Whete to place drogue charge on dual-deploy

[rocketcharlie]

So, I have always placed the ejection charge for the drogue chute in dual deploy, in a charge well on the bottom of the AV bay. It has always worked fine , but It seems to me when this charge fires it would tend to push the chute down inside the air frame. Wouldn't it be better to put the charge under the parachute? If anyone does it this way, could you tell me how you set this up and how you contain the BP ejection charge?

Thanks

 

[NateLowrie]

So, I have always placed the ejection charge for the drogue chute in dual deploy, in a charge well on the bottom of the AV bay. It has always worked fine , but It seems to me when this charge fires it would tend to push the chute down inside the air frame. Wouldn't it be better to put the charge under the parachute? If anyone does it this way, could you tell me how you set this up and how you contain the BP ejection charge?

Thanks

Think of it as pushing the fin can off the chute. Basically, momentum of the 2 parts separating is going to pull on the shock cord and the shock cord stretching taut is the thing that pulls the chute out of the airframe into the slipstream.

 

[Bobfly]

Hi Rocket Charlie,

I was concerned about the drouge charge placement too last year when I was working on my Level 1 and Level 2 projects. Giant Leap Rocketry suggested an old school deployment charge method. Giant Leap and many other vendors sell small plastic viles. One end of the tube has a plastic lid. You drill a small hole in the bottom of the plastic tube. This is just large enough for an ematch to slip through.

You then glue the ematch to the bottom of the plastic tube with a hobby hot glue gun. Then you can fill the tube with the correct quantity of black powder. You place some wadding in the tube and compress the lid down so that the black powder stays in contact with the ematch.

As as long as you have a long ematch wire, you can then tape the ematch down in the booster tube just above the top motor centering ring. This method works great!

All of the new rockets that I have built are setup in the more modern method of having the ejection cups just attached to the AV Bay lids. This method is much easier and works just fine. I will never again build a rocket utilizing the ejection charges installed low in the booster section. It is just too much work to setup for each flight. This is especially true since I am using two computers and two ejection charges for each event as backups.

Good Luck,
Bob

 

[mccordmw]

So, I have always placed the ejection charge for the drogue chute in dual deploy, in a charge well on the bottom of the AV bay. It has always worked fine , but It seems to me when this charge fires it would tend to push the chute down inside the air frame. Wouldn't it be better to put the charge under the parachute? If anyone does it this way, could you tell me how you set this up and how you contain the BP ejection charge?

Thanks

When the airframe separates, the top half will yank all that shock cord out along with the drogue. Don't worry about the charge being on top near the payload bay. It won't cause any problems. And remember, ground test! That will give you confidence that it all separates as planned.

 

[Bat-mite]

When the airframe separates, the top half will yank all that shock cord out along with the drogue. Don't worry about the charge being on top near the payload bay. It won't cause any problems. And remember, ground test! That will give you confidence that it all separates as planned.

In case it went unnoticed, ground test. Your charge should be big enough to separate the halves to about 75% of your harness length. This will pull out your drogue. Don't rely on guesswork.

 

[rfjustin]

When the airframe separates, the top half will yank all that shock cord out along with the drogue. Don't worry about the charge being on top near the payload bay. It won't cause any problems. And remember, ground test! That will give you confidence that it all separates as planned.

THIS, GROUND TEST.

Also, read this build thread and watch the ground testing video. Notice drogue charges placed above the drogue parachute and recovery cordage, no issues getting the sections separated.

https://www.rocketryforum.com/showthread.php?130046-4-quot-Punisher-(KCCO-The-Chive-themed)-Build-Thread

 

[Zeus-cat]

As the others have said, once the two parts separate the chute should just get pulled out; it shouldn't get stuck. If your rocket is 3 inches or larger in diameter you really shouldn't have any problems putting the harness and drogue chute in the rocket. If you don't have room either your drogue is too big or your booster section is too short. A drogue should be fairly small.

 

[ksaves2]

Doesn't matter where you put the drogue charge. Reason is usually the drogue is a small chute and will slide out easily so a "blow up" or "blow down" charge doesn't matter.

With a tight main, I like a "blow up" charge to push it out. Kurt

 

[rocketcharlie]

OK- looks like the jury is in and it's a solid verdict for it's fine to put the ejection charge above the drogue chute. Guess I was over thinking this, and I WILL do ground testing. I have just one more question though. I have heard of people using surgical tubing for the ejection charge. Where do they place this? Thanks everyone.