Totally Tubular - unique design and build

[Alan R]

My first post. I didn't want to just surf without contributing anything.

I built several rockets in my teens, including a couple of glider kits (hawk, orbital transport). I also made paper airplanes with a friend, and was always fascinated with this guy:

But I've never seen it attached to a rocket ... <evil grin>

I took a lot of notes and pics during the build, so mostly i'm just going to copy and paste stuff in this thread.

 

[Alan R]

it doesnt like my google pics

i need to figure out how pic posting works

 

[neil_w]

For easiest picture posting, either:
1) Copy/paste the image into the edit window
2) Drag the file into the edit window

I used to like that particular paper plane as well, interested to see how you turn that into a rocket.

 

[Alan R]

Oh, thank you for the posting tips. I was trying to use the image and link buttons, and they totally barfed on me.

Ha, ya, sit back and enjoy, it's a bumpy ride to the end of the thread.

 

[Alan R]

Note pasting time...

Idea was to convert the straw and paper loop airplane into boost glider.
I haven't seen that before. Ideally the loops (or body tube segments) would be much less drag than similar size winged gliders.
weight would be in the 36g range (similar to other small gliders), but lower drag should produce higher altitudes, resulting in longer glide times.

initial test: 1/4" balsa body. rear hoop 2.5" wide, 11" long (circ.); front loop 1.25" wide, 6.5" circ.
when i put this together I noticed that my original design for the pod at the end wouldn't work, but this was flight tested anyway. just taped the forward loop on top.
it does fly. yaay. but i think i can do better

Edit: reason it wont work with the pod in front is because the balsa spar needs to inside the front hoop

 

[Alan R]

FWIW, I created an OR file on this, but it kept getting tweaked along the way to match real world build. This is what it would look like in an ideal world without broken balsa, glue patches, scuffed body tubes, etc.

 

[Alan R]

More copy/paste from my notes:

internet research... lots of examples of this, but no scientific info on flight characteristics, optimum sizes or anything else. all of that is left to kids to experiment for themselves.
Good thing i still have my inner child.

so, seems most people use 1" strips of paper, but that's for a straw. Also seems that front is 1/2 size of rear.

Iteration 2. changed front hoop to 5.5" x 1"; changed rear hoop to 1.25 width.

a few flight tests... doesn't seem to be enough lift.

I'm pretty convinced the big hoop does the lifting, so increase the wing area ...

Iteration 3. rear hoop changed to 1.75" w.

this actually seems to fly pretty well.

 

[Alan R]

Next iteration. New boom design. pod moved back to 1-1/8" from front. Allows front loop to be mounted ahead of pod.
also had cool idea of making slot in boom for hoops, so size of boom now becomes 1/2" h x 10" (1" h at pod); with slots front and rear for hoops.

tried this out, seems to fly well, but looks like it might need a little forward weight (the pod has moved back, and body is about 2x heavier)

i drilled a small hole at the end of the hoop slots to prevent splitting the whole body, but they still split the balsa after a few flights... the bottom portion just broke off (at the drill hole, yaay, one part of my theory correct anyway) this is going to have to be plywood.

also realized that i cant trim down the middle, because the launch lug is going to be there. [Edit, thought it would look cool to run the launch rod down the hoops, but later realize this is an unstable and silly idea]
however, if we're going plywood, it wont need to be a full 1/2" body. could probably get away with 3/8".

 

[Alan R]

Other notes...
my heavy paper needs to be stronger for actual boost stress. need body tube segments, 3.5" and 1.75" dia. 1.75x1, 3.5x1.75
could possibly make my own tubes, double-walled cardstock glued together

eliminate the hoop slots, and change to just a full length piece of ply that "clamps" over the main body and inside the hoops, probably a slight extension over each end (1/8"?) for good gluing. long "c" shape facing down.

observations: when testing the glide, it seems that the hoops need to be exactly 90 degrees to the body. a slight flight curve occurs by simply rotating the front hoop a couple of degrees. -- means no need to change the pod into a hinged rudder (my first idea). save a lot of trouble.

unknownbut most likely) the hoop twist would also curve the boost flight (fins not straight!).

other idea: sand the pod into an airfoil on one side only, rounded front, tapered rear, and slighly concave on the opposite side - might introduce a slight glide curve that wouldnt interfere with boost phase because it would be covered inside the balsa sandwich of the pod hook


observations: the 1/4" birch plywood seems very heavy. no more floating thru the air nicely. i think i can scale it back to 1/8 since the hoops will be sandwiched under a balsa plank. its much stronger than the balsa, doesnt need to be near as thick as first iteration.
pod size can probably be reduced slightly also to 3/8" deep.

since i'm sandwiching the hoops, i can move the pod back to the front.

