JohnSherman

The Comventional rig was a Soviet era D-5 military rig. Usually with a triangle reserve and a baseball type constructed round main, originally a drogue deployed with an Static line and AAD activated drogue release. The smoke jumpers in Alaska use a copy of this H&C system. There is one at the Jump Shack on display.

The correct answer is to "Sit up and dump". Extend your arms out in front of you to raise yourself to a head high position. This directs the air flow over your back to sweeps the pilot chute up off your back and into the air stream avoiding a burble. Lift your head and look up to check your pilot chute canopy. Don't lift your head of stick your arms out to much to avoid entering a back loop. Keep your shoulders level to the ground. Dropping one will cause the bag to spin off your back creating line twists. We just want you to get into a head high position and ready to sit into the saddle. A 45 degree angle is enough. Being ready to grab you risers for immediate steering control is a good idea. What is being said about getting you fingers "snapped" is true. Watch out for it.

The wide stronger rubber bands did nothing to reduce line/bag strip (the same thing). Line dump is caused by the imbalance of the elements of the stow. See:http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D This was the beginning of our understanding. We don't get line/bag dump anymore. Note: Bag "snatch" from the container can be as much as 20G's. What ever stow method you are using had better take that kind of loading to avoid the phenomenon.

"Gear Fear" is the reason I do what I do. I had to know if was "OK". I looked at my Capewells the jump after I had my first cutaway. I wondered if they would release accidentally as they had been easy to release on the previous jump. I don't have it anymore.

Frankie recorded one record album that I know of. I proudly still have a copy in my collection. There is one tune he wrote about jumping out of his uncles airplane. Very funny. He is missed.

Riser length is determined by the designer as they play a part in defining the arc-anhedral. If the risers are too long then the top skin will have a bigger than desired bulge. If too short the bottom skin will bulge. Both affect the performance. Ask your manufacturer what is correct for that particular canopy. One inch won't make much difference.

Most manufacturers can vary the snivel distance to suit the buyer. Demo canopies are usually set to open soft and snivel a bit. If you demo a canopy and like it, but it snivels to much, ask the manufacturer if that can be adjusted. We often accomidate this kind of request when made. BTW: Snivel does increse as the canopy wears.

Certainly that was the intent. However the internal pressure of a ram air is ambient. The term "Ram Air" is misleading. A canopy inflates by ingesting air into the cells which are trying to expand from the reduced pressure on the outside. Nature hates a vacuum. After the cell fills it does not become ridge until a flow occurs over the top skin reducing the external pressure. That differential causes the wing to become ridge. As long as the wing is flying it has an ambient pressure on the inside and a reduced pressure on the top outside caused by the flow. In turbulence the "Boundary" layer (Reduced pressure area) is blown off disturbing the reduced external pressure and the wing relaxes into a loss of rigidity and it falls out of the air (Stalls). Ram air parachutes just like ridge wings loose lift and stall when the flow is irrupted. Sometime from AOA change and sometimes from turbulence. Air locks do inhibit ingestions of air (inflation) but they don’t do anything to keep the wing ridge in turbulence. As that rigidly is dependant solely on the reduced external pressure. An airlock canopy might stay inflated on the ground after landing forever but it is not producing lift as there is no flow.

If "Air Locks" worked then ridge wings wouldn't stall.

I would agree that the language was poor. However, Everyman Jack, who makes rigs, was on that committee and all knew that the rule was 3 seconds. It was 3 seconds before that version and is 3 seconds in the next version. There was never any discussion about raising it to a longer time. I don't buy the excuse of mis-interpretation. I don't read the language that way.

Sorry Councilman but those numbers are not additive. The opening time is 3 seconds or 300 feet from activation, RSL or no RSL. I know some manufacturers have made the interpretation that it allows 5 seconds but it is an intentional distortion so that they could get their rigs certified. I sat on the committee that wrote the rule and it was never intended to be interpreted this way. If you don't have an RSL and are trying to get a reserve pull within 2 seconds after cutaway you had better be fast. The non-additive allowance was provided to allow for testing and certification without an RSL. This has apparantly been clairfied in the latest revision of TS-135

