BackSpin— An experiment in mixing BackSlide and Horizontal Spin recoveries

[BABAR]

After @Dotini ‘s success, I am hoping to build on his sucess.

so this will be a mixture of recovery techniques

https://patents.google.com/patent/US6926576
http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf
a key on these is that some models that had imparted spin (unintentionally, I think) successfully “backslid “ until they stopped spinning at which point they went ballistic (literally.) I theeeeeenk that the spinning resulted in Horizontal Spin effect, which is half the battle.

Sooooo, what if we could keep it spinning? Looks like all the rockets in the above articles had normal planar fins. Perhaps some were canted a bit, but looks like that was unintentional, and canted fins won’t maintain a spin once the rocket goes horizontal anyway.

Edit: okay, @Rktman just showed me that was wrong

I have done horizontal spin successfully, but for the most part I did a James T. Kirk Kobayasihi Maru maneuver (to quote McCoym “He cheated.”) I dumped the nose cone or used it as a booster segment. I am not sure that segments that I successfully did horizontal spin on weren’t STILL stable (they would probably have lawn darted if they HADN’T spun, but they weren’t EXTREMELY stable rockets.

@Dotini has performed a bit of magic getting HIS rocket to horizontal spin WITHOUT a CG shift or other configuration change, just using a forward blowhole of the ejection charge to momentarily “stun” the smooth forward stabile trajectory, throwing the angle of attack from normal near zero to likely something likely 30 degrees or more off axis. The rocket begins to fall, and it’s a race to see which aerodynamic force will kick in first.

The EXPECTED result is that tail/fin drag vs pointy heavy nose OBVIOUSLY will pull the model nose down and it will auger in.

the HOPED result is that the “funky fins” will get this to start rotating, and because of the positive feedback (what starts as a randomly tumbling rocket with the right fin structure is amazingly easy to start rotation, and as it starts rotating AND falling goes more horizontal which brings it into a positive feedback loop with eventual PERFECT alignment for BOTH maximal spin AND maximum drag.)

the QUESTION is WILL IT GLIDE? (Calling @Rktman !) of course, I am not sure how the backsliders in the above links glided either.

on the other hand, the StovePipe was a rotating glider as well, the problem was to keep it rotating

http://www.spacemodeling.org/jimz/eirp_56.htm
Anyway, starting with three pairs of tube fins (going with 6 tubes around a central tube of same diameter.) aligning two tube fins in pairs is easy, and the pairs will automatically align with the long axis of the central core and provide automatic perfect spacing.

I am going to start with a short body tube base, I will add a length of body tube to it to get at least a 30 to 1 length to tube diameter ratio.

after seeing where @Dotini ‘s rocket took a crimp (not sure the cause, but suspect bent on impact) I may beef that segment up.


(just for fun I found somebody actually made a model of the Kobayashi Maru from the limited images from the Abrams movie.
I threw a pic in just for fun. Google it under shopping and you’ll find it.)

 

[Rktman]

Backsliders don't need to spin to glide backward (tail first). However in the case of my backslider, it spins continuously while gliding because I intentionally canted one of the fins about two degrees. (I'd read an article where the author/builder wanted his backslider to circle so he wouldn't lose it, so he experimented with canting one of his fins). Mine still makes a beeline for the horizon, but the rapid spinning was unexpected (though I probably should have anticipated it would). Backsliders actually glide quite well, covering far more distance horizontally then vertically.

BTW, my body is somewhat bent/crimped in approximately the same area (just forward of the fins) as @Dotini's since these rockets come in tail-first. Seems to be a common malady with long, thin rockets.

 

[BABAR]

Backsliders don't need to spin to glide backward (tail first). However in the case of my backslider, it spins continuously while gliding because I intentionally canted one of the fins about two degrees. (I'd read an article where the author/builder wanted his backslider to circle so he wouldn't lose it, so he experimented with canting one of his fins). Mine still makes a beeline for the horizon, but the rapid spinning was unexpected (though I probably should have anticipated it would).

Okay, did a search under your handle and didn’t find anything under backslide or backslider, so either I am missing it or you didn’t post anything on the forum on it. Can you post a link to it (assuming I missed it) or provide some more information here?

