C23d average peak force values?

[dpreguy 14]

Derek,
Finally. A discussion of this topic.

[Hooknswoop 19]

From AC-105-2D;

"(3) For a single-harness parachute system, the strength of the harness must always be equal to or greater than the maximum force generated by the canopy during certification tests. The rigger who assembles the system should record these limits in a place accessible to the user when he or she dons the assembly. For tandem systems, there may be additional limits for each harness. Some manufacturers may also specify minimum weights or speeds for safe operation.

(a) In the case where the harness is certified under the TSO-C23b “Standard” category, and the canopy is certified under TSO-C23b and TSO-C23d, the system is limited to the performance limitations of the canopy and may be determined by comparing the placarded force generated on the canopy to the 5,000-pound force capability of the harness. If the canopy is placarded at or above the 5,000-pound level, then the system is considered “unlimited.”

(b) In the case where the harness is certified under the TSO-C23b “Low Speed” category, and the canopy is certified under TSO-C23b and TSO-C23d, the system is limited to the placarded performance limitations of the canopy or the structural limitation of the harness (3,000 pounds), whichever is lower."

From AC-105-2E;

"(3) For a single-harness parachute system, the strength of the harness must always be equal to or greater than the maximum force generated by the canopy during certification tests."

"b) In the case where either the harness or canopy of a single-harness system is certified under TSO-C23b and the manufacturer has not specified operating limits, derive the maximum pack opening speed for that component from the strength test table in the National Aerospace Standards Specification (NAS)-804, Parachutes.
1. For the maximum operating weight of the TSO-C23b component, use the highest weight in the table less than or equal to the maximum operating weight of the other component and use the corresponding speed in the table as the maximum pack opening speed of the TSO-C23b component.
2. For the maximum pack opening speed of the TSO-C23b component, use the highest speed in the table less than or equal to the maximum pack opening speed of the other component and use the corresponding weight in the table as the maximum operating weight of the TSO-C23b component."

From PIA's response to AC-105-2D;

"The PIA proposal deliberately omitted the phrase “the strength of the harness must always be equal to or greater than the maximum force generated by the canopy during certification tests.” The intention was to remove an obsolete, unsupported, and ambiguous impediment to combining components approved and still manufactured under different standards. The industry has over 25 years of experience with such cross-TSO combinations, and has experienced exactly zero incidents attributed to different certification standards. That is not to say there have not been equipment failures. There have been. In each case, though, the failures have come from operating the equipment outside the designed and certified operating limits."

It seems to m that if the harness is certified to a maximum of 3,000 lbs force and the reserve parachute can generate more than 3,000 lbs force during deployment without structurally failing, the harness is not certified to accept the forces generated but he reserve during deployment.

The letter also states;

"With respect to 13.c.(3), The requirement for the harness to be stronger than the canopy appears in AC 105-2C, but nowhere else. There is no particular reason why we should prefer canopy failure to harness failure, and inclusion of this phrase results in operation limitations that do not contribute to safety. And it is, in fact, an unworkable and impractical standard."

I think the PIA missed the point here. It isn't that one component will fail before the other, it is that the reserve can generate more force during deployment, without failure, than the harness is certified to handle.

Furthermore in the letter;

"Also, as mentioned above, the C23b 3000-pound and 5000-pound forces generated during testing are minimums, not maximums, and it is possible for a test article to be capable of exceeding those minimums by a considerable amount."

I agree that the harness may be able to handle much more than the 3,000 or 5,000 minimum, that is what the harness was TSO'd to and we do not know how much more the harness can handle. Specifically, we do not know if the harness can handle the maximum force generated by the reserve during deployment.

Obviously this is not currently a safety concern. They are many of these TSO C23b, low speed category harness/containers in use today with reserves that are placarded with over 3,000 lbs average peak force. We are not seeing harness failures during reserve deployments.

The solution is to, once again, rewrite AC-105 in plain language, clarifying compatibility of major components.

One last note, does anyone know why Raven-M reserves omit the average peak force data from their placards?

Derek V

[mark 102]

Hooknswoop

it is that the reserve can generate more force during deployment, without failure, than the harness is certified to handle.

Why is this a problem?

Mark

[Hooknswoop 19]

Quote

Why is this a problem?

