Horizontal Spin Recovery - with Magnus Effect?

[Dotini]

Figure 13
https://www.apogeerockets.com/education/downloads/Newsletter447.pdf
For me personally, there is a great deal of allure to learning the technology of what is said to be the ultimate form of tumble recovery. Age, frailty and lack of access confine me to smaller launch areas. So naturally I'm averse to high altitude rockets and parachutes. But neither do I like my models hitting the ground nose first. So I feel motivated to improve my tumble recoveries.

What little I know of Horizontal Spin Recovery I owe to @BABAR and his astounding thread on this same subject. https://www.rocketryforum.com/threads/bail-out-bill-and-the-horizontal-spin-recovery-rocket.147210/

So have my dreams come true with this little-documented, even controversial technology? We shall see! I've started off with building two models side-by-side, each exploring alternate ways for the fins to generate the crucial spin. Whether or not a Magnus Effect can be harnessed is open-ended. It may even be harmful (in my case) if it causes the model to glide out of sight over the trees. So it's all to play for.

My first problem is to explain how, in aerodynamic theory, these Figure 13 fins actually act to generate spin. Figure 13 appears to show 3 large square fins with about a 30 degree bend halfway out from root to tip. Is this 30 degree angle somehow ideal? Can it be less, more or curved in an arc to achieve the same effect? I have my reading and experience, but little formal instruction to stand on. This thread will attempt, with your help, to answer these questions.

 

[BABAR]

Think of the fin ends like the "cups" of an anemometer. They are all facing the same direction RADIALLY, so they "catch" more airflow in one direction then another. At apogee, ejects nose and goes unstable, starts to tumble. The radially oriented "cups" catch a bit of air with an initially minimal tendency to START to spin. Preservation of momentum tends to turn the rocket perpendicular to spin, so a tiny spin turns it a little, which oriented it to catch more, until finally it is perfectly horizontal. It is in this case a vicious cycle with a positive outcome. Usually needs a good CG shift to start the tumble which starts the spin. The rocket is STABLE in launch config, so it doesn't spin on way up. Also has something to do with "right hand rule", but my physics runs out at that point.

 

[Dotini]

Think of the fin ends like the "cups" of an anemometer. They are all facing the same direction RADIALLY, so they "catch" more airflow in one direction then another. At apogee, ejects nose and goes unstable, starts to tumble. The radially oriented "cups" catch a bit of air with an initially minimal tendency to START to spin. Preservation of momentum tends to turn the rocket perpendicular to spin, so a tiny spin turns it a little, which oriented it to catch more, until finally it is perfectly horizontal. It is in this case a vicious cycle with a positive outcome. Usually needs a good CG shift to start the tumble which starts the spin. The rocket is STABLE in launch config, so it doesn't spin on way up. Also has something to do with "right hand rule", but my physics runs out at that point.View attachment 456622

At this point, I have a lot more glue than physics.



Next step, 24 lb linen skins for balsa fins and endplates. Then I'm contemplating slender bracing rods going from wingtip to wingtip.

 

[Mugs914]

Might try a half-tube fin. Cut a short length of tube in half length-wise and glue one edge to the body tube as if it were a regular tube fin with the right (or left, if you prefer) side missing. You end up with what the wind power folks call an S-rotor.

I'm picturing a BT-50 rocket, around 18" - 20" LOA with three fins made from BT-50 or BT-55, about 3" in length.

Less rotational mass, less rotational drag, better aerodynamic "power" to get the thing spinning once it turned sideways.

Easy to build too!

 

[Mugs914]

Something like this, just imagine the right side of each tube fin is missing...

BTW - This was whipped up in OR (file below) and is the same as the dimensions mentioned above. The fins are BT-50...

 

[Dotini]

Still lacking some glue, launch lugs and finish, the project is 23 inches long and weighs in at 0.72 oz. less engine. Looking more like a medieval waterwheel than a 21st century rocket, she also lacks a name.


Skins are linen applied with Elmer's, bracing dowels are 3/32" Birch, totaling 0.06 oz.

Endplates, if broken, can be belt sanded off in seconds and replaced in minutes.

