  (D 3049)

Jul 13, 2006, 6:42 AM
Post #48 of 134 (1196 views)
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In reply to:
even IF what you are saying is true, that heavier loads cause slower openings....
then a reserve that is supposed to open in 500 ft and save your life might take 1000 ft and you go splat.

That can be true. I think the blow up is a myth.


SethInMI  (A 47765)

Jul 13, 2006, 7:54 AM
Post #49 of 134 (1180 views)
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Phoenix:

I will try once more to convince you, by trying something that is commonly done in engineering when testing a formula: try the extreme case to see if that makes sense. Here I ran a 15k lb load from 160mph, simulating the cargo deployment blowup that was mentioned earlier. The kink in the load graph is where the chute finishes deploying.

If you deploy a 15k lb skydiver shaped load at 160mph, it would start to accelerate, then slow as the chute opened. The new terminal velocity for such a load would be ~80 mph, which is one reason you would need more than one chute to stop the load. The other reason is the peak load forces for this opening are >50k lbs, even though peak g forces are only about 1 g. At 50k lbs the parachute will blow up.

You can modify the opening time a bit, but the fact remains, higher suspended loads cause higher loading forces on the chute during opening.

Other than getting a trusted parachute designer to personally explain things to you, I don't know what else to say.

Seth
Attachments: 15kOpening.JPG (54.5 KB)


phoenixlpr  (D 3049)

Jul 13, 2006, 8:31 AM
Post #50 of 134 (1173 views)
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

I was not motivated enough to make my own model about the deployment of a canopy, but I have found this scientific publication:

Parks College Parachute Research Group
Outline of the presentation at the 2001 Parachute Industry Association Symposium


It is worth reading.

Quote:
Skydivers have asked us this question all the time: When does a jumper feel the greatest force from his/her risers? Does opening shock occur during the slider-descent phase or during the other two phases of parachute inflation? As mentioned before, the answer depends on the specifics of the parachute design being flown. In particular, it depends on:

1) The size of the pilot chute and whether it is of a collapsible type;
2) The size of the slider;
3) The size of the main parachute;

Other factors may also enter into the picture, but to a lesser extent, such as: the amount of steering line paid out by brake stowing, fabric porosity, suspended weight, etc.

So blowing up because of overload is just an unconfirmed a myth.


(This post was edited by phoenixlpr on Jul 13, 2006, 9:02 AM)


980  (D 980)

Jul 13, 2006, 9:25 AM
Post #51 of 134 (934 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

You are so out of line it’s not even funny anymore.

Willing to argue math with people who obviously understand it better than you, but also willing to contradict empirical evidence gathered over man hundreds and thousands of test jumps just because you do not understand the physics involved.

Here is a quote from the article that you linked:

“Here the reference parachute (labeled "chute 1") is characterized by the parameter set characterizing a Sabre 150 used by a 205lbs jumper falling at 176 ft/sec at deployment time and at 125 ft/sec prior to slider descent (deployment altitude was 4000ft MSL). The figure shows that for most values of the scale factor, smaller parachutes actually open harder than the larger ones, a trend which is opposite to that of instant openings. For example, if all the dimensions of this particular chute are doubled, the resulting 600 ft2 parachute would feature a maximum deceleration that is 40% smaller than the original 150 ft2 canopy (with same jumper!).”

Since they do not scale for suspended weight anywhere, we could say considering the case of a smaller parachute for the same weight jumper should have the same effect as a heavier jumper for the same size parachute.

This will tell us that at a higher wingloading parachutes open harder (both higher peak force and higher stress on parachute). This is a known fact supported by both theory and empirical evidence. Extrapolating this effect will get you to the point where the parachute fails during opening due to overload.

If you still refuse to believe the truth, do us all a favour and provide a reasonable physics theory on why or some empirical evidence to support your statement, rather than being so reactionary on this forum.

Thank you. Maybe next time link an article that supports your statements, not those of the people you are contradicting…


(This post was edited by 980 on Jul 13, 2006, 10:46 AM)


matthewcline  (D 21585)

Jul 13, 2006, 9:26 AM
Post #52 of 134 (933 views)
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Except it has happened.

I have watched this thread with a bit of a chuckle all the way. Mathematically maybe it can't happen. Realistically it does. Parachuutes have failed, "blown up", period. It happened becuase they where used out side the parameters the ywhere certified for.

The one I had fail was inside all parameters but deployment speed. It could not take 220 lbs exit weight at 160mph. The openning did not hurt more than any other brisk openning, the canopy failed before full openning shock could be transfered to my body.

There have been reserve failures, "blow ups", documented in Parachutist and Skydiving magazine.

Based on my personnal experience and the written reports I have seen I do not feel it is a myth.
But like you I could be wrong, I am Human after all.


SethInMI  (A 47765)

Jul 13, 2006, 9:52 AM
Post #53 of 134 (923 views)
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980:
you are correct, I see that article as further validation of the model I created, and what everyone is telling phoenix.

phoenix:
The spreadsheet I created matches well with the data measured in the article you posted. For example, the data in "Figure 2" shows shock loads of 4k-5k Newtons for a 200lb skydiver deploying at 110 mph. Using that data and a 3 sec opening time in my spreadsheet, you get 4.5k Newtons (1000 lbs) for peak loads.

