Quantcast

Ejection Charges

The Rocketry Forum

Help Support The Rocketry Forum:

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
Ok, So im assembling my Av bay tonight, Was wondering if it would be better to put both charge wells on the top for the main, or to put one up top and one for the drogue. I think i can compensate the amount of 4F to ensure the main, and the aft well for a motor backup.

Anyone care to show some AV bays, im open to ideas. !!

I have an RRC3 as well as an Eagle Tree Elogger package.
(https://www.eagletreesystems.com/index.php?route=product/product&product_id=54)

Thanks
Tom
 

timbucktoo

Well-Known Member
Staff member
TRF Supporter
Global Mod
Joined
Jun 13, 2014
Messages
8,115
Reaction score
1,279
Location
Cocoa Beach
If you put both charges on top you will probably blow the main at apogee (if I understand your setup).

ImageUploadedByRocketry Forum1501073069.855079.jpg
2.6" airframe

ImageUploadedByRocketry Forum1501073084.850708.jpg
Main side

ImageUploadedByRocketry Forum1501073097.050860.jpg
Drogue side
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
the RRC3 has a connection for the drogue as well as the main, Im concerned about the motor having a failure, as well as not being able to pop the main.

If I put both up top, it remedies my "main" worries.
If I put on up top and one down bottom it semi quells my fears but not all together..
 

rharshberger

Well-Known Member
Joined
Oct 13, 2014
Messages
9,795
Reaction score
1,766
Location
Pasco, WA
Should I vent the top AND bottom of the AV bay, other than the vent band ?
Yes, the vents are for the payload bays, static ports ("vent band" aka switch band) are for the altimeter to sample the air pressure, the avbay should be sealed completely from the payload bays.
 

djs

Well-Known Member
Joined
Jul 27, 2014
Messages
3,367
Reaction score
250
Vent on the top and bottom is probably not the right word.. you're looking for "holes for charge wires to run through", which are usually as small as you can make them.

If you're looking to go dual deploy, then you should have one charge on each end, with the drogue set for apogee, and the main set for a certain altitude. I would recommend testing on a lower altitude motor so you can see if everything "works" as planned.

Normally, I'm not worried about the main coming out as much as just making sure the rocket "splits" with the drogue deployment- either by drogue charge or motor eject. This way, I may not have a soft landing, but at least I'm not coming in ballistic. Then again, I'm flying fiberglass rockets, which can take a little bit of a beating if they don't have a main charge.
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
Ok, So im assembling my Av bay tonight, Was wondering if it would be better to put both charge wells on the top for the main, or to put one up top and one for the drogue. I think i can compensate the amount of 4F to ensure the main, and the aft well for a motor backup.

Anyone care to show some AV bays, im open to ideas. !!

I have an RRC3 as well as an Eagle Tree Elogger package.
(https://www.eagletreesystems.com/index.php?route=product/product&product_id=54)

Thanks
Tom
So, if I understand this correctly, you are using motor ejection as the primary method for deploying your drogue chute. You have 2 channels on the RRC3 and you want to know if you should use both on the main ejection or one on the main and one on the drogue. Did I get that right?

Based on the above, I would put one on the drogue side and one on the main side and set the RRC3 to pop your drogue charge at apogee

Consider the failures:
  • The most damaging failure you could have is not popping the drogue at apogee. That leads to most likely a ballistic recovery or you pop your main at high speed and most likely shred a good chunk of your rocket.
  • If your main doesn't come out, the rocket hits harder under drogue. Since it's a fiberglass rocket, there is a decent chance it comes out unscathed or with minimal damage.

I would configure the system to mitigate as much as possible the catastrophic failure of not popping the drogue. This configuration also helps if the motor delay is late.

Also, if you wire both charges for your main (one backup, one primary) the only things you are protecting against is the charge not being big enough to blow the main (a risk you should have practically eliminated with ground testing) or the ematch being bad (measuring the resistance of the matches should mitigate this risk). That configuration does not protect you from altimeter or battery malfunctions.
 

