DBTECH

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Posts posted by DBTECH

  1. The sleeve is inverted after deployment, and, like a D bag, does not extend behind the tail of the canopy.
    I would say that my sleeve has slightly less drag than a D bag, because of it's much softer material.
    (not that either have much drag, compared to even a small inflated pilot chute!
    Dave Brownell

  2. Some facts about deployment sleeves.
    The sleeve retaining line can be very short, as the sleeve will always invert from the top down, because of the huge pressure differential when the mouth is open. (ram-air pressure at open mouth, and a partial vacuum at the top of the sleeve) The above is true for a round parachute also!--yes, I have seen this.
    As far as the claim, for a sleeve causing canopy burning; this is in fact a fallacy, as the 'force per unit area' is way to small.
    Dave Brownell

  6. Subject: Ram-air Sleeve R&D Rev 7-6-01
    DB Technologies: Prototype sleeve for ram air canopies. Rev 7-6-01
    My latest project (1997) is a sleeve for a ram air canopy--one that I know will make packing a zero porosity canopy much easier.
    The sleeve is 39" long and 15" wide laid flat before loading. (was used with a Spectre-170) (now used with a Cobalt-135 & a Stiletto-135 after some shortening from the top.(6") After it is loaded with the podded canopy with the mouth turned up and the lines stowed it is 29" long (23" with Cobalt-135 or Stiletto-135) and 12" nominal in width. There are three locking stows. The first stow is made at the center, then the left stow followed by the right stow. The last four stows will be explained later in the text.

    The sleeve is then brought over the rig so that the mouth end is against the reserve wall and the lines are on the bottom of the pack tray. At that point I half the sleeve two times. First I bring the top over to meet the mouth end at the reserve wall, then I bring the remaining folded sleeve over also. Then I close the container. Unlike a D bag, the sleeved canopy "fills" the container, I believe better.
    The sleeve is made of 1.9 oz ripstop with appropriate reinforcements. The sleeve retaining line is 12" long. (TY 4--5/8") (one piece TY 4--5/8" bridle all the way to the canopy on my sleeve only. (21" ZP pilot chute used)
    My new line stow technology for the last four stows will now be described in the following text.
    For the last four stows there are two "pairs" of # 3 grommets with internal stiffeners. One above the other just below the left and right # 4 locking stow grommets.
    A continuous loop of 3/4" elastic strap, THREE inches long laid flat; then sewn at the center point is used for the four "Post" locking stows. This elastic strap has an elongation spec of 110%. This is more than most elastic shock cords. The center of this strap is then tacked on the inside of the sleeve at the center point between each of the two # 3 grommets. The spacing between the OD of the two grommets is 5/8" (1 1/2" cntr. to cntr.) The internal stiffener (.060" MDS) makes sure this dimension never changes. The tack points are pre drilled in the MDS stiffeners, as are the punched oversize holes for the grommets.
    At this point I bring the ends of the loops through the grommets. There is only about 3/4" of laid flat loop outside the grommets. The total laid flat length of each stow is of course 1 1/2", or half of the total loop length.
    The "Grip" on the line bite is more than adequate considering that I have two of what I call, "center mass lifting loops," one above the other mid span between the left and right stow points. They are made of 5/8" type 4 square weave with a laid flat length of 2" below the stitch point. Their purpose is to provide a line anchor at mid point between the 10 inch stow span. These midspan "Lifting points" will remove 33% of the load on the left and right stows during pilot chute extraction. But there is a lot more to it than that. With a 2 1/2" stow bite there is an equal mass of line on each side of the stows! ( 2 1/2" ea. side of the stows). These center "Lifting points" provide "Lift" for the remaining center 5" of line. (2 1/2" each side of the center.
    The easiest way to see the physics here is to imagine cutting all the lines halfway between the left stow point and the center lifting loop--and also the same cut on the right side. You would then have three lifting points with 2 1/2" of line on each side. The mass on each side of the three lifting points would be the same!
    Goodbye line dump forever! Enough tech talk, let's stow the lines!
    When stowing lines (post locking), simply bring the "bite" of lines through the proper center loop "on it's way" to being stowed. The bite of lines passes very easily through these loops because of there larger size. However, they do not hold the line with a tight grip. There is no need for that as the mass/load is equal on both sides.
    The need for very tight stows is no longer needed for the last four stows-because of equal mass on each side of the stow.
    I have had great on heading openings, with the exception of minor line twist on a few openings.
    As of 7-6-01 I have 300+ deployments on one of my prototype sleeves. Some of the early deployments were done with a psycho roll from the top, and one was S folded in the container. I believe that the psycho roll can increase the likelihood of line twist and a line over malfunction. It also does not fill the container very good.
    The best method is the one described earlier in the text.
    Interesting information: At line stretch the sleeve inverts from the top down. The mouth is the last to invert.
    Note: The four post locking stows/elastics are original after 300+ jumps--they still look new!
    I have built five new sleeves for field evaluation as of late 98.
    David B. Brownell
    DB Technologies
    Mesa, AZ.