The article just shows that model I am using is valid. And the model shows that increasing suspended weight increases peak shock. There is a reason the model matches the measured data, and that is it is based on basic physics, Fd=Cv^2 and F=ma. Thanks for posting the link!

Seth


phoenixlpr  (D 3049)

Jul 13, 2006, 9:55 AM
Post #54 of 134 (920 views)
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In reply to:
Since they do not scale for suspended weight anywhere, we could say considering the case of a smaller parachute for the same weight jumper should have the same effect as a heavier jumper for the same size parachute.

This will tell us that at a higher wingloading parachutes open harder (both higher peak force and higher stress on parachute). This is a known fact supported by both theory and empirical evidence. Extrapolating this effect will get you to the point where the parachute fails during opening due to overload.

Check peak opening forces on Figure2 (I've attached).
How does it support your point of you?


phoenixlpr  (D 3049)

Jul 13, 2006, 10:00 AM
Post #55 of 134 (917 views)
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Re: [SethInMI] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

I was wrong on the basic equation.

Fd=Cv^2 and F=ma could be terminal speed...

Forces on the risers: m*g - C * v ^ 2

Check figure 2 again: peak forces are higher on Sabre230 than Sabre 120 and opening takes longer on a 120 than on a 230.


(This post was edited by phoenixlpr on Jul 13, 2006, 10:15 AM)


mjosparky  (D 5476)

Jul 13, 2006, 10:42 AM
Post #56 of 134 (908 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Quote:
This will tell us that at a higher wingloading parachutes open harder (both higher peak force and higher stress on parachute). This is a known fact supported by both theory and empirical evidence. Extrapolating this effect will get you to the point where the parachute fails during opening due to overload.

This is a quote from your own reference. Read it and tell me what it says.

And just so you know it is not a myth, I have blown up canopies during drop tests and during live test jumps. Believe me it can happen.

You need to face the fact you are in over your head on this and "Your opinion is wrong".


980  (D 980)

Jul 13, 2006, 10:45 AM
Post #57 of 134 (904 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

sparky

actually that part is not from the article, it is my interpretation of the data that I quoted from the article

the quote from the article is in quote marks

I have changed the formatting to make it clearer.


(This post was edited by 980 on Jul 13, 2006, 10:47 AM)


SethInMI  (A 47765)

Jul 13, 2006, 11:31 AM
Post #58 of 134 (887 views)
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In reply to:
I was wrong on the basic equation.
Fd=Cv^2 and F=ma could be terminal speed...
Forces on the risers: m*g - C * v ^ 2

You are now on the right track. However, the equation you have is the net force on the system, which determines how fast it will decelerate. If there is no deceleration, like under a fully open canopy, then m*g - C*v^2 = 0. But at that point there is still m*g force on the risers.

The correct equation is:
Riser Force = Drag Force on canopy (initially low, spikes up then settles on value = m*g)

Think of it this way, the canopy weighs a lot less than a skydiver, so almost all the force exerted on the canopy as it opens travels down the risers and exerts itself on the suspended load.

To be very precise, in the system equation m*g = Cv^2 , C is the sum of drag on the canopy and the skydiver. Initially all drag is skydiver, but very quickly canopy drag becomes dominant.

Seth

Regarding your comment for Figure 2, with the same suspended weight, a longer opening will have lower peak forces. I am talking about different weights.


(This post was edited by SethInMI on Jul 13, 2006, 11:33 AM)


Scoop

Jul 13, 2006, 11:38 AM
Post #59 of 134 (883 views)
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Sorry if I'm pissing on anyones bonfire, but do you find it funny how forces can supposedly be calculated using equations. I think its all bullshit. You can have an idea but ultimately real world testing is the only thing I trust and believe. No amount of theory will change my mind. People used to say the world was a cube too, after all, they were wrong about that.

If a manufacturer states a figure because they've done some rough calculations based on experience and then tested their canopy to confirm this rating, thats good enough for me and most people I'd say. If you decide to exceed that then you are in the caution territory and anything you do is at your own risk.


phoenixlpr  (D 3049)

Jul 13, 2006, 12:00 PM
Post #60 of 134 (875 views)
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In reply to:
Regarding your comment for Figure 2, with the same suspended weight, a longer opening will have lower peak forces. I am talking about different weights.

Does maximum peak force depending on suspended weight? It does not seems so.


mjosparky  (D 5476)

Jul 13, 2006, 3:39 PM
Post #61 of 134 (855 views)
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In reply to:
In reply to:
Regarding your comment for Figure 2, with the same suspended weight, a longer opening will have lower peak forces. I am talking about different weights.

Does maximum peak force depending on suspended weight? It does not seems so.

The forces generated during deployment are the result of speed at deployment, load (weight) on deployment and fill time of the canopy. The final design of any canopy is a compromise of opening characteristics, performance characteristics, landing characteristics and numerous other factors.

You can design a canopy to open very softly with a load of 1000 pounds but there are trade offs. For one it will pack up the size of a refrigerator and take several hundred feet to open. A small elliptical will open much faster, (harder) then a larger rectangle canopy given the same load. The fill time on the elliptical is shorter so the load slows down faster.

The variables are endless and one action causes a reaction……. That is why testing is done on a new design. What looks good on paper may in fact be for shit in the real world.

