Overloading a Reserve, Again.

[azureriders 0]

I know this subject has been covered over and over, but after much searching I have found no thread directly related to my question, so here goes.

From my understanding, most reserves out there fall under the TSO-c23(c) which uses the limits of 254lbs and 150 knots. Before I go further, lets forget about the ability to safely land a smaller reserve, and the manufacture max weight. I know these are very important issues, but not the issue at hand. I am wondering about damage to the reserve by a terminal opening.


If I am 274# out the door on my Smart 220, am I just as likely to blow it up as I would be on a 170 sq ft reserve. Worded another way, if I am willing to accept the risk factor of jumping a 220, then why would I not jump a 170. After all, they are both TSOed the same.

Now before you go blowing a gasket, I have no, I mean NO intention of downsizing my reserve. I am however trying to become a better educated 'voice of reason' amongst the many other anvils that I jump with.

To those of you that have been involved in some reserve testing. Have you tested any beyond the TSO requirement and on to the point of destruction, did the smaller ones, of the same design, fail first. If a design did not survive the TSO test, was it necessary to take all sizes back to the drawing board, or only the smaller ones.

Ok, I think you get the point of my question. In my quest to become educated, I would also like to know more about the testing phase of reserve design. I have read that the test is taken to 1.2 times the amount of the TSO label. Now, is that 1.2 times 254#, 1.2 times 150 knots, both, either?????????

This quest is in response to being tired of hearing "all man, those things are tested way beyond any limits you will put on em" over and over until I am blue in the face.

[ryoder 1,401]

Get a copy of TSO-C23d and read it. Notice the reference to AS8015B. Now get a copy of that and read it. Same works for older TSO's.

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[JerryBaumchen 1,068]

Hi azureriders,

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If I am 274# out the door on my Smart 220, am I just as likely to blow it up as I would be on a 170 sq ft reserve.

First, I have never tested a reserve canopy. I have only used them to test other components.

Two discussions quite some time ago:

#1 with Bill Coe of PD) different reserve sizes are not constructed the same. It depends on where they fail and what reinforcing is req'd.

#2 with John LeBlanc of PD) It is very difficult to get some sizes of reserves to stay together during the Strength testing phase.

On the other hand, Geo. Galloway of Precision once said to me that every jump he made was illegal because his reserve (Raven) was limited to 254 lbs and he was 'slightly' over that weight.

My 2 cents is that you will have a far greater probability of a failure on an over-loaded canopy.

Anyone else?????

Jerry

[azureriders 0]

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My 2 cents is that you will have a far greater probability of a failure on an over-loaded canopy

Jerry,

My 2 cents agrees with yours. However my question remains, is a 170 sq ft reserve TSOed for 254# and overloaded by 20# more likely to fail than a 220 sq ft reserve TSOed for the same 254# and overloaded by the same 20#?

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On the other hand, Geo. Galloway of Precision once said to me that every jump he made was illegal because his reserve (Raven) was limited to 254 lbs and he was 'slightly' over that weight.

Makes me feel a little better about 'slightly' overloading mine.

Thanks for the reply

[azureriders 0]

Quote

Get a copy of TSO-C23d and read it. Notice the reference to AS8015B. Now get a copy of that and read it. Same works for older TSO's.

Good point Ryoder, as I have not read these documents and agree that I should. Can you, or somebody, tell me where the easiest place to download them would be?

[slotperfect 7]

Here you go. Happy reading!

Arrive Safely

John

[riggermick 6]

If I am 274# out the door on my Smart 220, am I just as likely to blow it up as I would be on a 170 sq ft reserve. Worded another way, if I am willing to accept the risk factor of jumping a 220, then why would I not jump a 170. After all, they are both TSOed the same.

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This is where the inverse square law comes in to play. Basicly stated: As the surface area insreases the energy of load is distributed over a greater area effectivly decreasing the overall load on any given point. Make sense? This all assumes that the canopies are equally loaded and constructed the same way dropped at the same air speed.

