Quantcast

Internal fillets -- how many?

The Rocketry Forum

Help Support The Rocketry Forum:

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,739
Location
Maryland
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.)
 

mccordmw

Well-Known Member
Joined
Jan 18, 2016
Messages
1,020
Reaction score
49
Location
St. Louis, MO
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.
 

rstaff3

Oddroc-eteer
Joined
Jan 18, 2009
Messages
11,759
Reaction score
14
I generally do both once I am in there. Not that I have ever thought it through.
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,610
Reaction score
3,433
Location
Butte, Montana
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
 

soopirV

Well-Known Member
Joined
Sep 1, 2010
Messages
1,157
Reaction score
6
I aim for red, but because I suck at it, end up getting the blue for free.
 

DAllen

Well-Known Member
Joined
Jan 18, 2009
Messages
4,949
Reaction score
955
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...
 

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
11,100
Reaction score
3,956
Location
Northern NJ
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?
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,610
Reaction score
3,433
Location
Butte, Montana
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
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,739
Location
Maryland
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.
 

rstaff3

Oddroc-eteer
Joined
Jan 18, 2009
Messages
11,759
Reaction score
14
Surviving landing is generally more of an issue with LPR and (most) MPR than losing a fin. Many HPRs too.
 

Buckeye

Well-Known Member
TRF Supporter
Joined
Sep 6, 2009
Messages
2,627
Reaction score
477
Red only, and barely at that.

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

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,856
Reaction score
1,261
All of them... Red, blue, and external.
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,887
Reaction score
2,131
Location
Melbourne Australia
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.
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
47
Location
Washington DC
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.
 
Last edited:

Nathan

TRF Supporter
Joined
Apr 20, 2012
Messages
2,129
Reaction score
437
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.
 

Latest posts

Top