Legalities/compatibility of major components. For example, it could be argued that a PD-113R reserve canopy is not compatible with a Mirage harness/container since the reserve produced more than 3,000 lbs force during testing and the harness is only certified up to 3,000 lbs force.

Derek V

[JerryBaumchen 1,047]

Hi Derek,

Quote

the harness is only certified up to 3,000 lbs force

As I said before, the harness is not certified/placarded to any rated loads if certificated under TSO C23(b).

And the other problem IMO is that some of us are rather sure that the weights/speeds in the charts in NAS 804 will not produce the force loads that are indicated in the standard.

And the FAA does not seem to say that it is, unless I read those excerpts from the two AC's incorrectly.

One other little fly in this ointment is that, not too long ago, a court ruled that an AC is not a regulation and is therefore not binding. This came out of a court filing by some drone folks. The FAA seems to disagree & have said that they will appeal the judge's ruling but I have not seen anything on any appeal.

Jerry Baumchen

PS) Mark, I agree completely with you on your comments about the speed issue.

[mark 102]

Hooknswoop

Quote

Why is this a problem?

Legalities/compatibility of major components. For example, it could be argued that a PD-113R reserve canopy is not compatible with a Mirage harness/container since the reserve produced more than 3,000 lbs force during testing and the harness is only certified up to 3,000 lbs force.

Derek V

It could also be argued that by adopting TSO-C2d and C23f, the FAA's current thinking is that it is okay with canopies being certified to higher weights and speeds than the harnesses they are assembled with.

In any case, regardless of TSO, we can never be sure a harness is stronger than the canopy it is assembled with. We can only know that approved components met some minimum performance standards during testing; no tests for ultimate strength are required.

Mark

[Hooknswoop 19]

Quote

In any case, regardless of TSO, we can never be sure a harness is stronger than the canopy it is assembled with.

I don't think that is the issue. It isn't about which component is stronger. The issue is wether or not the harness is TSO'd for the maximum force the reserve can put on the harness.

Under TSO C23d, the reserve is required to be placarded with the average peak force from the drop tests. If that force is higher than the harness was drop tested to, then the harness and reserve are not compatible, or at least that is what the AC is saying.
"(3) For a single-harness parachute system, the strength of the harness must always be equal to or greater than the maximum force generated by the canopy during certification tests."

In other words, if you are lifting a 1,000 lb object with a sling rated to 500 lbs, you have a problem.

Derek V

[mark 102]

Hooknswoop

if you are lifting a 1,000 lb object with a sling rated to 500 lbs, you have a problem.

That is not a good analogy. What we are doing in skydiving is using a 2-link chain to lift an object (one link being the harness and the other link being the canopy). It doesn't matter which link is strongest.

Mark

[Hooknswoop 19]

Quote

That is not a good analogy. What we are doing in skydiving is using a 2-link chain to lift an object (one link being the harness and the other link being the canopy). It doesn't matter which link is strongest.

I agree, it does not matter which is strongest. That is not what I am saying. It does matter if the reserve is producing more force during deployment than the harness can handle.

For example'

The PD-113R produced an average of 3,639 lbs of force during drop tests, without failing. (The 1,000-lb object in my analogy). this is the force the canopy produced. The max weight is 220 lbs and the max speed is 150-mph.

The Mirage was TSO'd under C23b, low speed which required demonstrating that it can handle at least 3,000 lbs of force from the reserve. (the 500-lb sling in my analogy).

The PD-113R produced more force during drops tests than the Mirage harness was demonstrated to handle during drop tests.

This sentance from AC-105-2E is very important;

"(3) For a single-harness parachute system, the strength of the harness must always be equal to or greater than the maximum force generated by the canopy during certification tests."

Let me try it a different way;

If you were going to lift an object that weight 3,639 lbs, how strong would the lifting sling need to be so that it didn't break when you lifted the load?

Derek V

[JohnSherman 1]

Quote

In TSO C23(b), while there is 'supposedly' testing to some load(s), the FAA does not have any req'ment for any placarding on any component, certifying it to any load carrying capability.

Ok, Here is how it works: TSO C23(b) has 2 categories of certification. "Low Speed" tested to 3000 pound shock load and placarded "Limited to use in aircraft under 150 MPH" and "Standard Category" tested to 5000 pound and not placarded because it is "Unlimited" as to weight and speed.