In the real world the manufactures of your 145 sq. ft. Cricket should not be used with an exit weight more then 160 pounds. Why do you think they would set this limit?Smile


(This post was edited by mjosparky on Jul 13, 2006, 3:59 PM)


ZigZagMarquis  (D License)

Jul 13, 2006, 3:43 PM
Post #62 of 134 (855 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Its okay... if PxLpr wants to think his reserve couldn't blow-up if overloaded, let him...

... can I get $20 on PxLpr on the Bounce Bingo Board?

Tongue


(This post was edited by ZigZagMarquis on Jul 13, 2006, 3:44 PM)


mjosparky  (D 5476)

Jul 13, 2006, 3:58 PM
Post #63 of 134 (851 views)
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In reply to:
Its okay... if PxLpr wants to think his reserve couldn't blow-up if overloaded, let him...

... can I get $20 on PxLpr on the Bounce Bingo Board?

Tongue

Sorry all the slots were taken 30 posts ago. I guess people know a good thing when they see it.Smile


phoenixlpr  (D 3049)

Jul 13, 2006, 9:03 PM
Post #64 of 134 (822 views)
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In reply to:
In the real world the manufactures of your 145 sq. ft. Cricket should not be used with an exit weight more then 160 pounds. Why do you think they would set this limit?Smile

I do know that overload does not improve flight characteristics.


phoenixlpr  (D 3049)

Jul 13, 2006, 9:06 PM
Post #65 of 134 (820 views)
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In reply to:
In reply to:
Its okay... if PxLpr wants to think his reserve couldn't blow-up if overloaded, let him...

... can I get $20 on PxLpr on the Bounce Bingo Board?

Tongue

Sorry all the slots were taken 30 posts ago. I guess people know a good thing when they see it.Smile

It's so nice to see that you are taking any debate so positive, so personal....


riggermick  (D 17071)

Jul 13, 2006, 9:24 PM
Post #66 of 134 (818 views)
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It's so nice to see that you are taking any debate so positive, so personal....
Oh my god! Get over it! He knows a whole lot more than you. Stop being so pissy !! When you have been "in" for a while you (personally) will understand!!! There are MANY more people who know much more than you can currently understand! Join the line.............It's long!



Mick.


phoenixlpr  (D 3049)

Jul 13, 2006, 9:34 PM
Post #67 of 134 (815 views)
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In reply to:
There are MANY more people who know much more than you can currently understand!

It was not a question.


mjosparky  (D 5476)

Jul 13, 2006, 9:56 PM
Post #68 of 134 (810 views)
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In reply to:
In reply to:
There are MANY more people who know much more than you can currently understand!

It was not a question.

No it was not a question, I think he meant it as statement of fact. But then what do I know?Crazy


In reply to:
I do know that overload does not improve flight characteristics.

I think you are starting to see the light. Smile


Pendragon  (D 104102)

Jul 14, 2006, 7:01 AM
Post #69 of 134 (773 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Let's look at it this way:

It is not necessarily true that the additional force to slow a heavier jumper is directly proportional to the mass difference. Force is a function of acceleration (negative in this case) - so stopping an object with only a small amount of kinetic energy but within a short distance can require the same force as a much larger object brought to a stop more slowly.

If a heavier jumper's deployment consumed more altitude, then the forces would be lessened. Similarly, a lighter jumper having a premature whilst head-down is going to subject their canopy to much greater stresses than someone just overloading it and going through a belly-to-earth delployment, especially since the excess energy is only proportional to additional mass but to the square of the velocity.

Body shapes may dictate that 2 jumpers of different exit weights fall at the same speed at terminal due to drag differences. If this is the case, and the loss of height during deployement was identical, only then would the braking forces have a ratio identical to that of the exit weights.

In reality, I'm not sure whether anyone can say for certain how the canopy will open under a given loading: this is a function of how the canopy pressurises, stages and presents drag to the relative wind, and may not correlate linearly with the speed of the relative wind. This in turn determines how quickly the body is slowed and the forces involved.


mjosparky  (D 5476)

Jul 14, 2006, 10:29 AM
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In reply to:
In reality, I'm not sure whether anyone can say for certain how the canopy will open under a given loading:

There are things called Somats and load links that will give you very exact data on openings. Smile


riggermick  (D 17071)

Jul 14, 2006, 11:05 AM
Post #71 of 134 (753 views)
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In reply to:
In reply to:
In reality, I'm not sure whether anyone can say for certain how the canopy will open under a given loading:

There are things called Somats and load links that will give you very exact data on openings. Smile



Brinnell blocks work well for measuring peak opening force, one on each riser. That's how we did it for TSO testing.



Mick.


mjosparky  (D 5476)

Jul 14, 2006, 11:33 AM
Post #72 of 134 (744 views)
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In reply to:
Brinnell blocks work well for measuring peak opening force, one on each riser. That's how we did it for TSO testing.

The Somats can give you at least 8 data points. You can get peak forces on each riser, deployment speed and duration and the latest interest rate from BofA.Smile


crewkeith  (B 24861)

Jul 14, 2006, 8:46 PM
Post #73 of 134 (717 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

have you had a terminal reserve ride yet?? and what is this stuff about smaller reserves opening slower? i think i still got bruises from my last one under a pd 113 6 months ago. go jump and take 30 second delay then pull silver handle. see what opening force is like. then when you get down.... if you get down push your thumb thru your reserve fabric. it aint that strong. shit happens cheif. even if your math says it cant.
bsbd
keith
p.s. nobody really wants you to bounce but this is kinda a silly argument.


mjosparky  (D 5476)

Jul 14, 2006, 10:33 PM
Post #74 of 134 (709 views)
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In reply to:
have you had a terminal reserve ride yet?