Lee, It has been years since I considered those calculations for Re. Thank you to Peter for his post saving me the pain. His post referencing the graph on page 5-29 in Kanacke and the subsequent comments tell the story as I know it. Many people mistaken flexible fabric bodies found on parachutes as equal to the flat ridged bodies usually found on aircraft. Those flat ridge bodies are more responsive to Reynolds Numbers while our rounded flexible bodies are not. We had long discussions at the University of Minnesota during the AIAA Aerodynamic Decelerator Systems Conferences about this subject. I believe it was a Dr. Lee from the “Temple of Heaven Parachute Company” of China who produced the definitive paper on this subject. Back then, I set up a spread sheet of a typical situation and substituted numbers to see the Reynolds effect. I found that 50,000 was the delineation point for my purpose, while Kanacki was more conservative with 100,000 as his low end. I learned back then that they weren’t worth the time considering and have ignored them ever since. You may need to consider them in your rocketry projects but we don’t need to for skydiving. Thanks to “Paratekk” for the download info. While I have an original loose leaf copy of the manual, severely worn, and signed by Theo, I am reluctant to share it. Now I don’t have too. John

Lee, Reynolds numbers are generally not needed in low speed applications such as personnel delivery. Reynolds numbers below 50,000 have little or no effect on the Cd. When we did the refueling drogue tests at NASA Ames we were working as high as 250MPH and found that Reynolds numbers were of no consequence. We just don't go fast enough to affect the viscosity. The only way a Cd can be determined is by testing. All of the Cd's I quote have been developed that way. My philosophy is to ignore the Cd and the So as single entities and relate to them collectively as "Effective Square Footage" (Cd*So). I have found that some manufacturers try to dodge the issue by declaring that their pilot chute is not the size (So) applied. If they are combined to the Effective size who cares what the physical size is. Cd*So= Drag/Q(Dynamic pressure) You can only measure Drag and Q in the tunnel or in the air. From them you can get the Cd*So or Effective Sq. Ft. which is what matters. If pilot chutes were placarded with the Effective Sq. Ft. then they would be able to be compared and their drag could be calculated for any speed. I agree that the price from Amazon is outrageous. I would recommend Dan Poynter or Mike Truffer as a better source. The book is apparantly out of publicatiion. John

The numbers quoted in the PC drag data chart .pdf are in error. While you show the time in FF you don't show the "Q" or Dynamic Pressure at the speed and altitude where the reading/calculation occurs. Further you assume all pilot chutes are equal except for size. This denies the existance of the Coefficient of Drag. Pilot chutes of the same size can have as much as a 300% differential in drag because of the design. This situation exists within our sport. The formula for Drag is Drag= Coefficient of Drag times the Plan form size, times the Dynamic pressure. D=Cd*So*Q (See: http://www.jumpshack.com/Q.htm for a chart of Dynamic pressure. The published Drag Coefficient of the MA-1, a U.S. Military pilot chute (36" diameter) is .65. 36 inches in diameter equates to 7.069 square feet and after the coefficient is calculated it has an effective size of 4.59 sq. ft. When you multiply the effective square footage times the Dynaminic Pressure (for this we will select a speed of 120MPH at 2000 feet) we get 35.21 pounds per square feet or 161.77 pounds total drag force. Much less than your 254 pounds after 12 seconds of FF with a 36 inch canopy. I suggest you refer to: http://www.amazon.com/...Manual/dp/0915516853 for a manual which will explaine the entire process. For a quicker reference see: http://en.wikipedia.org/wiki/Drag_equation John Sherman

Parachute Labs/Jump Shack make the ripcords for the MC-4 as they do for most rigs. Currently they only have 7 or 8 hundred in stock maybe they would sell you one of each. Contact: [email protected]

Rubberbands need never to be double wrapped, that is if the components of the line stows are ballanced. The conponents are the "bights" and the "stows". In size and mass 1 stow should equal 2 bights. See: http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D for a graphic depicting a balanced araingment. The article is an old one and has since been updated but the bit about the balanced line stows is fact. We use the same size standard Mil Spec Rubber band for all applications on our products from Tandem to minies. The Rubber band doesn't have to be tight to do it's job. By moving the stow inboard to the 25% point the mass of the lines is putting equal stress in both directions during bag extraction preventing line strip or dump. If your stow loops are on the edge of your bag the bight can easily be overcome by the mass of the stows between the bights. Maybe then you might need to double wrap but you will not get 100% results in line retentions. Additionally, We don't reccommentd anything but Mil Spec Rubber bands. They do break for a reason at 40 pounds. Additional reading:http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Rubberbands&SortBy=DATE_D http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Speedbag&SortBy=DATE_D http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Reserve_Speedbag&SortBy=DATE_D

Not only is the breaking strength of a rubber ban significant but the elasticity is also important. I an linking to an article I wrote before we designed the "SPEED" bag when we first learned about "Balancing the mass of the stow". This will perhaps provide more insight as to the importance of Mil Spec stow bands. http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D

Try it. You won't snag a flap on a Racer.

