Or, since the body will be hexagonal, six fine would be appropriate.
Neil_W's half-baked design thread
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(just throwing ideas out there), maybe this is an opportunity to try something finless, like an induction stabilized rocket. That adds a large degree of complexity and uncertainty, however. This might be your one and only design where fins are not part of the aesthetics.
This would be a good rocket for a BPS system if it were bigger, and if I had a BPS system, and if I did reloads, and and and.....
(if we had cheese, we could have a ham and cheese sandwich..... if we had ham)
(if we had cheese, we could have a ham and cheese sandwich..... if we had ham)
Right, I wasn't thinking anything as complex as BPS, but something much simpler like this.
Nytrunner
Pop lugs, not drugs
Simple? Ahhhhahahaha hehe
Ah, my naive suggestion having no idea how that rocket even works. One one of those things that looks so simple, but has a gazillion details that complicate everything.
Nytrunner, is it only stable during boost? Or is it stable during boost and coast as well?
This isn't supposed to be a build thread, but here's a bit more pencil experimentation I have nowhere else to post:
I glued six 1/8" square pieces of balsa to another short piece of scrap tube:
Getting these on straight wasn't too bad at 3.5" long, would be tougher at 20+".
Anyway, at this point you can see that the skin wouldn't sit down in the middle of the span against the BT:
And so I commenced sanding, like this:
(that is 220 grit sandpaper wrapped around a pencil.)
After what seemed about a million years, I had it sufficiently sanded down:
Yeah, the ribs in this pic are still a *little* too high; I sanded it a bit more after this.
Then I did another adjacent pair, yielding this:
That's pretty much exactly what I wanted. The sanding was incredibly tedious, though; I figured out that my 1/8" balsa could actually have been 3/32" tall to begin with , and it would still have been tall enough to support the skin. So that's what I will do "next time", to save me the need to remove a lot of excess wood.
I then glued on two pieces of skin, which for my initial test are 1/32" balsa, papered with label paper. End result:
Looks good, but I think the size of the ferrule was just a wee bit too small compared to the body. Here's a side view:
I sanded down the corner to blend in better (real pencils look like that, sort of), but it's a bit too much of a difference. On the other hand, another full layer of 1/32" balsa would make the ferrule too thick. Therefore, "next time", I'm going to put a layer of 105 lb cardstock onto the BT before the layers of balsa. That'll thicken it up just a bit, maybe still not quite enough but probably not worth further effort.
The papered 1/32" balsa skin seems perfectly adequate for this size rocket.
Oh, one last thing: putting clear fins on the vertices of the hex part would be really difficult. I'll probably be forced to go for the middle of three of the faces (unless I can come up with another place to put them).
And that completes my feasibility study of the pencil rocket. I'm not sure if/when I'll build it, but I'll probably include one (or two?) of the required nose cones in my next parts order, so I'll be able to start it up if I want to.
I glued six 1/8" square pieces of balsa to another short piece of scrap tube:
Getting these on straight wasn't too bad at 3.5" long, would be tougher at 20+".
Anyway, at this point you can see that the skin wouldn't sit down in the middle of the span against the BT:
And so I commenced sanding, like this:
(that is 220 grit sandpaper wrapped around a pencil.)
After what seemed about a million years, I had it sufficiently sanded down:
Yeah, the ribs in this pic are still a *little* too high; I sanded it a bit more after this.
Then I did another adjacent pair, yielding this:
That's pretty much exactly what I wanted. The sanding was incredibly tedious, though; I figured out that my 1/8" balsa could actually have been 3/32" tall to begin with , and it would still have been tall enough to support the skin. So that's what I will do "next time", to save me the need to remove a lot of excess wood.
I then glued on two pieces of skin, which for my initial test are 1/32" balsa, papered with label paper. End result:
Looks good, but I think the size of the ferrule was just a wee bit too small compared to the body. Here's a side view:
I sanded down the corner to blend in better (real pencils look like that, sort of), but it's a bit too much of a difference. On the other hand, another full layer of 1/32" balsa would make the ferrule too thick. Therefore, "next time", I'm going to put a layer of 105 lb cardstock onto the BT before the layers of balsa. That'll thicken it up just a bit, maybe still not quite enough but probably not worth further effort.
The papered 1/32" balsa skin seems perfectly adequate for this size rocket.
Oh, one last thing: putting clear fins on the vertices of the hex part would be really difficult. I'll probably be forced to go for the middle of three of the faces (unless I can come up with another place to put them).
And that completes my feasibility study of the pencil rocket. I'm not sure if/when I'll build it, but I'll probably include one (or two?) of the required nose cones in my next parts order, so I'll be able to start it up if I want to.
Whoa. That looks really good. Like you're holding a giant pencil in your hand. Did you add the color to the eraser with image editing software? But that ferrule looks really convincing.
