Ejection charge appears to have bulged the body tube.

[soopirV]

I'm glad that someone else has seen this effect. I your case, though, you are taping up the whole canister to achieve the higher pressures need to properly burn the 777 correct?

Yes- 2 layers or so. I recently read a post that advocated aluminum tape in place of electrical: the allegation is that it makes the charge more directional. Makes sense as long as the cap isn't taped with foil, but I also haven't tried it. If I can keep my container vertical, it may help keep the cap from going against the wall. I use CPVC charge holders that fit my vials (I have 2ml like Pratt, and 5ml for larger airframes). On one ground test, the holder shattered too. May switch to something made of ductile metal (copper?)

Don't use the lids. Just one layer of duct tape or masking tape. Kurt

I will try this (on the ground!) with 777, but all resources I've seen (albeit not many!) state that BP subs require great confinement for proper behavior.

As I've said in other posts tho, I am a neophyte when it comes to DD- I've had successful ground tests, but have not flown yet.

 

[ksaves2]

Yes- 2 layers or so. I recently read a post that advocated aluminum tape in place of electrical: the allegation is that it makes the charge more directional. Makes sense as long as the cap isn't taped with foil, but I also haven't tried it. If I can keep my container vertical, it may help keep the cap from going against the wall. I use CPVC charge holders that fit my vials (I have 2ml like Pratt, and 5ml for larger airframes). On one ground test, the holder shattered too. May switch to something made of ductile metal (copper?)



I will try this (on the ground!) with 777, but all resources I've seen (albeit not many!) state that BP subs require great confinement for proper behavior.

As I've said in other posts tho, I am a neophyte when it comes to DD- I've had successful ground tests, but have not flown yet.

Ok, on the lid thing. I use 4F so perhaps the lid might add when using a substitute. I found it led to more fragmentation of the tube. Kurt

 

[jmmome]

I have used similar canisters (the old Newton's Third), and have also made made my own from the AT BP plastic vials. I always wrap the circumference of the canisters/ vials with a couple of wraps of electrical tape. I also remove the snap cap and use flameproof wadding or the foam earplugs to hold the FFFF BP in place, and then seal the end with masking tape. Never had a canister shatter with this technique, and they have always fired successfully.

Mike Momenee
TRA # 12430 L3

 

[soopirV]

I have used similar canisters (the old Newton's Third), and have also made made my own from the AT BP plastic vials. I always wrap the circumference of the canisters/ vials with a couple of wraps of electrical tape. I also remove the snap cap and use flameproof wadding or the foam earplugs to hold the FFFF BP in place, and then seal the end with masking tape. Never had a canister shatter with this technique, and they have always fired successfully.

Mike Momenee
TRA # 12430 L3

That makes a lot of sense since you're "shaping" the blast through a low-resistance output. The vials seal very tightly, and when you tape 'em up, it really gets constrained (the b-word comes to mind). I'm going to try to ground test without the snapcap on 777 loads to see if dogbarf and tape are sufficient. My only concern is this is one ground test that won't fully approximate in-flight conditions...but maybe close enough if it's packed very firmly and g-forces can't shift the powder.

 

[jahall4]

Now, the only issue is if one uses a "blow up" the tube arrangement for the apogee charge with a long lead wire. If the canister is free and cocked to the side, it could blow out the side of a cardboard rocket. I had that happen twice before I got smart.

Don't understand "blow up" are you saying you pointed the canister forward having routed the lead wire aft of the laundry?

 

[jahall4]

I have used similar canisters (the old Newton's Third), and have also made made my own from the AT BP plastic vials. I always wrap the circumference of the canisters/ vials with a couple of wraps of electrical tape. I also remove the snap cap and use flameproof wadding or the foam earplugs to hold the FFFF BP in place, and then seal the end with masking tape. Never had a canister shatter with this technique, and they have always fired successfully.

Yes,Yes Mike!, that's exactly what I was thinking. Using a cap, and taping it is bad news and is only necessary if one in NOT using 4fBP! Wow, great to find some folks having the same problem and solution as I.

thx!

 

[dixontj93060]

Yes- 2 layers or so. I recently read a post that advocated aluminum tape in place of electrical: the allegation is that it makes the charge more directional. Makes sense as long as the cap isn't taped with foil, but I also haven't tried it. If I can keep my container vertical, it may help keep the cap from going against the wall. I use CPVC charge holders that fit my vials (I have 2ml like Pratt, and 5ml for larger airframes). On one ground test, the holder shattered too. May switch to something made of ductile metal (copper?)



