The Magnum Load's fins are too big and the wrong shape. And the fin can looks like it's smaller in diameter than the main part of the rocket (or am I misreading this picture?) Zoom in on the fin can.
More Half-Baked Designs Thread
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lakeroadster
When in doubt... build hell-for-stout!
But the fins are wrong, the transition is wrong, the nose cone isn't even close and the kit is $22 bucks.
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And the movie rocket looks more like a bullet than the kit that is supposed to look like one.
I just can't get over that solid pine nose cone not having enough weight. Maybe I'll gin up a design file myself and we can compare.
I just can't get over that solid pine nose cone not having enough weight. Maybe I'll gin up a design file myself and we can compare.
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But the fins are wrong, the transition is wrong, the nose cone isn't even close and the kit is $22 bucks.
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Well other than that, Mrs. Lincoln, how was the play?
lakeroadster
When in doubt... build hell-for-stout!
Here's the .ork file if it's of any use to you. Good luck and God Speed Joe Avins
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OK, unsurprisingly, I got about the same result. Still seems weird with such a heavy nose cone.
I'll see if I can make the fins a little bigger and still "right enough".
I'll see if I can make the fins a little bigger and still "right enough".
So I tried that. I upscaled the fins by 20% (so 44% by area) and that almost did it. Then I lengthened the body tube by 20%, which got me to over 1 caliber. An I still think it looms right enough to me.
Anyway, it's yours to build, so whatever way you want.
Anyway, it's yours to build, so whatever way you want.
lakeroadster
When in doubt... build hell-for-stout!
Looks nice, much more refined. Thanks for taking the time to tweek "The Damn Dirty Ape Rocket".
My plan was/is to simply scale the rocket, based on the photo. But that'll be down the road a bit.. I've got floors to replace... insulation to install and drywall to hang. Ugh..
boatgeek
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I swear I saw this concept here, but now I can't find it. Anyway, something truly half-baked. This is a booster for a hypothetical 2-stage, where the booster spins the stack up to ridiculous rotational speed, then separates the finless sustainer. I don't really know if it will work, but it will be fun to try. 24mm MMT, 4" diameter ring, transitioning to 18mm powered sustainer. This is upside-down because it will 3D print better that way. I'll start up a build thread before too long, though I have no idea whatsoever when I'll be able to launch it.
Are you sure you want to print that? It would be lighter if you use bent balsa. You could print a two piece form to sandwich moistened balsa to make the blades all come out the same.
I'm totally into multi-stagers where the different stages perform unique functions other than just making the whole thing go higher. We discussed it casually in my own half-baked thread, although I wasn't proposing anything like what you're showing there.
I have vague doubts that you will be able to achieve a stable sustainer that way, mainly because it seems to me that a normal paper body tube will have inadequate moment of inertia to make it work. But I will watch with interest to see.
Also I agree with Joe to make the booster nice and light with balsa: you want it to get things moving as quickly as possible to develop maximum rotation; no point having it drag any more weight than necessary.
I have vague doubts that you will be able to achieve a stable sustainer that way, mainly because it seems to me that a normal paper body tube will have inadequate moment of inertia to make it work. But I will watch with interest to see.
Also I agree with Joe to make the booster nice and light with balsa: you want it to get things moving as quickly as possible to develop maximum rotation; no point having it drag any more weight than necessary.
boatgeek
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I could, and I do have some balsa in the basement... But it would be a lot more effort to get the parts the same and aligned. I know I can print it, so we'll just need to print it as light as possible. this may end up being the proof of concept, followed by a lighter version. If the spinning sustainer doesn't work, I'll likely either add fins to the sustainer or just build it up to be a "normal" spinning rocket. The plus side of the latter is that I would be free to throw stupid large motors in like the stash of F79s in the closet...
Time to think a bit more, I guess.
And the booster should be stable on its own, so there's a bonus.
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Something you can do with a ring fin booster. Cut “windows” in the ring near the fin-spoke.
The booster will fall, airflow will cause it to spin, and it will align long axis perpendicular to fall trajectory, which gives you maximum drag. Works even for long boosters. Could easily be incorporated into your “spin-inducing upward boost” model.
https://www.rocketryforum.com/threa...nch-gap-stage-horizontal-spin-booster.149667/
The booster will fall, airflow will cause it to spin, and it will align long axis perpendicular to fall trajectory, which gives you maximum drag. Works even for long boosters. Could easily be incorporated into your “spin-inducing upward boost” model.
https://www.rocketryforum.com/threa...nch-gap-stage-horizontal-spin-booster.149667/
lakeroadster
When in doubt... build hell-for-stout!
Cool concept! To reduce weight maybe just get rid of the outer ring altogether?
Nytrunner
Pop lugs, not drugs
@Charles_McG has a finless upperstage on one of his Nike stagers. Is that the Deacon or the Recruit?
boatgeek
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I feel like the outer ring is important to hold the fins on, but I could be wrong on that. But since I don't really know and I like the look, I'm going to keep it. I might rescale a bit to match the Basement Balsa (tm) supply.
lakeroadster
When in doubt... build hell-for-stout!
