Dual deployment ejection (point of failure)

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Atlasboy

Well-Known Member
Joined
May 27, 2012
Messages
282
Reaction score
0
I'd like to do my launch build on a couple of dual deploy rockets a couple of weeks before launch because of some personal timing issues (obviously I'll do the engine build on site). I am mildly concerned about the following and am looking for some ideas to solve the concern. Specifically, I typically handle my dual deploy charges as follows. I connect the Quest Q2G2. I put it firmly into the bottom of the ejection charge well and then pour in the computed amount of 4f black powder. I then fill any remaining space with a flame retardant insulation and cover with metallic HVAC tape. I've used this process for many years and so far (fingers crossed) never had a deployment failure.

My concern is that I'd imagine it is at least possible that the tape could loosen after a week or two in which case either before or during launch the black powder might migrate out of the ejection charge well. I've thought of maybe using a glue gun on the edges of the metallic tape once on or perhaps a fastener of some sort around the tape (a plastic pull tie for example). Anyway, looking for something that will reduce the chances of this potential point of failure. Thanks.
 
Personally, I use centrifuge tubes, but I've seen people use rubber bands around the end of the charge well (holding down the tape).
 
Personally, I use centrifuge tubes, but I've seen people use rubber bands around the end of the charge well (holding down the tape).

+1 on that. For smaller charges of <2 g, I use 1.5 ml centrifuge tubes. They snap shut. For larger charges, I use a 15 ml centrifuge tube. I've never had duct tape pull off of those. They do an excellent job of containing the charge in a very reproducible manner. Consistency and reliability is key.
 
I use masking or blue tape. A strip or two over the top so it's secure. If I feel like I need to, I'll add a wrap around the well over the ends of the other strips. I pack the dog barf in pretty tight so nothing can shift.

Sometimes I end up not launching the prepped rocket, take it back home and fly it a month later. I double-check them before I launch, including giving the ematches a quick pull test to make sure they're secure in the terminal strip on the av bay cover. Never had a problem with things coming loose.
 
Never had metal duct tape come off anything I put it on, even months-years later.
I did fly one rocket with metal charge cups prepped over a year & everything was fine. [charge covered/sealed with aluminum duct tape]
 
Masking tape, here. Lasts for months. One wrap around the outside to hold in the e-match. Fill with BP and dog barf, two pieces over the top in an X shape, then one more wrap around the well.
 
As CJ said, the adhesive on metallic duct tape is really sticky and long lasting. I think your method with ematch, powder, pack with dog barf, cover securely with the metallic tape is just fine. The centrifuge tube method is good too, but to each his own.

As for leaving built charges with matches in powder around...well...keep 'em safe.

Mark
 
Centrifuge tubes for me too. Cut the bottom off and hot glue the ematch into place.

I do it a little easier. I drill a hole in the bottom, wrap some poster tape (sticky tack) around the bottom of the ematch, then pull it down thru the hole. The sticky tack plugs the hole. Then fill with BP, dog barf, and snap the tube closed. I do them in assembly line type fashion, so I can make them up pretty fast.
 
I use centrifuge vials and cylindrical foam ear plugs to fill the empty space. Maybe 10 cents of materials, no tape needed. Using J-Tek's, I haven't had a failure yet with various Ravens and Eggtimer altimeters. <knocking on wood>
 
Never had metal duct tape come off anything I put it on, even months-years later.
I did fly one rocket with metal charge cups prepped over a year & everything was fine. [charge covered/sealed with aluminum duct tape]

CJ, as is common, is correct about aluminum tape. The stuff is great.


Sent from my iPhone using Rocketry Forum
 
OP, you’ve had success for years the way you currently do it. I would not change a thing from what has worked for you. The duct tape will hold just fine.
 
Has anyone ever had or heard of any issues with leaving an ematch in contact with black powder for an extended amount of time (3 months or more) other than the safety risk. I thought I heard someone mention that the powder will corrode the ematch after some length of time.
 
Has anyone ever had or heard of any issues with leaving an ematch in contact with black powder for an extended amount of time (3 months or more) other than the safety risk. I thought I heard someone mention that the powder will corrode the ematch after some length of time.

Unless it’s stored in a very humid environment it should be fine. I’ve had BP charges left in my garage for several months with no ill effects. BP is really only corrosive after its been burned or ignited. Think about it. It’s sold in steel containers.
 
Has anyone ever had or heard of any issues with leaving an ematch in contact with black powder for an extended amount of time (3 months or more) other than the safety risk. I thought I heard someone mention that the powder will corrode the ematch after some length of time.

I've had a fully prepped rocket sit for a year and a half in my basement and flown with no problems.
 
The Al tape is commonly used in masking for electroplating, it sticks well even at temperatures above 55C in extremely acidic solutions and we have jigs it's been left on for months, probably years. Since the metal backing takes a bend and holds its shape there is no real tension or 'spring' for the glue to hold against so it doesn't tend to peel over time like normal tapes might. If really paranoid you could get some 1/16" o-rings slightly smaller in diameter than the OD of your charge well and roll that over the tube to hold the tape down, but I would say it's overkill.
 
Back
Top