General Centering RIng Sizing Question

[dford]

I'm wondering if there is a centering rIng size guideline for specific motors or thrust ratio to ring or centering sleeve size?

 

[Bat-mite]

I may be dumb, but I'm not following you. The CR needs to butt firmly against the MMT on the inside and the booster tube on the outside. The whole point of a CR is to keep the MMT centered and straight; so there can't be any wiggle. Or are you talking about thickness?

 

[dford]

I should have worded that better.
How thick for each motor class or thrust ratio to thickness.
Material wise, when is it beneficial to move into say, plywood or even fiber rings...is that ever necessary?
Is glueing stacks of lightweight wood to create a centering sleeve okay?
At what point should I consider a sleeve?
Can I simply place three or more centering rings rather than a sleeves?

Basically I don't like having to buy centering rings if I don't have to. Or any other parts that I can't make on my own to be honest.

I'm sure you aren't dumb, you aren't the first one to be boggled by my verbage

 

[blackbrandt]

It depends on build techniques, as you can see here: https://www.apogeerockets.com/education/downloads/Newsletter126.pdf

It depends on what size motor you're using.

I tend to use 1/8" ply for motors up to J. I'll glass the rings for larger body tubes.

 

[dford]

Duh. Apogee newsletter. Of course. Good info.

 

[byoungblood]

I prefer to use something a little heavier than the cardstock Estes uses with most of their LPR rockets because they've always seemed flimsy to me. I'm not worried so much about the thrust from the motor, but rather the strain put on them when a motor gets stuck in the tube (particularly on models relying on friction fit). My old Bullpup I built some 25 years ago probably won't fly again because one of the centering rings buckled trying to remove a stuck motor last time I launched it. On LPR models, I use my wife's Silhouette cutter, cut out some centering rings from cardstock and glue them together for something a bit more sturdy.

 

[Bat-mite]

Duh. Apogee newsletter. Of course. Good info.

Pay particular attention to page 4, where he starts talking about attachment points. That is absolutely true. The highest likelihood of failure comes from the rings detaching from the MMT or the booster, not from the rings crumpling or shredding. Three CRs well-epoxied, with the epoxied areas pre-sanded/scuffed, is plenty sufficient. My level 3 rocket has three plywood CRs, pretty thick. But if the glue-joints broke, watch out!