Neil_W's half-baked design thread

For equivalent stability (according to OR), 3 fins vs. 6:




I added a little more sweep on the fins. Six-fin version uses smaller fins; it's not a totally crazy idea. It continues to be somewhere between difficult and impossible, though, to judge what appearance will be like when the fins are clear.

I'm not happy with mass/stability relationship here. I actually need some nose weight to get this thing into the proper range to fly on a D16, and that is putting it around 5 oz. For a D12 I'll need considerably more nose weight; I'll probably have to do some sort of removable weight system to make that work. Or, I just go with an 18mm mount and commit to Questjets.

The 6 is too busy. There will be a lot of glint and flash in light, opposed to 3 which will allows wide angle viewing of the pencil without obfuscation by fins.

Plus, think of how nice it'd be to sand two sides at ease instead of trying to fit the paper in between 6 fins.

Your call as always
(consider hanging the fins back over the ferrule a tad. Not adhered, just there)

neil_w said:

Or, I just go with an 18mm mount and commit to Questjets.

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No, commit to composites, Q-Jet or otherwise. I'm sure Aerotech's D10 and D21 would do just fine.

Nytrunner said:

Let's not be silly here

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Wait a minute. We're asking people not to get silly and go overboard on a Neil W design thread? Next you'll be asking us to cut it out with the ring fins.

jqavins said:

'm sure Aerotech's D10 and D21 would do just fine

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Discontinued. What's on the shelf is all there is left

boatgeek said:

Wait a minute. We're asking people not to get silly and go overboard on a Neil W design thread? Next you'll be asking us to cut it out with the ring fins.

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We need to take our silliness seriously around here. Or something like that.

Just keep your hands off my ring fins.

Nytrunner said:

Plus, think of how nice it'd be to sand two sides at ease instead of trying to fit the paper in between 6 fins.

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My current "plan" would not require any such sanding. Rather, the entire body would be painted yellow and finished before the fins are on *or* the ferrule is attached. Then I'd attach the ferrule, then glue in the fins and try to be as neat about it as possible.

You're probably right though that the 3-fin size, although larger, would stay out of the field of view better.

I really wish I had a decent way to make the fins removable.

(consider hanging the fins back over the ferrule a tad. Not adhered, just there)

Click to expand...

That's a good idea, need to fiddle with that to see if I can buy some more stability.

Nytrunner said:

(re: D10 and D12) Discontinued. What's on the shelf is all there is left

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There's probably nothing wrong with designing for the Questjets at this point in time. There's even less wrong with putting in a 24mm mount, and using Questjets with an adapter, and then if and only if I really want to use a D12, hang an additional weight to the nose.

An 18mm mount would probably facilitate stronger TTW fin attachment, but that's probably not an important consideration.

Nytrunner said:

Discontinued.

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I just bought some D21s from Discount Rocketry that arrived in the mail yesterday. D10s I couldn't find, and I guess that's why. A shame.

I do like the D16s, but when it comes to lifting a heavy rocket, when you need a punchy motor, go D21. For what it's worth, here's a plot of data from ThrustCurve.

I guess I burned one of the last of the D10s on Saturday. The graph highlights what a shame it is that it's gone.

Yes, the D10 has a great curve. The D21 is really overkill for a 5-6 oz rocket though (nothing wrong with that, just not *necessary*.)

It's interesting to compare the D16 and the D12. Although the D12 has a *much* higher peak, the D16 does spool up quite a bit more quickly, and in theory should get things moving off the rod just fine (although my sims show the D12 being faster off the rod).

Overkill, yes, but available. When sims show the D12 and D16 both questionable, and you can't get ahold of a D10, D21 may be your friend, overkill or not. That's why I ordered them for Office Supplies (and then didn't get them in time; and then D12 was OK).

Agreed. But we’re talking about a ~5 oz rocket here....

neil_w said:

Agreed. But we’re talking about a ~5 oz rocket here....

