More Half-Baked Designs Thread

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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.

View attachment 434988

You could maybe grab an off the shelf cpu fan or use a ducted fan R/C plane motor for this and cut the blades down to fit in a tube
 
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.

I feel ya there. We have to produce clean math/analysis on the clock, so folks get what they get during free time!
 
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... 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.
First dividing 300 ft/s by three for uncertainty in the sim. Then dividing 200 RPS by three because it won't really spin up losslessly. Then rounding 66-2/3 down to 60. All in all, you've dropped the unaltered result by a factor of ten, i.e using the full 300 ft/s and knocking nothing else down would have given 36,000 RPM. I'm sure you're right in knocking the estimate way down, and if it somehow did do 36,000, which it won't, it'd surely rip itself apart.

One reason you didn't mention for that second factor of three is the energy taken up by the rotation. Even with no friction, the fins generating "lateral lift" to induce spinning rob the vehicle of forward thrust. As a rough WAG, you might take the kinetic energy at burnout that OR predicts, then split that same energy between vertical and rotational energy based on that fin pitch ratio you stated. Or, you might just figure it's already wrapped up in the factor of 10 you've already applied.

If it does get anywhere even near 3600 rpm balance will be super critical. So keeping symmetry throughout the design will be important.
In the design, and even more difficult in the build. There are a lot of fillets to match. There are variations in balsa density to consider. And more, I'm sure.
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.
With all due respect, I think that's a very bad idea. If the rocket wants to spin between two parallel rods than it is in an excellent position to impart that spin to the rods as a twist of the overall configuration. That means that each rod, taken on its own, has a significant bend. MAJOR rod whip is then guaranteed unless the two lugs leave the rods at the same moment, down to a fraction of a millisecond. Dual rails would probably be stiff enough, but...

Placement and filleting of the two lugs would also present one more challenge to maintaining perfect balance during the build. One should be able to get it better than a single lug. When maintaining balance among two pairs of buttons - which weigh more than lugs - one may or may not come out better balanced than with a single lug.
 
First dividing 300 ft/s by three for uncertainty in the sim. Then dividing 200 RPS by three because it won't really spin up losslessly. Then rounding 66-2/3 down to 60. All in all, you've dropped the unaltered result by a factor of ten, i.e using the full 300 ft/s and knocking nothing else down would have given 36,000 RPM. I'm sure you're right in knocking the estimate way down, and if it somehow did do 36,000, which it won't, it'd surely rip itself apart.

One reason you didn't mention for that second factor of three is the energy taken up by the rotation. Even with no friction, the fins generating "lateral lift" to induce spinning rob the vehicle of forward thrust. As a rough WAG, you might take the kinetic energy at burnout that OR predicts, then split that same energy between vertical and rotational energy based on that fin pitch ratio you stated. Or, you might just figure it's already wrapped up in the factor of 10 you've already applied.

In the design, and even more difficult in the build. There are a lot of fillets to match. There are variations in balsa density to consider. And more, I'm sure.

With all due respect, I think that's a very bad idea. If the rocket wants to spin between two parallel rods than it is in an excellent position to impart that spin to the rods as a twist of the overall configuration. That means that each rod, taken on its own, has a significant bend. MAJOR rod whip is then guaranteed unless the two lugs leave the rods at the same moment, down to a fraction of a millisecond. Dual rails would probably be stiff enough, but...

Placement and filleting of the two lugs would also present one more challenge to maintaining perfect balance during the build. One should be able to get it better than a single lug. When maintaining balance among two pairs of buttons - which weigh more than lugs - one may or may not come out better balanced than with a single lug.

Meh. Depends on the size of the launch rods, I'd use two 1/4" dia and design the launch lugs to be inside the rocket.

Look at the mass of the rocket and the loads the booster can generate and the time they have to generate a spinning force.

I'm assuming this will be a lpr.
 
Meh. Depends on the size of the launch rods, I'd use two 1/4" dia and design the launch lugs to be inside the rocket.

Look at the mass of the rocket and the loads the booster can generate and the time they have to generate a spinning force.

I'm assuming this will be a lpr.

Yes LPR, likely D12-0 to A for the first flight, maybe getting a little bigger if it works. The booster might fly on a pretty wide range of 24mm motors if it flies well on its own. I'm thinking to launch from a 1/8" x 3' launch rod since that's what I have. I might put two lugs on opposite sides so it's balanced though.

Question for the group: the basement Balsa is 1/16" thick. What's the minimum leading edge radius I can bend with this? That will set my fin thickness. Do you have a good link for the procedures for using Windex/water to bend the balsa? I'll need to do some redesign to make this work with the materials at hand.
 