Zeus-cat

Well-Known Member
Joined
Mar 14, 2009
Messages
4,595
Reaction score
800
After I run the wires for the ejection charges through the bulkheads I seal the holes with epoxy. You don't want any of the ejection charge gasses to enter the avbay.
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
After I run the wires for the ejection charges through the bulkheads I seal the holes with epoxy. You don't want any of the ejection charge gasses to enter the avbay.
Use well nuts, they are removable and seal just fine. This also means you don't need terminal blocks because you can run the ematch leads through the well nut hole into the bay.
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
So, if I understand this correctly, you are using motor ejection as the primary method for deploying your drogue chute. You have 2 channels on the RRC3 and you want to know if you should use both on the main ejection or one on the main and one on the drogue. Did I get that right?
100% correct ! And Thank you for answering my question !!
 

Exactimator

Well-Known Member
Joined
Feb 17, 2014
Messages
861
Reaction score
152
So, if I understand this correctly, you are using motor ejection as the primary method for deploying your drogue chute. You have 2 channels on the RRC3 and you want to know if you should use both on the main ejection or one on the main and one on the drogue. Did I get that right?

Based on the above, I would put one on the drogue side and one on the main side and set the RRC3 to pop your drogue charge at apogee

Consider the failures:
  • The most damaging failure you could have is not popping the drogue at apogee. That leads to most likely a ballistic recovery or you pop your main at high speed and most likely shred a good chunk of your rocket.
  • If your main doesn't come out, the rocket hits harder under drogue. Since it's a fiberglass rocket, there is a decent chance it comes out unscathed or with minimal damage.

I would configure the system to mitigate as much as possible the catastrophic failure of not popping the drogue. This configuration also helps if the motor delay is late.

Also, if you wire both charges for your main (one backup, one primary) the only things you are protecting against is the charge not being big enough to blow the main (a risk you should have practically eliminated with ground testing) or the ematch being bad (measuring the resistance of the matches should mitigate this risk). That configuration does not protect you from altimeter or battery malfunctions.
+1 for all the reasons listed.

And +1 to the responses about sealing your av bay from the payload and booster sections to prevent ejection gasses from hitting your electronics. Epoxy, hot glue, clay all work. The vents holes go in the switch band.
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,740
Location
Maryland
This whole discussion is moot, because you can't program the drogue charge of an RRC3 for a set altitude. Your options are apogee +1, +2, +3, etc.

May I recommend you purchase and read the dual deployment chapter of Modern High Power Rocketry 2? Sounds like you will need to learn a lot about how to size your charges, static ports, shear pins, drogue, and a host of other things.
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
This whole discussion is moot, because you can't program the drogue charge of an RRC3 for a set altitude. Your options are apogee +1, +2, +3, etc.

May I recommend you purchase and read the dual deployment chapter of Modern High Power Rocketry 2? Sounds like you will need to learn a lot about how to size your charges, static ports, shear pins, drogue, and a host of other things.
Modern High power rocketry, as in the E book I bought 9 months ago? Or the static ports that NEED to be in the Vent band? Or the nylon sheer pins ? or the drogue and its size in relation to the weight of my loaded rocket?

Im sorry, I should have titled the thread, "this is my first dual deployment and im scared out of my mind, and for the past 2 weeks I have been non stop worrying about the what if's"

So.. whats a better place to ask than to ask the SAME people who have more experience and have already learned what To do and what NOT to do.

your right by the way. I do have a lot to still learn.
 

djs

Well-Known Member
Joined
Jul 27, 2014
Messages
3,367
Reaction score
250
Im sorry, I should have titled the thread, "this is my first dual deployment and im scared out of my mind, and for the past 2 weeks I have been non stop worrying about the what if's"
Gotta start somewhere- and better to ask questions than start wiring things up that you don't understand.