I like the look to... kind of like the rotor on a turbo charger.
But since you are using the ring... you should be able to make those fins really, really thin.
Charles_McG
Ciderwright
Recruit. The Recruit was flown with a vacuum adapter nozzle that makes a great cone fin. I’ve flown it a single stage test - haven’t gotten to the Terrier Recruit yet. This year’s flights got taken up with Nike Tomahawk and Terrier Malemute flights.
boatgeek
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I like the look to... kind of like the rotor on a turbo charger.
But since you are using the ring... you should be able to make those fins really, really thin.
Looking like a turbo isn't entirely accidental... My theory (and I don't know if it's a good theory) is that the rounder leading edge will help reduce the chances of aiflow separating along the back side when the angle of attack is off nominal. And honestly, the angle of attack is always going to be off nominal. Paranoia about flow separation comes from working mainly with boats since water is a lot less forgiving than air in that regard.
In theory* if this thing hits 200-300 ft/s on boost, we'd be looking at 3600+ RPM. I don't think we'll really get there, but it'll be interesting to see how high it does go and how hard it spins.
* In theory, there's no difference between theory and practice.
How do you calculate that?
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Scroll down to the bottom of the page and look at the “twisted” rocket.
https://www.flickr.com/photos/oflittleinterest/with/9108288272/
You might find it interesting
Reference @Sascha i think
Also this, which I think is what you are thinking, minus the ring
https://www.spacemodeling.org/jimz/eirp/eirp_128.pdf
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So, does this thing have a launch lug, rail guide, whatever somewhere? It's not clear to me how it gets off the pad...
Also, don't rapidly spinning objects that are longer than they are wide have a tendency to adjust their spin access so they're tumbling the long way?
Also, don't rapidly spinning objects that are longer than they are wide have a tendency to adjust their spin access so they're tumbling the long way?
boatgeek
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With a combination of rash assumptions* and a bit of math...
The pitch of the blades is about 0.5 meters. In other words, if you screwed the rotor through Jello** or some other substance without slipping, it would advance 0.5m in one revolution***. OpenRocket said a really rough version of this would go about 300 ft/s. That's close enough to 100 m/s for this analysis, since I don't have real weights or anything to go on. With no slip across the blades, that would give us 200 RPS. I totally don't believe that's going to happen, since it will take time to spin up, there are aerodynamic losses, etc. etc. So hey, about 1/3 of that sounds like a plausible upper bound. 200/3 is an unpleasant number, so call it 60 RPS or 3600 RPM so we stay all Base Babylonian and stuff.
I promise that more engineering goes into the boats I design than this. At least by the time they're built.
Any aero engineer who wants to give me rational slip numbers would be much appreciated.* Never make assumptions about rashes!
** Not recommended, at least not without washing thoroughly afterwards.
*** One of the cool things about the fin shape is that I'm holding pitch constant across the radius rather than holding fin angle constant. That means the fin is angled quite a bit more at the tip than at the root. In theory, that should make the rotor more efficient.
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Launch lug placement may or may not be a problem, depends on whether it needs to start spinning while on the rod or not.
Sascha’s rocket ran the rod right up the middle.
Sascha’s rocket ran the rod right up the middle.
boatgeek
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I hadn't gotten that far yet. There will be a launch lug on the side of the body tube. Since I'm sold on going to balsa fins, this will be a more standard launch lug.
To the second point, yes that is a potential issue. I'm hoping that effect will manifest far enough into the flight and/or that aerodynamic restoring forces will be enough that it won't be an issue before apogee. I have flown a canted fin rocket successfully--that one spun up really nicely and didn't tumble along the way.
lakeroadster
When in doubt... build hell-for-stout!
If it does get anywhere even near 3600 rpm balance will be super critical. So keeping symmetry throughout the design will be important. Please.. please... please start a build thread for this.
And for launch lugs... maybe a dual lug - dual launch rod arrangement would work best. Stop any spinning until it gets "off rod" and pointed toward the heavens.
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I like it, I'm also looking forward to the build thread.
One way around the spinning on the launch rod thing would be to do a cluster with two or three motors, and have the launch lug through the center. However, that doesn't work when used as a booster.
One way around the spinning on the launch rod thing would be to do a cluster with two or three motors, and have the launch lug through the center. However, that doesn't work when used as a booster.
I'm not sure if the spinning on the rod issue is important.
However, spinning saucers are usually launched with very little rod, maybe for that exact reason. They don't require a high speed for base drag stability, so the idea is to get them off the rod as quickly as possible so they can start spinning. For this rocket, it's possible similar considerations will apply, but it won't have the base drag to provide stability at lower speeds.
In any case, I don't know of any *realistic* way to actually do something about the spinning, other than just let it climb the rod and start spinning once it's free.
However, spinning saucers are usually launched with very little rod, maybe for that exact reason. They don't require a high speed for base drag stability, so the idea is to get them off the rod as quickly as possible so they can start spinning. For this rocket, it's possible similar considerations will apply, but it won't have the base drag to provide stability at lower speeds.
In any case, I don't know of any *realistic* way to actually do something about the spinning, other than just let it climb the rod and start spinning once it's free.
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