Adding extra ejection BP to CTI motors

CTI motor instructions say that if you need extra BP, you need to put it on top of the cardboard disk that holds stock BP in place.

I need to add 3 or 4 grams of powder to deploy my rocket (4" x 85" rocket that needs to separate into 7 pieces). I wonder how can I secure the BP to the motor well, and how can I ensure the stock charge ignites my extra powder.

Ari.

Try making a cylinder of blue tape above the well and pour all the bp in. Then fold it down.

CarVac said:

Try making a cylinder of blue tape above the well and pour all the bp in. Then fold it down.

Click to expand...

I use white cheap making tape. It holds better. Same method

Thanks guys. I'm not clear on what you attach the tape to--do you wrap the black plastic liner or the entire aluminum case?

Ari.

An additional 3-4 grams is a lot, Ari... are you sure that's the desired charge?

What motor are you using, here? 54's tend to stick up a bit past the end of the case --38's are more flush --may be difficult with a 38, particularly if you're using spacers. Perhaps consider electronic deployment?


Later!

--Coop

It's a 5G 38mm. Ground testing shows that even 5 grams is marginal. There are 5 couplers and a nose cone to pop.

Ari.

Here are a couple of ground tests. It's disconcerting how much BP it takes to separate these sections.

Ari.

[video=youtube;Gix9Ze3V_zE]https://www.youtube.com/watch?v=Gix9Ze3V_zE[/video]

Are you talking grams or grains?? I have never used 5 grams in any rocket yet. Even in my 11.5"X 34" space in my Redstone I use only 4 grams. 5 grams is way to much.
GP

I know, right? But it just refuses to separate with normal-size loads.

Ari.

You must have something way to tight. Are you sealing off the MMT before the test? If you used 5 grams in the video test somethings is very wrong it barley come off the tube.
gp

I agree; it feels like something must be wrong. It's going to take a lot of powder, but it shouldn't need more than a few grams; a 7.5g BP charge is really starting to get into the territory where you have to be ultra-cautious to avoid injury (twisted anti-RF leads, shunts, etc.). EDIT: right, motor eject, that's what the thread was about. Still, it's scary, ok?? /EDIT

It looks like, in the second video, the entire rocket leaves the ground when the charge goes off; is the motor mount tube sealed the way it will be on the real flight?

If you really need that much BP, split it into smaller charges and do electronic deploy for all of them in parallel. Run the leads through the shock cord from an av-bay in the nosecone, or something like that.

I do have a plug for the MMT, a pretty elaborate one at that. I describe it in the main build thread: https://www.rocketryforum.com/showt...ube-fin-breakapart-rocket&p=427231#post427231 . If I didn't plug the MMT, you'd see a jet of flame coming out the bottom.

The rocket moving up in the video is the NC pulling on the shock cord. It means it has enough momentum going up to pull the rest of the rocket behind it, but the force it applies is insufficient to pull the last two sections off the fincan.

Ari.

Coming back to the thread's subject, I manage to wrap some masking tape around the plastic liner and then insert it into the casing, like so. The friction seems to hold it pretty tight.

Once I figure out how much powder I actually need, I wonder if this is what you guys are recommending to hold it.

Ari.

That's what CarVac was talking about I think.

Ya thats what it's suppose to look like. Jason did that to my LOC IV at MWP on a 29mm and it worked great. We used blue tape though.

Estes BT-20 tubing works on the CTI 38mm motors.. Small slice of 1/2" or so, use 5min epoxy, it slides perfectly down into the ejection mudule.
Fill with powder and close the end with masking tape.
Done it dozens of time.
I always plan to use the CTI charge as a backup at apogee.

Are you using fff or ffff type BLACK POWDER or a substitute?

4F, black powder.
I would like to test some Pyrodex.
My take more and packing it tightly but have not tried it yet.

Out of curiosity... Have you checked the calibration of your scale?

I use 3-4 gr at most..... and that's with shear pins.

Did you vent the section(s)?
If so how big are the hole(s)?
Try confining the BP a little better.

JD

Are you guys still talking about my 4" Tubularity?

Ari.

iter said:

Are you guys still talking about my 4" Tubularity?

Ari.

Click to expand...

I think so. We are trying to understand why it uses so much powder. You are using true black powder right? I asked earlier but I think someone else answered.

The main reason for asking is that substitutes tend to require very tight containment or they are weak due to incomplete burning.

The design is one that makes it hard because as soon as it separates the pressure is lost. Could you make the couplers really loose and add a burn string to tie the top to the bottom?

Dave A said:

4F, black powder.
I would like to test some Pyrodex.
My take more and packing it tightly but have not tried it yet.

Click to expand...

My question was not clear but was meant for the original poster...

UncleVanya said:

I think so. We are trying to understand why it uses so much powder.

Click to expand...

I know the problem and I am no longer trying to solve it. The difficulty is in Blue Tube's dimensional instability. It shrinks and swells with temperature and moisture changes. And when I'm trying to open 5 very tight couplers, I need a lot of BP. The other difficulty with BT is the weight. The rocket is almost too heavy for breakaway recovery.

I now have Tubularity sitting in my office as a conversation piece (the "remove before flight" streamer is everybody's favorite).

Ari.