Kettle meet pot. You are 65 pounds over the maximum recommended weight for an expert canopy pilot on your PD-113.Smile


(This post was edited by mjosparky on Jul 15, 2006, 12:56 AM)


phoenixlpr  (D 3049)

Jul 15, 2006, 6:17 AM
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In reply to:
have you had a terminal reserve ride yet??
Yes. I had.


RMURRAY

Jul 15, 2006, 6:53 AM
Post #76 of 134 (875 views)
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In reply to:
I had one ride on a GlidePath Crickett 147.

MSW is 160 lbs, I was around 200-220 lbs with gear.
I had a soft, stand up landing.

I was just testing that rig and none told me about the limit of the reserve. It was not fair from the seller.

I sell a lot of gear for friends. When I sell a reserve I always ask experience level and exit weight. Sometimes, I will not sell the reserve to a interested buyer. For example a Raven 135-M is an OK reserve but only for someone with an exit weight of up to 150 lbs OR unless they have landed one heavily loaded (know what they are doing). I had a -M for many years and it was overloaded too much. Never had to put a jump on it but finally moved on to a PDr, they are bullet proof and handle being overloaded well - like the other modern reserves.

rm


phoenixlpr  (D 3049)

Jul 15, 2006, 12:07 PM
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In reply to:
I sell a lot of gear for friends. When I sell a reserve I always ask experience level and exit weight. Sometimes, I will not sell the reserve to a interested buyer. For example a Raven 135-M is an OK reserve but only for someone with an exit weight of up to 150 lbs OR unless they have landed one heavily loaded (know what they are doing).

I had a different case. I demod a gear before buying and the case ended that I had to buy that rig. The seller was telling anything about what reserve was there. Most of the people choose their gear, some are chosen by a gear.

I'm planing to use it until 2011 or as long as its airworthy.


(This post was edited by phoenixlpr on Jul 15, 2006, 12:08 PM)


mjosparky  (D 5476)

Jul 15, 2006, 3:36 PM
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In reply to:
The seller was telling anything about what reserve was there.

Did you ask or even read the packing data card?Smile


phoenixlpr  (D 3049)

Jul 15, 2006, 10:04 PM
Post #79 of 134 (844 views)
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Re: [mjosparky] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

We don't have packing data card, we have a gear book. A small logbook for the canopies with other info like container, AAD in case of reserve.
The gear was in good shape and reserve pack was valid. Gear books remain ed in a 3rd party who was a kindda mentor of mine in that time. I trusted them and that was a mistake.


mjosparky  (D 5476)

Jul 15, 2006, 11:06 PM
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
We don't have packing data card, we have a gear book. A small logbook for the canopies with other info like container, AAD in case of reserve.
The gear was in good shape and reserve pack was valid. Gear books remain ed in a 3rd party who was a kindda mentor of mine in that time. I trusted them and that was a mistake.

Just to be sure I understand. In your country they use a type of logbook something like we use a "packing data card" for reserve canopies. Does this logbook stay with the reserve canopy if the rig is split up? Is there a second logbook for the harness/container?

It sounds like you are saying that this “logbook” stays with someone other then the owner of the rig. Is this right?

In the US we have a problem with packing data cards. There is only one with a complete rig and if the rig is split up the card goes with the reserve canopy. I think there should be a mandatory second card for the H/C so a rigger working on it has a history available.


strop45  (D 957)

Jul 16, 2006, 12:46 AM
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Re: [mjosparky] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Humm!. I don't know much about skydiving, but do understand the basic laws of physic at least as well as most of the posters in this discussion.

My take is that both sides are partly correct.

Weight affects terminal velocity For the same drag, a heavier object falls faster. (if you don't believe this, try wearing a weight belt).

Opening the canopy increases the drag and therefore the velocity decreases. During de-acceleration the tension in the lines and canopy fabric is only dependant on the velocity, however with higher weight the time taken to de-accelerate is increased and therefore the stress is present for more time.

The longer the force is present the more likely that the lines/fabric will reach breaking point and fail.

Conclusion, if you exceed the design/certification limits you run the real risk that the canopy will fail.


(This post was edited by strop45 on Jul 16, 2006, 12:55 AM)


phoenixlpr  (D 3049)

Jul 16, 2006, 2:38 AM
Post #82 of 134 (852 views)
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In reply to:
Just to be sure I understand. In your country they use a type of logbook something like we use a "packing data card" for reserve canopies. Does this logbook stay with the reserve canopy if the rig is split up? Is there a second logbook for the harness/container?
One (small)book per canopy. The H/C is registered in those books.

In reply to:
It sounds like you are saying that this “logbook” stays with someone other then the owner of the rig. Is this right?
It was with a 3rd party util I payed the rig.

In reply to:
In the US we have a problem with packing data cards. There is only one with a complete rig and if the rig is split up the card goes with the reserve canopy. I think there should be a mandatory second card for the H/C so a rigger working on it has a history available.
AFAK In Finland the repair logs seems to be in the book of the reserve, but I'm not a rigger.


mjosparky  (D 5476)

Jul 16, 2006, 11:50 AM
Post #83 of 134 (829 views)
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In reply to:
During de-acceleration the tension in the lines and canopy fabric is only dependant on the velocity,

And the velocity is dependant on the weight. Lower weight, lower velocity.