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24 mm mount gives you more options, and hopefully Estes D12s will still be available at your local store. Seems like an Estes D12 should handle the load easily, this is likely to be one of your more aerodynamically smooth creations.

https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf

Just hope it’s flight characteristics don’t mimic the namesake, I.e., the Estes Skywriter

BABAR said:

24 mm mount gives you more options, and hopefully Estes D12s will still be available at your local store. Seems like an Estes D12 should handle the load easily, this is likely to be one of your more aerodynamically smooth creations.

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D12 absolutely would be great except it will need more nose weight.

Otherwise...

flight characteristics don’t mimic the namesake, I.e., the Estes Skywriter

Click to expand...

neil_w said:

D12 absolutely would be great except it will need more nose weight.

Otherwise...

Click to expand...

So you’re saying you will need a little lead in the nose?

(Sorry, I’ve been corrupted by @k’tesh)

BABAR said:

(Sorry, I’ve been corrupted by @k’tesh)

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You're fine.

You'll know you're ruined if you start throwing 5 of them together in one post for no discernible reason

Shall we plumb the inky depths, then mark our territory? Or is this where we draw the line? (This makes five, write?)

jqavins said:

Shall we plumb the inky depths, then mark our territory? Or is this where we draw the line? (This makes five, write?)

Click to expand...

Good application of ferrule, but felt kind of mechanical to me. And number 2, this isn't erase. Let's try to remain on point here.

Nytrunner said:

(consider hanging the fins back over the ferrule a tad. Not adhered, just there)

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This helps quite a bit, both in terms of CP and appearance.

In that picture, I have 1.5" of attached fin root, and then 1" overhang out back floating over the ferrule. Given that this isn't going to be a high-performance rocket (based on sims it probably won't break 200mph), does this seem workable? It'll be 3/32" Lexan. Don't know how to judge risk of flutter here. I'm generally unconcerned about the fins staying attached, although maybe I should be?

I can always increase the length of the glued fin root, if necessary, but goal would be to minimize it to the extent possible.

You've got that nice soft eraser to land on so you'll be fine

In serious, check out the fins on the Falcon 9 kit. they only have ~1/2 of their root fixed, the rest is just resting on the tube and can flex plus they sweep back much farther than yours ("flimsier"). It flies fine until folks stick stupid motors in it

Nytrunner said:

In serious, check out the fins on the Falcon 9 kit. they only have ~1/2 of their root fixed, the rest is just resting on the tube and can flex plus they sweep back much farther than yours ("flimsier"). It flies fine until folks stick stupid motors in it

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Cool, that's what I would hope for.

Those overhangs are not going be doable with score and snap method, will need to borrow my Dad's Dremel I think. Gonna grab a Lexan panel at Home Depot and start playing with that.

Yeah, go with a Dremel or oscillating tool. Using score and snap, I threw away about two or three fins for every usable one I made. Much cleaner results with the oscillating tool. Plus a million uses around the house with the proper attachments.
Laters.

Forgot to mention, if you want something removable for display, how about a strap on fin can?
For a lpr rocket, you can use a slip on fin sleeve and tape to secure. You can add a flange on the end of the body tube for insurance, but not necessary. See this thread, post #32:
https://www.rocketryforum.com/threads/does-anyone-make-sell-the-titan-gemini-anymore.154229/page-2
Don't know if the eBay vendor has your size fin can. If not you can make your own. And the acrylic weld cement is very strong.
But don't know the brand name or type. He just included a small unlabeled vial in the kit.
Flexible but quite strong:

To get more glue length on the root without more fin showing you could go with something somewhere along these lines:

First in a series: Goony Cutter


(Apologies for the quick-and-dirty paint job)

Cutter? Based on an actual rocket?
Whooosh, over my head.

kuririn said:

Cutter? Based on an actual rocket?
Whooosh, over my head.

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It's neil_w's design, the Diamond Cutter I think was the full name.

https://www.rocketryforum.com/threads/diamond-cutter-build-thread.129671/


My first ever scratch build. I'll try to provide proper references in the future.

I like it.
Neil's Goonies.
Limited edition collectibles.

Trying to see if any of them look interesting enough to build...

I like it

-Bob

Gooneil's