Seriously. This is getting to glue thread level of emotions!
Back to the OP. If you're buying the grains why would you go thru the bother of making a case? they're pretty available and at a fairly cheap price considering that someone had to make it.
Wind angle is important. 55 degrees is optimal for rocket motors constructed of straight cylinders of filament wound material. That does not mean that other wind angles wont work. they just wont be as strong. BUT if the case can withstand 2000psi with optimum wind and 1000psi with non optimum wind for example, running the motor at 500psi wont be a problem. not trying to do a full class on motor design, but why not use what other engineers have determined to be the best? look at this for some information...
https://www.polymerjournals.com/pdfdownload/994244.pdf
The Wayback Machine is your friend.@beeblebrox the link to the journal article is broken, could you provide a title so I can hunt it down? (If this 8 year-old thread can be revived)
It might be worth adding that an equal pressure rating can be attained with non optimum winding angles, it's just the casing wall will need to be thicker and the vessel heavier than for optimal winding.Wind angle for the case is VERY important, it affects the overall pressure rating, but, as important it affects the mode of failure and the case deformation under pressure. Also important to the wind angle is the method used to hold the ends on.
The optimal wind angle for a body tube would be completely different to a motor case. A motor case is a pressure vessel pure and simple. A body tube has no internal pressure. Most of the load will be from longitudinal buckling (from compressive forces) and bending moments and whatnot and it would rely on the rigidity of the resin much more than a pressure vessel.The wind angle for a motor case might not be good for a body tube.
A refurbished AT O525O with 22 pounds Swamp Gas. Fins glassed to the motor case. Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.
Tony
The wind angle for a motor case might not be good for a body tube.
A refurbished AT O525O with 22 pounds Swamp Gas. Fins glassed to the motor case. Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.
Tony
Yeah, a few things to unpack here,I would agree with that. It appears that the case had no longitudinal fibers. With the wrap angle being so far off the longitudinal axis, it was basically relying on the tensile strength of the adhesive to resist bending on the tension side. With the comments above about potentially sub-optimal resin content, plus the fact that the fibers constitute a massive number of very small-radius potential crack initiation sites when loaded in the transverse direction, the failure is not totally surprising.
Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.
Yeah, a few things to unpack here,
- Motor Case - Under Pressure BETTER body tube, so the motor case stress go DOWN axially if it is also the body tube. Easy to think about, the pressure creates axial stress in tension, during launch on a 'body tube less design' the tube is in compression, canceling out some of the axial forces.
- Having pressure will increase Brazier buckling loads (high load to failure)
- Centaur was (is) actually stabilized by the pressure in the tank.
- Another way to look at this is to understand there is no axial forces on a tie rod cylinder just hoop
What's more, what happens at burnout in the case of utilising internal pressure for tensile rigidity. Works well for tanks, but not so well for motor/combustion chambers.I understood tfish's post and photos to mean the part that failed was not the pressurized part. It was the recovery bay part, which appears to have no axial fibers, just 45 degree-ish angled wraps.
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