Yes LPR, likely D12-0 to A for the first flight, maybe getting a little bigger if it works. The booster might fly on a pretty wide range of 24mm motors if it flies well on its own. I'm thinking to launch from a 1/8" x 3' launch rod since that's what I have. I might put two lugs on opposite sides so it's balanced though.

Question for the group: the basement Balsa is 1/16" thick. What's the minimum leading edge radius I can bend with this? That will set my fin thickness. Do you have a good link for the procedures for using Windex/water to bend the balsa? I'll need to do some redesign to make this work with the materials at hand.
For Alcubierre I bent 1/16" balsa to 5" diameter. That worked OK, but required some good clamping to hold it while drying. It expanded slightly when removed from the form (double-laminating it into a loop cured that). Probably could have gone a bit smaller, but much more and I think I would have needed a stronger dose of ammonia.

Process is simple, at least how I did it: dribble some Windex onto the wood, rub it in so the whole piece of wood is uniformly wet (do both sides). Bend around form, clamp carefully to hold in place while drying.
 
Increases the complexity (which is often not a good thing) but allows you a central launch rod.

Three 18 mm to three 18mm cluster (B6-0 or A8-0 if you can find them, to B6-4 or A8-5 for first flight)

The As are apparently still available

https://www.acsupplyco.com/estes/engines.htm
Allows you to run the lug up the middle.

3D print your motor mounts and your central hole nose cone.

Chute packing will be a bit of a challenge (you may need to run a lug equiavelent, maybe a micro Maxx tube, up the middle), and it WILL need to be mass symmetrical or this puppy will wobble itself to death.

With rotation and 6 motors, the smoke trail will be cool!
 
For Alcubierre I bent 1/16" balsa to 5" diameter. That worked OK, but required some good clamping to hold it while drying. It expanded slightly when removed from the form (double-laminating it into a loop cured that). Probably could have gone a bit smaller, but much more and I think I would have needed a stronger dose of ammonia.

Process is simple, at least how I did it: dribble some Windex onto the wood, rub it in so the whole piece of wood is uniformly wet (do both sides). Bend around form, clamp carefully to hold in place while drying.

OK, that's helpful. If my limit is 5" diameter, then I'll need to laminate the fins with front and back skins. I might do cross-grain (aka 2-ply plywood). It'll take a bit more effort in the airfoiling department, but that's probably OK. Or if I go off the cray-cray deep end, I could laminate fiberglass over balsa core fins out of the super-fine FG cloth I have. Much thinking!
 
Increases the complexity (which is often not a good thing) but allows you a central launch rod.

Three 18 mm to three 18mm cluster (B6-0 or A8-0 if you can find them, to B6-4 or A8-5 for first flight)

The As are apparently still available

https://www.acsupplyco.com/estes/engines.htm
Allows you to run the lug up the middle.

3D print your motor mounts and your central hole nose cone.

Chute packing will be a bit of a challenge (you may need to run a lug equiavelent, maybe a micro Maxx tube, up the middle), and it WILL need to be mass symmetrical or this puppy will wobble itself to death.

With rotation and 6 motors, the smoke trail will be cool!

I like this concept, but it's probably more than I want to take on at this moment. If I were to do it down the road, I'd have canted motor mounts to amp up the spin. That's probably more a thing for a single-stage oddroc on the order of a Quinstar.
 
You know, if you go 24 mm to 18 mm, and you keep the mass low, this puppy isn’t going to be on the rod that long, so it may not start significantly rotating until it clears the rod.

Since the sustainer will never be flown single stage, you could incorporate your bilateral lugs (for balance) into your 3D printed booster at little or no mass penalty (since you are making a hole, not a structure!) and no rotational drag penalty since it will be inside the ring!

Looked at thrust curves for C11 vs D12, you only save a little mass with the C12, but you lose a lot of post rod burn time (albeit low thrust), and D12 has slightly more oomph off the pad

https://www.rocketreviews.com/compare-estes-c11-to-estes-d12.html
Here is a thread on balsa bending

https://www.rocketryforum.com/threads/best-method-to-bend-balsa.139470/
@Rktman seems a master, as suggested by his avatar.
 
Rear and side views, shown without fins and motor mount. The blue parts would be hollow. Blue parts are semi-transparent in the side view. Colors are used to differentiate pieces, not to reflect any eventual paint scheme. Any actual design along these lines would surely be taller than shown.

1603217523800.png
 
Why the two parachutes? Two piece recovery?

Yep. On these small rockets where a lot of weight is added to the nose cone, it makes sense (at least to me), to have the nose cone come down separate from the body.
 
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Replaceable Cartridge Baffles

I don't know, maybe this is old hat. I've mused now and then about a problem with baffles, to wit, they're not repairable or cleanable. This morning I had a flash of genius, stupidity, or mediocrity; I'll let you all decide which.