 

[Dotini]

Think of the fin ends like the "cups" of an anemometer. They are all facing the same direction RADIALLY, so they "catch" more airflow in one direction then another. At apogee, ejects nose and goes unstable, starts to tumble. The radially oriented "cups" catch a bit of air with an initially minimal tendency to START to spin. Preservation of momentum tends to turn the rocket perpendicular to spin, so a tiny spin turns it a little, which oriented it to catch more, until finally it is perfectly horizontal. It is in this case a vicious cycle with a positive outcome. Usually needs a good CG shift to start the tumble which starts the spin. The rocket is STABLE in launch config, so it doesn't spin on way up. Also has something to do with "right hand rule", but my physics runs out at that point.View attachment 456622

I thought the right hand rule had to do with electricity? But I'd like to know more if it also applies to aerodynamics. My fins are twisted oppositely to Figure 13.

Anyway, I'm rushing to complete and test my Magnus Effect (?) model by the weekend. Probably weighing close to 2 oz. with, I suppose, 1/2 A6-2, A8-3 , or A8-0 for 1st flight. Any recommendations? I will have a 1/4" blow hole below the cone.

 

[BABAR]

Are you going to blow the nose cone out?

ALL of my Horizontal Spin Recovery rockets have been designed specifically to be either unstable or minimally stable post deployment/ejection. In the case of single stage that means blowing the nose cone. For boosters, just using a long gap and dumping the sustainer was effective.

I HAVE NEVER DONE THIS WITH RETAINED NOSE CONE.

Tim Van Miiligan’s now infamous figure 13 had a lateral port at the front. I have NOT tried this yet. It MAY work.

here’s the problem.

in order to successfully launch the rocket, the rocket MUST be stable in launch configuration, meaning CG ahead of CP.

At motor burnout, just before ejection (and if you don’t blow the nose or do SOMETHING to alter the configuration) , the rocket is MORE stable then it started (because it has burnt the propellant in the rear, so if nothing else changes, the rocket is STILL aerodynamically STABLE.) At this point, persistent stability is NOT a good thing.

your hope (if you don’t blow the nose) is that that forward side port will “kick” the nose sideways, so the angle of attack goes from the normal range of rocket flights (usually 0 degrees, maybe up to 10 or 15 degrees if it hits a really strong crosswind) up to like 30 to 90 degrees. The idea (hope? Prayer?) is that your angle of attack is so catywampus that the rocket fails to regain stability

at this point, one of two things is gonna happen.

as the rocket falls, it’s either gonna go nose down, stay stable, and come in ballistic (generally considered poor form), or

it may start spinning, and do a backslide type recovery. Note that the models DESIGNED for this had a length to diameter ratio of 30 to 1 and small fins.

if you are dumping the nose, you’re fine. If NOT, please try this in an extremely isolated area (I like your low tide beach option!) where there is ZERO chance of an innocent (or not) bystander who is not aware of the launch risks and actively watching (and avoiding) the rocket.

If you have any rounded or otherwise non-pointy nose cones, this would be a good time to use them.

good luck!

 

[BABAR]

Something like this, just imagine the right side of each tube fin is missing...

BTW - This was whipped up in OR (file below) and is the same as the dimensions mentioned above. The fins are BT-50...

View attachment 456627

That would be cool! I have an idea for a backslider that was going to use a ring/waterwheel, but I like your idea better. The low lateral mass is certainly a plus, and the DIRECTION of spin SHOULD be forgiving on ground impact (should land on the curve of the tube, not the cut edge.)

I am thinking this may be easier to build, and have as much or more rotational effect with even less lateral mass.

7 iso-diameter tubes, the long middle tube as the body, 6 short but otherwise identical tube fins. Somehow God worked it out so 6 identical tubes fit perfectly around a central same diameter tube.

glue the tube fins in pairs on the table top (automatic perfect alignment) then glue the pairs onto the body (also automatic perfect alignment)

allow to dry and fillet the outer tube-tube joints.

draw longitudinal lines along the far lateral edge of each tube fin

cut each line the length of the tube fin

second parallel cut along the clockwise edge just short of the fillet.

advantages over your idea (which I REALLY like)

I think it will be stronger, there is less “free edge” for fin flutter (the broken rings are going to be much weaker than “complete” tube fins)

easier alignment, maybe easier build. The cuts don’t need to be perfect. As I said, I think this style of 6 tube fin rocket is almost automatically aligning itself as you build.

I theeeeeenk the direction of spin WILL be favorable for impact. If it was spinning the OTHER way impact is gonna be harsh.

thanks for this!

 

[neil_w]

Here's my stupid idea, which I don't know how to implement but I'll bet @BABAR could make it work.

Stack two of the rotary fin cans at the bottom of the rocket. At ejection, have the one in front slide forward to the front of the rocket (rubber bands, burn strings, etc.). This would make it unstable, and would put the rotary cans at the two ends of the rocket, where I would speculate they would have a better chance of operating properly (that is, get into a horizontal position and rotate.

