Ejection charge canisters

k3td said:

Thanks so much for the suggestion so far. I would prefer something that doesn't have to be mounted to the altimeter bay so I have the option of placing the main deployment charge at the top of the tube next to nosecone if I want to deploy the main out the bottom of the tube instead of blowing the nosecone off.

Click to expand...

Handeman said:

That seems like a good idea, but doesn't really work because of the way ejection works. The charge pressurizes the tube and unless the chute, burrito, etc. is air tight enough to act as a piston, the position of the charge doesn't make a lot of difference. You do get some force on the recovery to push the recovery out of, or into the tube, but it's not enough to overcome the much larger forces of the two halves of the rocket moving apart.

My L1 rocket was DD and used an apogee charge that was placed on the top of the motor so it pushed the recovery out of the booster tube. After a dozen flight or so, I found out it really didn't matter where the charge was placed since my apogee recovery gear didn't really seal the tube.

I used a 3" piece of duct tape, folded in half the long way, the match and powder poured into the center and the tape close around everything. Fold all the flaps together and wrap a second piece of duct tape around the charge. This still doesn't give as strong of ejection force as putting the powder in a canister, packing with dog barf, and taping with masking tape.

My recommendation is to put the charges in canisters on the end of the av-bay. Just make sure you don't over do the charge sizes, especially the apogee charge.

Click to expand...

Samuron said:

I needed something smaller, because I have a 2.6" 12" long bay, and need less than .5 grams of charge.

I found these at Home Depot; they're "SharkBite" 1/2 in. Plastic PEX Barb Plugs, 5 for $3.47.

The well is .32" x .75", perfect for what I need.

Click to expand...

KenECoyote said:

+1 My "mind sim" wink says that putting it in the nose may also increase the possibility ever so slightly of ejection gasses passing by the chute and venting out without pushing off the nose. In a way, can't the chute in front act almost like a baffle? Just my thought and I don't have evidence to back it, but I've had many flights and one big preoccupation for me is to cut down on errors/failures.

Click to expand...

Handeman said:

That seems like a good idea, but doesn't really work because of the way ejection works. The charge pressurizes the tube and unless the chute, burrito, etc. is air tight enough to act as a piston, the position of the charge doesn't make a lot of difference. You do get some force on the recovery to push the recovery out of, or into the tube, but it's not enough to overcome the much larger forces of the two halves of the rocket moving apart.

My L1 rocket was DD and used an apogee charge that was placed on the top of the motor so it pushed the recovery out of the booster tube. After a dozen flight or so, I found out it really didn't matter where the charge was placed since my apogee recovery gear didn't really seal the tube.

I used a 3" piece of duct tape, folded in half the long way, the match and powder poured into the center and the tape close around everything. Fold all the flaps together and wrap a second piece of duct tape around the charge. This still doesn't give as strong of ejection force as putting the powder in a canister, packing with dog barf, and taping with masking tape.

My recommendation is to put the charges in canisters on the end of the av-bay. Just make sure you don't over do the charge sizes, especially the apogee charge.

Click to expand...

k3td said:

Looking for suggestions and best practices on ejection charge canisters. I have aluminum charge canisters, but they are bigger than I need for 3" and 4" rockets, and I'm concerned about ensuring the FFFFg BP stays contained and in contact with the J-Tek e-matches I plan to use with my Raven 3.

I see Pratt Hobbies has canisters available that use a filament based igniter. Has anyone used these with a Raven 3?

Thanks,

Click to expand...

markkoelsch said:

The Pratt canisters work well. Used them exclusively for about 15 years.

Click to expand...

llickteig1 said:

I disagree with most of this post.

It most certainly can make a difference having the ejection charge in the opposite end of the tube where the main is coming out. A hefty charge can push the laundry up so that it gets stuck. I've had trouble with certain models with the charges above the 'chute. I switched to charge below, and it now works every time.

You absolutely DO NOT need a canister to tightly contain BP for most normal HPR flights up to say 25,000' or 30,000'. Using a plastic vial wrapped with duct tape or electricians tape will do the trick. Or the finger of a rubber glove. Or my charge containment of choice - surgical tubing.

A piece of surgical tubing with ends held tightly with strong cable ties (not the cheap thin ones) has worked for me 100% of the time on dozens of flights for 10 years or more. Jim Jarvis has proven there are limits to these, but they are extreme.

A surgical tubing ejection charge at the end of an e-match wire can be placed anywhere inside the 'chute bay you need and it will get the job done.

--Lance.

Click to expand...

cwbullet said:

I avoid centrifuge tubes in cardboard rockets because I have had the lids puncture the wall.

I have used or tested just about all of the possibilities. Gloves and tape are very cheap and they work.

Click to expand...

Handeman said:

Interesting. I posted what I did based on my experience. So far, I've never had a rocket where it mattered where the charge was placed. Obviously my experience does not mean it isn't an issue in some rockets, just that I've never had the problem. Is there a particular type or design of rocket or common conditions where charge placement becomes important?

I completely agree that you do not need a canister for BP charges. They will work just fine without. Flying on the east coast, I don't know about 25K or higher, but in our lower waivers I've never heard of an issue. My question is, have you noticed the difference between loosely contained BP charges, like in a surgical glove finger tip, and more tightly contained like packed in an av-bay mounted ejection canister with dog barf and tape? There certainly isn't a difference like a BP substitute would have, but I have noticed a distinct difference in the force of the BP charge when loosely contained vs. tightly contained. That is why I recommend a tightly contained charge.

Click to expand...

Banzai88 said:

Prep as normal, remove the lid, fill empty space with expanding foamy ear plug, seal with tape.

Click to expand...

k3td said:

Thanks so much for the great suggestions and feedback. I decided to try some of the Aerocon charge holders.
https://aeroconsystems.com/cart/electronics/black-powder-ejection-charge-holders/

One more question - I read references to using a hot glue gun to secure the e-match head inside the bottom of the canister. Is there any reason 5 minute epoxy wont work?

Click to expand...

k3td said:

Thanks so much for the great suggestions and feedback. I decided to try some of the Aerocon charge holders.
https://aeroconsystems.com/cart/electronics/black-powder-ejection-charge-holders/

One more question - I read references to using a hot glue gun to secure the e-match head inside the bottom of the canister. Is there any reason 5 minute epoxy wont work?

Click to expand...