  7. I've had D-bags made from 1.9 Nylon ripstop, but never F-111 or ZP.
    I do see a durability issue with F-111 or 1.2 ZP.
    The Nylon mesh idea sounds sounds good--maybe I should build one of my ram-air sleeves with Nylon mesh for faster compression of the canopy. (loaded sleeve compressed when installing in container)
    Dave Brownell

  8. I've heard that Mike Mullins's King Air has been down with a blown engine since the sixth--no call yet as to when he will be up and running. I heard this today from Bob Sinclar at Eloy--he normally resides/jumps at Coolidge in the winter.
    Dave Brownell

  10. I went to Skydive Arizona at Eloy today (Sun) after not jumping for five weeks!--(holidays/severe chest cold) The first skydive I was on, was a four way RW jump, out of a Super Otter, 'planned' for 13.5K feet AGL. Our four way was to follow out a larger RW group, about 10 seconds after their exit.
    I was sitting on the bench seat near the rear of the plane directly across from the front edge of the door. At about 8000 feet AGL, there was a very loud bang and turbine scream, followed by an adverse yaw corrected 'now' by the pilot, and a quick nose pitch-over, also done by the pilot during this 0-2 seconds!
    I knew that it had to be a case of catastrophic engine failure! It was the right engine that failed--the right engine is not the critical engine, so that fact helped performance on only one engine. (left engine running) This engine failure happened several miles from the DZ. The pilot maintained 8000+ feet AGL to a normal jump run ground track to the spot, at which time we exited without floaters, as per the pilot's instructions.
    This is just one more example of ongoing aircraft operating costs, as this latest loss will cost Skydive Arizona plenty. A new engine is $250,000.00- much less for a mid time.
    Dave Brownell
    Mesa, AZ

  12. Alan said--
    That is odd. One of the properties of Spectra is that it is more dimensionally stable than Dacron or the gutted 550 that is commonly used for main closing loops. It is less resistant to damage from heat though and is more likely to shrink than stretch. Typically, the standard reserve closing loop that comes from the mfgr is Spectra because it doesn't stretch, among other reasons. The CYPRES loop is Spectra. It has not been widely used as a main loop because it is so easily damaged by the friction heat generated by someone zipping out a pull-up chord.
    DB> You beat me to it--I totality agree with your post. I'm using 1000lb Spectra for a main closing loop, because of it's stability and longevity. And yes, I never withdraw a pull-up cord without first bringing it under the pin, to avoid heating the Spectra.
    BTW-I use a 550lb Spectra 'loop' for a pull-up cord. (17" laid flat)-works great.
    Dave Brownell

  13. I totally agree with TK on his numbers presented--I've always said that PC's in tow are caused by bridle routing factors, not tight closing loops.
    We've left one cause out here--and that is an actual pilot chute malfunction, which again, is usually bridle related-(as rare as it is)
    Dave Brownell

  14. As I recall, I made up a 10" bridle extension, for psycho packing of a Triathlon 160 I once owned. I kept the bridle in the center of the canopy, as I rolled it up. (highly recommenced)
    Dave Brownell