Hear's an dea for the fins. Maybe it's a repeat.
Since the ferrule and eraser are made as a different piece, attached to the hexagon by a coupler, you could make that part twice. For display, one just as you've got (plus color) and one for flight one that's got slots cut through the ferrule for clear fins. It may not be pretty, but that's why there's a separate display piece.
Since the ferrule and eraser are made as a different piece, attached to the hexagon by a coupler, you could make that part twice. For display, one just as you've got (plus color) and one for flight one that's got slots cut through the ferrule for clear fins. It may not be pretty, but that's why there's a separate display piece.
Great meeting you today!
Interesting idea. Of course it means lots more work for me...
Also, the eraser assembly would need to be swappable, which in and of itself would take some thought, unless the whole thing is a rear-eject pod. If I went with an 18mm mount (iffy for this rocket), I could probably make rear-eject work. Big advantage of rear-eject would be that I don't need to have an unsightly seam anywhere in the body.
Consensus from today seems to be that I need to build this rocket. It's not going to the top of the priority list, but I can start working on it in the background.
One thing I learned today that was a bummer is that plasti-dip is actually shiny, which kind of pulls the rug out from my plan to use it for the eraser (I don't know why I thought it would be a rough finish, I really had no basis for thinking that). Whether it could be sanded rough I don't know, never touched the stuff before.
Failing, that, is there any other clever solutions for the eraser, other than just flat pink paint? I wonder if I made sure that the surface was not smooth before painting, if the finished paint surface would retain that. But I really don't know whether I would achieve the desired texture or not.
Hmm....
Interesting idea. Of course it means lots more work for me...
Also, the eraser assembly would need to be swappable, which in and of itself would take some thought, unless the whole thing is a rear-eject pod. If I went with an 18mm mount (iffy for this rocket), I could probably make rear-eject work. Big advantage of rear-eject would be that I don't need to have an unsightly seam anywhere in the body.Consensus from today seems to be that I need to build this rocket. It's not going to the top of the priority list, but I can start working on it in the background.
One thing I learned today that was a bummer is that plasti-dip is actually shiny, which kind of pulls the rug out from my plan to use it for the eraser (I don't know why I thought it would be a rough finish, I really had no basis for thinking that). Whether it could be sanded rough I don't know, never touched the stuff before.
Failing, that, is there any other clever solutions for the eraser, other than just flat pink paint? I wonder if I made sure that the surface was not smooth before painting, if the finished paint surface would retain that. But I really don't know whether I would achieve the desired texture or not.
Hmm....
boatgeek
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Could you do a flat clear coat over the top of whatever color coat you do? Maybe texture-color paint-flat clear?
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Eraser:
Can you turn a piece of balsa, sort of like a tail cone, except flat and eraser shaped (kind of like a coupler with a hole for motor mount tube) and sand it rough?
Fins:
Put a ring fin below your eraser. Decorate it with notebook paper, maybe cursive writing or ABCs.
Something like this
https://www.rocketryforum.com/threads/hiding-your-fins-in-plain-sight-240-calories-of-fun.47954/
Doubles as a display stand
Rear Eject: great idea, may want an external shock cord mount as with rear eject otherwise falls pointy end first.
A small loop of Kevlar, maybe around your launch lug region. Easy to hide, and you can detach the shock cord from it with a snap swivel so it is hidden during display.
I know, I know, I need to get back to the Stop sign.......
Can you turn a piece of balsa, sort of like a tail cone, except flat and eraser shaped (kind of like a coupler with a hole for motor mount tube) and sand it rough?
Fins:
Put a ring fin below your eraser. Decorate it with notebook paper, maybe cursive writing or ABCs.
Something like this
https://www.rocketryforum.com/threads/hiding-your-fins-in-plain-sight-240-calories-of-fun.47954/
Doubles as a display stand
Rear Eject: great idea, may want an external shock cord mount as with rear eject otherwise falls pointy end first.
A small loop of Kevlar, maybe around your launch lug region. Easy to hide, and you can detach the shock cord from it with a snap swivel so it is hidden during display.
I know, I know, I need to get back to the Stop sign.......
Amsterdam
__________
Neil that pencil mock up is perfect! Love the touch of knocking down the flat ends into the ferrule.
If I were making a giant pencil. I’d paint the eraser on with acrylic craft paints, I think it would offer the closest color match and they come in Matte/flat finish. They dry very dull.
If you mix in Elmer’s glue or modpodge you wouldn’t have to worry about coating it either. For a even brush on finish I aim just shy of 20% glue to paint.
Oh and clear lexan fins gets my vote,
If I were making a giant pencil. I’d paint the eraser on with acrylic craft paints, I think it would offer the closest color match and they come in Matte/flat finish. They dry very dull.