Some might ask. "Why is weight not specified in the "Low Speed" category placard?
Weight is not significant in the differential loading of the human body in a parachute deployment scenario. That is to say that if you double the weight you will only increase the opening forces by 10%. OK now put you eye ball back into your head and look at the "Decreasing Load Factor" (The X1 factor) in the design guide. The chart produces a factor of one tenth of one percent of the pounds per square foot loading. In the context of the model doubling the weight will only increase the force by one tenth.

Mike Furry once said "Harnesses should be so strong that we start shedding body parts before they come apart." He is correct and "Standard Category" harnesses are that strong. Based upon what little research I can find and looking at anecdotal information from the past 50 years it appears that a human body can't take much more than 3000 pounds and survive. Line dump on a square can and has produced more than 3000 pounds. Harnesses have failed under these conditions.
However, it is difficult to deploy a parachute at over 150 MPH which is the limit for the "Low Speed" category.

This type of approach provides compatibility between components and avoids the unanswerable question about weight and speed posed in the earlier portion of this thread.

[pchapman 261]

mark

What we are doing in skydiving is using a 2-link chain to lift an object (one link being the harness and the other link being the canopy). It doesn't matter which link is strongest.

True on its own, but is does matter if you are led to believe that both links are equally strong, but they aren't.

So it is, "Hey, this reserve and harness are both good for 275 lbs and 150 kts".

But then one finds out that that in that case (with the added 1.2 factor), the reserve can create 4000 lbs of force and the harness's tests only created 3000 lbs of force.

Maybe the harness is strong enough, but it hasn't actually been tested to the same level as the reserve. And you wonder, what speed and weight your two link chain really is good for.

It isn't like a paragliding harness where I think certain certification pull tests are done on the ground. (Not that that is perfect either, if one picks the wrong test cases for a harness. Like the Squirrel Stronglite BASE rig when deployment forces are in a certain direction.)


And thanks Hooknswoop who remembered that the compatibility stuff is in AC-105.

[dpreguy 14]

Although I'm not signing up to do the tests, if the human body can only handle a certain limit of lbs of opening shock, then couldn't harnesses be mfg to handle that limit, and let the canopies be designed for whatever loads the mfg chooses, and then drop the requirement that the harness be stronger than the canopy? If the canopy is designed for more, then that's OK, but not necessary.

Also, I am trying to find, as one poster said, that the part of the testing that says the 3 second deployment requirement is abandoned? ( If it is, then is there no standard now? Or is there a new one (say 4 seconds...)? How many seconds is too many? Or is this simply not a true statement.

[dpreguy 14]

Oops. I read it wrong. 3 second rule is still in effect.

[rapaz 0]

I just pack a PR 160, comes with number 4 links stainless steel, wichard, safe working load 621 lbs x 4 = 2484 lbs, this reserve can handle some forces more than 3000 during TSO tests???, so my question is how much is the maximum load that #4 links resist before fail, also PD uses in some models ( like the reserve manual said) #5 links, 990 lbs safe working load.

[pchapman 261]

Peguet makes the real Maillon Rapide links.

Their chart online shows a Working Load Limit of 280 kg (617 lb) for stainless #4. The "BL", breaking load, is shown as 1400 kg. The ratio perfectly matches the idea that the Working Load Limit is set at 20% of the breaking load, or a 5 times factor, which is also mentioned in Poynters. 1400 kg is 3087 lbs.

(I don't know what the Yield strength would be for that steel, at what proportion of the breaking load -- the Ultimate load -- the material would not deform permanently.)

#4 Stainless are ok for all PD reserves, right? The manual (Revision G is current) just suggests #5's may work better with bulky reserve risers.

[riggerrob 558]

We agree that Maillon Rapide #4 stainless steel connector links have a minimum breaking strength of 3,000 pounds(calculated differently than SWL).

Most other reserve manufacturers use Maillon Rapide #5 links. #5 work better with bulky Dacron lines.

Most tandem manufacturers install Maillon Rapide #6 on their mains and a few install them on their reserves.

Most (man-rated) MIL SPEC connector links have an MBS of 3,000 pounds.

[Hooknswoop 19]

Quote

this reserve can handle some forces more than 3000 during TSO tests???

I think is the root of the confusion of the issue of compatibility. The reserve is "handling" 3000+ clubs, it is producing 3000+ lbs of force.

Derek V