PDR vs PDO performance

[SkydiverNigel 1]

gowlerk

******Bottom line, I'm not seeing any credible evidence to show that PDOs are less safe than PDRs.

Here's what Mark Procos from UPT had to say on the topic:

BPA Skydive the Expo 2015 - Equipment Compatibility with Mark Procos

Softer openings was one of the design goals for the OPT. That means covering longer distance, which may make it less safe than a PDR under specific circumstances (where many other variables and decisions come into play). On the other hand, it may be safer than a PDR at higher speeds or in situations where canopy size is a factor. I have not seen sufficient evidence to conclude that the OPT is inherently less safe than the PDR, but I do have my Vigil set to 1,250 ft to account for the longer snivel.

Nice. That is by far the most realistic and sensible thing I've seen written about this subject. Design is compromise, and PD did not get something for nothing when they built in a short snivel.

Interesting presentation, but a bit short on actual data, and sometimes Mark P contradicts himself.

Around 22:00 says '....softer openings doesn't necessarily mean longer openings...' which makes sense to me: can just mean the opening is spread more evenly over time, rather than mostly happening in one big jolt.

Earlier he had said '3 secs, 300' ' was a myth, though later he comments that it's the de facto unofficial standard reserve manufacturers aim for, and meet. Without showing any data, he then states PDOs may take more than 2.0-2.5 secs to open, but certainly less than 3 secs. I took that to mean PDRs and other reserves are closer to 2.5 than 3 secs.

What I did learn was reserve openings are complex with plenty of nuances: 'dynamic corners', the burble, pilot chute design and placement, cutter placement, weight and body position. Different AADs are also different in the the ways they arm and fire.

But I still see no data to make me believe PDOs are less safe than PDRs. I can certainly believe there are Youtube videos showing atypical behavior, but as I said earlier, these are not under controlled conditions and I wouldn't change my practice based on an n=1 event. That's just me, though. Other posters can believe and do whatever they like.

I aim to pull at 3000', certainly not lower than 2500'. And like another poster, I've set my Cypres's to fire at 1250'.

[gowlerk 1,903]

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But I still see no data to make me believe PDOs are less safe than PDRs.

I did not and have never said that. They are two different canopies of two different designs. Why would anyone think that they both open in the exact same time? One opens in less time/distance than the other. Both are certificated canopies that meet the standard. I consider both to be "safe". But they each have different strong and weak points, relative to each other.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[masterrigger1 2]

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Around 22:00 says '....softer openings doesn't necessarily mean longer openings...' which makes sense to me: can just mean the opening is spread more evenly over time, rather than mostly happening in one big jolt.

Your theorem makes no sense if given the same time and distance traveled in both scenarios.

The sniveling canopy would have to make up time and distance in the second stage of the opening to equal the other canopy. The result to equal the other would be a faster, harder deceleration at the bottom end.

MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[masterrigger1 2]

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Both are certificated canopies that meet the standard.

It is not "the standard" is "a standard".
The confusion is that the TSOs are the same. They are not. Riggers should know not to mix certain components to be safe. For instance do not install a OPT into a container with a AAD set for 750'. It probably will not work in time. Why do you think PD pushed for the higher opening altitudes with USPA?

Not to mention the issue with line twist on most openings.

MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[mxk 1]

masterrigger1

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Around 22:00 says '....softer openings doesn't necessarily mean longer openings...' which makes sense to me: can just mean the opening is spread more evenly over time, rather than mostly happening in one big jolt.

Your theorem makes no sense if given the same time and distance traveled in both scenarios.

The sniveling canopy would have to make up time and distance in the second stage of the opening to equal the other canopy. The result to equal the other would be a faster, harder deceleration at the bottom end.

MEL

Not that it matters given that the OPT probably does take a bit more time and distance to open, but draw a speed vs. time plot with two points representing the start of deployment (e.g. t=0, speed=120) and end of deployment (e.g. t=3, speed=12). A straight line between those two points is the optimal deceleration profile with the lowest possible peak force. The area under that line is distance traveled. Now draw a curve between the same two points that starts above the straight line and crosses it in the middle. You can draw it such that it has the same area (i.e. distance) and time, but higher deceleration in the middle of deployment. Or you can have higher deceleration initially, flat middle, and another jolt at the end. Infinite possibilities.

