Reefing line cutter

Hi All,

Has anybody had any experience using reefing line cutters for dual-deployment recovery? I know that they've been successfully used in amateur rocketry, but I haven't seen or heard of anybody using one in a sport rocket. I assume that's because most people tend to build kit rockets and don't build their own parachutes. However, it seems that it would be an easier way to add dual-deployment to an existing rocket, rather than the more common drogue/main setup with multiple body tube sections.

How about it folks, has anybody tried it? Does anyone know of a company selling reefing line cutters, either pyrotechnic or mechanical? Or maybe someone would point me in the direction of a web site that has information about these devices? I have a few ideas for how to design one, but it's always nice to learn from the mistakes of others.

Regards, Michael Newton

Reply to
Michael Newton
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One idea I had (I've never tried it, use at your own risk) would be to take a bit of nylon string and coat it with a mixture of glue and black powder, then at the desired moment ignite this with an electric match... it _should_ burn through the string and release it pretty effectively. (One would probably want to contain the whole assembly in a metal tube to avoid scorching surrounding materials, and running electrical connections up the suspension lines without causing tangles is left as an exercise for the reader!)

-dave w

Reply to
David Weinshenker

I've used a piece of spectra string with a pyro charge to realease a main . Cheap alternative to a Blacksky AARD. Basical I take a 3/8" od plastic tube and pass the string thru it . Stick a daveyfire in one end and seal with hot glue. Fill the other end with very thick almost dried out Ignightor man pyrogen. Tamp a little wading in to seal it. Black powder burns to fast to be reliable. Used it in several rockets for everything out the end deployment. It's small size allows dual deploy in smaller space constrained rockets. Could be used for reefing. Gary Deaver

Reply to
Deaver

I have not used a line cutter. There are two options: burn the line or cut it. Pyrotechnics are used in both cases. Others have provided ideas for burning a line.

How to you plan to initiate the line cutter? Timer or altimeter? If a timer, how will the timer be started? If altimeter you have the problem if the ejection charge tricking the altimeter into believing that it has reached a low altitute.

Deaver said: "I've used a piece of spectra string with a pyro charge to realease a main." My question: Is there any chance of the line continuing to burn?

Dean

Reply to
Dean Roth

Dave,

You wouldn't need to run electrical connections up the suspension lines, just build the entire system into a self-contained unit. The unit would be placed inline between the parachute's suspension lines and the static line to the rocket body. It would have an altimeter inside that fires a black powder charge at a specified descent altitude. The charge could either burn through the reefing line, or it could actuate a guillotine blade that severs the reefing line. The unit itself would have to be built strong enough to take the load, but that shouldn't be too difficult to accomplish. Alternatively, you could attach the unit to the static line, somewhere below the parachute risers but not inline between the two. Then it would only need to be strong enough to take the load of the reefing line.

While searching for info on these doohickeys I found a cool mechanical unit that is used on cargo parachutes. Multiple units are attached directly to the crown of the parachute. They have a pin that retracts to release the reefing lines. The problems are that they're a bit too big for smaller parachutes, and they have a built-in timer that actuates the device after a programmed delay. I didn't check, but I'll bet they're pretty expensive too. I suppose you could mount a single one of these the same way I described above, but I'd rather have a unit that's actuated by an altimeter.

Regards, Michael Newton

Reply to
Michael Newton

Dean,

There's also the mechanical option. But, I have no experience with servos, and I think a pyrotechnic device would be a bit simpler to design and possibly more reliable as well.

Can you direct me to a web site or something describing these ideas?

An altimeter. You could even use two altimeters each with its own pyrotechnic charge for redundancy.

I'm afraid I don't follow. I assume you mean the ejection charge that initially deploys the reefed parachute at apogee. But I fail to see how that could ?trick' the altimeter. Would you please explain?

I doubt that it would be able to maintain a flame in the slipstream. But, I suppose you could coat a few inches of the line with a flame retardant a bit up the line from the device. Or wrap a few inches in heat shrink tubing.

Regards, Michael Newton

Reply to
Michael Newton

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This link is to a PDF newsletter with an article from CAR's Earthrise newsletter on a parachute burrito. You may be interested in this set up. I have a Yank Mystic Buzz in which I added a small electronics bay to the nose cone for a hybrid deployment timer or altimeter and I may try this setup for dual deployment.

Layne Rossi CAR S767 L2

Reply to
L & K

This is similar to what I have done only I use a nomex parachute bag. The string and PRM hold the bag just inside the body tube. Blacksky style. Spectra is stronger and burns -melts better than nylon . Spectra fishing line works good . Ignghtor pyrogen seams too work better than black powder. Advantages are that the recovery weight is kept forward for good cg. No clean up like the mechanical devises. Gary Deaver

Reply to
Deaver

Others have posted ideas to rmr for burning a line.

Barometric rocketry altimeters detect ground at power up, apogee (lowest air pressure) then wait for a programmed low altitude (higher air pressure).

I assume you want to cut the reefing line at a low altitude post apogee. When the ejection charge fires to separate the nose cone and rocket and deploy the parachute at apogee, the altimeter for activating the reefing line cutter will be tricked into believing that the desired low altitude has been reached due to the pressure rise in the rocket.

Dean

Reply to
Dean Roth

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