Spin recovery concept and build thread

mooffle

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Hopefully the title says it all, I'm wanting to build a lateral spin recovered rocket in the style of a mosquito. Assuming I can get some quirks worked out this will turn into a build thread.
In the attached .ork files I have added a tube coupler, overridden to have the mass of empty engine casings after ejection. The stability is very near 0. The fins have square tabs that will likely be 90 degrees to the rest of the fin (in OR they are just part of the fin but straight boost shouldn't care, right?)
For boost the engine is held in with a size up motor hook (13mm use an 18mm hook, 18 uses a 24), at ejection the motor is kicked rearward and "hangs out" past the fins. The 13 mm model doesn't have a engine hook mass because I don't have one on hand to weigh

If anyone has done sideways spin I'm open to pro's and con's of this design. My biggest question though is regarding where the spin surfaces lie. Is 90 degrees from the rest of the fin the best location? Does the spinning part not being lined up over the recovery CG cause it to tumble instead of spin or is it irrelevant as long as the stability is at 0?

I noticed some threads using tube fins to accomplish spin but I have no idea how to sim the tube to get it to work. Unless I just extend the fin tabs to match the circumference?
 

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BABAR

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Horizontal spin recovery is cool. It just looks magical seeing the rocket orient with long axis perpendicular to the fall.

It is also, IMO, completely impractical WITHOUT ring fins. Non-Ring fins will almost certainly break due to rapid rotation when rocket contacts Terra all-too-Firma.

Thought experiment. Do not try this at home.

You are in a room with padded walls. You are standing in the middle of the room. You stick your arms straight out and start spinning around as rapidly as you can and you slowly walk into a padded wall.

What happens?

If you are spinning rapidly enough, even if you approach the wall slowly, it’s still probably going to hurt.

Now imagine the same thing with non-padded walls.

Ouch!

Standard (radial) fins do the same thing when they hit the ground. Even if the rocket is descending slowly, because it is SPINNING fast, the rings hit the ground at high rotation velocity and are likely to break.

Ring fins impact evenly, and don’t offer any “radial” rotating edge.

As to how to get it to rotate, put the ring on radial fins and cut “windows” in the rings next to the fins (either all on clockwise side or vice versa, but all have to be the same).

It’s kind of like a water wheel. I don’t exactly know what gets it started, but it works.

You need a good CG shift from front to back to keep the rocket from going ballistic. You can TRY the old Astron Scout,

This used a long engine hook and motor was SUPPOSED to kick back but stay with the rocket, making it unstable and tumbling.

Much easier, more reliable but less elegant, is to dump the nose cone for separate recovery by chute or streamer.

 

mooffle

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I think I subconciously ripped off the scout design as I was thinking about a featherweight model and browsing JimZ's site. I was looking at bail out Bill before I made this post too, haha!

Agreed, nose pop is usually the cleanest way for CG shift, but I do like a good challenge.
Attached is the 13 mm model after some tweaking. I really like the ring fin spinner, so I'm going to steal... er... borrow your design.
The thinner long fins are to simulate each section of body tube tail fin. I have a section of 24ish cm circumference tube so divided by 3 and minus a few cm to account for the spin holes is why they are what they are.

I may tweak the 18 mm one and see what the results are like, however sticking to mini engines for this project just seems to make more sense (safety concern mostly).
 

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mooffle

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There were issues in the sim getting that ring directly over the CG so 13mm it is, parts are all cut and the first fin is drying on the cradle.
 

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BABAR

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There were issues in the sim getting that ring directly over the CG so 13mm it is, parts are all cut and the first fin is drying on the cradle.
That ring will work great as a ring fin.

However, The nose-tail length is going to be very narrow to cut adequate "windows" to achieve spin rotation on descent.
 

mooffle

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I was having trouble in the sim making the ring wider. Stability margin ended at about .6 (for a small rocket this should be fine right?) and any wider dropped it pretty significantly or I would have to move it so far back that it was no longer above the CG.

Hopefully I don't have to abandon the spin recovery which would be super cool but I'm going to finish the build with no windows/spin mechanism and see how it tumbles.
Alternatively maybe just adding some 'tabs' to the ring that when impacting the ground are less likely to break or at least much easier to glue back on.
 

BABAR

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I was having trouble in the sim making the ring wider. Stability margin ended at about .6 (for a small rocket this should be fine right?) and any wider dropped it pretty significantly or I would have to move it so far back that it was no longer above the CG.

Hopefully I don't have to abandon the spin recovery which would be super cool but I'm going to finish the build with no windows/spin mechanism and see how it tumbles.
Alternatively maybe just adding some 'tabs' to the ring that when impacting the ground are less likely to break or at least much easier to glue back on.
Hmmmm..... maybe put three small side fins on your spoke fins, each directed clockwise, along the forward edge of the sweep. Surprisingly it takes very little “consistent asymmetry” to get the spin started,

Something like this?
 

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BABAR

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Another option is to cut the spokes from thin plastic curved bottles, they have a little “give” to them (they kind of bounce when they hit.)
 

dhbarr

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Hmmmm..... maybe put three small side fins on your spoke fins, each directed clockwise, along the forward edge of the sweep. Surprisingly it takes very little “consistent asymmetry” to get the spin started,

Something like this?
Could use rail buttons there.
 

mooffle

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Smartasserry is 100% encouraged.

Hmmmm..... maybe put three small side fins on your spoke fins, each directed clockwise, along the forward edge of the sweep.

I'll throw this back into my sim, with three spoke find for stability the ring could get pushed farther back and the roll fins could go in front and inside the ring. The only thing I can think is that might be pushing the bounds a bit much for what a 13mm can push. The 18 may fare better.