In reply to:
The longer the force is present the more likely that the lines/fabric will reach breaking point and fail.

Fill time of a canopy plays a role in this. The shorter the fill time is the faster peak loads are reached. It is this sudden onset of peak load that is more likely to damage the canopy. Canopies with a longer fill time can take the same loads without damage because it comes on slower.

Conversely when the peak forces are stretched over a longer period of time the jumper can be affect more. A human can take more g’s in a spike than he/she can over an extended period.

I hope this makes senseSmile


mjosparky  (D 5476)

Jul 16, 2006, 11:53 AM
Post #84 of 134 (828 views)
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

If the H/C and the reserve get split up, the logbook goes with the canopy, correct? How do you keep track of the history of the H/C?

Open to response from anyone who's country has a way to handle this problem.Smile


strop45  (D 957)

Jul 16, 2006, 1:39 PM
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Re: [mjosparky] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Fill time of a canopy plays a role in this. The shorter the fill time is the faster peak loads are reached. It is this sudden onset of peak load that is more likely to damage the canopy. Canopies with a longer fill time can take the same loads without damage because it comes on slower.

Conversely when the peak forces are stretched over a longer period of time the jumper can be affect more. A human can take more g’s in a spike than he/she can over an extended period.

I hope this makes sense

Thanks for your reply. Smile Makes good sense. Fill time is obviously a very important factor in determining the load on the lines and fabric (and the jumper). I guess that this is why terminal reserve openings are generally less fun than main canopy openings and hence this thread.

I also think that your comments about ability of jumpers to take g's also applies to some extent to canopies/lines.

Imagine two jumpers of different weights and body shapes such that they both had the same fallrate. For a given canopy both would cause the same peak tension loading in the lines/fabric, however the heavier jumper would cause it to be present for longer, hence more total load and higher risk of failure.

Looking at it another way, the kinetic energy in a moving object is proportional to its mass, i.e. for a heavier jumper you are asking the canopy to absorb more energy. The manufacturer has rated the canopy to only absorb a certain amount of energy without failure, if you put more load on it than this, it may fail.


phoenixlpr  (D 3049)

Jul 16, 2006, 2:36 PM
Post #86 of 134 (815 views)
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Re: [mjosparky] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
And the velocity is depending on the weight. Lower weight, lower velocity.
Impulse and kinetic energy is depending on speed and weight. Velocity is not depending on weight.


mjosparky  (D 5476)

Jul 16, 2006, 2:59 PM
Post #87 of 134 (811 views)
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In reply to:
In reply to:
And the velocity is depending on the weight. Lower weight, lower velocity.
Impulse and kinetic energy is depending on speed and weight. Velocity is not depending on weight.

I may be using the wrong word, but I will guarantee you that if you strap on 40 lbs. of lead you with be falling faster than without it. (all other things being equal) How fast you go in freefall depends on surface area to mass or weight. That is why FF’s fall faster than RW flyers.

I am done with this.Crazy


Ron

Jul 16, 2006, 7:28 PM
Post #88 of 134 (792 views)
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In reply to:
IMHO the overloaded reserve blowing up on opening has no base, that's just a myth.

Here is an example of a reserve blowing up.

Quote:
http://www.dropzone.com/...post=1121963#1121963
After the opening shock, I looked up to see my bright, white reserve, and to my horror, see several cells blown out.

Why ignore people with real world experience?


(This post was edited by Ron on Jul 16, 2006, 7:31 PM)


crewkeith  (B 24861)

Jul 17, 2006, 8:59 AM
Post #89 of 134 (756 views)
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Re: [mjosparky] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

yeah but still under max weight

.


phoenixlpr  (D 3049)

Jul 17, 2006, 9:56 AM
Post #90 of 134 (745 views)
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In reply to:
Why ignore people with real world experience?

Opening from higher speed than certified was not a question.


Ron

Jul 17, 2006, 10:16 AM
Post #91 of 134 (744 views)
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In reply to:
Opening from higher speed than certified was not a question.

Neither should be weight, but you debate that?

See how your arguments make no sense? You claim that only one (speed) is important, not the other (weight). There is a reason why the people who make these things have both a speed and weight listed.

I still can't understand how you think you know more than the makers of the canopies, and the people who test themCrazy

Do you really think you know more than the people who make and test these things?


phoenixlpr  (D 3049)

Jul 17, 2006, 10:21 AM
Post #92 of 134 (740 views)
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Have you read the thread or just the last post? Crazy


Ron

Jul 17, 2006, 10:29 AM
Post #93 of 134 (736 views)
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In reply to:
Have you read the thread or just the last post?

The whole thread.

You debate guys like Sparky who have more test jumps than most people have jumps. I'd bet that Sparks there has more jumps on experimental equipment than you have total jumps.

You are clearly not an idiot. You have alot of book smarts. Sparky has the actual experience of dealing with these things.

I wonder what makes you think you know more than the makers and testers of the equipmentCrazy


(This post was edited by Ron on Jul 17, 2006, 10:36 AM)


phoenixlpr  (D 3049)

Jul 17, 2006, 10:41 AM
Post #94 of 134 (732 views)
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In reply to:
Ever notice that EVERYONE has disagreed with you? But you still claim to know better than ALL of them?
How dare you ask questions if EVERYONE could be disagreed with you?