I missed your other thread- what rocket is this? Kit or scratch built? That will help determine drogue size.

an RRC3 is a good altimeter. It's programmable, but honestly, the "default" settings work just fine (assuming you bought it new). Drogue goes below the av bay, main goes above. Shear pins should be between the upper payload bay and the nose cone. AV bay should be semi-permanently attached to upper payload bay so it doesn't separate when the main charge goes off. I use a machine screw for this. What size shear pins are you using and how many?

Do you know what size to make the static ports? It's in the RRC3 manual, but can be a little complex to figure out from their instructions. Generally it should be an odd number (I use 3), and larger is better than smaller (within reason).
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,740
Location
Maryland
Modern High power rocketry, as in the E book I bought 9 months ago? Or the static ports that NEED to be in the Vent band? Or the nylon sheer pins ? or the drogue and its size in relation to the weight of my loaded rocket?

Im sorry, I should have titled the thread, "this is my first dual deployment and im scared out of my mind, and for the past 2 weeks I have been non stop worrying about the what if's"

So.. whats a better place to ask than to ask the SAME people who have more experience and have already learned what To do and what NOT to do.

your right by the way. I do have a lot to still learn.
No insult intended. It's just that in a forum, you get people's scattered thoughts and preferences, whereas in the book, you get detailed instructions and pictures.
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
Scrab 54 Fiberglass, 38mm.

its a 54mm Tube, and the manual says 2-1/8 holes, I however was opting for 3- 5/32 holes in the vent band.

The RRC3 is brand new. The Eagle tree is also brand new.

The av bay is the only thing that doesn't fit really snug, and I also was going to use machine screws that way I have complete access to it if I want to move the bay from bird to bird.
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
No insult intended. It's just that in a forum, you get people's scattered thoughts and preferences, whereas in the book, you get detailed instructions and pictures.
No insult taken. Just scared outta my mind honestly. Pictures and words are just that. Experience to me trumps both.
 

djs

Well-Known Member
Joined
Jul 27, 2014
Messages
3,367
Reaction score
250
Scrab 54 Fiberglass, 38mm.

its a 54mm Tube, and the manual says 2-1/8 holes, I however was opting for 3- 5/32 holes in the vent band.

The RRC3 is brand new. The Eagle tree is also brand new.

The av bay is the only thing that doesn't fit really snug, and I also was going to use machine screws that way I have complete access to it if I want to move the bay from bird to bird.
Ok- I had the same rocket- flew it many times until it had a unforeseen rapid disassembly on an EX motor.

To be honest, I flew this rocket drogueless. Drogue chute was always too big- too much drift. What I did do though was keep a nomex chute protector (but no chute) attached to the drogue line. This acted like a streamer, I guess, without allow it to get tangled.

3- 5/32 holes should be just fine.
 

KennB

I-95 Envoy
TRF Supporter
Joined
Mar 6, 2010
Messages
2,441
Reaction score
239
Location
Amesbury, MA
Tommy,
As I'm going to be sitting under where your rocket is going to go up, I vote with the folks that are recommending using one of the charges to ensure drogue deployment. As stated elsewhere, at least breaking the rocket apart will lessen the chance of an invisible, ballistic recovery.
 

ttabbal

Well-Known Member
Joined
Jan 19, 2009
Messages
1,082
Reaction score
22
The static ports don't NEED to be in the switch band, that's just where it makes sense to put them if you happen to have one. You need a place that cannot be blocked by the parts shifting in relation to each other etc. and the simplest way is the switch band. Same reason you put the switch there. There are loads of other ways to do it, but for a first go at dual deploy, the classic design is simpler and less likely to cause issues for you.

Shear pins are not really required, though they do help a lot to prevent main at apogee. You could, for example, make it a tighter friction fit with masking tape. But the pins are more reliable. Whatever you do, ground test over and over to ensure you know what happens with a couple charge sizes. You want to KNOW that the pins will shear and the nose will separate with (for example) 1g of powder the way you pack it in your charge holders. You also don't want so much that the recovery system has to absorb huge shock loads from the charge. I like to ground test till I get the same results with the same charge at least 3 times. For most rockets, #2 nylon screws are a good choice. For the apogee event, you might not need pins. Many people just make a snug friction fit. All you need to prevent is drag separation, so a small vent hole in the body tube and a snug fit is generally good enough. If you want to be really sure, you can pin it. Either way, ground test.

