Triangle vs Circle Question

[les]

HMM - tried to set up a poll but it evaporated.........
Went to edit and would not let me add a poll then..... Oh well


Trying to steal a page from NewWay Rockets, except instead of square tubes I'm looking to go triangular.

The rocket I thinking of playing with uses BT5, BT20, and BT50 tubes.

My question gets into sizing the triangles.

I have 4 5 options (I used the BT20 for my example in the pix below)

Left Most pix - Area of the triangle = area of the tube
Base length is the same as the tube diameter
Triangle small enough to fit in the tube
Right Most pix - Triangle large enough so the tube would fit inside the triangle






My thoughts

While being able to install the round tube inside the triangle would allow me to strengthen the triangle tube by cheating and inserting a regular circular tube, I think it is too big.

Fitting the triangle inside the tube just makes the triangle too small

I think the real choices are selecting the size to have the same area or having the triangle base length matches the diameter.

A last minute choice I added, but did not draw up, is something in between the Equal Area and the Base=Diameter options.
Then the question would be where in the middle (average?)

Thanks
Les

 

[SolarYellow]

Rockets are round because that is the most efficient shape for them both structurally and aerodynamically. If you're going to do something else, do whatever makes you happy. Having read your post, I really don't understand what you are trying to accomplish. You seem to be asking what would be best. Round would be best. Anything else, do whatever you want to do because you're doing it for some other reason, such as it looks good to you. In that case, do whatever looks good to you.

 

[les]

Yes - thinking of trying to do something different.
As I stated, NewWay has some fantastic square tube rockets (I have 16 of them)
I want to try using triangular tubes.......

 

[Raythain]

At least for BT-20, I’d use the last design. You want the option to use an 18mm motor mount in the design.

I’d say as a broad approach, make sure you can fit an engine mount tube of the largest size motor you’d want to use in a model.

Interested to see what you come up with.

 

[kuririn]

A drawing of your concept and what you are trying to accomplish would be helpful.

 

[BABAR]

You are overthinking this.

You gotta put a motor in it. To my knowledge all hobby rocket motors are cylindrical, specifically round cross section.

So unless you are gonna do a weird transition from a cylindrical motor mount to a smaller triangular cross section (which seems pointless to me, pun intended), your motor mount needs to fit INSIDE the triangle.

Whether you want to go minimum diameter (post 1 pic 1 row 2 item 4 on right) or LARGER is up to you. I think @jqavins did a triangular mailing tube that worked quite well. You can also search on this forum under Gyskelion for a triangular helicopter rocket.

You don’t need triangular tubes, they can easily be made from card stock or mat board or foam board, each has pros and cons. Nose “pyramids “ are also not that hard to fashion from card stock.

Fin attachment is kind of fun for squares and triangles. You can go traditional perpendicular or just extend of the side panel planar with the side (again, see Gyskelion or TiddlyWink.)

Love to see some pics, rough or fancy, of your ideas.

 

[kuririn]

You don’t need triangular tubes, they can easily be made from card stock or mat board or foam board, each has pros and cons. Nose “pyramids “ are also not that hard to fashion from card stock.

Or candy boxes.

 

[BABAR]

Or candy boxes.
View attachment 576399

So 13mm or MicroMaxx?

 

[kuririn]

So 13mm or MicroMaxx?

Pfffftt

 

[jqavins]

I think @jqavins did a triangular mailing tube that worked quite well.

Nope, wasn't me. I know that a god few people have done it.

 

[billeblurzz]

Jim Flis did it!

 

[billeblurzz]

 

[Alan15578]

There were a lot of triangles in my 21 Ft. A Superroc. Trusswerk I, and it could be cantilevered from the engine unit.

 

[kuririn]

View attachment 576413
Jim Flis did it!

Twice!

 

[jqavins]

You are overthinking this.

You gotta put a motor in it. To my knowledge all hobby rocket motors are cylindrical, specifically round cross section.

So unless you are gonna do a weird transition from a cylindrical motor mount to a smaller triangular cross section (which seems pointless to me, pun intended), your motor mount needs to fit INSIDE the triangle.

I'd like to agree, but it's too obvious. Assuming you're not making a really dumb mistake, it should be obvious that number four (or an even larger triangle) is the only choice unless you're not planning what we think you think you're planning, which is to say, not planning the sorts of things pictured in a posts 11 and 14 above.

What are we missing? Why is there a question?

 

[SolarYellow]

A three-motor cluster might be fun.

 

[vcp]

Back when didn't FSI stuff come in triangular boxes? I flew one of those once.

 

[John Kemker]

Back when didn't FSI stuff come in triangular boxes? I flew one of those once.

I remember Estes motors coming in triangular boxes, as well.

 

[lakeroadster]

I remember Estes motors coming in triangular boxes, as well.

Not triangles as I remember... But nonetheless, wouldn't these make for a neat lil LPR rocket....

The Estes SSS

 

[John Kemker]

Not triangles as I remember... But nonetheless, wouldn't these make for a neat lil LPR rocket....

The Estes SSS

View attachment 576583

Well, just demonstrates that I'm positive for CRS: Can't Remember S***.

