My 10 inch diameter...Paper Rocket.

I just so happened to run across this recently here.

I'd better give credit, that's a rocket made by steatlh6 (very cool btw)



Something like that, except 2 rods out each side to build the fin onto?

I figure a true through the wall slot for the full chord would lose a considerable about of structural integrity, even with extra CRs. So, 2 1/4" , one angled down, holes for dowels instead of a slot for fins.


Just thinking out loud again...?

Right now he skin/tube has no structural strength really, it's just a skin. I don't know how you are going to poke a hole in a thin skin and glue a dowell into it and have any strength for bending loads. On this model you have a thicker skin which supports the rod. Unless you can guarantee you can glue the dowell completely to a centering ring and the stuffer tube to keep the dowell from moving when the fin gets a sideways landing load.. The strength of the model will come from your stuffer tube and the centering rings supporting the skin. You can do interlocking tabs/slots in the cr's or as on my falcon just slot the fins that slide over the cr's using the extra glue area to lock the fins to the cr's and prevent any bending/landing loads from crunching the thin skin. The root joint will also give structural strength to the model. You can also see how I laminated carbon inside the foam fins, you could do something like that with cardboard, or foam board or as you were proposing just do dowels on the bottom and leading edge. You can also see my parachute bay at the top of the falcon, like you are proposing I just eject the top 2" of the nose, I used a 29mm stuffer tube to reduce weight and just the top 12" has a 4" tube for the parachute. I used a coupler for the cone shoulder since it is hollow and allows the chute to fit into the top portion easier(ie not waste space with a solid shoulder for the cone). The coupler has a light ply plate at the top that the recovery attachment goes to. You can also cut some styrfoam to fit inside the paper cone top to give it some structural strength for when hits the ground on recovery.

Frank

Frank, thanks for the detailed explanation, and of course, pics are always good. Judging by yours, I'm going to need a few more CR's, but the skin is rather rigid for it's size.

I think I'll take some time and do some more research. This project started out moving quickly, but now I'm to the point of...wondering.

Maybe 2 stuffer tubes, one for the motor, etc, with a larger diameter around it? The rods/dowels would be glued in through a total of 3 tubes, and tied into the CR's

More ideas are welcome (and highly encouraged at this point )

I used the smallest stuffer tube I needed for my motor diameter to reduce weight in the aft end, but this is on a 7' tall rocket so it adds up. Since my skin was foam I couldn't rely on it for any support to the fins so had to rely on tying them to the cr's and the stuffer tube. if you think your skin can support more then maybe you don't have to do that as much.

I came up with a visual for my angled dowel idea..

I guess pics are good, oops

I'm just using the 'heavy' tubes for prototyping...



The top dowel could be angled down from the stuffer tube to match the leading edge, poking through the skin. I could butt a CR up to each of the dowels for more support.



The top dowel is obviously too long, and the bottom one is short, and not through the tube, but it would define the outer shape of the fin.



The cardboard is just there for reference, I would like to figure out a way to skin the fins as well...

I could tie those two together with another (vertical) dowel, and maybe a little more ribbing in between them at different angles? Make sense?

I can't find any cocktail napkins or I'd be done designing it by now

I picked up a couple sheets of foam board tonight, scored at the local DG I'll maybe start on some CR's.

For what it's worth... 2 full sheets of 20 1/16" x 29 11/16" x 3/16" 'Readi Board' weigh 220.3 grams with no labels. I'll save THAT as a 'density of mass' in OpenRocket. Or is that me...dense? Dents? Uh...

Edit- by -those- dimensions, I figured it to be .03482 oz/in 3....Saved material

I've done some searching here on ---dowel fins--- but what I'm finding is that they have been used to finish the edges of honeycomb type material. I haven't found them used as either an outer skeleton or internal structure for them yet. No wifi doesn't help

So......


You all are going to force me to make more prototypes and take more pictures again..aren't you?! Well that's just fine then...maybe I'll just do that!!

I'm still under my $10 budget!

Jeff: I believe that you are overthinking things, again . think aircraft construction and look up 'longeron'. a piece of square stock fastened to the frames(centering rings) and the skin(tube) should provide enough structure to attach fins to the rocket.
Rex

Rex R said:

Jeff: I believe that you are overthinking things, again .

Click to expand...

Thanks Rex...I -needed- that. You know of me all too well

I still have something YOU gave me a while back that's part of the inspiration, actually...