 

[BABAR]

Here's my stupid idea, which I don't know how to implement but I'll bet @BABAR could make it work.

Stack two of the rotary fin cans at the bottom of the rocket. At ejection, have the one in front slide forward to the front of the rocket (rubber bands, burn strings, etc.). This would make it unstable, and would put the rotary cans at the two ends of the rocket, where I would speculate they would have a better chance of operating properly (that is, get into a horizontal position and rotate.

I like it! How about two telescoped tubes, 2 fins on the rear 180 degrees apart, 2 on the forward end, with “slots” that slide over the rear fins. The ejection pushes the outer tube forward (or if you prefer, ejects the rear backward!). You won’t need to move the tubes very far to get this unstable. You do need a big vent that opens when the two are in position to decompress the gas. Also will need some sort of cord connecting them at full extension as a “stop.” I tried just using a slide inner motor mount and and outer thrust ring, the piston blasted right through it.

 

[Dotini]

Magnus? X-1 (working name) nears completion, at 1.78 oz with A8-3, and about a yard in length. This experiment has a certain, uh, agricultural quality to the empennage, but X-2 will be a significant improvement, and is almost off the drawing board.



First launch is scheduled for early tomorrow morning.

 

[mooffle]

Late to this thread, I would have kicked the engine backward to effectively move the fins toward the middle.

Dotini what method did you end up using? If you aren't changing the shape somehow it will probably be ballistic.

 

[Dotini]

Late to this thread, I would have kicked the engine backward to effectively move the fins toward the middle.

Dotini what method did you end up using? If you aren't changing the shape somehow it will probably be ballistic.

For Magnus? X-1, I'm doing it pretty much exactly like Van Milligan's Figure 13. This is in order to have a known, well tested starting point of reference. I'm pretty confidant I will get some degree of backsliding, spin and glide. However, X-2 will be different, and so will X-3.

 

[Dotini]

Note exhaust port below cone, length/diameter ratio of 48/1. The fins may be a bit long.

 

[Ronz Rocketz]

With the spent motor still intact, the rocket will probably fall aft downward which might still spiral down. Less likely to impale someone. I like the fin supports.

 

[BABAR]

@Neil may chime in here.

barrowman and simulator programs calculate stability, but I think they assume a minimal (less than 10 degree) angle of attack. Ignoring winds, perhaps with the exception of some gliders and Odd Rocs, rockets are always LAUNCHED at a zero degree angle of attack, and any angle of attack encountered after that occurs either due to winds (steady or gusts) or some sort of perturbation of flight path usually secondary to rocket dysfunction (eccentric nozzle, broken fin, etc.) so I am not sure the “usual rules of stability” apply with severe changes in angle of attack. But even with winds up to 20 mph (max per NAR safety code) assuming good speed off the rod shouldn’t be that far off.

imagine the most stable rocket you can think of (just think something the exact opposite of @Daddyisabar!)

now stick it sideways on the rod with the motor rotated 90 degrees, so rocket faces sideways,motor Faces up.

even thought the ROCKET is stable based on all the Barrowman Equations and RockSim and OpenRocket and @Daddyisabar MindSim, the FLIGHT is going to be short and NOT in a good way.

back around 1999 and published in 2003 Pete and Bob Alway started playing around with BackSlide recovery

I have added two sites, and I have added the text from one at the end of this post. There is also a model design, which I have NOT copied here but is on the website.

upshot is that, “What if you launch/fly the rocket at normal near zero angle of attack, and then at ejectioN (hopefully apogee) you use the ejection charge to kick the rocket sides. At a moment in time the rocket is, if not necessarily motionless, at least presumably at 30 degrees or more angle of attack. The article below describes rockets that were stable by Barrowman equations (not sure RockSim or OpenRocket existed then) but NOT stable by cardboard cutout (a problem I have always had with the cardboard cut out model is that it seems like a rocket with two fins of a given size is just as stable as one with three, four, or fifty fins of the same given size, also doesn’t do box or ring fins well—- then again, not sure Barrowman or sim programs do those perfectly or even well either!)

anyhoo, your rocket is hanging there either motionless or definitely catywampus to the airflow, it’s options are to either nose down and go ballistic, or tumble and start spinning.

@Dotini, YOUR rocket is definitely going to be STABLE by BOTH Barrowman and cutout method, so classically it SHOULDN’T work, but look at this segment I cut from the PATENT website

“Certain models with large fins and the resultant center of gravity forward of 60% of the distance between BCP and CLA developed high spin rates during the boost phase of the flight, presumably due to accidental canting of the fins during construction. At ejection, these models transitioned to a backward glide until the spinning stopped, whereupon the rockets become forward stable and nose-dived.”