If you mix in Elmer’s glue or modpodge you wouldn’t have to worry about coating it either. For a even brush on finish I aim just shy of 20% glue to paint.
Oh and clear lexan fins gets my vote,
I should try that. I was so fixated on the idea that the finish should be rubbery that I overlooked the basic fact that a pink eraser is pretty just an extremely flat pink finish (appearance-wise).
I will probably do a bit of experimenting with surface prep to see if I can get non-smooth base for the paint. Gonna see what happens when I rough-sand my label paper.
That will *definitely* take experimenting, because I've never tried that before.
Preferred fin implementation right now is 3 Lexan fins just above the ferrule, at the center of each face. Way too hard to put at the vertices, although that would look nicer. I'm putting together an OR model to see how big the fins will need to be. Lots of weights to calculate to come up with something realistic, will take me a little while to get there.
The construction test sample that you had with you on Saturday did have it as swappable. I hadn't meant to open a large worm can.Interesting idea. Of course it means lots more work for me...
As for the eraser texture, I wonder if there's a rough material you could wrap it with that would have the right texture. Maybe "paper" it with 220 grit sandpaper before the pink paint, or something like that. Nah, sandpaper would be too heavy, but perhaps there's something along that line. Low grade construction paper, maybe? If it's the right color you could just apply it then spray with matte clearcoat. Maybe.[/S]
It may be that flat pink paint is all I really need here.
However, I just made a test piece which is a label-papered piece of balsa. On one half I left the paper as-is, on the other half I sanded with 220 and then 400 to fuzz it up a bit. You can definitely feel (but not see) the difference. Will see what it all looks like after paint.
However, I just made a test piece which is a label-papered piece of balsa. On one half I left the paper as-is, on the other half I sanded with 220 and then 400 to fuzz it up a bit. You can definitely feel (but not see) the difference. Will see what it all looks like after paint.
Nytrunner
Pop lugs, not drugs
I was imagining vertices would be the easiest. Mount them to the inner tube as usual, and just trim the side of the flat panel that fits around it
There are ribs at the vertices, so I'd either need to (a) cut out the end piece of rib, or (b) not extend the rib all the way out in the first place. Given the flimsiness of the skin, I'm nervous about leaving even two inches of it unsupported.
Nytrunner
Pop lugs, not drugs
Exactly! The fin IS the rib!
Hmm, maybe, but that means I have to glue balsa to lexan and not make it look like crap. Also any flutter of the fins will fight the skin, but probably that close to the BT I don't need to worry about it.
Must ponder, and even moreso, try it out on my little test piece.
Must ponder, and even moreso, try it out on my little test piece.
The center of the faces has the advantage that the balsa sheet is fully supported by the tube. I see the predicament, it was easier to visualize being able to hold the test piece. I don't think that fins in the middle of the faces would look bad. Actually, it has the advantage of leaving the straight lines of the hexagon vertices uninterrupted all the way between the ferrule and top of the pencil.
Nytrunner
Pop lugs, not drugs
30 minute epoxy. Rough up what will basically be the "tab" of the fin, and the epoxy will form its own fin pocket. Those will be the strongest corners of the whole thing.
Plus, the fins will have extra support instead of being a free cantilever off the face of the tube.
Plus, the fins will have extra support instead of being a free cantilever off the face of the tube.
Ah, I see, that drawing helps me see what you described. True, it may have a strength advantage. I guess it comes down to details of the technique & execution, and some choices.
Well, it'll be TTW, so the fin should have some support from the BT. In any case, I'll need to do a test run.
How about:
I'll just make some support ribs on either side of the slot. Those will support the skin pieces quite rigidly. Will the fins be adequately strong in this arrangement? Not sure. But being 4" away from the bottom of the rocket, they shouldn't take too much punishment on landing....
I'll just make some support ribs on either side of the slot. Those will support the skin pieces quite rigidly. Will the fins be adequately strong in this arrangement? Not sure. But being 4" away from the bottom of the rocket, they shouldn't take too much punishment on landing....
Nytrunner
Pop lugs, not drugs
Is that a through the wall-and through the panel fin? There's a new take on the technique
Think of how much easier it'll be to sand with them at the vertex
Think of how much easier it'll be to sand with them at the vertex
On the vertecies looks better. Fact, or just my opinion? My opinion is that this is a fact.
And maybe fins on all six vertecies.
Nytrunner
Pop lugs, not drugs
Let's not be silly here
I'm not being silly. Using all six vertecies would emphasize them and, therefore, the "hexagonishness" of the airframe. It would also allow each one to be a little smaller than they'd need to be with only three (not as small as half, unfortunately) which means that, ironically, six fins might be less obtrusive overall than three. Am I contradicting myself by suggesting that they'd draw more attention to the airframe shape and less to themselves at the same time? Maybe. In my mind that's how it would look, that's my story, and I'm sticking to it.
