SethInMI

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.

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 It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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 It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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 It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[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 It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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. It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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! It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

Tom, I think that statement ignores the "forward throw" of the exiting jumper. And I changed the underlined "second" from minute. Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

Yeah, thanks for the post Tom. As a newbie, I appreciate your attempts at education. You have a nice way with words, have you considered writing a book? Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

After reading this whole thread I can make one point that hasn't been made, and agree with several others. My contribution: I don't think AADs are really that expensive. Sure they cost $1200-1100 new, but you have 12 or maybe more (Vigil) years of life (with servicing costs extra). This is about ~100.00 a year, and I don't think of that as being a burdensome cost. Now maybe the same people who bitch about paying the USPA dues will complain about that cost, but until jump tickets go down to $2 apiece, $100 annual cost will be a small percentage of the cost of being a skydiver. Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

My Girlfriend of two years laughs out her orgasms. It always brings a bemused smile to my face, it is so strange, yet so very nice, as she seems to be having one hell of a good time. It always starts with her stiffening, and then a silent "body" laugh that persists for a moment or two then breaks out into sustained seconds of laughter, then she's all relaxed and smiles. It's quite the event. Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

Well I sent my measurements to Sunpath last year when I was rig shopping and they came back with a number that matches skybytch's calc. 75 (6'3) - 36 inseam - 20 = 19 MLW. I was recommended to find a C19 harness. HTH, Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

This is just semantics. To try and stay with the original context (100 J "experienced" skydiver going in): An A-licenced skydiver has experienced 25 J, and has show basic proficency in exiting/tracking/landing etc. USPA considers this skydiver capable of jumping alone, incl. gear check, spotting, deployment, and landing. If a licenced skydiver goes in, and the media refers to her as experienced, they are correct in a certain respect, they have 25 Js worth of experience. A hell of alot more than some 1st or 2nd jump student. But compared to a 2000 J swooper or big-way jumper they don't know shit. So here is a different way to phrase the original question: At what jump number should media reports change the deceased skydiver description from novice to experienced? Let's play the numbers game! (We need a poll!) It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

I remember a mention about the 100 J "experienced" freeflyer who went in, and poster(s) saying he was not "experienced" in his view. I thought to myself at the time, "He was experienced. He had experienced 100 Jumps, enough for the USPA Coach rating. If the USPA trusts someone with 100 J to be a Coach, that means they trust them enough to give advice/answer noob questions, which in my view means they are experienced." Experience is a difficult thing to capture in a jump number, and even to be a Coach means getting a B licence (freefall body control and canopy control ability) and the completing the Coaches course (answer questions/perform checks ablility). I can't comment to much on skydive experience, but on software programming experience, we often say at work: "We need an experienced programmer" This really does not mean we want someone who has written X lines of code or has been a programmer for Y years, it means "We want someone who knows his/her shit, who writes tight code and can meet deadlines." I have worked with programmers who have been coding for years and they can't write worth crap. So I think experience is way more than a jump number, its ability, attitude, etc. But if forced to put a number on it, I think in the wuffo/noob (like me) mindset, 100 J would be considered experienced. Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

AWD and turbos are indeed where its at. I love my Subaru Impreza WRX STi. Nothing powers out of a turn like AWD with 3 LSDs.

I can't say for sure, but I am going to try to get a Triathlon 190 in a J3 once it comes in from Aerodyne (for $700! Thanks DZ.com). It should be similar (but not the exactly the same) as the Spectre. I was encouraged to do so a rigger I know who has put many jumps on a Tri 190 in a J3. I also got a good feeling from looking at Aerodyne's website, were I found pack volume info: Triathlon 190 : 420 cu in. Pilot 168: 416 cu in. That means the Tri is 1% bigger in pack volume than a smaller size Pilot. I would think that means they fit in the same container. Perhaps you can ask PD about a pack volume comparison between say a 190 Spectre and 170 Sabre 2 or something. Seth It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

I have a similar question, so I will just attach to this thread... Will a 190 Triathlon fit in a Javelin J3? It has a pack volume of 420cu. A 168 Pilot has a 416cu pack volume, and a 169 Safire comes in at 452cu, according to the manuf. websites. I can't find any pack volumes for Sabres. The only recommendation on Sunpath's site says 170zp max. Would it work if the reserve was a Raven I (180 sqft)? Thanks, Seth Looking at the numbers, are icarus and aerodyne measuring the same? A 188 Pilot, 440cu, is less than a 169 Safire? Can I fit a 188 Pilot in a J3???