There is more to it than just that but it is a factor that affects the outcome of heavy drops dramaticly.



To those of you that have been involved in some reserve testing. Have you tested any beyond the TSO requirement and on to the point of destruction, did the smaller ones, of the same design, fail first. If a design did not survive the TSO test, was it necessary to take all sizes back to the drawing board, or only the smaller ones.
_----------------------------------------------------------


There is no requirement in TSO 23D to test every size, just the overall design. However there are rate of decent required in 4.3.7 not to exceed 24 ft/sec with a max of 36 ft/ sec in an unalterd post deployment configuration. so as you can see it is a little more vague than it seems.
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Ok, I think you get the point of my question. In my quest to become educated, I would also like to know more about the testing phase of reserve design. I have read that the test is taken to 1.2 times the amount of the TSO label. Now, is that 1.2 times 254#, 1.2 times 150 knots, both, either?????????
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Good luck in your quest, The FAR's and the TSO testing documents can be ambigious in places and therefore subject to different interpretations.

Mick.

[azureriders 0]

Quote

This is where the inverse square law comes in to play. Basicly stated: As the surface area insreases the energy of load is distributed over a greater area effectivly decreasing the overall load on any given point. Make sense?

Mick,

Yes, that makes perfect sense to me and is almost word for word of how I would have described it. I do understand how the inverse square affects scalling of a loaded object. I own a construction company and have dealt with such several times. I just wanted to make sure there was not something else I was missing.

I recieved an IM the mentioned that the 'fill' time of a smaller reserve is much quicker than a larger reserve, and that 'fill' time has a lot to do with the failer of a canopy. Makes sense to me, although I had never thought about it before.

So, the educated census seems to be that a smaller reserve is more likely to fail than a larger reserve when they are both loaded at the same weight and deployed at the same fall rate. Glad to know my opinion was right along with the educated guys.

Thanks alot,

Any more educated input??

[riggermick 6]

Any more educated input??

[billvon 2,435]

>This is where the inverse square law comes in to play. Basicly
>stated: As the surface area insreases the energy of load is
>distributed over a greater area effectivly decreasing the overall
>load on any given point. Make sense?

Hmm, not to me.

The inverse-square law says that strength is inversely proportional to the square of the distance from the source of some radiation/force. It's more applicable to things like radiation than materials strength.

There's also the squared-cubed law, which states that strength goes up as a function of cross-sectional area (i.e. it's size squared) but weight goes up as a function of volume (i.e. it's size cubed.) Which is why ants can't be the size of elephants; their legs wouldn't hold them. But that doesn't seem to apply here either; the weight of a parachute is pretty negligible when compared to the overall system during opening.

So let's consider two 7-cell reserves, one 100 square feet and the other 200 square feet. Assume design is similar, exit weight is similar and opening speeds are similar. Each line sees a similar load; the collection of 40 lines going to the canopy still carries 100% of the load no matter what the canopy size, so each attachement point sees a similar loading. Since the construction of the line attach points, and the configuration nearest the line attachement point is the same in both canopy sizes, they would seem to resist failure near the attachement points equally well. (Unless I'm missing something, which is entirely possible.)

There's one caveat to the above. The final (post deployment) vertical speed of the larger reserve will be slower than the final vertical speed of the smaller reserve - so if opening _times_ are the same, I'd assume forces would be higher on the larger canopy (more deceleration required.) But there's nothing that says opening _times_ have to be the same, and indeed the amount of reefing would have a big effect on maximum loads seen.

However, all the above doesn't speak to what happens between the attachement points; I don't understand what happens there very well. I've seen about a similar number of mains fail near line attachement points as fail from blowouts in the center of a cell; I don't know if reserves are similar in that manner.

[azureriders 0]

Bill,

I always (well, now I should say normally) get a lot out of your post, but I have to say that is the most meaningless post I have ever read from you.

No, seriously what you have said does make since and I have thought as well about the fact that both canopies have the same number of lines and atachment points, therefor sharing the same force per line no matter the size. But I still don't know????????????????

