JohnSherman

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Gear

  • Main Canopy Size
    200
  • Reserve Canopy Size
    180
  • AAD
    Vigil

Jump Profile

  • Home DZ
    Deland
  • License
    D
  • License Number
    2105
  • Licensing Organization
    USPA
  • Number of Jumps
    2500
  • Years in Sport
    52
  • First Choice Discipline
    Formation Skydiving
  • Second Choice Discipline
    Style and Accuracy

Ratings and Rigging

  • AFF
    Instructor Examiner
  • Tandem
    Instructor Examiner
  • Rigging Back
    Rigger Examiner
  • Rigging Chest
    Rigger Examiner
  • Rigging Seat
    Rigger Examiner

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  1. JohnSherman

    Interesting cross port design...

    Can't find one with the proper characteristics. 1.1 isn't permeable enough.
  2. JohnSherman

    Interesting cross port design...

    All FireBolts have always been made this way. Some 20 + Years. It is how Parachute Labs does all of their canopies, AngleFire Reserves, Blackhawk Mains and Reserves and Nighthawk mains and reserves. Racer Tandem Reserves and Mentor Student Canopies. It is done to reduce rib distortion.
  3. JohnSherman

    NASA VAB Pilot Chute Test

    The participants were representatives from Strong, UPT, PLI, Mirage Sys. as well as 8 NASA Engineers and 4 NASA managers and some 6 or 8 photographers from the Skydiving world. There were 14 pilot chutes tested 2 each from 2 of the represented companies and one military surplus. One each from the other two companies present which leaves 7 unrepresented. Some manufacturers were invited but could not make the trip as it was on short notice. There were additionally; 3 drogues and one rocket recovery parachute tested. They will not be reported on.
  4. JohnSherman

    Are "good" pins good enough?

    The military/government has no such test. They do require this test: When the pins are initially formed they have a blade length of about 3 inches. They are mounted to the cable then the end of the pin is bent 90 degrees. This bend makes attaching a holding fixture to the blade of the pin, for pull testing to 300 pounds, possible as a straight blade would have a propensity to pull out of a compression grip. Some other folks were testing by "hook gripping" at the junction of the pin shank and the cable. This doesn't stress the blade which is required. This was a principal reason for pin failures getting into the field some years ago. We have done loop load vs. pin pull force tests in the past and were convinced then of our current position.
  5. JohnSherman

    Are "good" pins good enough?

    Ripcord pins are made from .188 dia 302SS Cond A (303 is also allowed but I don't use it) they are then rotary swaged to a diameter of .094 using the rotary Swag process of cold forming as you can't harden SS with Heat treat. The overall length of the blade is dictated by the end user but is usually 1.25 inches. Column strength of the blade is tested by inserting it into an .096 dia hole one half inch deep and applying an 8 pound weight to the end. The results is checked in a go-no go gage of .104 dia to the full depth and the pin must fall out without friction after insertion. This process and design was originally for a pin and metal cone thru a 9/16 and 7/16 grommet situation. The amount of allowable bend was critical as the thru hole in the cone was about a half inch deep/thick. Today we use 1/4 inch grommets with a cloth loop. A far less critical arrangement. Yes, the pin can bend in that configuration but it is usually from dropping or throwing the rig down or against something as the rig is compressed when it hits something and this causes the rest of the rig to want to expand causing a great load on the loop and subsequently on the pin causing a bent pin. The good news is that is can still be pulled even with a bend. The Military still uses this pin on their center pull chest reserve with cloth loops and even with the rough treatment they get have had no problem. Larger diameter pins would cause a harder pull with the same loop load. Additionally, the shank and cable would also have to be enlarged to obtain the necessary strength as the blade would still have to be cold formed to make it hard enough. The thicker pins used on some assemblies have no greater column strength as they are not cold formed from a larger diameter. Don't let size fool you.
  6. JohnSherman