I believe all the Always rockets had straight fins, with spin, if any, induced accidentally. Given the positive feedback effect of the horizontal spin effect, once yours STARTS spinning it shouldn’t stop until impact.

so I am excited to see your project and look forward to a flight report. I am gonna start playing with these, I just need to have a place where a ballistic recovery is okay. I am also likely gonna try it starting with BT-5 rockets, and maybe rounded nose cones (or maybe get some Nerf Darts for noses




Okay, end of my diatribe. The rest of this is web sites and other information, apparently there is a limit on words and I am past it, so I can’t put The Whole thing here

interesting reading here on these two sites

https://www.freepatentsonline.com/6926576.html

http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf

 

[neil_w]

@Neil may chime in here.

I dunno. To me, @Dotini's rocket looks like it should come in ballistic, just going purely by mindsim. It's possible that *sometimes* it will achieve a horizontal spin, but I have a hard time imagining that it will do it *reliably*. But I'm just guessing.

That's why I like the idea of (somehow) getting a horizontal spin can to the front of the rocket at ejection; that would pretty much guarantee (I think) that it couldn't come in ballistic, even if the horizontal spin failed to materialize.

 

[BABAR]

I dunno. To me, @Dotini's rocket looks like it should come in ballistic, just going purely by mindsim. It's possible that *sometimes* it will achieve a horizontal spin, but I have a hard time imagining that it will do it *reliably*. But I'm just guessing.

That's why I like the idea of (somehow) getting a horizontal spin can to the front of the rocket at ejection; that would pretty much guarantee (I think) that it couldn't come in ballistic, even if the horizontal spin failed to materialize.

What do you think of the idea that you can build rockets that are stable by Barrowman equation (and presumably by programs like OpenRocket) but are UNSTABLE on cardboard cutout? Seems to me that any really long thin rocket with any fins all WOULD be stable by cardboard cutout?

 

[neil_w]

Cardboard cutout doesn’t seem relevant at all once you’re dealing with aerodynamic surfaces that are not perpendicular to the surface if the airframe (and hence don’t show up properly in a cardboard cutout).

Why are we talking about cardboard cutouts? They are at best a tool for crude estimation.

 

[BABAR]

@neil_w

From this

http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf
We are interested in models that pass the Barrowman test—the CG is in front if the Barrowman CP (BCP), but fail the cardboard cutout test—the CG is behind the CLA. This can be bad if you launch from a short rod in high winds; an otherwise stable model goes unstable. But our hypothesis is that this condition, a CG ahead of the Barrowman CP, but behind the center of lateral area, leads to a miracle

Such a model is stable under boost, going forward as long as the angle of attack is low, but it can experience a high angle of attack if it is pointing straight up at apogee. When it experiences a high angle of attack for a moment, and loses its stability. When the air hits the model moving sideways, the model wants to point so that its CG is ahead of the CP. But at high angles of attack, the CP is the center of lateral area, which is ahead of the CG. The model wants to point backwards. But if the model goes straight backwards, the angle of attack goes low again, and now the CP is ahead of the CG. The model wants to turn around again. The model wants to crash, but backwards or forwards? It settles into a compromise angle of attack moving backwards. It glides.

 

[Dotini]

Well, I'd say I had a qualified success today at Dahl field. We launched the Magnus! X-1 on an A8-3. After apogee and upon ejection charge activation, it kicked over, went tail first (backsliding), then started spinning horizontally and rolling sideways into the wind. I suppose that is evidence of the Magnus effect! It landed horizontally. Unfortunately, upon landing, the body tube was kinked directly in front of the motor. I have all this on video, but something didn't work when I ltried to insert it. I'll get my friend Blair to help me with that.

Friends, that was a bittersweet flight. The scientist in me was ecstatic, but the model maker was subdued.

I also launched a revamped die Glock, and got an excellent flight. The landing, though improved, still needs work.

We finished off with thrilling smoke and thunder from the Mega-Vortico, attracting attention from the across the field. (It's the size of four baseball fields).


Kinked tube upon landing. Pretty sure this was my own fault, as I mishandled the rocket upon inserting the taped up motor into the tube. Rookie mistake. It was perfectly straight from cone to nozzle when I put it on the 46' launch rod.

I made a very nice hole in the (detachable) forward section, using a brad point @ 1700 rpm with the tube supported internally with a snug fitting dowel and externally by a vee block.

