Dual deploy from a single compartment? - Tether release it!

If you are flying anything over an I-class motor, then you are probably already using dual deployment in your recovery system. The problem with dual deployment is that they (usually) use 2 chambers for each parachute - one for the drogue, another for the main.

That was a problem for me with the ‘Hurricane’ rocket build. I didn’t have the space for two parachute chambers, and adding a second one simulated at a much lower altitude. What was the solution? A tether release dual deployment setup.

A tether release setup utilizes one chamber for both drogue and main parachute. When the rocket reaches apogee, everything is ejected (nose, drogue, main chute). The main is however restrained and not allowed to inflate until the appropriate altitude is met during descent. Once the rocket reaches the correct altitude, the charge for the main parachute cuts the retaining cord and allows the chute to inflate.

Some folks have drilled bullet casings in their setup. They drill the casings right through, running the retaining cord (fish line) through it, fill the shell up with black powder, and then seal it. The basic idea is to have the charge cut a string that was holding your main chute from inflating.

In the ‘Hurricane’, i basically utilized a drinking straw as bullet casings is illegal to use in my country. The straw is cut to about an inch and pierced right through the middle with a hot needle sewing needle.  A fishing line is then fed through the holes and an igniter placed on the inside of the straw. The straw is then filled with BP and sealed with hot glue or crazy glue/superglue.
































Next, I rolled the chute like normal – keeping the shroud lines on the inside. The rolled parachute is then placed in computer paper for protection – this is where some guys use nomex to make what they call a burrito for the chute. The fish line with the pyro-straw wraps around the chute really tight and tied into a knot and will hold until the pyrostraw is fired. For extra protection, a piece of aluminum tape is placed under the straw so that it doesn’t burn through the paper and burn the chute. A small square of poster board can be used here as well.


The most important part of this setup is the tether. The tether was simply a nylon cord where one end connects to the fishing line, and the other connects to the shock cord. The purpose of this is to keep the ejection forces off the parachute itself and prevents it from breaking the lead wire. I made a small video ato demonstrate what i did.

And here is a video