Drogue size isn't that important and there is room for a lot of debate on the ideal size. My opinion is that having a small drogue is good, but it doesn't need to be much. You want the parts falling at a pretty good clip. I've done drogueless with just the harness holding the parts together as well. It works, but it seems more prone to tangling the main so I don't do it anymore. I want the parts to fall in an inverted "V" shape, too much drogue makes them parallel to each other, increasing the risk of tangling the main.

As mentioned, the apogee, NOT the main, is the important event. If your rocket and motor allow for it, use the motor eject as a backup apogee event. Just use a delay a couple seconds longer than you would use normally. Perhaps increase the powder in it. The idea being that if the apogee event fires but doesn't separate, use more power for the backup.

Make sure the powder can't move in relation to the ematch. If it's anywhere close, it will "probably" work, but that's not good enough in my opinion. I want to know it will work. I pack it with dog barf and tape over the end to make sure things aren't moving around in flight. Another option is to not pour loose powder in at all, put it in some sort of container and seal the match in there.

Take a breath and relax. Overthinking and over-worrying will make it worse and make mistakes more likely. Make a checklist, and follow it. Make certain that you don't put things in backwards, main at apogee is more likely that way.

I can't stress this enough... REMEMBER TO ARM YOUR ELECTRONICS. :)
 

djs

Well-Known Member
Joined
Jul 27, 2014
Messages
3,367
Reaction score
250
Lots of good advice here. One thing about electronics- learn what "good" is supposed to sound like. An RRC3 will have different beeps depending on if the drogue, main, or both are connected. I've had to pull rockets off the pad because I only got continuity on one channel (drogue, but not main, or vice versa). I knew this because of the beeps. Usually it's just a loose wire issue that's fixed quickly back at my car, and it's back out to fly again.

Not sure where you are launching this, but if you ask someone on site who seems like they know what they're doing, they most likely would be glad to offer advice. Especially, as was mentioned above, they don't want a rocket coming in ballistic nearby them!
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
Tommy,
As I'm going to be sitting under where your rocket is going to go up, I vote with the folks that are recommending using one of the charges to ensure drogue deployment. As stated elsewhere, at least breaking the rocket apart will lessen the chance of an invisible, ballistic recovery.
Kenn, its you whom im trying to impress...
 

Titan II

Well-Known Member
Joined
Aug 24, 2013
Messages
968
Reaction score
153
BTW.....you can program a drogue charge on a RRC3 for a set altitude.....you use the aux channel. That being said.....

Keep it simple for now. Set the RRC3 for drogue at apogee and main at whatever you decide. Use the motor as the secondary drogue charge if the delay is long enough.

For the future....I use the aux to fire a secondary main in single altimeter rockets (which is rare), but would not recommend this until you have a better understanding of the RRC3 and dual deploy dynamics in general.
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,740
Location
Maryland
Here is a couple of pictures that may help. The wiring diagram for my L3 bird, and the actual picture of it.

L3 Wiring.png

av-bay.jpg
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
Scrab 54 Fiberglass, 38mm.

its a 54mm Tube, and the manual says 2-1/8 holes, I however was opting for 3- 5/32 holes in the vent band.

The RRC3 is brand new. The Eagle tree is also brand new.

The av bay is the only thing that doesn't fit really snug, and I also was going to use machine screws that way I have complete access to it if I want to move the bay from bird to bird.
3 holes 5/32" diameter will be fine. I wouldn't even mess with setting the RRC3 and just run it on the standard settings.