 

[Alan R]

next iteration: the last was way too heavy
reduced plywood spar to 3/16", reduced pod height to 3/8". moved to front.
flight test is telling me double-wall index stock way to heavy. still doesn't "float" well.
found a styrene(?) rent sign, cut the hoops out of it (12" and 6") much lighter weight than previous fins, stronger than the single sheet index stock.
and it glues with model cement...

next iteration. i increased front hoop to 7"x1.25, rear to 12"x2" still not acting right. play some more.

maybe i need more front lift. duh. upping to 1.5x8

played with it in the park. still too front heavy. maybe move the pod back.

 

[Alan R]

new spar: this one made from some scrap ash, left over from a woodworking project.
3/16" w x 1/4", pod moved backward, but increased the length. I increased the length because i'm worried about the boost. I think it needs a little more area to push against.

same hoops as last time 12x2 and 8x1.25. this seems to fly much better. still not 100%

added a heavy thumb tack to the tail. seems to fly well outside most of the time.
i.e., good enough to try it with a booster finally.

Thanks to John from the club for bringing me some body tube and nose cones yesterday. and engine hooks!! thank you thank you! I'll be busy working on the pod for a few days.

[Ya, these are not pretty, but I'm just shooting for functional right now]

 

[Alan R]

started cutting the pod hook out of ash and it broke off, grrr, silly me, needs to be cross-grain like fins. but my piece of ash isnt that wide. back to the plywood.

cut the hook from plywood. plywood a little thicker than the ash, glued some cardstock on each side of the spar to compensate.

 

[Alan R]

started on the motor mount for the tube, cut the slot, set the hook, except a hook needs a strap. ok, more cardstock to the rescue.

thrust ring installed. played with the pod hook, originally designed to be about 1/2" above end of tube - except the strap in the way. grrr.

we dont need no stinking straps. or motor hooks.

ripped off the motor hook and strap, glue was only set an hour or less. although, motor hooks make a nice marker for setting the thrust ring...
masking tape on the motor will be fine for flight.

waiting for glue to dry on everything. hey, maybe i have time to do some sanding on redstone fins. oh joy.

started sanding on the pod piece this morning. wrapped 80 grit around an old engine to give it a curve on the bottom so it fits on the bt-20.

got tired of sanding. locked down the dremel and sanded the curve nice and fast. the big diameter sandpaper works well for the curve i need.

note to future self: extend the balsa sandwich a little below the pod spar because it has to fit down to the body tube on a curve.

glued hook to body 1/2" from the rear of the pod.

made a clamp for the spar but the balsa split and one end piece broke while cutting.
no problem, we got glue.

 

[Alan R]

off topic. got a little frustrated with my redstone, the fin guide seems to be just a hair off. didnt notice of course until i had 2 fins glued on at 180d - NOT. grrr..

looked for a fin jig online, nothing really caught my eye. too big, too much trouble, too expensive, or not thought out well.
designed a quasi-universal fin jig in tinkercad. should fix that problem forever now. just need to find somebody with a 3d printer. sure it will need some tweaking after the first print, but looks good.

I'm sure there are things i need to know about tolerances, print head size, etc in order to tweak this.

 

[neil_w]

That is interesting, bears some resemblance to a jig I once designed but never built, because it was simply too complex (there's your oxymoron for the day). Although I'm looking at it and can't completely tell how it's supposed to work. Could you explain?

One note about TinkerCad: by default it uses a relatively small number of sides for its circles. You'll want as many segments as possible to maximize chance of fitting on round body tubes:


I've used 3dhubs (www.3dhubs.com) for all my printing. Note that your jig there is a very substantial chunk of plastic and will cost accordingly; the quick estimate I got showed $25 for PLA in my area. If you're new to 3D printing, you'll probably want to do a little experimenting before going all the way with a design like that, because you don't want the whole print to be a waste because you got one dimension slightly off.