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I don't understand what happens there very well

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the most meaningful part of your post

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[riggermick 6]

Quote

>This is where the inverse square law comes in to play. Basicly
>stated: As the surface area insreases the energy of load is
>distributed over a greater area effectivly decreasing the overall
>load on any given point. Make sense?

Hmm, not to me.

The inverse-square law says that strength is inversely proportional to the square of the distance from the source of some radiation/force. It's more applicable to things like radiation than materials strength.

There's also the squared-cubed law, which states that strength goes up as a function of cross-sectional area (i.e. it's size squared) but weight goes up as a function of volume (i.e. it's size cubed.) Which is why ants can't be the size of elephants; their legs wouldn't hold them. But that doesn't seem to apply here either; the weight of a parachute is pretty negligible when compared to the overall system during opening.

So let's consider two 7-cell reserves, one 100 square feet and the other 200 square feet. Assume design is similar, exit weight is similar and opening speeds are similar. Each line sees a similar load; the collection of 40 lines going to the canopy still carries 100% of the load no matter what the canopy size, so each attachement point sees a similar loading. Since the construction of the line attach points, and the configuration nearest the line attachement point is the same in both canopy sizes, they would seem to resist failure near the attachement points equally well. (Unless I'm missing something, which is entirely possible.)

There's one caveat to the above. The final (post deployment) vertical speed of the larger reserve will be slower than the final vertical speed of the smaller reserve - so if opening _times_ are the same, I'd assume forces would be higher on the larger canopy (more deceleration required.) But there's nothing that says opening _times_ have to be the same, and indeed the amount of reefing would have a big effect on maximum loads seen.

However, all the above doesn't speak to what happens between the attachement points; I don't understand what happens there very well. I've seen about a similar number of mains fail near line attachement points as fail from blowouts in the center of a cell; I don't know if reserves are similar in that manner.

OK, the inverse square law is maybe a bad analogy but it is the only one I could think of at the time. But looking at diagrams of the inverse sq it does shed some lighton how a force is distribited over a larger area for the same load/ speed/ weight.

If more fabric is involved between the load attachment points (as in a bigger canopy) then a greater volume of material will available to absorb/ attenuate more of the shock loading than with a much smaller canopy. In addition to longer lines (more material), the larger cells (or more of them) and their accompaning load tapes will be scaled up accordingly, giving still more material to help absorb the load. This coupled with a longer fill time due to the larger cells, will further degrade the inital forces on the entire platform.

Take, for example a 20 lb load applied to a very very small canopy that causes it to fail during opening, that same 20 lb load applied to a much larger canopy will have little effect due to the attenuation charicteristics of the increased volume of material it has to overcome and its increased size which will increase the fill time dramaticly. It should be pointed out that a parachute doesn't just stop once it has been deployed, it undergoes a series of "slow down intervals". These are most often witnessed by the inflation (spreading) of the bottom skin which slows the load and brings it to a near vertical position, followed by the cell inflation which causes the wing to pressurize and start to take flight in a close to horizontal fashion. However the closer the intervals are together the quicker the opening will be.

When ram air canopies are scaled up it is not a linier process, there are many dynamics that are changed due to the scale up process. Cell size, performance, material considerations and angles all have to be re-calculated in order to produce similar results. All of this has a direct bearing on the loads felt and how they are distributed.

I'm not a canopy engineer (I'm a H/C engineer) but I've been around a few like Gary Douris and Ernie Villaneuva of Free Flight (Amigo reserves, Preserve reserves, BRS etc) and this what I personaly gleaned from them. Jerry B, you're a mechanical engineer, if you're listening (looking?) what is your take on it? Am I right or have I completly missed the mark?

The way I see it is; The more material and distance between the load points, the greater the attenuation properties of the article in question. Am I thinking correctly?


Bill, Jerry, your thoughts on the matter would be greatly appreciated.

Good discussion!!

Mick.