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


Ron

Jul 17, 2006, 11:18 AM
Post #95 of 134 (723 views)
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In reply to:
I have my opinion as long as someone can prove me that my point is wrong.

I wonder what makes you think you know more than the makers and testers of the equipmentCrazy


phoenixlpr  (D 3049)

Jul 17, 2006, 11:34 AM
Post #96 of 134 (721 views)
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In reply to:
I wonder what makes you think you know more than the makers and testers of the equipmentCrazy

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?Crazy


RogerRamjet  (D License)

Jul 17, 2006, 12:03 PM
Post #97 of 134 (713 views)
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In reply to:
In reply to:
I wonder what makes you think you know more than the makers and testers of the equipmentCrazy

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?Crazy

Oh well, here goes....

I don't know how current drop testing for TSO is done, but here is what I witnessed at Z-Hills in the late '70s. Strong was going for a TSO on a reserve. They did several drops at maximum allowed velocity for that canopy (I don't recall the velocity, too many years ago) and tested the reserve to failure. You know how? By adding 25lbs of weight to the dummy after each drop until the reserve blew up.

Think whatever you like, but velocity AND weight count....


phoenixlpr  (D 3049)

Jul 17, 2006, 12:22 PM
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Oh well, here goes....

I don't know how current drop testing for TSO is done, but here is what I witnessed at Z-Hills in the late '70s. Strong was going for a TSO on a reserve. They did several drops at maximum allowed velocity for that canopy (I don't recall the velocity, too many years ago) and tested the reserve to failure. You know how? By adding 25lbs of weight to the dummy after each drop until the reserve blew up.

Think whatever you like, but velocity AND weight count....

I'm not a test dummy. How is a drop test executed?


RogerRamjet  (D License)

Jul 17, 2006, 12:37 PM
Post #99 of 134 (702 views)
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In reply to:
In reply to:
Oh well, here goes....

I don't know how current drop testing for TSO is done, but here is what I witnessed at Z-Hills in the late '70s. Strong was going for a TSO on a reserve. They did several drops at maximum allowed velocity for that canopy (I don't recall the velocity, too many years ago) and tested the reserve to failure. You know how? By adding 25lbs of weight to the dummy after each drop until the reserve blew up.

Think whatever you like, but velocity AND weight count....

I'm not a test dummy. How is a drop test executed?

At that time, we had a Cessna 196 (Cessna 195 with a 450hp engine) that was used. A drop dummy that could have weight added internally, and a rail system that allowed pushing the dummy out of the aircraft. The aircraft made a constant speed pass at 500ft agl and the dummy was manually pushed out. The reserve had to inflate without failure up to the speed AND weight being sought for the TSO. Strong also chose to continue adding weight until the reserve actually failed (or was required to, I do not know what the rules were/are). At any rate, every reserve I saw tested that summer eventually failed when enough weight was added. You can decide what that means for yourself. I think it means that if you exceed the specified exit weight by enough, you risk blowing up your canopy. Surely the canopies are over rated to some extent to allow for variations in materials and such, but just how far do you want to push it?


(This post was edited by RogerRamjet on Jul 17, 2006, 2:33 PM)


labrys  (D 29848)

Jul 17, 2006, 1:26 PM
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Quote:
Imagine two jumpers of different weights and body shapes such that they both had the same fallrate. For a given canopy both would cause the same peak tension loading in the lines/fabric, however the heavier jumper would cause it to be present for longer, hence more total load and higher risk of failure.

If peak force being present for longer periods of time increases the risk of failure wouldn't that also mean that the reserve could only be used x number of times? I know that any canopy will wear out with time and use, but I'm trying to get a feel for how this particular argument works. My approach might be too simple, but here goes:

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

If twice the max weight causes or significantly increases the risk of blowing up the canopy, then wouldn't opening at just the max weight 2 times result in the same risk? I'm assume the canopy also doesn't "heal" from the damage induced during a normal opening at max weight.

Even if the time under load is not linear, what is the difference between max weight and twice max weight, 10 times longer, 100 times longer?

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

This is not intended as a challenge to the fact that the canopy has a higher risk of failure at higher suspended weights, it's just a question about this particular example.


phoenixlpr  (D 3049)

Jul 17, 2006, 1:47 PM
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In reply to:
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.

In reply to:
Are reserves also rated for how many terminal openings they can sustain?
AFAK some reserves have limitation of maximum number of deployment.


labrys  (D 29848)

Jul 17, 2006, 2:33 PM
Post #102 of 134 (1204 views)
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Quote:
You have a really interesting definition of peak force.

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


strop45  (D 957)

Jul 17, 2006, 2:57 PM
Post #103 of 134 (1197 views)
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Re: [phoenixlpr] Was: Recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.


Ron

Jul 17, 2006, 3:10 PM
Post #104 of 134 (1194 views)
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In reply to:
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?


JerryBaumchen  (D 1543)

Jul 17, 2006, 3:27 PM
Post #105 of 134 (1191 views)
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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.

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  (D 1014)

Jul 17, 2006, 9:09 PM
Post #106 of 134 (1177 views)
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Re: [JerryBaumchen] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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  (D 3049)

Jul 17, 2006, 10:37 PM
Post #107 of 134 (1169 views)
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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.

In reply to:
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.