 

[les]

ARrrrrrggggggh

Getting old - senile - brain fart - DUMMY

Nearly 43 years as an engineer
25 years as a BAR

And... Dumb - just dumb, idiotic, brain-dead, brainless, doltish, witless, dunderhead, lamebrain stupidity

I'd like to agree, but it's too obvious. Assuming you're not making a really dumb mistake, it should be obvious that number four (or an even larger triangle) is the only choice

Just really dumb......

So unless you are gonna do a weird transition from a cylindrical motor mount to a smaller triangular cross section (which seems pointless to me, pun intended), your motor mount needs to fit INSIDE the triangle.

I was more looking just at the aesthetics, and......... well - obviously the motor mount needs to fit inside the triangle

Think it may be time to store away the glue, hang up my knife.
Maybe, just maybe, I can start over, maybe with some RTF rockets. May be more my speed.......

sigh...

 

[BABAR]

Think it may be time to store away the glue, hang up my knife.
Maybe, just maybe, I can start over, maybe with some RTF rockets. May be more my speed.......

sigh...

Not at all time to hang up the spurs.

We need more people building outside the cylinder.

If you are looking for performance, okay, 3FNC or 4FNC is likely the only option, but if you want to create something that either looks or flies or recovers (or any combination thereof) out of the ordinary, go for it.

Only 2 rules:

Be Safe

Have Fun!

 

[jqavins]

OK, now I'll switch to brainstorming mode. What if you make make the triangle smaller than the motor mount, but not smaller than the opening in the engine block. That is, for an 18 mm MMT, make the triangle fit a 13 mm tube. So, from the end it would look like this:

BUT, the circular MMT with the triangular points sticking out is only as tall as it needs to be to hold the engine, and you add cut bits of nose cone to cover the circular arc open segments and blend into the triangle above.

 

[stealth6]

Referencing the pic in Kuririn's post #9.

If it was me, and assuming I'm doing this for aesthetics more than anything else, this shows the direction I would be thinking in. And by that I mean make your cross-section something like a "stuffed triangle". Your sides would be curved a bit. Sure this makes it a lot more challenging to actually build, but it would be pretty cool (in my opinion), and ain't that half the point? That "challenge" would be fun (and ain't that the other half of the point?)

Kinda like this:



s6

 

[jqavins]

Or, if the tube has some flex to it, perhaps made from card stock with the first triangular support being well ahead of the MMT, you could start with a triangle and then stuff circular MMT into is, so the back end takes this shape, and the card stock flexes into its own transition shape.

 

[stealth6]

Yeah, I thought of that, but it would be a bit too random, or unintentional looking for me. Also, I'd want something a bit more structurally sound as that design would inherently mean that the body tube was a bit flexxy (is "flexxy" a word?). I'd certainly try that out as a mockup up or "proof of concept", but I'd want to build it with "real" curved sides, along with the matching nosecone, for the fun/challenge of doing so.
As always though, that's just me.

s6

 

[jqavins]

My thinking, which may be totally wrong, is that if there's a triangular support, i.e. a centering "ring", about three to six inches up from the top of the MMT, the resulting curve should be pretty well matched between the three sides. And the very fact of that curvature would give that section enough stiffness to happily do without any intermediate supports. I think.

 

[BABAR]

Yeah, I thought of that, but it would be a bit too random, or unintentional looking for me. Also, I'd want something a bit more structurally sound as that design would inherently mean that the body tube was a bit flexxy (is "flexxy" a word?). I'd certainly try that out as a mockup up or "proof of concept", but I'd want to build it with "real" curved sides, along with the matching nosecone, for the fun/challenge of doing so.
As always though, that's just me.

s6

Randomness isn’t hard to overcome.

For minimum diameter like your post 24, I think likely would conform quite naturally. You could add “spokes” (internal strakes?) if you wanted to be a bit more definitive. if you want to exceed a minimum diameter relative to the motor mount you could create internal geometric centering devices (which would in a normal rocket be centering rings, here “centering triangles”?) but would obviously need to conform to your triangular, stuffed configuration here, to essentially create any outline you want.

As for structural integrity, if you want a minimum diameter, you could do pretty well simply by attaching the fins where the outer body actually contacts the internal body tube, or if desired actually goes through the wall. So structurally is easy to handle as well. Nosecone building might be a little bit of a challenge, but those familiar with card stock (calling @GlenP ) could probably manage it without too much trouble. Ideally 3-D printer might be able to make the perfect nose, pyramid, or other equivalent nose structure.

 

[GlenP]

With this cross section you can have the BT-20 motor mount fit into the slotted sides of the triangle, no transition needed, just have enough overlapping portions for a structurally sound joint. You can fill in the gaps with a little triangle piece of balsa, or a thick glue fillet.



trying to make a rough sketch of it like this:




or you could blend the triangle portion of the body with triangular fins, like on the Centuri Vulcan, to hide the BT-20 motor mount completely.

https://www.spacemodeling.org/jimz/ka-10.htm

 

[neil_w]

Something like the method I used on my Deluxe Skywriter would probably work, maybe a bit more challenging if you go for the Wankel design like @stealth6 is proposing. Mainly need corner support of correct shape and then let the skin confirm. 1/32" balsa could be very good for the skinning.
https://www.rocketryforum.com/threa...m-pro-max-limited-edition.155761/post-1947135