Take a deep breath and relax. The Av-Bay not fitting snug isn't too big of a deal. If you are worried about it, you can pin the drogue end with shear pins too. Most important things:

  • Make sure things are secure on the sled. Zipties can help with the battery.
  • Figure out how you're going to arm it. The switches should be accessible from the vent holes. Try to get them as close as possible to the hole.
  • Ground test your charges. Load everything up, shear pins in, and then fire the charges in your backyard, preferably at 1 in the morning. Easiest way is to run the ematch leads through a vent hole. You are testing that your charge configuration is good enough to separate the rocket. Test both the drogue and the main. Be sure to stuff a motor case or shirt or something in the motor mount tube to simulate having a motor installed and prevent the gas from escaping out the motor tube.
  • Before you make the charges, hook the ematches you are using up to the RRC3 and run a bench test. Make sure the RRC3 beeps out good continuity. Turn the RRC3 off and prepare the charges.
 

djs

Well-Known Member
Joined
Jul 27, 2014
Messages
3,367
Reaction score
250
preferably at 1 in the morning.
This is probably not good advice :)

Actually, charge testing a rocket like this isn't as loud as you think it would be. It's more startling. I use my aerotech launch controller to test the charges- that way I'm a good 20 feet away from it.

The goal is to be looking for the rocket parts to separate, the chute to come out, but not separate so far that it reaches the end of the shock cord and snaps back. If it's doing that, you have too much charge.

If everything works well, then do it again with the same size charges, to make sure it's repeatable. Some people keep trying smaller and smaller charges until it stops working, and then go to the size that's marginally enough to separate the rocket. I don't really think this is a good idea.

Finally- make sure you attach all quick links, otherwise you'll accidentally shoot your nose cone into the fence, leaving a dent on the fence, and blunting the tip of your nose cone. Don't ask how I know this.
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
This is probably not good advice :)

Actually, charge testing a rocket like this isn't as loud as you think it would be. It's more startling. I use my aerotech launch controller to test the charges- that way I'm a good 20 feet away from it.

The goal is to be looking for the rocket parts to separate, the chute to come out, but not separate so far that it reaches the end of the shock cord and snaps back. If it's doing that, you have too much charge.

If everything works well, then do it again with the same size charges, to make sure it's repeatable. Some people keep trying smaller and smaller charges until it stops working, and then go to the size that's marginally enough to separate the rocket. I don't really think this is a good idea.

Finally- make sure you attach all quick links, otherwise you'll accidentally shoot your nose cone into the fence, leaving a dent on the fence, and blunting the tip of your nose cone. Don't ask how I know this.
I am glad someone caught that little gem. Let's me know you're reading my post. Your right, 1am isn't the best time to do it...:wink: Also, +1 to everything you said about ground testing.
 

CPUTommy

Thrust cures All
Joined
Oct 26, 2011
Messages
1,126
Reaction score
151
Location
Massachusetts
My neighbor is a fireman and I'm a former cop, pretty sure he is cool with ground testing, I skimmed the posts as I'm almost home and just picked up my $140 dollar spray paint order.
 

Bobfly

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jul 3, 2017
Messages
225
Reaction score
65
Hi Tom,

The RRC 3 is a great altimeter. I own about a dozen of them. Each of my rockets has one or two RRC 3's installed in its AV Bay. I prefer to fly all of my 4" or larger rockets with two RRC 3's for total redundancy. That's two seperate altimeters, two seperate batteries, and two seperate sets of ematches in two seperate black powder cups. That's two seperate ejection charges for apogee and two seperate ejection charges for the main Parachute.

I just completed a 3" rocket that does not have room for two RRC 3 altimeters. For this rocket I am using the RRC 3's drouge output for the primary drouge deployment at apogee. The motor charge will serve as the drouge backup. The RRC 3's main output will serve as the primary deployment charge for the main parachute. The RRC3's third output will activate a second deployment charge for the main parachute.

I highly recommend that you purchase the LCD accessory for the RRC 3. The LCD makes programming and testing the altimeter much easier. Someone else made a good point about the ground testing. That's a great idea.

Good Luck,
Bob
 
Top