One could build a baffle into a coupler, as it often done, and then not glue it into place. Think of the full assembly as a cartridge. Make the airframe in two pieces, with the baffle cartridge holding them together, but relying on friction fit on both ends. Or removable rivets. If it's friction fit then one should probably add rings inside the body tubes to ensure the cartridge is not pushed too far into either piece, but with rivets that would not be necessary.

Your baffle is charred or turning into a rattle? Make a new one. Want to try out a different baffle design concept? Make a new one, and go back to the old one if it isn't satisfactory.
1605287791239.png
 
Here's one I thought I had posted years ago. Two swoopy fins and two tube fins.
1617645094738.png

I only discovered I had not posted it when I went looking for the post so I could reply to it with an update. I've changed the fins from two quarter ellipses to a quarter circle and a half circle.
1617645195011.png
The pictures on the body tube are two different arrangements of the fin shapes. The black one is just the two fins with the body tube removed, which looks like some fantasy throwing weapon. The silver and yellow one moves the lower half up and left so the semicircles meet, and could be a fantasy cultures symbol of peace.

Maybe it should be called the "Peace Through Strength" missile.
 
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.

View attachment 434988

Apparently boatgeek time is kind of like Elon Musk time. So 6 months ago I said I'd be starting a build thread "soon." And so... now is "soon."
 
Here's one I thought I had posted years ago. Two swoopy fins and two tube fins.
View attachment 458502

I only discovered I had not posted it when I went looking for the post so I could reply to it with an update. I've changed the fins from two quarter ellipses to a quarter circle and a half circle.
View attachment 458503
The pictures on the body tube are two different arrangements of the fin shapes. The black one is just the two fins with the body tube removed, which looks like some fantasy throwing weapon. The silver and yellow one moves the lower half up and left so the semicircles meet, and could be a fantasy cultures symbol of peace.

Maybe it should be called the "Peace Through Strength" missile.
If you use balsa for the swoopy fins it will be “Piece through Strength”
 
Has anyone done this? I bet someone has done this. Boattails move one's CP forward. Ringtails are quite effective at moving one's CP aft. When a boattail is placed inside a ringtail, which one wins?
1620923529352.png
The ring's pylons are visible in the bottom view. If it helps, the pylons could be extended forward to fill the boattail's profile up to the bottom of the body tube, but I bet that wouldn't help much if at all.

Looking at it, I see that it's similar to some air dropped bombs, and also to some torpedoes. But torpedoes can have guidance systems (the modern ones all do, if I'm not mistaken) and the bombs only have to be nominally stable.

Of course I could, and will, try it out in RS, and maybe OR too. (Wait, are ringtails that feature that OR lacks until the next release that's been just around the corner for a couple of years, or are ringtails available today?) I'm just not sure how far to trust the simulations for a model that's rather far, but not terrifically far into the weirdness zone.

If this works, it just begs to be tube launched. Before I spend the time to do the research, does anyone happen to know of a standard BT size (OD) and a common pipe size (ID) that are a good match for the purpose (close but not tight)? Don't trouble yourself looking, as looking is my job unless someone already knows.
 
Has anyone done this? I bet someone has done this. Boattails move one's CP forward. Ringtails are quite effective at moving one's CP aft. When a boattail is placed inside a ringtail, which one wins?
View attachment 464060
The ring's pylons are visible in the bottom view. If it helps, the pylons could be extended forward to fill the boattail's profile up to the bottom of the body tube, but I bet that wouldn't help much if at all.

Looking at it, I see that it's similar to some air dropped bombs, and also to some torpedoes. But torpedoes can have guidance systems (the modern ones all do, if I'm not mistaken) and the bombs only have to be nominally stable.

Of course I could, and will, try it out in RS, and maybe OR too. (Wait, are ringtails that feature that OR lacks until the next release that's been just around the corner for a couple of years, or are ringtails available today?) I'm just not sure how far to trust the simulations for a model that's rather far, but not terrifically far into the weirdness zone.

If this works, it just begs to be tube launched. Before I spend the time to do the research, does anyone happen to know of a standard BT size (OD) and a common pipe size (ID) that are a good match for the purpose (close but not tight)? Don't trouble yourself looking, as looking is my job unless someone already knows.

Comparing BMS tubes with PVC Sch 40 pipe...
T5 OD .544", 1/2" pipe ID 0.622"
T50H OD .990", 1" pipe ID 1.049" (you can get even closer with foil lined tube)
T55 OD 1.325", 1.25" pipe ID 1.380"
T204 OD 2.024", 2" pipe ID 2.067"
T300 OD 3.000", 3" pipe ID 3.042"

Note all pipe ID's are "average" so you might want to take your tube to the hardware store to check fit.

