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  1. 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?
  2. JohnSherman

    canopy design question

  3. JohnSherman

    Canopy measuring methods - different manufacturers

    The correct engineering method is "inflated plan form". This entails drawing the canopy in its inflated form and measuring the sq. footage as viewed from above. This shortens the physical span because of the perspective from above foreshortening it. The cord is additionally foreshortened by the attack angle being involved. If the canopy was designed in CAD 3D it is easy to measure the perimeter. However, early canopies were not designed this way 'cause CAD wasn't readily available. Other methods require different approaches to measuring the cord. If the airfoil is not cambered then it is tip to tip. If it is cambered then it is the “X” or horizontal axis is used. We use this method (inflated plan form) as it is the way we were taught. It does put us at a slight disadvantage when being compared to canopies from other manufacturers as our canopies will look smaller.
  4. JohnSherman

    Stowing slider in a rubberband: any downsides?

    It is standard procedure within the competition to refute anything developed by Jump Shack. There is no down side to the procedure. We have been requiring it, in our manual to use a rubber band on all canopies since the beginning of Ram-airs in the 70's. I believe most manufacturers do now endorse the concept. Having said that let me caution you to the fact that while the rubber band on the slider will keep the slider from "falling" or inertially being pulled down the lines during opening it will not hold/help if the canopy begins inflation (spreading) and forces the slider out of the rubber band and down the lines before you reach line stretch. This can only be prevented with a bag which will not allow line dump/strip.
  5. JohnSherman

    Re: [teason] Hard Opening Incident-DeLand 5/25/2013

    MEL, Would you please provide (to this forum) the Data Graph for Altitude and acceleration from the data logger used for these "real life test data". Additionally, I would be interested in the canopy and D-bag type/configuration used in these tests. Also how many test were made and what are the distributed results. JS
  6. JohnSherman

    Pia manufactorer tours?

    Not a chance! Do you think we want hords of riggers stomping through our production facilities disturbing the workers and getting in the way. Do you think we want you to be stealing our secrets then going home and competing with us? Seriously; I suppose there will be something from some of the companies. We are not planning anything formal that I know of just come by and if we are open (normal hours, I think) someone will break loose and show you around.
  7. JohnSherman

    Reserve stains from grommets and dye bleeding?

    I would also reccommend a test for acid.
  8. JohnSherman

    Canopy operning forces

    The INTERNAL pressure of a ram air never exceed ambient! Neither during opening or full inflation. It is the external pressure which reduces and because the ambient is greater we have a differential which causes the inflated ridgity. Line burn does not cause blowouts. In My total experience with Ram air canopies I have never seen a line burn except from a accidentally pre-packed malfunction. The greatest force occure at "Snatch". The line attachment knot tightnest will relate to the location of the bridle attachment and the amount of brakes to a lesser extent.
  9. JohnSherman

    USPA and PIA Issue Joint Skydiver Advisory

    From: John B. Sherman To: USPA & PIA Subject: Skydiver Advisory dated April 1, 2010 (We are all the April fools) I have just read the subject advisory and find it to be a complete “Cop Out” and cave-in to the special interests of the manufacturers who have had these failures/fatalities. It is a Pablum-laced document that fails to identify the problems, their frequency and where they were found. It falls way short of fulfilling your fiduciary responsibility to warn the skydiving public. It paints the complete industry with the same brush and is a reflection on all manufacturers, even those of us who were not on the list. You have damaged the reputation of manufacturers who have taken great care to avoid these specific kinds of failures, and shattered the confidence of users of non-offending rigs. Why? Paragraph 2 instructs the rigger to remove the rig from the wearers back and lay it on a table for bag extraction evaluation. This is poor advice, as it changes (releases) the tension of the riser covers and changes the whole dynamic of the retention system. The bag should be extracted while on the wearers back. Additionally, this evaluation process will not reveal the root cause failure on most of the rigs, as it makes no provision or allowance to evaluate the pilot chute drag. I call for the immediate complete disclosure of any and all data known to USPA & PIA concerning failures of the reserve system after confirmed AAD firings at the correct altitude. I understand there are eight such occurrences. Additionally, I understand there have been 7 deaths where the reserve pull or RSL activation was characterized as “Too low”. This information too should be released. The owners of rigs similar to those, which have failed, have a right to know the facts. By not revealing that information you are depriving them of their right to be warned, which is the responsibility of your organizations. As you know, you are liable for such actions. If we have another fatality of the type described above, on a rig that appears on the list, a good lawyer will clean us out. Some might say this data is already in the public domain. This is probably true but it is fragmented and not in a consolidated form that would connect it to its own AAD report. Furthermore, sending data to the PIA technical committee, whose chairman is an employee of one of the companies on the list, is certainly a conflict of interest. While I personally don’t believe this specific individual would violate a trust, it is an appearance of a conflict of interest that must be avoided. This breach of trust and the exposure to liability of our organizations, in the production of the subject document, is so serious that the individuals responsible for its generation should resign or be fired. I notice that the documents don’t identify the writers, I wonder why… and who they are. John Sherman