Plugged forward closures

[edwinshap1]

For my L1 cert, i intend to go all out. Custom minimum diameter mach buster with dual deploy. I figure if i'm going to put my bird up a mile on it's first flight, i don't want to lose it, so it's an all or nothing shot (+i still will have 2 casings, so all is not lost)

My question is: I bought a 38/240-480 set, and it comes with the normal forward closure, i'm wondering if, even with dual deploy, can I use the normal forward closure with a delay grain, but not add the ejection charge? It will contain the pressure of the propellant, but there won't be an explosion in the booster section that i'll have to worry about. What do you guys think?

 

[Gillard]

if you crumple up some estes type wadding and put it where the BP would have been with a bit of tape over it, and\or put some grease on the delay grain then there will be no problems.

however, wouldn't you be best getting your level one on a relatively standard rocket, and then go min diameter later, even if later means later that day

also, if your going dual deployment, why not use the motor ejection to split the rocket, and then let the altimeter(s) take care of the rest of the recovery?

 

[cjl]

You can fly a normal closure plugged just fine - just grease the front of the delay element when building the motor, and stick some wadding in the charge well (and cover it with masking tape or something like that).

(You definitely still need the delay though - you can't leave that out)

 

[Heisenberg]

Another option would be to use the motor ejection as a backup to the dual-deploy apogee charge. I do this all the time. Gives me some piece of mind that at least I will get the drogue out if the altimeter fails.

 

[llickteig1]

Another option would be to use the motor ejection as a backup to the dual-deploy apogee charge. I do this all the time. Gives me some piece of mind that at least I will get the drogue out if the altimeter fails.

You can do that, but a well-built and light "...minimum diameter mach buster..." could require a longer delay than some Aerotech RMS motors have available.

The techniques described by other posters will usually work just fine.. They won't absolutely prevent blow-by of the delay, which can happen in AT motors. If you have the option, acquiring a plugged closure is slightly more optimal. If you get the tapped plugged closure, you have a great place to attach your recovery system in your minimum diameter rocket by adding a welded eye bolt and jam nut.

--Lance.

 

[Rocketman248]

Why does everyone always recommend to plug and grease the forward closure when not using motor ejection? I've never done anything like that, and I've never had any problems.

Sorry, just had to get that off my chest. It's been bugging me for a long time.

 

[troj]

Why does everyone always recommend to plug and grease the forward closure when not using motor ejection? I've never done anything like that, and I've never had any problems.

Sorry, just had to get that off my chest. It's been bugging me for a long time.

It's all about mitigating potential problems. Greasing the delay inhibits the exposed side, making it less likely that you'll get "thrust" out of the forward closure.

-Kevin

 

[Rocketman248]

See that still doesn't make sense to me. Not having black powder there doesn't increase the chance of a blow-by.

I dunno. Maybe it's just me.

 

[MarkII]

Does greasing the forward end of the delay have something to do with preventing the hibachi effect?

 

[edwinshap1]

Well i figured i could grease the delay and wad the ejection well up. Also, this all comes up because if i buy a cirrus dart for my L1, i literally would only be able to launch on an H123W. any other motor would require too long of a delay, and i figure if i'm going to put hardware into the rocket to eject the chute, why not put hardware in the rocket to give it dual deploy. The thing i can't work out in my head is if the E-bay is between the chutes, and the ebay can slip in/out of the tubes it's coupled with, how do the e-charges not simply shove the chutes further into their payload tubes instead of out with the ebay.

 

[troj]

See that still doesn't make sense to me. Not having black powder there doesn't increase the chance of a blow-by.

I dunno. Maybe it's just me.

Blow by? No. But a delay that wants to burn faster than it should, especially if you used a short delay, could result in thrust out the forward end at the end of the burn.

Grease the forward end of the delay and you've made it burn more slowly.

-Kevin

 

[MarkII]

Well i figured i could grease the delay and wad the ejection well up. Also, this all comes up because if i buy a cirrus dart for my L1, i literally would only be able to launch on an H123W. any other motor would require too long of a delay, and i figure if i'm going to put hardware into the rocket to eject the chute, why not put hardware in the rocket to give it dual deploy. The thing i can't work out in my head is if the E-bay is between the chutes, and the ebay can slip in/out of the tubes it's coupled with, how do the e-charges not simply shove the chutes further into their payload tubes instead of out with the ebay.

Both CTI's and AeroTech's 29mm reloads have delays as long as 14 seconds. Wouldn't that be enough?

 

[edwinshap1]

Both CTI's and AeroTech's 29mm reloads have delays as long as 14 seconds. Wouldn't that be enough?

on the aerotech H123W yes, for any other reload it's too short...i think H242 is 15 seconds minimum, and even then it's still going up at 30+ f/s

 

[cbrarick]

The thing i can't work out in my head is if the E-bay is between the chutes, and the ebay can slip in/out of the tubes it's coupled with, how do the e-charges not simply shove the chutes further into their payload tubes instead of out with the ebay.

Because the charges just cause separation of the rocket. aAfter that we expect the cord to drag everything else out. Don't forget that when the charge blows, it imparts a relative velocity - the two tubes are accelerated away from each other, and it's up to that speed to pull out the rest of the cord and all the laundry. This is why we ground test high power rockets before we fly them...as well as starting with a known good amount (based on other flyer's experience or calculators like the one on EMRR). A good ground test should cause separation with enough force to pull the laundry out, not just cause them to come apart 3"

 

[Handeman]

Blow by? No. But a delay that wants to burn faster than it should, especially if you used a short delay, could result in thrust out the forward end at the end of the burn.

Grease the forward end of the delay and you've made it burn more slowly.

-Kevin

What you're describing is a delay that burns through before the propellant was done burning. I would call that blow-by, and some wadding in the well won't help that at all.

I have never used a plugged closure on dual deployment. I've also never greased a delay element or put wadding in the well. I've never had any kind of issue with any dual deployment flight.

If you want to grease the delay or put wadding in the well, that's fine, but I would say that is kind of like taping a pillow to the back bumber of your car. It won't hurt anything, but it really doesn't do anything for you. I have similar feelings about overbuilding a rocket, but that's just me.

 

[Adrian A]

I agree that the tape, grease, wadding etc. isn't going to prevent a blow-by situation when the motor is pressurized, but there is still a bunch of low-pressure smoke and junk that can come forward when the delay finally burns through, long after the motor is done burning, and it's good practice to block that part. I have mounted altimeters directly in front of a motor had the charge removed but wasn't plugged, and gotten some spurious recorded data when the delay burned through.

 

[edwinshap1]

Because the charges just cause separation of the rocket. aAfter that we expect the cord to drag everything else out. Don't forget that when the charge blows, it imparts a relative velocity - the two tubes are accelerated away from each other, and it's up to that speed to pull out the rest of the cord and all the laundry. This is why we ground test high power rockets before we fly them...as well as starting with a known good amount (based on other flyer's experience or calculators like the one on EMRR). A good ground test should cause separation with enough force to pull the laundry out, not just cause them to come apart 3"

alright, that's what i was thinking, but it just seemed a little too good to be true thanks