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14456Re: [GPSL] Parachute positioning and balloon interference

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  • Jerry Gable
    Aug 12, 2014
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      I assume you are taking your altitude into account.  Most calculators I have seen assume you are at sea level.  The air density affects the decent rate significantly as you go up in altitude.

      You said that your payload is 18" below the chute.  I don't know if that is your shroud line length or this is below that.  Short shroud lines can greatly affect the decent speed as well.

      I like this site for info on parachutes: http://www.nakka-rocketry.net/paracon.html.  It is where I got the pattern I use for my parachutes as well as the source of most of my knowledge on the subject:)
      Jerry Gable
      Balloon Flights from APRS-IS
      Launch Notifications by email, twitter, & APRS

      From: "Michael Hojnowski kd2eat@... [GPSL]" <GPSL-noreply@yahoogroups.com>
      To: 'GPSL Balloon Reflector' <GPSL@yahoogroups.com>
      Sent: Tuesday, August 12, 2014 11:32 AM
      Subject: Re: [GPSL] Parachute positioning and balloon interference

      I'm not presently using a vented chute, though I like the idea.

      On our last launch - 150g balloon + 107g payload, it landed with 38 grams of balloon still attached,  If the chute was working fully, our descent rate should have been something like 5.0m/s.  Our actual was more like 8.9 m/s.  As it happens, our payload was fine with that, and in fact, I was ASSuming 8 m/s based on experience.  Still, it sure would be nice to work out this problem.

      I like the idea of the tension release, especially if we can realize it in 20g.  The idea definitely warrants some experimentation.

      Mike / KD2EAT

      On 8/12/2014 2:20 PM, Barry Sloan wrote:

      First thing I’m wondering is whether your chute has an air dump opening at the top. If it doesn’t I’m guessing that the chute is often swinging side to side to allow the trapped air to escape with such a light payload attached so close to the chute and attaching the payload further away may make it harder for the chute to do this. I don’t see the remains of the balloon flying around and tugging and/or hitting the chute affecting it much, but if the remains weigh as much, or much more, than your light payload they would certain increase the descent speed over what the speed with just the payload would be.
      Barry VE6SBS
      From: GPSL@yahoogroups.com [mailto:GPSL@yahoogroups.com] On Behalf Of Michael Hojnowski kd2eat@... [GPSL]
      Sent: Tuesday, August 12, 2014 11:55 AM
      To: GPSL Balloon Reflector
      Subject: [GPSL] Parachute positioning and balloon interference
      Hi Gang,

      I've done several launches where we observed the descent rate to be MUCH
      higher than the projections based on various parachute calculators.
      I've grown suspicious that the parachute's function is being severely
      hampered by the remains of the balloon flying around and tugging and/or
      hitting the chute on the way down.

      I've seen some mechanical means used to release the balloon when lift is
      removed, but we're flying very light (100g) payloads. I haven't seen
      anything that would work with something so light.

      Presently we're flying with the payload directly attached to the chute
      with short cords (maybe 18"), and the parachute then connected to the
      balloon by a much longer 10' long cord.

      Any thoughts or suggestions would be appreciated!
      Mike / KD2EAT

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