I'm guilty of it too, it is a bad habit to get into . keep in mind that if the skins touch you lose a good bit of strength. some 3mm foam board inside a balsa* frame, skinned with paper ought to give you a nice sturdy fin. *a basswood root might do better than balsa.
Rex

McKailas Dad said:

I picked up a couple sheets of foam board tonight, scored at the local DG I'll maybe start on some CR's.

For what it's worth... 2 full sheets of 20 1/16" x 29 11/16" x 3/16" 'Readi Board' weigh 220.3 grams with no labels. I'll save THAT as a 'density of mass' in OpenRocket. Or is that me...dense? Dents? Uh...

Edit- by -those- dimensions, I figured it to be .03482 oz/in 3....Saved material

I've done some searching here on ---dowel fins--- but what I'm finding is that they have been used to finish the edges of honeycomb type material. I haven't found them used as either an outer skeleton or internal structure for them yet. No wifi doesn't help

So......


You all are going to force me to make more prototypes and take more pictures again..aren't you?! Well that's just fine then...maybe I'll just do that!!

I'm still under my $10 budget!

Click to expand...

I have framed large foam fins using dowel stock. The dowels were slightly too large (another used what I got thing). I laminated the foam in drywall tape and yellow glue (and beer labels). This was very draggy and flew on 38mm H motors. The surface mount fins held on fine under chute. Not so much under power. Two of the fins sheared off but were mostly intact. Amazingly strong for such huge fins.

rstaff3 said:

...(another used what I got thing)....

..I laminated the foam in drywall tape and yellow glue (and beer labels)...

...This was very draggy

Click to expand...

You sound like my kinda guy lol

I knew somebody obviously has done it, but conformation and pics are good.

I hadn't realized until I saw the 'web version' (I'm usually on the App) of this it's had over 1500 views?! Thanks, I'm glad there's an interest, that motivates me!

Dang, I'd better get back at it

Big definitely gets our attention. This is also one of those threads that you check out because you figure that you may learn something along the way. Then, there is the "watch NASCAR to see a good wreck" thing going on too:wink:

I got the stuffer tube rolled today. I used a BT80 tube as a mandrel, and went with 3 wraps of, again drywall tape and yellow glue.

It ended up at about 33 inches long, and is 101 grams, compared to the 155 grams of the (thicker sized) BT80 tube that is 34 inches long.

My early estimates were around 1000 grams, no motor, but it may be well under that. By suggestion, I am using foam board for centering rings verses using cardboard. That saved a considerable amount of weight.

I have decided on 4 fins, I figured it may have less chance of damage on landing. I have a lot of longer balsa sheets in hand that I'm considering using instead of the dowels. More of a ribbed internal design like RC planes, as Rex suggested.

I pic of my stuffer tube, on the left.

Yea, I know, exciting stuff



Time to start making centering rings, and figure out how the heck I'm going to make the fins...

I'm still thinking of stabbing through the 'skin' to tie the main ribbing into the stuffer tube. Uncharted territory for me, but that's what makes it fun!

Sorry ThirstyBarbarian, I kinda stole this pic from your thread.

I'm thinking somewhere along the lines of this for fins, but have never built a model airplane in my life...



I have enough balsa and basswood laying around to play with some different designs, but not quite sure how to engineer something like that.

My plan is to skin it with just paper, so obviously the strength would have to be 'internal'. I also didn't particularly want a perfectly 'flat' fin. Something more like an Honest John 3D-ish type shape.

Eh, if it were easy, everybody would be doing it! Rex knows..I -like- to make things complicated!

with that type of construction 80% - 90% of the strength comes from the skin, be it paper, balsa, plywood, or monocoat(just iron it on ). the ribs (in theory) should be fairly easy*, likewise the spars. the leading and trailing edges might be a little tricky...I think one could do them using square stock balsa.
*unless you have access to a laser cutter, one would probably want to paper them before attempting to cut notches in them.
Rex

Laser cutter?

I have -both-



Hmmm?!

forgot to mention that a flat 'build' board(something you can drive pins into to hold the parts when gluing) is needed. right skin the ribs it is .
Rex

Alright...

Rex had told me I was overthinking this, he wasn't kidding!

I threw my bar napkin designed, uber complicated, ribbed, sparred, skinned, and no-clue-how-to-make-it-anyway fin idea in the trash!

After seeing the thread here -

https://www.rocketryforum.com/showthread.php?119772-X-20-Dyna-Soar-with-titan-booster

Is when I realized... KISS!