In reply to:
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  (D License)

Jul 18, 2006, 5:07 AM
Post #108 of 134 (1156 views)
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Quote:
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...


riggermick  (D 17071)

Jul 19, 2006, 1:42 AM
Post #109 of 134 (1119 views)
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In reply to:
In reply to:
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.

In reply to:
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.

In reply to:
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  (D 5476)

Jul 24, 2006, 8:45 AM
Post #110 of 134 (1071 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
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?


LongWayToFall  (A 52639)

Jul 30, 2006, 5:32 PM
Post #111 of 134 (1014 views)
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Re: [phoenixlpr] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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  (D 5476)

Jul 30, 2006, 5:51 PM
Post #112 of 134 (1011 views)
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Re: [LongWayToFall] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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


LongWayToFall  (A 52639)

Jul 30, 2006, 7:55 PM
Post #113 of 134 (1002 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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  (D 5476)

Jul 30, 2006, 11:18 PM
Post #114 of 134 (986 views)
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Re: [LongWayToFall] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.

In reply to:
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.


imstu  (C License)

Jul 31, 2006, 8:00 PM
Post #115 of 134 (943 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.----------------
This brings up a point that is close to home for me... I have been fighting a hard opening problem for a while now. I was jumping Sabre 1 190s (2 different canopies/rigs) and kept getting hard openings. It got so bad that I became afraid to throw my PC because I didn't know how bad it was going to hurt each time.Frown I tried working with different packers to help my openings but most of them were still painful. The answer I got most often was "Of course it hurts...you're jumping a Sabre". Not much help. I started jumping Stilettos. First a 170 them a 150. I noticed the 170 seemed to fly funny in brakes and didn't have much flare. (I later found out the outer lines were shrunk 8.5 inches). The 150 was VERY shaky when in brakes. It would seem to try to turn one way then the other until I released the brakes. My openings were inconsistant. Most were still quite firm though. Not too long after starting on the 150 I had a spinning opening that I should have cut, but didn't because I had opened very high (4500'). I spun so hard that my shoes got tight and painful and my vision started to come in from the sides (tunnel vision you get shortly before blackout). I managed to release my brakes and pull them which slowed the dive then kick like hell to get out of the twists. Got to the ground (and cleaned out my underwear) then repacked SLOWLY AND CAREFULLY. Much to my surprise, the next opening didn't spin at all. Instead, it opened so hard I tore up the muscles in my neck and upper back so bad I couldn't jump for 2 months. I took this canopy to my rigger and asked him why it was trying to kill me. We measured the outside lines and they were shrunk 7 3/4 inches. I am currently switching between one of my Sabre 1 190's and a new Stiletto 170. Depends on where I am jumping and how recently I've jumped. Mostly I jump the 170. Where I was headed with all this is; I am using zero-p pilot chutes and I am wondering if they may be contributing to my hard openings? If anyone has any other thoughts I am VERY willing to listen to them. I have been very careful with my body position/speed before I throw and I propack. Any help would be GREATLY appreciated! Thank you for your time.
Stuart
Tucson, Az


bob.dino  (E 2185)

Jul 31, 2006, 9:53 PM
Post #116 of 134 (928 views)
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Re: [imstu] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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  (D 5476)

Jul 31, 2006, 10:21 PM
Post #117 of 134 (924 views)
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Re: [imstu] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.


imstu  (C License)

Jul 31, 2006, 11:16 PM
Post #118 of 134 (912 views)
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Re: [bob.dino] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Jumping canopies that are seriously out of trim can result in funky openings.
In reply to:

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.
Quote:
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. Tongue 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


imstu  (C License)

Jul 31, 2006, 11:41 PM
Post #119 of 134 (907 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Quote:
With out knowing more about you (fill in your profile) I would not attempt to offer any advice.
In reply to:
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  (D 3822)

Aug 1, 2006, 7:57 PM
Post #120 of 134 (854 views)
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Re: [imstu] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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......


AceJack

Aug 2, 2006, 12:50 AM
Post #121 of 134 (837 views)
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Re: [br0k3n] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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  (D 5476)

Aug 2, 2006, 4:16 AM
Post #122 of 134 (826 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.Smile


980  (D 980)

Aug 2, 2006, 6:00 AM
Post #123 of 134 (822 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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

way to go on an awesome first post! Crazy

Quote:
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

Quote:
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?

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

wrong

Quote:
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

Quote:
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


(This post was edited by 980 on Aug 2, 2006, 6:01 AM)


Premier billvon  (D 16479)
Moderator
Aug 2, 2006, 10:04 AM
Post #124 of 134 (804 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

>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

Aug 4, 2006, 3:24 AM
Post #125 of 134 (762 views)
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Re: [billvon] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

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.


mjosparky  (D 5476)

Aug 4, 2006, 4:34 AM
Post #126 of 134 (435 views)
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In reply to:
You still have not provided any explanation to why I'm wrong.

I gave you several reasons you were wrong but it seems you choose to ignore them.

In reply to:
Are the smaller canopy built weaker than the larger ones?

One of the factors would be the fill time; this will make the peak force greater on a smaller canopy.