For materials this is going to be balsa for sure (I don't even like plastic nose cones) plus I have many many many scrap bits to go through.
 

mooffle

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So... patience is definitely important. I cut those parts last night and started gluing, fin 3 of 3 is drying. However after trying out internal spin fins found that they won't hurt my stability much but if I swept the spokes more then the boost is more stable and the spinners sit right on top of the cg. This may turn into a side by side build thread.
 

mooffle

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Last update for the night while the glue dries.
The body tube is so small that I had to attach to a transition and bt50 that was laying around to keep it weighted down over the edge of the table.
For the hook mount I just sliced a section of bt lengthwise. I thought I had a sleeve but the tube actually fits quite snug and the gap on the opposite side is almost perfect for the launch lug to match up to.

Next I just have to figure out the vent hole sizing and locations.
 

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mooffle

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Experimental designs are my favorite. At least a third of my fleet is this kind of stuff.
Ring attached, I never get three find this close to 120° so that's exciting. You might notice the ring is slightly out of round. To get it attached I over sized the fins by a few mm and slowly sanded them down until snug. Better that than too loose.
 

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mooffle

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Anyone have experience with vent holes for pistons or that sort of thing? Obviously I want the vent small enough to build pressure and push the engine back, but big enough to actually, ya know, vent. And maybe not cause a micro-explosion.
The mini motors inside diameter is close to 10mm I was thinking just under. Maybe 8 but is there a rule of thumb?
 
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Anyone have experience with vent holes for pistons or that sort of thing? Obviously I want the vent small enough to build pressure and push the engine back, but big enough to actually, ya know, vent. And maybe not cause a micro-explosion.
The mini motors inside diameter is close to 10mm I was thinking just under. Maybe 8 but is there a rule of thumb?
IIRC Tim Van Milligan (Apogee Components) stated that the size of the vent hole or holes should equal the size of the motor's inside diameter. But since you want to ensure the pressure is enough to kick the motor back, slightly smaller would be fine. The Scout I built as a kid had a hole (or two?) about the size a paper hole punch makes (about 1/4") and it used a larger 18mm motor.
 

mooffle

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Found the instructions for that kit and looked like two or three holes.
Taking that idea, a 1/4 is 6+mm diameter and I can always bore it out bigger if I need to. I started with a 1/16th drill bit by hand and worked my way through my entire set with a few passes from each bit stopping at 1/4. Sanding such a small tube is pretty hard and there is a fair amount of fuzz left, so I'm going to let some glue harden it up then hopefully smooth it out better.

The nose cone base is also covered in glue for a little bit of extra longevity against such close ejection blasts.

Also, if you look at my ork files you will all see my lame working title for this little bugger along with zero attention to colors, feel free to throw ideas out there.
I may have this thing done this weekend! So much for a drawn out build thread
 

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mooffle

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After 'flight testing' and 'recovery testing' aka throwing it in the air with various engine positions, it didn't nose down in any comforting way so hopefully a tiny bit of extra fin area helps, sims show little effect. However as long as it will boost straight the tossing resulted in a decent tumble effect so the rocket as a whole shouldn't be a loss.

I've opted for tabs on the outside of the ring instead of holes or inside tabs. When the motor is back the CG is almost dead center to the ring, I'm worried inside fins won't catch the air right, and as Babar pointed out its narrow for windows and I'd rather not start from scratch now. The tabs are at the midpoint between the three fins, the ring seems rather springy there and might absorb some shock.
 

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After 'flight testing' and 'recovery testing' aka throwing it in the air with various engine positions, it didn't nose down in any comforting way so hopefully a tiny bit of extra fin area helps, sims show little effect. However as long as it will boost straight the tossing resulted in a decent tumble effect so the rocket as a whole shouldn't be a loss.

I've opted for tabs on the outside of the ring instead of holes or inside tabs. When the motor is back the CG is almost dead center to the ring, I'm worried inside fins won't catch the air right, and as Babar pointed out its narrow for windows and I'd rather not start from scratch now. The tabs are at the midpoint between the three fins, the ring seems rather springy there and might absorb some shock.
With the direction of the tabs, the spin orientation in combination with the tabs you may be okay! It would be a problem if it spun the other way. I am liking this.

Hope for a good flight report. Gonna need good eyes to find it, no chute or streamer to help out visibility. Might consider some fluorescent paint.
 

mooffle

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Finished 1 coat of primer, it's in for the 2nd coat of red right now.
I don't have mylar tape but do have aluminum, I'm thinking a few small cm wide strips so as it spins (or tumbles) it'll really flash. And to contrast the red maybe gold or white accent colors.
 

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mooffle

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Not spin recovery, but similar asymmetry. The ring was about 1/16" too big, so I cut a small piece out. I expect that we both will have interesting flights. Looking forward to your flight report.
View attachment 437676
Is this an Estes Sprite or sprite inspired?


Fully painted in red after 2 primer coats and 2 red. I almost skipped the second coat until I got inside and noticed just enough of the gray poking through that I was too bothered to let it go. I'm glad too, it turned out pretty well. Tonight will be the final decoration with aluminum/gold tape strips and accent colors.
It still needs a name, for some reason this is always the hardest part.

Editors note: this is also the 2nd shot with a new camera (read old and used but decent dslr), I'm excited to start getting launch shots with it!
 

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mooffle

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Decorated, named, and done! Meet the Lepton, with micro Feynman diagram logo.
Went mostly red with silver and some sparkly orange craft tape from a project my wife did for last fall. She also turned me onto those markers and I use them in just about every model I make. I can't argue that they are better than decals or give a better look than other methods I see people use, but they sure are fun.

I'll update with some flight photos as soon as weather is halfway decent.
 

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