In other words, if you can spread out the deceleration more evenly over time, you can certainly have a canopy that opens softer in the same time and distance. You were assuming that it's the OPT with the suboptimal profile.

[pchapman 261]

mxk

A straight line between those two points is the optimal deceleration profile with the lowest possible peak force. The area under that line is distance traveled.

Nice use of basic physics.
To expand a little for others, the slope of the line is the acceleration (deceleration) since it is the rate of change of speed.

You point out one scenario where you can have the same distance and time, but harder or softer openings.

Still, there are scenarios that are mathematically correct but might not be very feasible for an actual parachute. Eg, lets say an Optimum has a smoother steadier deceleration over its 3 sec opening. If a 'conventional' reserve started to open harder and faster at the start, it would be difficult for it to take as much distance as the Optimum. The conventional reserve's speed would already be low, and the canopy spread wide, so it couldn't just "hold off" and pretty much stop decelerating long enough for it to keep adding enough distance to equal the Optimum at the 3 sec point.

The sketch shows some scenarios. The second one down is a situation of a quicker initial opening that mathematically gives the same total distance. But as I noted above, the more likely scenario is the 4th one down, where the quicker initial opening leads to less distance used.

[inline "deceleration.jpg"]

[SkydiverNigel 1]

gowlerk

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But I still see no data to make me believe PDOs are less safe than PDRs.

I did not and have never said that.

Erhh...and I never said you did ;-))

[SkydiverNigel 1]

@mxk and pchapman:
Thanks for explaining what I meant better than I could have done.

@masterrigger1:
Why do you say a PDO '...probably won't open in 750ft'?

Extraordinary statements require extraordinary evidence, which I'm just not seeing. And the recent PIA report on reserves didn't show a propensity for any reserve to open in line-twists - the other odd statement in your post. I need to check.

...I'll do what I should have done in the first place and ask the manufacturer (in one of the earlier replies John Leblanc is quoted saying they take the same time to open. I think I believe him).

[masterrigger1 2]

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@masterrigger1:
Why do you say a PDO '...probably won't open in 750ft'?

Because they obviously take longer to open. When Airtec tested systems to come up with a target firing altitude after extensive test drops, 750' was the answer. It gave about 100-200 above the deck on the systems tested on average. When the OPT came along, the openings were longer which made the buffer disappear in some instances.

The openings are longer. 1.
PD said so themselves in their first ads and then went kind of mum on the subject.

2. I have watched many of them in videos and real life.

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And the recent PIA report on reserves didn't show a propensity for any reserve to open in line-twists - the other odd statement in your post. I need to check.

IMO that PIA study was the biggest the worst waste of time ever. The study was geared towards pilot chute load,etc. It had nothing to do with canopies. Once the canopy is out of the bag, the pilot chute is out of the equation?

Also,the problem of slow opening reserves/parachute systems and people dying under them did not arise until after the TSO'd 23d and 23e gear came into play.

As far as the line twist are concerned. Do you have your head in the sand or what FCOL?
A Russian just died from them and they are on 75-80% of every OPT deployment video.
I can think of about 3-4 more that got out of the twist just seconds before landing.

Heres just a few:

https://www.youtube.com/watch?v=FiJkwrsCbVs

https://www.youtube.com/watch?v=ctim2aDfQJs

https://www.youtube.com/watch?v=k8zFf6SfOYw

https://www.youtube.com/watch?v=17pd_MgaA50 (See if you can spot the OPT. There are several reserve rides on this video)

https://www.youtube.com/watch?v=4tF6iXI70-Y



MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[masterrigger1 2]

Peter,
Here is a paper that was produced a few years ago (2005) on parachute inflation and opening.It was for a space vehicle so it has way more info that is needed. Never the less, it is good info.

http://www.mrc.uidaho.edu/~atkinson/IPPW/IPPW-3/Parachute%20Course%20Material/06%20Parachute%20Inflation%20Wolf.pdf

MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[degeneration 5]

masterrigger1

As far as the line twist are concerned. Do you have your head in the sand or what FCOL?
A Russian just died from them and they are on 75-80% of every OPT deployment video.
I can think of about 3-4 more that got out of the twist just seconds before landing.

