Post Mortem on failure

[BrAdam]

Okay, there is no smilie for eating crow. If there was I would probably have to fill the page. I am graciously bowing to 455 Buick who pointed out the paint cracks. This area of the tube does in fact have a small dent in it where the shoulder of the cone sits on the inside. Now I don't believe the cone pushed the tube apart I think it along with the 79PSI BP load mentioned by Coop did. The interesting part is that this dent is also on a small spilled drop of CA on the inside of the tube likely hardening a small area which did not allow the tube to flex. The pressure from the BP likely caused the tube to burst after that and the propagation of the split happened on the internal wrap spiral. This cannot be seen on the outside of the tube but the inside split on the spiral encompasses about 300 degrees of the tube and about 5 inches of length. It did stop at the top where it was saturated with CA.
So when the tube gets rebuilt I will use two. That is the way the cone is designed. 3 or 4 on larger rockets which I already do.
I don't have a count on the number of times this cone has been ejected from this section of tube. I must be consistent in which pin hole I used though because there is no paint cracking or dent on the other side. All of these ejections must have weakened the tube and this one was the straw that broke its back.

Again, I bow to all. Still would like to see some math but will probably diagram this one out as a 2d model across the axial plane of the pin and tube.

 

[Binder Design]

Please post a photo of your ejection charge holder. I looked at this whole thread, sorry if I missed it.

 

[BrAdam]

This is trimmed down. It had an additional 1.25" of tube on it. Still needs to be de-burred.

 

[Binder Design]

This is trimmed down. It had an additional 1.25" of tube on it. Still needs to be de-burred.
View attachment 169782

Ok, just wanted to rule out a loose canster on a wire becoming a projectile. I agree with troj.

 

[CarVac]

"Shear pins"

Sheer is a description of being thin, pure, or steep. Shear is the failure mode for shear pins. Just saying.

Also, symmetrical pins really are better. You need at least 1.5-2 calibers of sliding length of the coupler before it's safe to use one pin, and I'd still only do that with stiffer materials than cardboard.

 

[BrAdam]

Yes, shear, already corrected myself. Not sure why autocorrect picked that and I never bothered to go back and read post. I think once I saw it I just kept on going with it till later in the post. In any event. Yes.