Internal fillets -- how many?

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Bat-mite

Rocketeer in MD
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intfillets.png

All,

Do you generally put your internal fillets only in the red -circled areas, or also in the blue-circled areas? In other words, for a three-fin rocket, would you use six or twelve internal fillets?

(For the blue circles, I am NOT asking if you put external fillets -- thank you.)
 
I've only ever put internal fillets at the point where the fins contact the motor mounts. Combined with the external fillets, I don't see how extra ones on the inside of the airframe tube would offer any additional needed support; just more weight.

If you want to skip the external fillets to have a more angular military look, I would put ones on the inside.
 
I generally do both once I am in there. Not that I have ever thought it through.
 
I do both red and blue. The red ones maximize the ability to resist impact forces at the outer ends of the fins, but the internal blue ones strengthen the body tube. It's a small amount of work. I use chopsticks.


Steve Shannon
 
I aim for red, but because I suck at it, end up getting the blue for free.
 
All of them. If I am going through the trouble of sticking something in there to spread the glue - might as well hit 'em all while I have all the materials out. That said, I do tend to make them a bit smaller so I'm not adding a ridiculous amount of weight on the wrong end...
 
What for LPR? I haven't done any internal fillers at all, because there's no room to work in there, and I've assumed it's not really necessary. Should I be doing anything with internal fillets on TTW LPR builds?
 
What for LPR? I haven't done any internal fillers at all, because there's no room to work in there, and I've assumed it's not really necessary. Should I be doing anything with internal fillets on TTW LPR builds?

Have your fins fallen off?
I bet you're just fine.


Steve Shannon
 
It really comes down to structural integrity vs. added weight. With a very lightweight LPR, the amount of glue needed to create internal fillets may well make the rocket unstable, whereas with a heavier rocket, you have more leeway. The purpose of an internal fillet is to prevent the fin from breaking its root mount and going cockeyed.
 
Surviving landing is generally more of an issue with LPR and (most) MPR than losing a fin. Many HPRs too.
 
Red only, and barely at that.

Sometimes, foam may be the best course of action, and you get everything in one shot.
 
Red only for me.

What for LPR? I haven't done any internal fillers at all, because there's no room to work in there, and I've assumed it's not really necessary. Should I be doing anything with internal fillets on TTW LPR builds?
I usually just double-glue. Apply glue (PVA) to parts and mate, then unmate. When the glue goes off a little I apply a little more to the fin and then mate (with clamp) for the final time.
 
What for LPR? I haven't done any internal fillers at all, because there's no room to work in there, and I've assumed it's not really necessary. Should I be doing anything with internal fillets on TTW LPR builds?

Heck NO! I have many LPR and MPR models with over 50 flights that are butt white glue joined to Estes type Craft Tubes that have NO fin seperations..some chips in ding from landing on hard stuff but the joints are still strong after 2 or 3 decades.
Remember Neil: If the "Double Glue Joint Method" is used the Joint becomes Stronger then the Materials it is joining.
 
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I try to put internal fillets everywhere that I can reach where two pieces of fiberglass are bonded together. That also includes where the centering rings contact the airframe tube, motor tube, and fin tabs. Maybe it's not necessary but I'm not concerned with the additional weight of a little epoxy.
 
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