Knotting for weather balloon

[halofuji]

Hello,

Can someone suggest me a good knotting style to tie a weather balloon with a payload mass of about 500g? Simply put: I have a square bag that is about 800g in weight. I need to tie it to a weather balloon to send it up high. I want to know a good method to tie so that the bag wont rotate not come lose?

Thank you for your help

[Dan_Lehman]

Some photos of your equipment (what is to be tied, and what it's
to be tied to), and more description of them will help.

In general, I think I'd be looking to make some secure bindings
on the bag, which binding then would be tied to itself for the
vertical support.  Now, in order to prevent (or reduce) rotation,
there will need to be some help from the anchorage, to allow
support legs to diverge; or else one should be attaching the
bag with some non-rotational structure, not cordage.

--dl*
====

[DerekSmith]

Hi halofuji,

As you only have one fixing point to your balloon, you will not be able to stop rotation.  The slightest aerodynamic imbalance in your payload and it will spin as the balloon rises.  The only way you can stop this is with dynamic stabilisation, i.e. steering fins on your payload.  Using modern RC flight components, you should be able to do this for only a few grams of payload penalty.

As for the attachment, the key issue is that the attachment should stay fast even through the extreme buffeting that happens during most flights.  Following are instructions for a very robust attachment.

1.  Bunch (twist) up the neck of the bag
2.  Tie a Constrictor knot about mid way up the neck.
3.  get a toilet roll tube and wrap the balloon line around it six times.
4.  Make a loop in the balloon line and pass it through the middle of the tube and out the other side.
5.  Pass the neck of the bag into this loop, bend the neck at the Constrictor, and pull it gently into the tube.
6.  Gently slide all the coils of cord off the tube onto the doubled over bag neck, then tear off the tube.
7.  Arrange the coils around the doubled bag neck , so they tightly grip the area where the Constrictor sits.
8.  Tighten up all the coils

Good luck