Heres just a few:

https://www.youtube.com/watch?v=FiJkwrsCbVs

https://www.youtube.com/watch?v=ctim2aDfQJs

https://www.youtube.com/watch?v=k8zFf6SfOYw

https://www.youtube.com/watch?v=17pd_MgaA50 (See if you can spot the OPT. There are several reserve rides on this video)

https://www.youtube.com/watch?v=4tF6iXI70-Y

MEL

Of those 5, how many were using a skyhook, and how much do you think that was a contributing factor to the twists over the reserve itself? Genuine question, or is that bringing in another can of worms?!

Sky Switches - Affordable stills camera tongue switches and conversion adaptors, supporting various brands of camera (Canon, Sony, Nikon, Panasonic).

[mathrick 2]

AFAIK, when Skyhook first came out (before OPT was on the market), UPT's testing showed that Skyhook deployments are less likely to develop line twists than either a plain RSL or manual activation (assuming the jumper did not wait around forever to "get stable"). Whether OPT changes that, and/or whether OPT is inherently more likely to develop line twists, I don't know.

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

[pchapman 261]

masterrigger1

on parachute inflation and opening.It was for a space vehicle

http://www.mrc.uidaho.edu/~atkinson/IPPW/IPPW-3/Parachute%20Course%20Material/06%20Parachute%20Inflation%20Wolf.pdf

MEL

Thanks!
Actually got that one already, that's from the International Planetary Probe Workshop #3.There are some other fun parachute related papers in the same folder, although nothing to do with sport parachutes! (One NASA page has the files too. Other sources for interesting parachute aerodynamics are of course T Knacke, G Peek & J Potvin, and JS Lingard.)

[keithbar 1]

masterrigger1

***
@masterrigger1:
Why do you say a PDO '...probably won't open in 750ft
I can think of about 3-4 more that got out of the twist just seconds before landing.

Heres just a few:

https://www.youtube.com/watch?v=FiJkwrsCbVs

https://www.youtube.com/watch?v=ctim2aDfQJs

https://www.youtube.com/watch?v=k8zFf6SfOYw

https://www.youtube.com/watch?v=17pd_MgaA50 (See if you can spot the OPT. There are several reserve rides on this video)

https://www.youtube.com/watch?v=4tF6iXI70-Y



MEL

. Clicky someone please

i have on occasion been accused of pulling low . My response. Naw I wasn't low I'm just such a big guy I look closer than I really am .

[SkydiverNigel 1]

masterrigger1

Peter,
Here is a paper that was produced a few years ago (2005) on parachute inflation and opening.It was for a space vehicle so it has way more info that is needed. Never the less, it is good info.

http://www.mrc.uidaho.edu/~atkinson/IPPW/IPPW-3/Parachute%20Course%20Material/06%20Parachute%20Inflation%20Wolf.pdf

MEL

1) Reference cited is highly technical = good.
Relates to round canopies = likely completely irrelevant.
2) You have the famous PD ad? I'll believe it when I see it.
3) As others (mrk, pchapman) have explained better than me, softer openings don't have to mean longer (time or distance) openings. Why is this so difficult to understand?

[grantunderland 0]

The last one (only clicky and I'm lazy) might have been a skyhook activation, but you can clearly see the reserve bag log not being connected to any main. I am not a rigger, but given the way that thing came out of the bag I'm surprised it was able to be salvaged. That oscillating RPC sure doesn't seem to be helping things either

[masterrigger1 2]

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2) You have the famous PD ad? I'll believe it when I see it.

When I get back to the shop in about two weeks, I will surely dig it out for you.

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3) As others (mrk, pchapman) have explained better than me, softer openings don't have to mean longer (time or distance) openings. Why is this so difficult to understand?

1.First, parachute openings are very complex.

2. The basic formulas that were presented were just that; basic physics in the simplest form that do not apply to the scenario at hand IMHO.I can draw a graph to represent anything and make numbers match the graph.

3.I do understand the above.

MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[pchapman 261]

SkydiverNigel

3) As others (mrk, pchapman) have explained better than me, softer openings don't have to mean longer (time or distance) openings.

Softer openings indeed don't have to result in longer time or distance... but they MAY. Which allows for MEL to put forward the case that the Optimums do take a longer distance.