Placement of the electronic deployment charge.

Thanks guy's for your help on the baby wipes question.

Now I need some good advice about the placement of the deployment charge in an altimeter controlled rocket. The rocket in question is a 10" Thumper, about 32 pounds loaded. The altimeter bay is amidship, with a dual deployment option. For this first flight I will fly 2 redundant GWiz altimeters and have only a single apogee deployment (Keeping it very simple). There is a hole in the bays aft bulkhead for wires to an explosive charge. Do I use a 4 foot wire and place the charge's below the chute in the traditional top of the motor config ? Or will this fowl the parachute ? What's a good foolproof way to do this ?

Thank's Rocketeer in Rodeo

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I have a friend who does something like what you are suggesting, and it has worked every time. My fear would be the shock cord getting tangled up in the e-match, but he has yet to have a problem.

I have another friend who mounted a removable bulkhead inside his rocket, high enough to support the largest motor he is gonna fly. On the bulkhead he has mounts for banana plugs which are connected to the ejection charge. He has also yet to have a problem with the leads getting tangled up with the chute.

My vote is to just try it and see what happens. Being just a drogue, you're not going to be too lost if you have any problems.

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The wires on e-matches are long, yes, but that doesn't mean to extend them down to the motor. E-matches are used in the fireworks industries as well and are made for lots of different applications. For dual deployment, your wire only needs to be long enough to fit into the canister you're using to hold the black powder and connect to the terminals on the altimeter. Placement of the charge is irrelevant as all you are doing is expanding gas into a chamber.

You also should seal up any holes you run the wire through with either plumbers putty or a touch of 5 min epoxy as I've seen many do. The main thing to keep in mind is you don't want the gases to get into your altimeter chamber. Some people also use terminal blocks to avoid having to seal the holes every time. I'm curious as to how many dual deploy flights you've done and what motor your using to loft the 32lb rocket.


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. Do I use a 4

Many I know put the charge at the bottom facing up from the motor mount, so it blows everything out.

Alway seems to wrok, and I've never seen a e-match wire cause an issue on the recovery Harneses.

Now I have a friend who puts charge containers on his ebays firing down.

I've seen that actually push off the ebay and push the drouge chute back down into the body tube and foul.

if it was drougeless, then it never seemed to cause an issue.

Myself, I like the fact the charge is "blowing" the stuff I want out if it's mounted down at the bottom.

You are making a cannon, and your nomex pad is the cannon wadding and the parachute is the ball.

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Cranny Dane


I'm curious about that big rocket. I'm just starting out with a 2.25" ship with a dual deploy Perfect Flite and I sure wouldn't want to risk such a nice rocket on a first time flight. You test the deployment charges on the ground? On my little ship I am going to ground test the main by running the terminal block wires out of the vent port. Use the launch panel to test blow the nosecone off and use a parachute on it. (Won't mount the shock cord) To do the drogue. I will use an empty engine casing and run the ematch wires through the ejection charge holder of the engine and out the bottom of the EMPTY casing. Will detach the upper body tube and see if the electronics bay blows cleanly from the model with a chute. This way I can test without the electronics inside and make sure I get the 4F charge right.

Kurt Savegnago

Booms wrote:

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I've been doing it that way for years and never had a problem. What you might want to think about is to use binding posts on the bulk head for your rematch lead connection. This way if the ematche wires do get tangled with the recovery system then the rematch leads won't get ripped out the altimeter.

Ted Novak TRA#5512 IEAS#75

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You should plug (or mostly plug) the empty casing to keep the ejection gas from exiting the wrong end. If you're using a reloadable case just screw on the forward closure and run the test lead through the touch hole in the closure.

Don't point the rocket straight up for this ground test, else you'll risk landing the ejected nose cone back on the airframe. :-)

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Steve Humphrey

In all of my apogee-only rockets, I've tucked the electronics in the nose cone and use the dangling wires method a bunch, and not had a problem. I try to make the wires short enough they don't reach the parachute attachment point. A connector is on the base of the N/C to attach the leads.

A "neat" installation is to use a piece of tubular kevlar and run wiring internally, terminating in a connector attached to the recovery harness at a point far enough along that you can tuck it into the airframe ahead of the chute. When I do this, I sew a nomex blanket to the harness at the same point. This allows you to use very short leads on the ematches themselves.

Be sure to seal any holes between the charge and the altimeters. Combustion by-products and altimeters do not mix.

Kevin OClassen

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Kevin OClassen

I use terminal blocks on the outside of the bulkhead on both ends of the altimeter bay. I put the charge at the bottom near the motor to deploy the drogue chute and put the other charge near the top bulkhead to blow the main out/up -- always worked for me.

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Bruce Sexton

Well thanks a lot for the idea's, I think I'm going to go with the banana plug suggestion. Why, I even seem to have a gold female and male set on the back of this here old loudspeaker project. I'll just grap a pair of wire snippers (click, click) and I'm half way there.

Thanks for the quick and accurate help.

The Rocketeer in Rodeo.

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