  15. >>If we assume that the Cypres's current draw is 0.5 milliamp (0.0005 amp) during
    >> an 'on' period, of let's say, five hours, that would calculate to 54 watt seconds of
    >>that energy-or 150 times the battery energy that would be needed for shutdown!
    >>5 hrs is 18,000 seconds)
    >I think that's a bit high. The 16LF877 from Microchip (typical FLASH
    >based controller) takes 600uA at full speed, 35uA at low speed, and 1 uA
    >when sleeping. If the CYPRES processor spends most of its time sleeping
    >when on the ground (a scheme any sane programmer would implement) and it
    >uses a similar processor, then you're looking at an average current of 1.5 uA, or 9 uW.
    >Over 14 hours, that's about .45 watt-seconds, comparable to your estimate for the
    >.36 watt-seconds needed for shutdown.
    -bill von
    DB> 1uA when sleeping-600uA at full speed--Do you know what the quiescent current is external to chip components--current level at the altitude sensor?--leakage current at fuseable link driver--(probably a pwr mos fet)
    Dave Brownell

  16. >Get a Kill line PC. It will make a huge difference in the way any canopy flys.
    >Especially if it's a breazy day. I have seen it deform even the largest student
    >canopies on breezy days.
    What do you mean!? The forward 'airspeed' is the same--breezy day or not!
    Dave Brownell

  17. Lisa said--
    >Airtec recommends letting the Cypres turn itself off. They say turning it off takes more
    >out of the batteries than letting it stay on 14 hours and turn itself off.
    DB> Is this what SSK Industries says, is it Airtek, or is it the designers themselves?
    Show me the numbers that support this claim.
    Dave Brownell

  18. >>"uses more power to shut a Cypress off, then to just let it turn off automatically"
    >That's what I've always been told. It makes since.....to turn that little light on 3 times
    >and running the computer 3 times instead of just once for the auto shut off.....
    DB> Until proven otherwise with data from the designer, I consider this total fallacy.
    An LED's current is about 12 milliamps (0.012 amps) The total time this LED is on when shutting down is about maybe five seconds. The energy the LED uses during this five seconds far exceeds the energy consumed by the computer 'during the shut down period'
    If we assume 0.012 amps at 6 volts for 5 seconds, that would be 0.36 watt seconds of energy.
    If we assume that the Cypres's current draw is 0.5 milliamp (0.0005 amp) during an 'on' period, of let's say, five hours, that would calculate to 54 watt seconds of energy-or 150 times the battery energy that would be needed for shutdown! (5 hrs is 18,000 seconds)
    Dave Brownell
    DB Technologies

  19. This is an earlier post regarding the question of ear problems. db
    I would not jump with a cold/sinus congestion, but if you feel it's minor, then---
    If your Eustachian tubes are relatively clear, you should be able to clear/pop your ears by blowing on your pinched nose "slightly," thus, pressurizing/clearing your ears. (equalizing/creating pressure in the middle ear space)
    As we ascend to higher altitudes the expanding air in the middle ear space exits easily through the Eustachian tubes. It's the re - pressurization of the middle ear space on descent that presents varying problems for many people. (like a check valve)
    I recommend never jumping with a cold, as this can drive mucus into the middle ear space via the Eustachian tubes, (when/if your middle ear spaces try to equalize/clear during the jump) possibly causing a middle ear infection. (or worse) If your ears do not equalize/clear on descent this 'can' result in a ruptured ear drum. The potential for a ruptured ear drum will depend on the absolute pressure in the middle ear space at exit, and the altitude that will be descended, and of course, if your ears don't equalize/clear. (air entering into the middle ear space via the Eustachian tubes)
    A good rule of thumb is; if you can clear/pop your ears by blowing on your pinched nose slightly, on the ground, and at jump altitude, you are probably OK to jump. There is also a slight plus here at altitude, as you are slightly pre-pressurizing the middle ear spaces before the jump. (as long as you don't swallow after) HA-HA All of the above will all but eliminate the chance of a ruptured ear drum. As said before, I recommend never jumping with a cold.
    BTW: Ruptured ear drums normally heal with minimal scar tissue, but I would listen to your doctor as far as returning to jumping. (and only when I could pressurize/clear my ears with minimum sinus pressure. (nose pressure)
    Decongestants can also help clear your sinuses after a cold.
    Yes, I do Scuba dive also.
    Dave Brownell
    Mesa/Eloy, AZ