A canopy deployment does not consist of just a single factor. It is a dynamic event and involves many actions happening very quickly. Changing one will affect the outcome of the others. Don’t try to over simplify it. It must be analyzed in its entirety.


imstu  (C License)

Aug 4, 2006, 8:35 AM
Post #127 of 134 (424 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Quote:
A canopy deployment does not consist of just a single factor. It is a dynamic event and involves many actions happening very quickly. Changing one will affect the outcome of the others. Don’t try to over simplify it. It must be analyzed in its entirety.
This is exactly what I would like to learn. Where can I find information on all the events involved in deployment? I would like to have a much better understanding of the events and their cause/effect relationship. I know there are MANY variables involved and finding out about them has proven difficult so far. Is there any resources out there such as books, websites, etc.? Thank you for your help.
Stuart.


riggermick  (D 17071)

Aug 4, 2006, 10:03 AM
Post #128 of 134 (416 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

 Like I said, I'm here to learn I'm all ears.






Doesn't sound like it.




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.






Or maybe several hundred years of collective experience in a sport/ industry that you have almost zero in, provides "them" with a greater insight. Oh what am I saying??? of course YOU are right because you are of above normal intelligence, like MOST of the people you are argueing with.

(sigh) Here we go again kids.



Mick.



BTW: Fill out your profile, it adds (some) credibility to your statements, no one likes to talk with people who don't have the guts to identify themselves.


mjosparky  (D 5476)

Aug 4, 2006, 10:42 AM
Post #129 of 134 (408 views)
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In reply to:
Where can I find information on all the events involved in deployment?

A good place to start is Pointer's Parachute Manual, Vol. I & II.


imstu  (C License)

Aug 4, 2006, 11:00 AM
Post #130 of 134 (404 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Quote:
A good place to start is Pointer's Parachute Manual, Vol. I & II.
Thank you Sparky! I'll try to find these.
Stuart


mjosparky  (D 5476)

Aug 4, 2006, 1:51 PM
Post #131 of 134 (388 views)
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Re: [imstu] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Quote:
A good place to start is Pointer's Parachute Manual, Vol. I & II.
Thank you Sparky! I'll try to find these.
Stuart

Try Para Gear.

http://www.paragear.com/default.asp


AceJack

Aug 4, 2006, 11:23 PM
Post #132 of 134 (365 views)
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Re: [mjosparky] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

Thanks sparkey thats the answer that I'm looking for. Without that bit of insight I could not for the life of me figure out why a smaller parachute would blow up. It seems that the quicker fill time coupled with the fact that it takes longer for a heavier object to decelerate would cause the canopy to open at higher airspeed and overstress the canopy.
I do realize that there are many variables affecting the opening sequence and that I'm oversimplifying things. I will however get a copy of the book you recommended as I find this subject fascinating.

I apologize if I seem to come across as a smartass and a know it all. This was not my intention. Thats why I want to stress again that I am a newbie. I do not proclaim to be right or wrong on any subject. I am merely presenting the information I gathered from reading this forum and questioning it to further my understanding. Some of my comments are directed only to those who want to discredit me without giving any real information. To the rest of you, thank you, you've been extremely helpful.


riggermick  (D 17071)

Aug 4, 2006, 11:51 PM
Post #133 of 134 (361 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
Thanks sparkey thats the answer that I'm looking for. Without that bit of insight I could not for the life of me figure out why a smaller parachute would blow up. It seems that the quicker fill time coupled with the fact that it takes longer for a heavier object to decelerate would cause the canopy to open at higher airspeed and overstress the canopy.
I do realize that there are many variables affecting the opening sequence and that I'm oversimplifying things. I will however get a copy of the book you recommended as I find this subject fascinating.

I apologize if I seem to come across as a smartass and a know it all. This was not my intention. Thats why I want to stress again that I am a newbie. I do not proclaim to be right or wrong on any subject. I am merely presenting the information I gathered from reading this forum and questioning it to further my understanding. Some of my comments are directed only to those who want to discredit me without giving any real information. To the rest of you, thank you, you've been extremely helpful.



Ahhhh grasshopper, now that you have taken the pebble from my (sparkeys) hand the real learning can begin!!Sly. BTW it is always a good idea to question CW, just be cautious of how you approach it. I like the fact that you are THINKING, ultimatly it leads to awareness. Look into becoming a rigger , just being around the field will amaze and astound you and will ultimatly fill in all the gaps that you currently suffer from. It's fun too!! Who knows you may become the next Dominia Jalbert!! Who you ask? look him up in poynters and other publications. He is considered by some to be the father of the ram air parachute. Ya never know until you try.

Mick.
PS: hook a brother up and fill out your profileSmile


mjosparky  (D 5476)

Aug 5, 2006, 4:51 PM
Post #134 of 134 (344 views)
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Re: [AceJack] recommended specs on reserve exit weight, do you go over max? [In reply to] Can't Post

In reply to:
I am merely presenting the information I gathered from reading this forum and questioning it to further my understanding.

I hate to say it but a great deal of the information you will gather on this forum will have little or no basis in fact. Skydivers tend to take thinks like excerpts out a causal conversation and turn them into hard and fast “facts”. “My buddy says his rigger said this so”, next thing you know someone thinks he is a parachute designer.

Continue to do your research and really look hard at what people preach as gospel. With just a little knowledge and common sense you will be able to see probable fact from fiction.

If you can find a copy of it, “A short course on Decelerator System Technology” by Helmut G. Heinrich makes for good light reading.

Like Mick said, you want information, give some information. File out your profile.


(This post was edited by mjosparky on Aug 5, 2006, 4:53 PM)



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