I will try this (on the ground!) with 777, but all resources I've seen (albeit not many!) state that BP subs require great confinement for proper behavior.

As I've said in other posts tho, I am a neophyte when it comes to DD- I've had successful ground tests, but have not flown yet.

Triple 7 is not your best choice here. Again, after much testing, I found that in a high percentage of cases, even with tight confinement (and I have used Triple 7 a number of times successfully in copper tubing), the burn was too slow. Often this would lead to the burn melting the plastic tube on the side breaching the confinement and weakening the blast wave.

 

[ksaves2]

Don't understand "blow up" are you saying you pointed the canister forward having routed the lead wire aft of the laundry?

Precisely that. Run the wires from a terminal block aft pointing up to the chute to "push" it out. If the chute is a tight fit, it's better to "push" it out than try to "pull" it out.
If the dual deploy rocket has larger diameter tubes and the drogue is small and fits loosely, blowing down from a canister mounted on the bulkhead is perfectly fine.
In that case it's easy to "pull" the loose fitting drogue out of the tube.

That's where I was coming from. Kurt

P.S. To avoid headaches, try to get some 4F to use. It's some much easier and one less thing to worry about on descent.

 

[jahall4]

That sounds like bad idea since the canister could get cross-ways in the tube. Which I think was what you where saying I'd think the best thing to do is use a smaller cute. ;-)

 

[Tim51]

Don't use the lids. Just one layer of duct tape or masking tape. Kurt

In my case I do use the lids, and a little bit of tape.

 

[jahall4]

Thanks to everyone's replies I think I have a solution that will work pretty good for 4F BP users. I post pictures soon.

 

[jahall4]

Okay here is my 1st attempt at a solution:



(… and no, I’m not trying to “soften” or somehow lessen the force of the charge. So don’t make some numskull comment like that unless you want to be severely chastised :wink

The pipe insulation is intended to server 2 purposes 1) keep the canister oriented longitudinally in the body tube and 2) act as a spacer between anything that it might come in contact with, namely the body tube.

If the insulation happens to contain parts of a shattered canister, that’s a nice bonus, but the goal is to not shatter the canister in the first place.

If anyone is still interested, I did take photos of the assembly processes I can post.

Cheers

 

[soopirV]

Let us know how it goes!

 

[ksaves2]

H'mmmmm, I'm glad to see I'm not the only one who's tried that. I've nixed the cap and use dog barf to take up any extra space in the tube that's not filled with powder and tape. Sometimes I cut a cardboard endcap to place on the powder and the dogbarf goes on top to keep it in place. One of the blowouts I had I used the cap and taped it on. Not a good idea as it fragmented the tube that blew out the side of the cardboard rocket. I like to leave an easy egress for the force to project and not blow out the sides of the container. Of course when flying a glass rocket there is more leeway involved. Kurt

 

[jahall4]

What I think got me in trouble was using a larger charge in a 2g canister, WITH a plug, AND the cap, AND a longer piece of tape. Just to much containment. Use the plug and cap OR tape, but not both. In fact the ear plug works so good that if there is enough plug in the canister to grip the inside, nothing else is needed.

I really like to use the 3M Classic ear plug. With the ear plug one can be more deliberate and consistent about the assembly. Compress the plug and insert it down to the BP. Once the ear plug expands to grip the wall of the canister simply trim it off flush.

 

[jahall4]

Okay here is my 1st attempt at a solution:

View attachment 290154

(… and no, I’m not trying to “soften” or somehow lessen the force of the charge. So don’t make some numskull comment like that unless you want to be severely chastised :wink

The pipe insulation is intended to server 2 purposes 1) keep the canister oriented longitudinally in the body tube and 2) act as a spacer between anything that it might come in contact with, namely the body tube.

If the insulation happens to contain parts of a shattered canister, that’s a nice bonus, but the goal is to not shatter the canister in the first place.

If anyone is still interested, I did take photos of the assembly processes I can post.

Cheers

For those that are interested I tried this technique for the first time at NSL 2016. If your were there on Memorial Day afternoon you might have seen this rocket launch. The pipe insulation which I’m now calling a “bumper” was not recovered. I suspect it simply slipped of the end of the canister, but as this picture indicates the canister remained intact. There was no damage to the inside (or outside) of the body tube and recovery was perfect.



I’ll use this technique going forward and post here. Everyone, thanks for your help solving this problem. Any additional feedback would be appreciated.

Also, if anyone has a picture of the rocket at NSL I’d love to have a copy.