What is considered as "too many fins"? (L2 high powered build)

[Nytrunner]

AT aft closures should be similar. Anyone have dimensions on those for Ben? I only fly CTI 54s

 

[Ben Martin]

AT aft closures should be similar. Anyone have dimensions on those for Ben? I only fly CTI 54s

I'm trying to make the retainer pretty universal, but I will most likely use AeroTech motors.

 

[Nytrunner]

Aerotech 54: https://www.aerotech-rocketry.com/c...h_rms_ext_dim_dwgs/54mm_hp_rms/hp_54-1280.pdf

Anyone have snap ring dimensions for him? Loki, etc....

 

[Ben Martin]

Aerotech 54: https://www.aerotech-rocketry.com/c...h_rms_ext_dim_dwgs/54mm_hp_rms/hp_54-1280.pdf

Anyone have snap ring dimensions for him? Loki, etc....

Height appears to be universal, that's a good sign.

 

[heada]

Model your retaining sizes after AeroPack retainers. They fit all the major manufacturers (AT, CTI, Loki, etc.) Better bet would be to actually buy an AeroPack retainer as they're actually pretty cheap for what you get.

 

[Ben Martin]

Model your retaining sizes after AeroPack retainers. They fit all the major manufacturers (AT, CTI, Loki, etc.) Better bet would be to actually buy an AeroPack retainer as they're actually pretty cheap for what you get.

I wouldn't consider over $50 for a 54mm retainer cheap. I can't seem to find specific dimensions for them either.

 

[heada]

I wouldn't consider over $50 for a 54mm retainer cheap. I can't seem to find specific dimensions for them either.

https://aeropack.net/retainerdimensions.asp

I understand you're printing most of the parts yourself for this rocket but it's not unheard of for a HPR rocket with a 54mm mount to end up costing nearly $1000 once all parts are included. On that scale, $50 for 100% positive motor retention is indeed cheap.

 

[Ben Martin]

https://aeropack.net/retainerdimensions.asp

I understand you're printing most of the parts yourself for this rocket but it's not unheard of for a HPR rocket with a 54mm mount to end up costing nearly $1000 once all parts are included. On that scale, $50 for 100% positive motor retention is indeed cheap.

That is very understandable, but I was just referring to my project's budget. Thank you for the link.

 

[mperegrinefalcon]

too many fins?

When they all morph into a cone or solid mass at the bottom!!

(Actually, there is a point at which the air flow between closely spaced fins come to a stop, essentially acting like a big solid object..)

I have seen someone at a launch use a circular aluminum heatsink as a fincan before. It fit perfectly over a 29mm motor and was beautiful. It was 25 thin aluminum fins I think. 29mm minimum diameter.

 

[Ben Martin]

3D printed fin test

 

[Ben Martin]

Progress:

Printed new centering ring, it fits nice and snug!

 

[HASTE]

I hope this printing isn't using any of the propitiatory design work from a certain 24mm project.
Nice work so far.

 

[Nytrunner]

I hope this printing isn't using any of the propitiatory design work from a certain 24mm project.
Nice work so far.

And I've been trying sooooo hard not to say anything on those lines (-_-)

 

[Ben Martin]

And I've been trying sooooo hard not to say anything on those lines (-_-)

Uhhh what? I know nothing about a proprietary design. Every part was made from scratch in Inventor based off the OpenRocket file.

 

[Nytrunner]

Uhhh what? I know nothing about a proprietary design. Every part was made from scratch in Inventor based off the OpenRocket file.

Please ignore that, it's utterly irrelevant to your build. Somewhat of a forum inside joke that you are blissfully unaware of (I hope you stay that way).

 

[Ben Martin]

Please ignore that, it's utterly irrelevant to your build. Somewhat of a forum inside joke that you are blissfully unaware of (I hope you stay that way).

Went straight over my head. I'll continue on my merry way.

 

[Ben Martin]

Went straight over my head. I'll continue on my merry way.

All of the parts I have printed so far: 2 notched centering rings for fins, a tapered and airfoiled fin, and the baffle system.

I will probably have to end up coating the baffle system with something to keep it from melting. Also, after some research I found out that PETG does not like to be glued to anything, so I guess my 30min epoxy will be an experiment.

 

[dhbarr]

I hear Weld On 16 works for PET-to-PET, but Weld On 4 not as much. I have no personal direct experience.

Gorilla Superglue is also supposed to be okay due to a small percentage of dissolved rubber.

 

[Ben Martin]

I hear Weld On 16 works for PET-to-PET, but Weld On 4 not as much. I have no personal direct experience.

Gorilla Superglue is also supposed to be okay due to a small percentage of dissolved rubber.

Those all sound iffy for a 54mm HPR.

 

[dr wogz]

Of course, you do have some good blanks for making molds.. if you want to think about it that way...

(Yeah, some plastics are a pain to glue..)

 

[Ben Martin]

Of course, you do have some good blanks for making molds.. if you want to think about it that way...

(Yeah, some plastics are a pain to glue..)

Making molds using what?

 

[dr wogz]

Cheesy grin!! Use the 3D printed parts to make moulds to cast the parts in resin, fiberglass, carbon etc..

You make a 2 piece mold, a negative of the parts, typically out of silicone.
You then part them, remove the plastic part, and either lay up the halves with fiber n epoxy or you just pour in a resin of some kind.. look up mold casted parts..

 

[Ben Martin]

Cheesy grin!! Use the 3D printed parts to make moulds to cast the parts in resin, fiberglass, carbon etc..

You make a 2 piece mold, a negative of the parts, typically out of silicone.
You then part them, remove the plastic part, and either lay up the halves with fiber n epoxy or you just pour in a resin of some kind.. look up mold casted parts..

I was planning on just using the 3D part itself Haha. Might add carbon fiber or fiberglass centering rings later on.

Maybe I'll print up a few more just to try our molding.

 

[nh4clo4]

What is the span on your fins? A good rule of thumb is to make the span at least as large as the body diameter. Possibly larger.

+1.

I don't think there is any added value in 3D printing your fins. Just get standard fiberglass stock and you should be fine with 4 fins.

P.S. My level two rocket had 9 fins.

 

[Ben Martin]

+1.

I don't think there is any added value in 3D printing your fins. Just get standard fiberglass stock and you should be fine with 4 fins.

P.S. My level two rocket had 9 fins.

3D printed ~ free

My current design have a pretty low span (3" at tip) so I'll probably be remaking them.

 

[nh4clo4]

3D printed ~ free

My current design have a pretty low span (3" at tip) so I'll probably be remaking them.

LOL. For some reason I was only seeing the first page of this thread when I posted my reply. I just saw the rest of it and the setup looks great. Sorry for the distraction...

 

[Ben Martin]

LOL. For some reason I was only seeing the first page of this thread when I posted my reply. I just saw the rest of it and the setup looks great. Sorry for the distraction...

Haha, all good. I appreciate you taking the time to give some feedback. I definitely think that 3D printing fins are going to be a challenge and a good learning experience. My first test fin flexes at the edge so I don't think it would hold up very well during flight.

 

[Andrew_ASC]

You can increase the cord length and thickness at the tips for more stiffness. It will look slightly awkward and naysayers that haven’t printed anything in their lives will say your fin is suboptimal design. Frankly, I don’t really care what they think. I’ve had success with printed airfoil fins much thinner than yours. As long as it doesn’t flex much your fine.

 

[Ben Martin]

Progress: Printed 2 non-notched centering rings for the middle and top of tube.

Photo is of all printed parts so far.

 

[Ben Martin]

Printed a new fin version that has slots for carbon fiber rods. It is also properly airfoiled this time.