  22. This is an earlier post regarding the question of ear problems. db
    I would not jump with a cold/sinus congestion, but if you feel it's minor, then---
    If your Eustachian tubes are relatively clear, you should be able to clear/pop your ears by blowing on your pinched nose "slightly," thus, pressurizing/clearing your ears. (equalizing/creating pressure in the middle ear space)
    As we ascend to higher altitudes the expanding air in the middle ear space exits easily through the Eustachian tubes. It's the re - pressurization of the middle ear space on descent that presents varying problems for many people. (like a check valve)
    I recommend never jumping with a cold, as this can drive mucus into the middle ear space via the Eustachian tubes, (when/if your middle ear spaces try to equalize/clear during the jump) possibly causing a middle ear infection. (or worse) If your ears do not equalize/clear on descent this 'can' result in a ruptured ear drum. The potential for a ruptured ear drum will depend on the absolute pressure in the middle ear space at exit, and the altitude that will be descended, and of course if your ears don't equalize/clear. (air entering into the middle ear space via the Eustachian tubes)
    A good rule of thumb is; if you can clear/pop your ears by blowing on your pinched nose slightly,
    on the ground, and at jump altitude, you are probably OK to jump. There is also a slight plus here at altitude, as you are slightly pre-pressurizing the middle ear spaces before the jump. (as long as you don't swallow after) HA-HA All of the above will all but eliminate the chance of a ruptured ear drum.
    As said before, I recommend never jumping with a cold.
    BTW: Ruptured ear drums normally heal with minimal scar tissue, but I would listen to your doctor as far as returning to jumping. (and only when I could pressurize/clear my ears with minimum sinus pressure. (nose pressure)
    Decongestants can also help clear your sinuses after a cold.
    Yes, I do Scuba dive also.
    Dave Brownell
    Mesa/Eloy, AZ

  23. Justin asks--
    Dave,
    For those of us that are pretty much skydiving newbies, could you explain what "bag strip" is in simple terms? I have a vague idea, but I could be wrong.
    DB> If we have, let's say, 200 lbs of pilot chute drag. (200 lbs on bridle) That would also translate to the canopy 'assembly' pushing on the bag closing flap with 200 lbs at bag launch!
    For the record--this translates to 32 G's of bag acceleration! (200 over 6 minus 1)
    (32 G's with a 6 lb canopy)
    Looking at the mechanics of a closing flap--half of this 200 lbs is shared by each end/side of the closing flap. (100 lbs ea side) This now means that the two locking stows each have 50 lbs of tension on them at bag launch! (locking stows stretched out much at bag launch)
    Bag strip/definition--If the locking stows fail at 'bag launch'--this will result in the canopy remaining just above the rig, with the free bag long gone!--or (worst case scenario) in the pack tray, with the free bag long gone!
    When Para Flite first came out with the reserve free bag system on the Swift system back in the early/mid eighties, they used Mil-spec rubber bands for the two locking stows. This system was TSO'ed. Shortly after it's release, there was a least one fatality due to bag strip! The one I recall, was at Quincy. This was with one pilot chute-not two!
    As I recall, shortly after that, they went to the 1/8" elastic bungee that we see today. (rigs were recalled) The 1/8" bungee is a continuos 'laid flat loop' with each end of the loop being a locking stow.
    Dave Brownell

  24. Other than the reasons stated by others in the industry, I will not use the Catapult system, for reasons of potential bag strip, due to two times the 'usual' pilot chute drag at any said deployment speed. The drag of two inflated pilot chutes can easily exceed 140 lbs at 120 MPH. (200+ lbs at 150 MPH)
    Dave Brownell
    Reflex owner