Fin Patterns

[Ted Curtis]

I was wondering where I might find fin patterns, specifically for a 3" tube with 29mm motor mount. Looking for fin through wall designs to fit slotted Estes tube from Leviathan. Something resembling an AGM design and corresponding thin, long fins (forget what they are called) to mount above for a larger AGM navy missile like scratch build. Thanks.

 

[dr wogz]

Fins can be any shape, within reason! it's up to you to decide what you think is 'cool' or effective, or .. yes, there are certain shapes that have advantages over others, but I don't think that's what you're after.

Start with Open Rocket. you can play with fin shapes all you want, to achieve all sorts of things. You can then print out the fin template to cut them. It'll even do the math to figure out your TTW tabs.

You are referring to 'strakes' those long but not very high fins seen amid ship such as an AGM navy missile.. Again, model them in Open Rocket.

 

[Ted Curtis]

Fins can be any shape, within reason! it's up to you to decide what you think is 'cool' or effective, or .. yes, there are certain shapes that have advantages over others, but I don't think that's what you're after.

Start with Open Rocket. you can play with fin shapes all you want, to achieve all sorts of things. You can then print out the fin template to cut them. It'll even do the math to figure out your TTW tabs.

You are referring to 'strakes' those long but not very high fins seen amid ship such as an AGM navy missile.. Again, model them in Open Rocket.

Thank You dr wogz, very helpful. I think I am looking to build a 3" version of Estes Tartar, a rocket of the month plan I built years ago. Strakes was the word I was looking for altho the plans I have (courtesy of JimZ, #83) call them runway fins. I need to adapt them to TTW. Here is a pic of the Tartar along with a 2.6 version I built with 24mm. I wanna go bigger! thanks.

 

[dr wogz]

I think you can get away with surface mounted strakes. they aren't that big (tall) and have a large base for gluing to. I have, in the past, added a 1/8" x 1/8" tab on the root edge of a fin, and drilled a corresponding 1/8" hole in the body tube. That seems to offer a bit more 'mechanical strength' to a fin..

Learn Open rocket. It's freeware, and a very good rocket design & simulation program. use it to design your rocket, but also to test the design on various motors..

 

[Ted Curtis]

I think you can get away with surface mounted strakes. they aren't that big (tall) and have a large base for gluing to. I have, in the past, added a 1/8" x 1/8" tab on the root edge of a fin, and drilled a corresponding 1/8" hole in the body tube. That seems to offer a bit more 'mechanical strength' to a fin..

Learn Open rocket. It's freeware, and a very good rocket design & simulation program. use it to design your rocket, but also to test the design on various motors..

thanx, do you know the length of the fin tabs to meet up with a 29mm tube with a 3" airframe? new to open rocket, just figuring it ot.

 

[K'Tesh]

OpenRocket has a tool that will let you compute the fin tabs automatically. You just have to make sure that your body tube's outer diameter (OD) is correct, AND your motor tube's OD is also correct.

 

[dr wogz]

you can work it out pretty easily..

(BT OD - MMT OD) / 2 = tab depth

example:
2.91" OD for the BT (Body Tube)
1.365" OD for the MMT (Motor Mount Tube)

(2.91-1.365)
2 = 1.545 / 2 = 0.7725" tab depth

 

[JonathanOtt]

OpenRocket has a tool that will let you compute the fin tabs automatically. You just have to make sure that your body tube's outer diameter (OD) is correct, AND your motor tube's OD is also correct.

View attachment 376454

Do you have to account (accurately) wall thickness (on both tubes, or just the BT) too?

 

[K'Tesh]

Do you have to account (accurately) wall thickness (on both tubes, or just the BT) too?

With fin tabs, No. All that matters is the OD of both the body tube and the motor tube (those do have to be accurate). Because the fin sits "on" the motor tube, but has to go through the body tube. For the rest of the sim, yes it does (to make sure that everything fits together).

 

[JonathanOtt]

With fin tabs, No. All that matters is the OD of both the body tube and the motor tube (those do have to be accurate). Because the fin sits "on" the motor tube, but has to go through the body tube. For the rest of the sim, yes it does (to make sure that everything fits together).

Okay, I can visualize that now. I had too much on my mind when I asked that question.

 

[Ted Curtis]

you can work it out pretty easily..

(BT OD - MMT OD) / 2 = tab depth

example:
2.91" OD for the BT (Body Tube)
1.365" OD for the MMT (Motor Mount Tube)

(2.91-1.365)
2 = 1.545 / 2 = 0.7725" tab depth

Yeah, I thought about it shortly after posting and had a 'duh' moment, easy calculation. Thank you. I assume that securing the TTW tab to the actual motor tube is optimal. I am not sure if it's necessary, but I am building heavy for this rocket. Any tips on material, as far as sheets of wood I can buy at hobby lobby? Basswood vs plywood etc, thin sheets of balsa layered and coated with epoxy finish cure? I don't have much in terms of laser cutting techniques or even table saw. Just exacto and a skill saw. BAR and trying, thanks.

 

[GlenP]

I like to use existing rockets as a guide in a similar class, dia, length, weight, power.
For example, a 3" dia 29mm power rocket:
https://www.apogeerockets.com/Rocket_Kits/Skill_Level_3_Kits/Onyx
this uses 1/8" plywood fins.

 

[Ted Curtis]

I have embraced Open Rocket, Love tinkering with new designs and extremely helpful in regards to flight profiles and especially delay times.

 

[jqavins]

For the rest of the sim, yes it does (to make sure that everything fits together).

Not to mention for the weight, since the weight of a tube is directly proportional to its wall thickness.