It also looks like there might be a lot of separate pieces there; if so, save them to different files so they're all printed separately (even if you include them all in one order). In Tinkercad when you export to STL you can either do the whole design or just selected objects; use that option to export in multiple pieces.

 

[Alan R]

so, you stick the central hub in your motor mount, the long wings or whatever we call them come up over your body tube and have a small gap in them. you put the fins in the gaps, and they just squeeze the fins in place while you glue. I dont know about the springiness of 3d plastic, but ideally they would be able to spring open and accommodate anything up to about 1/4" width.

designed so it could be used on anything from bt-20 to bt-60.

edit: The central hub and wings are all one piece (maybe i should do another 'group' in the model to make that clearer).

the two extra pieces are sleeves that go over the central 18mm hub. one is for 24mm tubes (fits on the 18mm hub), and the second is 29mm and fits over the 24mm piece. they could be split into separate files. And made "rounder" I guess. those pieces would certainly benefit from more facets.

didnt know about adding more facets. i missed that. just started using that program a few days ago. the "roundness" doesn't really matter so much for the 18mm i think, as it just needs to be snug in your engine mount.

also, the only online price i got was $45, was hoping i could find a friend who might do it for about half that.

 

[Alan R]

Other things I wonder about with this: the circle 'springs' at the bottom may be too small and don't open as much as needed, or they're stressed too much and need to be thicker, etc. stuff like that.

and thanks for the tip about 3d hubs, they quoted me $27, which is about what i was expecting. I'll let them build me one and should have it back next week.

 

[neil_w]

What material did you choose?

The "springiness" of the typical inexpensive materials you'll print with is very low... you most likely will not be able to spread the plates apart at all, much less have them provide a good grip. Also you'll want the gripper plates to always be parallel, which they won't be even if you manage to spread the springs out. I expect you'll need to rethink that aspect of the jig.

My overly-complex fin jig was also the first thing I did in Tinkercad. Still haven't come up with a design that accomplishes everything I'd want it to...

 

[Alan R]

darn. I thought it was such a brilliant idea. but, I'll build a new bird next week and try it out anyway. HA

 

[Alan R]

back on topic ... where was i ...

used epoxy to glue plastic hoops to wood spar, added the (now glued back together) balsa clamp over hoop mounts and glued the length and front/rear overhang to the spar. put a launch lug on the pod.

swing test success. cg is about 1/2" above end of motor at the base of the pod. got it swinging pretty fast, very stable.

it's ready for its first experimental flight. I'll try it next week on a 1/2A, or maybe A8 motor. Nothing more on this til Monday. Big launch in the desert and I'm anxious to see it.

I also need to give it a shot of bright orange and maybe some glitter so i can see it.

 

[burkefj]

I like the idea, where is your glide CG located?

 

[Alan R]

I took a pic just for you burke... slightly aft of center.

 

[dhbarr]

This is wonderful stuff.

 

[jadebox]

off topic. got a little frustrated with my redstone, the fin guide seems to be just a hair off. didnt notice of course until i had 2 fins glued on at 180d - NOT. grrr..

A trick I came up with as a kid building rockets, uhem, many years ago is to use the fin guide that wraps around the tube to mark the fin and launch lug locations on the tube and draw the lines as normal. Then, remove the guide, flip it over and slide it back on the tube. Line up the launch lug lines on the tube and guide, then make new marks and lines for the fins. You will end up with two lines for each fin. Just center the fins between the lines.

 

[Alan R]

Thanks for the comments. Cool idea jadebox.
One note about that Redstone build... i'm going to leave the scale modeling to all those OC types out there, it's not for me. Too much frustration with the details. But ever since I was a kid, I always just thought it was a cool looking rocket. I think that kit is also a rite of passage for many people.

 

[Alan R]

I'm going to have to find a new name for this, since there is already a (probably copyrighted) "Totally Tubular" rocket made by Quest .. https://jonrocket.com/store/products/totally-tubular-model-rocket/cat-1_39_53

 

[jadebox]

I'm going to have to find a new name for this ...

I can help with that, too.

https://www.rocketreviews.com/rocketry-name-generator.html

 

[Alan R]

LOL, oh that's good. I'm kind of partial to
Titanium Rotational Integral Prime Improbable ... we just shorten it to TRIPI

 

[dhbarr]

Twobfin
Hoop Jumper
Portable Holes
Hollow, Man

 

[Alan R]

I have officially decided this shall be called the Loophole.