Please explain this. Again, I am no expert in extreme flight profile rocket design. In my mind double walling the phenolic is going to add much more weight than if I added a couple more layers of FG, and, in fact, would be even heavier than if I went to a G12 Profusion airframe.
My hypothesis is that you experienced a radial failure of a single walled section of your rocket. I will first explain how I arrived at this, and then I will describe my remedy that I posed before.
You explain in the report that you desired a lightweight tube and you achieved this by designing the rocket around phenolic with a single layer of 6oz glass. Radially, as you showed in your report, phenolic with a single layer of glass is not all that strong.
This leads into my assumptions:
1. The booster section was of a standard design and not zipper less. I assume the rocket was designed in the standard HPR scheme where the rocket separates at the altimeter bay and also at the nosecone.
2. There is some damage that makes it appear as though you "scraped" the altimeter bay against the inside of the booster.
3. Your altimeter bay coupler is more robust than a single thickness of phenolic tubing.
4. The altimeter bay is intact, as is most of the upper section of tubing apart from the zipper.
So now for my idea:
Your airframe experienced a radial failure just above your motor case.
This would explain the relative good condition of everything north of that point, especially the altimeter bay. I would assume that your CG of this rocket was somewhere near or just below the top of the fore end of the motor casing. Should there be any radial force, say a crosswind or any other turbulence, this is the approximate location that the rocket would "rotate" around.
Your rockets' initial failure was right at the top of the motor, just ejecting everything above that point. In this EXTREMELY turbulent environment, the insane deceleration, and centrifugal force experienced by the cord and main chute, it easily sheared the pins in the nosecone and ejected. The quick inflation of the chute resulted in the zipper, but this ejection scenario explains the relative good condition of the nosecone shoulder.
So, how do we fix this given the current material selection?
1. Add more glass (you knew this)
2. Epoxy a coupler into every area of the rocket that is only a single layer of phenolic tube.
I think #2 is a lightweight option that will help significantly. Basically, install a coupler of the appropriate length such that the motor butts up against one end of said coupler, and the altimeter bay butts up against the other end. Further up, the fore end of the altimeter bay butts up against the second coupler, and the nosecone shoulder butts up against the fore end of the second coupler. Essentially, it's a "rocket within a rocket."
Or, you can redesign the rocket in a very minimal matter using a design that Tony A. uses, but using better materials.