What is the point of a closed forward enclosure?

[pollux]

I've got a few Aerotech reloadable cases. They came with, or the spacing kit came with, open forward enclosures. Great.

So I'm moving toward dual deployment. What is the point of getting a closed forward enclosure? I can just not put in the black powder, and leave the delay charge in for trailing smoke. And I'm good, right?

I get that some of the closed enclosures have the threaded end for attaching a rod or an eye-bolt. That is cool and I will want to do that at some point. But until then....?

 

[heada]

Most times they're tapped which allows you to use an eyebolt in the motor as a recovery attachment point.

And yes, you can just skip the BP. You should always include the delay grain.

 

[pollux]

Most times they're tapped which allows you to use an eyebolt in the motor as a recovery attachment point.

So besides that, what is the point? Is there a point?

 

[heada]

So besides that, what is the point? Is there a point?

You don't want the motor to try to pressurize the aft section of the rocket before your electronics fire the charge. Even without the BP, it does release some gases at delay burn out. With a plugged closure, there is no chance of that. Also it gives a sealed aft section so when the charge fires, you don't vent into the motor but that isn't much of a concern.

 

[blackjack2564]

If u build a minimum diam. project, it's the easiest way to attach your recovery gear. And/or you attach motor so u don't lose the case if friction fit is your method of motor retention.

 

[pollux]

You don't want the motor to try to pressurize the aft section of the rocket before your electronics fire the charge. Even without the BP, it does release some gases at delay durn out. With a plugged closure, there is no chance of that. Also it gives a sealed aft section so when the charge fires, you don't vent into the motor but that isn't much of a concern.

but that would be true even if I were using a delay charge, right? I could solve that with some tape or a plastic fitting, I’d thing. Otherwise we’d all be having problems all the time?

 

[heada]

If the motor delay is 10 seconds but you need a 12 second delay to get to apogee, then having a charge well, even if covered, will vent gases into the aft section 2 seconds early. You'd want to use a plugged closure for that.

There is a min diameter setup I was looking at that would need almost a 20 second coast time. There is no delay long enough so I have to use a plugged closure. That motor also only comes as a plugged motor. (LaserLOC 2.1 with a Loki L1400 hits 20k feet and needs a 29 second delay)

 

[Steve Shannon]

If you build a rocket that doesn’t use motor ejection, using a plugged forward completely prevents blowing hot gases into your rocket in case you have a seal failure.

 

[Buckeye]

If the motor delay is 10 seconds but you need a 12 second delay to get to apogee, then having a charge well, even if covered, will vent gases into the aft section 2 seconds early.

Hmm, I do this all the time with seemingly no ill effects. I install the delay grain, eliminate the BP, stuff the charge well with dog barf, and securely tape. Do you have a use case or data that shows how gasses vent into the booster and what happens when they do?

 

[heada]

Hmm, I do this all the time with seemingly no ill effects. I install the delay grain, eliminate the BP, stuff the charge well with dog barf, and securely tape. Do you have a use case or data that shows how gasses vent into the booster and what happens when they do?

I don't have data except for personal experience. Every person that has asked me about this fails to consider filling the charge well and securing sealing it. Every time the plan is to simply leave out the BP and leave the top the delay grain exposed. This would not create the pressure and volume that having the BP there would create but even the delay grain burning creates some pressure and when it burns through, some of that would vent into the aft section unless its sealed securely (plugged closure, filled and sealed charge well, sealed MMT, etc.)

 

[Cl(VII)]

If you build a rocket that doesn’t use motor ejection, using a plugged forward completely prevents blowing hot gases into your rocket in case you have a seal failure.

This! One less thing to go wrong, nothing lost (assuming you didn't intend to use motor eject), and something gained in an additional recovery harness/internal motor retainer attachment point.