Get an independent rigger to check the new lines. Have an highly experienced jumper, familure with that canopy, test jump it. The new lines could have errors in them which might affect performance. Even the factories have made mistakes.

Bill, Just in case you are not speaking with you tong in cheek, I offer the following info. At the last PIA meeting Robert Feldman, Attorney for UPT et ux, raised this item and had it put on the agenda to go to USPA as a request. It is biased upon the USPA directive about low reserve openings, or failure to deploy within 750 feet after AAD confirmed firing. I did a poll on this form predicting this action. Under Gear & Rigging: "Should the AAD activation altitude be raised to 1250 feet?" Booth is behind it because his reserves and others, won't always open within the required distance of 300 feet. He has publicly stated on Youtube at the PIA convention http://www.youtube.com/...5#p/u/30/tQuJr5wuvSw that this is his desire, to raise all altitudes. John PS; I would support this increase if there was a smattering of proof that it would help. But if a PC won't pull a bag out in 750 feet then I don't see any reason it would do any better from a higher altitude. We don't need more altitude just gear which works. JS

We don't limit product as to number of jumps. We have Type 17 risers over 20 years old and with thousands of jumps. They are still good. We are a loft/manufacturer and we take good care of our gear. In the US there is generally no life limit on aviation product. People don't understand it is a "Progressive Maintaince" program. The Rigger, who Certifies the equipment as good for the next 180 days, is the person who determines the life limit. If you can't get it Certified by a rigger it has reached it's life limit. It is the riggers job to determine airworthyness. I know of gear (Racers) over 20 years old, with thousands of jumps, which are still airworthy. I know, Main risers are not subject to Certification but the Riggers talents can and should be used to evaluate your complete rig. I would suggest that a posible reason for the failure we are discussing in this thread might be due to "Needle Weave" webbing. It has the charisteristic of sudden failure if an edge is nicked. I do know that there have been Type 17 risers made with this type of webbing and that they should be destroyed.

That is just not true. Bill, you said you can't use Spectra line on Tandems. I have been using Spectra line on tandems for 20 years and never had a line break and don't have an opening shock problem. The Firebolt opens onheading softly with 1000 pound spectra and always has. The reason this was believed was because the smaller diameter line has a tendency to be less retained in the rubber band and if the stows are not balanced the bites pull out easily. That's line dump. The type of line has little to do with opening shock. ALL of the other factors are far more signifficant. The way to avoid "Killer " opening shock is to control the entire opening process. Avoid line/bag dump/strip and rubber band your slider up. If it opens soft once it can open soft every time, just control the variables. You gotta learn them before you can control them.

Not accurate: We don't use or need the reinforcement. All the reinforcement does is reduce the mechanical advantage of the middle ring by thickening the webbing and reducing the length of the leaver. The reinforcement seen in the riser was for the cutting problem of the middle ring to the harness ring. See:http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=T17STUDY&SortBy=DATE_D Additionally Type 17 mini-ring risers can accept a 3600 pound load if manufactured correctly. For a 200 pound person that would be 18G's. Pleanty strong enough for any skydiving. We don't limit ours.

In the US the rules are: If the original application to the FAA for TSO has life limits specified in it then it can be limited to that time and can not go beyond it. It is still subject to the 180 day inspection cycle. This can't be changed, by the manufacturer, after the original approval is issued except by a grounding recall issued by the FAA. If the original application does not have a life limit then there is no life limit, if falls into the "Progressive Mainainance" process. That means that it is only good for 180 days and then must be re-certified for another 180 days. This can go on until a certifying rigger won't certify it any longer.

For what it is worth I will add my $0.02. Reversed risers and risers without the traditional grommet arrangement are exactly what Bill said they are. Dangerous. I feel so strongly that about it that I think they should be band from the sport. If I ran a DZ and someone showed up with that kind of set up I would not allow it to be used. The tab grommet looses half of it's mechanical advantage and on mini rings that makes it 15 to 1. Therefore if you weigh 150 pounds it will have a 10 pound loop load. Anything over 10 pounds loop load gets very difficult to pull if not impossible. The "Suck through" goes from 60 pounds to 30 pounds. Easy to get on a hard opening. Now for those of you who would disagree I suggest to you that the 2 men who have tested the 3 ring the most are both saying the same thing. Dump those type of risers for the traditional ones. John Sherman