I am going to use that technique to make the fins. It's a two ply foam board design, with a single carbon fiber rod through the middle......Really??!

I had NO idea that 'simple' of a fin design would hold up to an H117 Dark Matter. I would have placed my bet on...confetti

Thanks Frank, you just made this project much easier


Now I just have to track down some CF rod. I don't know if I know any bow hunters, but I know HobbyTown carries rod and tube. Preferably local...

lol. it occurs to me that you might have missed my Depron flyer, a bt60 based bird 23" long. I used 3mm depron for the centering rings and fins. dry weight sans 12" chute, 48g afraid to fly it on an E motor Ds pretty much put it out of sight...methinks a C11 would be about right. fins and rings are skinned with cardstock.
Rex
edit
Hobby town USA in West Allis does not carry CF rods.

Rex R said:

lol. it occurs to me that you might have missed my Depron flyer...

Hobby town USA in West Allis does not carry CF rods.

Click to expand...

Yup, I missed that one!

I've missed a LOT!!


CF rod? Maybe not in West Allis but the HobbyTown in Delafield does!

I haven't priced either, and not sure if they would be too large of diameter, but I may check on carbon arrow shafts.

Lol, I just checked Walmart online, they have 29" x .37" CF shafts for around $7.00. There's a 24-7 one a few miles from my house.

Iirc, the CF rods at HTown were more expensive. Their website sucks and it's 2:30am, I'll have to call them later...

If you haven't worked with carbon rod before, just be careful with any saw/sanding dust. You do NOT wanna get that stuff in your lungs (this is what I have been told - don't know for sure or what it does - just to avoid it).

I cut my carbon with a razor saw so there isn't much dust floating around, but the warning is good. You do want to design your fins for both flight and landing, depending on your weight and chute size, sometimes I'll angle the carbon through to the corner of the fin that will make contact with the ground to give it some strength there, or use fins that don't stick down below the fuselage so that the fuse takes the major landing load.

Frank

burkefj said:

....sometimes I'll angle the carbon through to the corner of the fin that will make contact with the ground to give it some strength there, or use fins that don't stick down below the fuselage so that the fuse takes the major landing load.

Frank

Click to expand...

That was the concept I was thinking with angling the dowels, to try to have them take the hit of the landing.

Of what little I know of 'structures' a tube is stronger than a rod. Would it make much difference in this case? I hate to assume, but wouldn't a tube be lighter as well?

if I was laminating 1/4 foam sheet I'd use a 3/16" or so carbon tube, you are right they are lighter.

Arrow shaft may be a bit large for laminating the foam board.

Frank

McKailas Dad said:

That was the concept I was thinking with angling the dowels, to try to have them take the hit of the landing.

Of what little I know of 'structures' a tube is stronger than a rod. Would it make much difference in this case? I hate to assume, but wouldn't a tube be lighter as well?

Click to expand...

Admittedly, this build has been done almost completely backwards. I made the nosecone, rolled the body tube and stuffer, cut a couple centering rings...THEN and am now doing research on how to build it.

Yea, well...


I appreciate the tips and comments, they have been very helpful!

burkefj said:

if I was laminating 1/4 foam sheet I'd use a 3/16" or so carbon tube, you are right they are lighter.

Arrow shaft may be a bit large for laminating the foam board.

Frank

Click to expand...

I found "small diameter" CF arrow shafts (tube) to be .37" ($5.00 on clearance at a Walmart lol) and the foam board I have in hand is just under a 1/4", I'm getting .20"

I'll sneak my digital scale in to see what they weigh lol

I finally checked HobbyTown, they have .21"OD x 40" CF tube for $5.49.

https://www.hobbytown.com/search.aspx?searchtext=Carbon fiber tube&refine=

I'm figuring (ok, assuming) the HobbyTown tube would be considerably lighter, but I'm not sure what diameter would be strong enough in my case.

The HT website lists 5 different diameters (OD) -- .210, .196, .188, .157, and .125....?

I would probably go with the .21 or the .196. I have a feeling that it will be plenty light enough and match the fin thickness well.

RocketFeller said:

I would probably go with the .21 or the .196. I have a feeling that it will be plenty light enough and match the fin thickness well.

Click to expand...

Thanks for the suggestion!

The .37" arrow shaft seemed excessive, in both diameter and weight. If (ok, -when- lol) I copy Franks design, the .21OD tube should sandwich nicely in between two sheets of ~1/4" foam board.