    AAD Fatality Thought

    This is a great discussion. It's about time. I believe it is rig/canopy specific and that it has to do with bag extraction effort vs. pilot chute drag capability. There are videos which show it happening. There have been about 20 of these instances recorded. All have been with the main closed. There are some rigs on which this has never happened and there are rigs on which it has happened numerous times. The distribution is not aligned with rig sales distribution. The problem is easy to define with a simple test. During the FAA/Rigger Investigation with the same rig from an incident. Assemble the rig with a fresh AAD charge and pack job. Packed with both main and reserve. Add enough weight to the harness reach AAD firing speed. You could use bar bell weights in the leg straps. You will need enough weight to achieve about 7 pounds per square feet of rig surface area, which I would guess at 3 sq ft. or, 25 pounds which will give you the weight of the rig plus the 25 pounds enough to reach the necessary speed. Tape down all lose webs and stuff. Toss it out at an altitude high enough to satisfy the AAD firing requirements. We would expect it to fire at 750 and to deploy the reserve before it hits the ground, if it does it won't go far from less than 450 feet. If it doesn't leave it there and call the manufacturer. If it doesn't we will know the answer. If you can't get the involved rig from the incident get one just like it with the same canopies. The Deland test project seems to be stalled, however there are other testing activities occurring. We should have data by Symposium.
  7. JohnSherman

    Odd malfunction twice in a row

    Brake Fires on both!
  8. JohnSherman

    A Cautionary Note about Velcro alignment

    We began supplying "Snap Toggles" standard on our reserve risers about 6 months ago. When it was confirmed by several drop zones that "brake fires" were the biggest cause of malfunctions, something we have believed for many years. There have been no known fires of a snap toggle in the 20 years in service, so we felt it was time to upgrade the reserves.
  9. JohnSherman

    A Cautionary Note about Velcro alignment

    Happy to, here you go. [inline Racer_Risers.jpg] [inline Snap_toggle.jpg]
  10. JohnSherman

    white powdery stuff seen on opening

    I doubt this is the answer but for grins I offer it. In the very early days of the sport I was taught to pack my 28' Single Blank Gore, C-9, 1.1 oz, round canopy with talcum powder. This was to condition the fabric to make it subtle and last longer or so we were told. We were only required to do this for the first 25 jumps or so. As a result we learned to mix baby power with dye to give the powder color for demos. When the canopy opened it gave off a puff of the powder whatever color it was. I did it for demos until I bought me first PC at 32 jumps. Yes, I was doing demos with less than 10 jumps.
  11. JohnSherman

    Mirage MARD is out

    Drop them side by side from any reasonable height and you will be able to see for yourself. When they are new, both perform exactly the same in the wind tunnel or from a free drop. Old ones of either type will not do as well as new ones but not by much. FYI: The Power Racer Pilot Chute (SRP) is the one with the 4 inch diameter top and the 32 inch diameter canopy. The MA-1 has a 36 inch canopy and a 6 inch top. The MA-1 has a publisher Cd of .65. The SRP has a published Cd of .83. Calculate the Cd*So (effective size) of both and you will understand the similarity. Remember Pilot chute terminal occurs at about .6 seconds after inflation/release as opposed to humans who take about 12 seconds to reach terminal after launch.
  12. JohnSherman

    Mirage MARD is out

    That's what we called it when we first looked at development of the MARD idea Eric Fradet brought to us some 20+/- years ago. Jarrett named it the "Air Snare" when we developed and rejected it several years ago. We just don't need it. It is slower than a conventional deployment at high speeds and the same at low speeds. I believe it is better to depend on a good pilot chute with a good launch and high drag which is consistent, rather than a malfunctioned main which has infinite variable drag capabilities. The first thing we don't need is complexity. The second thing we don't need is inconsistency. "KISS"
  13. JohnSherman

    A Cautionary Note about Velcro alignment

    Correct !! They call them "Snap Toggles"
  14. JohnSherman

    A Cautionary Note about Velcro alignment

    Good job Peter. Here is a riddle for you: When don't you have to worry about the velcro on your reserve toggles damaging your container?
  15. JohnSherman

    A Brain Teaser for Gear Wonks

    The problem with the horizontal wind tunnel and the stream of water analogy is that neither have the gravitational component which is the weight of the object. If we go to a vertical wind tunnel or could run the water up vertically then the gravitational component would come into play and would resist the flow. Without gravity or something to resist the flow you have no Drag. To keep the analogy horizontal and in water we could say the air we skydive in is like a still water lake and we are plowing through it in a gravity strength powered submerged body. Put a pilot chute out thru the turbulence into the still water and that will give you a look at the same thing that happens in the air.