 

[mooffle]

Friends, that was a bittersweet flight. The scientist in me was ecstatic, but the model maker was subdued.

This seems to be the fate of many prototypes. Glad I was wrong and that it worked, @neil_w and I must have similar mindsims because I totally would have put money on ballistic.
After doing more reading this makes a lot of sense why I've seen my own slender rockets recover horizontally after semi-failed chutes and streamers.

 

[Dotini]

Emotionally I don't quite know what to feel. In my first attempt, I briefly got my hands on the Holy Grail of tumble recovery, the Magnus Effect. Yet I lost the ship on the voyage.

 

[Sandy H.]

Well, I'd say I had a qualified success today at Dahl field. We launched the Magnus! X-1 on an A8-3. After apogee and upon ejection charge activation, it kicked over, went tail first (backsliding), then started spinning horizontally and rolling sideways into the wind. I suppose that is evidence of the Magnus effect! It landed horizontally. Unfortunately, upon landing, the body tube was kinked directly in front of the motor. I have all this on video, but something didn't work when I ltried to insert it. I'll get my friend Blair to help me with that.

Friends, that was a bittersweet flight. The scientist in me was ecstatic, but the model maker was subdued.

I also launched a revamped die Glock, and got an excellent flight. The landing, though improved, still needs work.

We finished off with thrilling smoke and thunder from the Mega-Vortico, attracting attention from the across the field. (It's the size of four baseball fields).


Kinked tube upon landing. Pretty sure this was my own fault, as I mishandled the rocket upon inserting the taped up motor into the tube. Rookie mistake. It was perfectly straight from cone to nozzle when I put it on the 46' launch rod.
View attachment 457196
I made a very nice hole in the (detachable) forward section, using a brad point @ 1700 rpm with the tube supported internally with a snug fitting dowel and externally by a vee block.

X-acto, coupler, glue and a 2" shorter rocket may make the scientist happy a second time at least. Possibly some 'additional detail work' will make the modeler less upset. Maybe a really short roll-pattern. . .

Cool project.

Sandy.

 

[Dotini]

X-acto, coupler, glue and a 2" shorter rocket may make the scientist happy a second time at least. Possibly some 'additional detail work' will make the modeler less upset. Maybe a really short roll-pattern. . .

Cool project.

Sandy.

Yeah, I hadn't done much detail work on X-1, since I was in such a rush to catch the good weather. It has some flaws. I'll carefully remove the damaged section and evaluate repairs before going ahead with X-2, which is held for want of vital parts. And I'll get to back to work on my ringtails until my X-2 parts arrive.

 

[Kelly]

I thought the right hand rule had to do with electricity? But I'd like to know more if it also applies to aerodynamics. My fins are twisted oppositely to Figure 13.

Aerodynamics doesn't care about handedness. In fact, nothing in physics does - the right hand rule is simply used to remember human-derived conventions, such as which way should be named 'positive' on x,y,z axes, or which way magnetic fields point relative to a charge that humans have chosen to name 'positive'.

 

[BABAR]

Aerodynamics doesn't care about handedness. In fact, nothing in physics does - the right hand rule is simply used to remember human-derived conventions, such as which way should be named 'positive' on x,y,z axes, or which way magnetic fields point relative to a charge that humans have chosen to name 'positive'.

Hmmm, true regarding aerodynamics, not sure correct on angular momentum

https://courses.lumenlearning.com/boundless-physics/chapter/vector-nature-of-rotational-kinematics/

 

[Kelly]

Hmmm, true regarding aerodynamics, not sure correct on angular momentum

But I think this, itself, is just a convention as well. We choose to define the angular momentum as following the right hand rule, just to have a convention. If we instead defined it oppositely, nothing would change. If you assume instead that there is a left hand rule for angular momentum, and work through the examples in that link, you get the exact same results.

 

[Dotini]

But I think this, itself, is just a convention as well. We choose to define the angular momentum as following the right hand rule, just to have a convention. If we instead defined it oppositely, nothing would change. If you assume instead that there is a left hand rule for angular momentum, and work through the examples in that link, you get the exact same results.

Perhaps there is a practical difference in the way the fins are oriented, right or left. At the top of its arc at exhaust port kickover, the Figure 13/Magnus Effect rocket will slew around, slide backwards, feel the wind, and start spinning. My test rocket slewed clockwise, felt the wind, then turned counterclockwise and spun rolling horizontally into the wind. If the fins had been oriented the other way, it may have reacted differently under the same circumstances.