The 3" one is awfully tempting. If it were mine, I'd use a long ogive nose cone for the transition so that there's a cleaner airflow into the fin/ringtail. Going down to a 29mm motor mount would give quite a bit of space for fins.
 
The 3" one is awfully tempting. If it were mine, I'd use a long ogive nose cone for the transition so that there's a cleaner airflow into the fin/ringtail. Going down to a 29mm motor mount would give quite a bit of space for fins.

I was thinking along similar lines. I'd want to build small to start (with a launch lug if need be) so that an unstable flight is minimally dangerous. Definitely a heads up flight. Start with something like 13 mm to BT 55. If that's successful, try 18 mm to T204. Then go mid power with 29 mm and T300 once I'm confident. Of course that was without the specifics, but 3 inch give or take and 29 mm or maybe 38 is what was in my head for the end game.

(I said I wasn't asking anyone to do the research for me. When I saw the email that had enough of the text to see you had anyway I thought "That's got to be either Neil or boatgeek." Thanks.)
 
(I said I wasn't asking anyone to do the research for me. When I saw the email that had enough of the text to see you had anyway I thought "That's got to be either Neil or boatgeek." Thanks.)

Awww. At my old job, we had what a younger engineer called the answer triangle, a spot in the aisle about 5' from three senior engineers (including me). If one had a question, you'd walk to the middle of the answer triangle, and ask your question loudly. One of the three of us could usually answer it off the top of our head.
 
Awww. At my old job, we had what a younger engineer called the answer triangle, a spot in the aisle about 5' from three senior engineers (including me). If one had a question, you'd walk to the middle of the answer triangle, and ask your question loudly. One of the three of us could usually answer it off the top of our head.

I love the idea of an answer triangle. In my mind, it is marked out with striped safety tape on the floor, hanging signs strung up from chains, with lights, a bell, and a bit of confetti from a cannon.
 
I've worked in places where there was an answer triangle. Sometimes I was one of the answerers, sometimes not.

I also used to work in the "Joe Region". If you said "Hey, Joe" in a carrying voice at normal volume, four of us would stand up to answer you. Three of us were in the same group (wire harness design) and the other one was married to another in our group, Sue. Sue didn't work within earshot.
 
Tube launched is always cool, but you're going to run into the same challenges tower guys have, balancing guide length with transportability and setup.

This is an interesting projuect. Conventional rocket design says "make sure you have enough fin in the airstream" so that there's good airflow craeting the proper lift/drag to give stability.
Here it looks like you're relying on the air flow following the boattail so that it gets to the ring (and any ribs supporting it). I do beleive the extra ring area and resulting nooks and crannies of the support will be superior than simple fins whose spans don't extend past the body diameter, but how much better remains to be seen.

Build it, fly it (standing reasonably aways back), film it
 
Awww. At my old job, we had what a younger engineer called the answer triangle, a spot in the aisle about 5' from three senior engineers (including me). If one had a question, you'd walk to the middle of the answer triangle, and ask your question loudly. One of the three of us could usually answer it off the top of our head.
A couple of position ago we had The Table and the Smoke Pit. I saw so much wasted effort prevented in those two places I tried to make sure everywhere I've gone since has them.
 
I kind
Has anyone done this? I bet someone has done this. Boattails move one's CP forward. Ringtails are quite effective at moving one's CP aft. When a boattail is placed inside a ringtail, which one wins?
View attachment 464060
The ring's pylons are visible in the bottom view. If it helps, the pylons could be extended forward to fill the boattail's profile up to the bottom of the body tube, but I bet that wouldn't help much if at all.

Looking at it, I see that it's similar to some air dropped bombs, and also to some torpedoes. But torpedoes can have guidance systems (the modern ones all do, if I'm not mistaken) and the bombs only have to be nominally stable.

Of course I could, and will, try it out in RS, and maybe OR too. (Wait, are ringtails that feature that OR lacks until the next release that's been just around the corner for a couple of years, or are ringtails available today?) I'm just not sure how far to trust the simulations for a model that's rather far, but not terrifically far into the weirdness zone.

If this works, it just begs to be tube launched. Before I spend the time to do the research, does anyone happen to know of a standard BT size (OD) and a common pipe size (ID) that are a good match for the purpose (close but not tight)? Don't trouble yourself looking, as looking is my job unless someone already knows.


I kind of did this with a rear eject bomb rocket I designed, though not for the reasons you mentioned. I did it just to make it look more bomb like and because I had the parts lying around. But a few designs I experimented with where the ring tail is the same diameter as the body tube proved not to be very stable. There's a lot more pressure from water around a torpedo with this design than there is air pressure from a rocket. I suspect, however, with a sufficiently long boat tail stability could be achieved. My designs tend to be 3D printed, so the boat tail is never long enough.
 

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