DO I need a plugged forward closure?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Swissyhawk

Well-Known Member
Joined
Sep 11, 2013
Messages
261
Reaction score
4
Back in April I did my first DD rocket. It was 4" FG using an AT I245G motor. I had two altimeters for redundancy. I decided not to use motor injection for additional redundancy because the motor had a medium delay and I thought there was a good chance it might go off before apogee. I built the motor just like I normally would with the only exception being that I left the BP ejection charge out (I still had the delay element in it.) Everything worked well and it was a great flight.

I had not heard of plugged forward closures (or at least I hadn't paid attention to them) until a week ago when I was reading the thread on the AT EZ reloads, so I looked one up. It said it was for when you have electronics and aren't using the motor ejection. OK that makes sense, but I'd like to know is there a downside to not using it, like I did? Am I going to get myself in trouble? What could happen? Do I really need a plugged forward closure if I'm not using motor ejection?

Thanks.
 
if I don't use motor ejection as a back-up I put a glob of grease to cover the hole in the forward closure where the BP would go. I've never had an issue.
 
Back in April I did my first DD rocket. It was 4" FG using an AT I245G motor. I had two altimeters for redundancy. I decided not to use motor injection for additional redundancy because the motor had a medium delay and I thought there was a good chance it might go off before apogee. I built the motor just like I normally would with the only exception being that I left the BP ejection charge out (I still had the delay element in it.) Everything worked well and it was a great flight.

I had not heard of plugged forward closures (or at least I hadn't paid attention to them) until a week ago when I was reading the thread on the AT EZ reloads, so I looked one up. It said it was for when you have electronics and aren't using the motor ejection. OK that makes sense, but I'd like to know is there a downside to not using it, like I did? Am I going to get myself in trouble? What could happen? Do I really need a plugged forward closure if I'm not using motor ejection?

Thanks.
There is a rare occasion where the thrust can blow by the delay element and burn through the touch hole for the ejection charge. It isn't very common, but it does happen. If you find a good deal on a plugged closure, I would get one - it eliminates the possibility of that problem.

One more benefit is that you can get a plugged closure that is tapped for an eye bolt. I use these often on minimum diameter birds to attach the recovery harness.

Just like everything in rocketry - there are several right answers.

--Lance.
 
I've been flying DD since 2007 and have never used motor ejection backup and have never used a plugged forward closure. I've had an issue or two along the way, but never anything to do with the standard forward closures and delay grains.

That doesn't mean there isn't a reason for buying and using the plugged closures as Lance pointed out.
 
Some people just leave out the ejection charge, pack the charge well full of dog barf and tape the crap out of it.
 
Some people just leave out the ejection charge, pack the charge well full of dog barf and tape the crap out of it.
Yea, I wouldn't do that. Relying on dog barf to hold back the internal pressure of a motor while possible, is not a risk I would take. A better way is to contain the pressure with a proper closure.

--Lance.
 
Last edited:
Some people just leave out the ejection charge, pack the charge well full of dog barf and tape the crap out of it.

Yea, I wouldn't do that. Relying on dog barf to hold back the internal pressure of a motor while possible, is not a risk I would take. A better way is to contain the pressure with a proper closure.

--Lance.

I'm not sure what you guys are talking about. I've been flying DD with AT motors and leaving the powder charge out for 8 years now. I've never put grease in the well or dog barf or taped anything in it. I've never had anything happen that even remotely indicated the motor delay was involved in anything. The delay grain burns until well AFTER the thrust is done (the delay time). The delay grain holds back the internal pressure of the motor burn, that's what it is designed to do. When it finally burns through many seconds after the motor is done burning, if there is no powder there for the ejection charge, nothing happens!

Don't over think this. It's simple. Assemble the motor according to instructions and leave the BP out. It will work just fine for a DD flight and have NO adverse affects.
 
Sorry, but I have to say that I wonder if people don't sit around and dream up cases where VERY rare events happen.

It would be possible for some thrust to blow past the delay element. But think about it - if the charge is there you have an immediate ejection while under thrust. And while it may happen, it doesn't happen with any regularity. In fact, if I posted about it, chances are someone here could tell me what I did wrong without actually seeing the motor.

Now my experience is strictly with AT motors. But... The instructions actually address the issue of not using the ejection charge. And memory isn't strong enough to give exact details, but I recall them saying to put a thin film of grease on the delay grain. I want to say on the end next to the charge well. I would presume this is because the delay grain itself could yield some excess and obviously un-needed flame. Which is why one posted about grease and another dog barf.

Something about the plugged closure (for AT), is that it is tapped. And there are options to use this as the motor retainer. Though logic would indicate that such would either need some adapter or you could only use one size of case.

Kirk
 
I just had a burn through of an rms ez forward unit, while using no ejection charge. I had never had any issues with standard delay parts, however since I didn't want this to happen again, I bought a long burn plugged closure and use it now and is is very easy to clean up and reload as a plus.
If all works as it should you don't need it, but things don't always work, since I run redundant electronics I decided it was one less failure mechanism so got one. If you search for titan II on page two you can see some impressive photos of the fireball.
One downside is you get no tracking smoke, for me I don't fly high enough to need it, you might.
 
Last edited:
I'm not sure what you guys are talking about. I've been flying DD with AT motors and leaving the powder charge out for 8 years now. I've never put grease in the well or dog barf or taped anything in it. I've never had anything happen that even remotely indicated the motor delay was involved in anything. The delay grain burns until well AFTER the thrust is done (the delay time). The delay grain holds back the internal pressure of the motor burn, that's what it is designed to do. When it finally burns through many seconds after the motor is done burning, if there is no powder there for the ejection charge, nothing happens!

Don't over think this. It's simple. Assemble the motor according to instructions and leave the BP out. It will work just fine for a DD flight and have NO adverse affects.
So listen to Handeman. Because he has never experienced a certain anomaly in his vast 8 years experience at rocketry it won't happen. He is the almighty rocketeer.
 
Something about the plugged closure (for AT), is that it is tapped. And there are options to use this as the motor retainer. Though logic would indicate that such would either need some adapter or you could only use one size of case.

At the risk of stating the obvious, I think the threaded, plugged forward closure is most useful as a shock cord anchor (add eyebolt, locknut).

Mark
 
I've had 5 blow by's over the years, most were from Redlines, back when that delay problems happened...... but a white lightning long burn right at motor burn out toasted 2 rockets.
Witnessed way to many more to remember who..what & when.

I never use delays anymore. I just filled the interior well with epoxy and don't use any delay-insulator-o-rings etc. any more. Since I always fly electronics it's a non issue for me anyhow.

Hey..... it's a rocket...what can go wrong? LOL
 
I've had 5 blow by's over the years, most were from Redlines, back when that delay problems happened...... but a white lightning long burn right at motor burn out toasted 2 rockets.
Witnessed way to many more to remember who..what & when.

I never use delays anymore. I just filled the interior well with epoxy and don't use any delay-insulator-o-rings etc. any more. Since I always fly electronics it's a non issue for me anyhow.

Hey..... it's a rocket...what can go wrong? LOL

This is a good conversion - no clue if that makes it a research motor. I fly almost all research launches anyways, so not an issue for me. I plugged some Kosdon closures this way.

Some like the delay for tracking smoke. I tend to agree that if there was burn though it would light the BP and cause a problem. A plugged closure solves this, but the risk of burn though is the same with or without the BP. I only had issues with a bad batch of SU F30 motors from AT. Removing the ejection and filling the charge cavity with epoxy made them nice saucer motors.
 
Back
Top