I am still struggling with conceptually understanding how the RingHawk glider you built figures out which way is “up” and manages a stable glide, now I am equally baffled as to how a longitudinally spinning rocket with straight (or slightly canted) fins generates any lift while spinning. Then again, there is lots I don’t understand! Maybe if the angle is right the body tube itself generates some lift?

OTOH, the fact that you have made a spinning glider makes me think this project IS viable

 

[teepot]

I had a big bertha lose it's nose cone at ejection. The body fell and was spinning along the long axis like mad. It landed without damage. The chute and nose cone drifted off into the sunset never to be seen again. I've seen the same thing at a couple of launches. The nose cone separates with the chute and the body spins while falling. No ballistic descent.

 

[Rktman]

I never got around to posting a build thread for it.

I'm guessing the spinning doesn't contribute as much to lift as it does to stability, like those old Whamo! Turbo Tube toys that you threw like a football.
Here's what the Alway brothers had to say about it: http://www.lunar.org/docs/LUNARclips/v9/v9n4/superroc.shtml

I think a longitudinally spinning rocket (like a backslider) doesn't produce any Magnus Effect lift. It would if it were flying sideways (or falling vertically) while spinning. And I think the larger the diameter of your ring tail, the more lift it would produce, again assuming it's falling flat and spinning (larger surface area to affect airflow). Just my conjecture.

 

[Dotini]

After @Dotini ‘s success, I am hoping to build on his sucess.

so this will be a mixture of recovery techniques

https://patents.google.com/patent/US6926576
http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf
a key on these is that some models that had imparted spin (unintentionally, I think) successfully “backslid “ until they stopped spinning at which point they went ballistic (literally.) I theeeeeenk that the spinning resulted in Horizontal Spin effect, which is half the battle.

Sooooo, what if we could keep it spinning? Looks like all the rockets in the above articles had normal planar fins. Perhaps some were canted a bit, but looks like that was unintentional, and canted fins won’t maintain a spin once the rocket goes horizontal anyway.

Edit: okay, @Rktman just showed me that was wrong

I have done horizontal spin successfully, but for the most part I did a James T. Kirk Kobayasihi Maru maneuver (to quote McCoym “He cheated.”) I dumped the nose cone or used it as a booster segment. I am not sure that segments that I successfully did horizontal spin on weren’t STILL stable (they would probably have lawn darted if they HADN’T spun, but they weren’t EXTREMELY stable rockets.

@Dotini has performed a bit of magic getting HIS rocket to horizontal spin WITHOUT a CG shift or other configuration change, just using a forward blowhole of the ejection charge to momentarily “stun” the smooth forward stabile trajectory, throwing the angle of attack from normal near zero to likely something likely 30 degrees or more off axis. The rocket begins to fall, and it’s a race to see which aerodynamic force will kick in first.

The EXPECTED result is that tail/fin drag vs pointy heavy nose OBVIOUSLY will pull the model nose down and it will auger in.

the HOPED result is that the “funky fins” will get this to start rotating, and because of the positive feedback (what starts as a randomly tumbling rocket with the right fin structure is amazingly easy to start rotation, and as it starts rotating AND falling goes more horizontal which brings it into a positive feedback loop with eventual PERFECT alignment for BOTH maximal spin AND maximum drag.)

the QUESTION is WILL IT GLIDE? (Calling @Rktman !) of course, I am not sure how the backsliders in the above links glided either.

on the other hand, the StovePipe was a rotating glider as well, the problem was to keep it rotating

http://www.spacemodeling.org/jimz/eirp_56.htm
Anyway, starting with three pairs of tube fins (going with 6 tubes around a central tube of same diameter.) aligning two tube fins in pairs is easy, and the pairs will automatically align with the long axis of the central core and provide automatic perfect spacing.

I am going to start with a short body tube base, I will add a length of body tube to it to get at least a 30 to 1 length to tube diameter ratio.

after seeing where @Dotini ‘s rocket took a crimp (not sure the cause, but suspect bent on impact) I may beef that segment up.View attachment 457658View attachment 457659


(just for fun I found somebody actually made a model of the Kobayashi Maru from the limited images from the Abrams movie.
I threw a pic in just for fun. Google it under shopping and you’ll find it.)

Very interesting project which I will follow closely. I'm learning a lot and having loads of fun, already working on X-2 and beyond, seeking the Holy Grail of Magnus Effect. How will you induce spin in your model? There are several ways - I don't know how many - but my friend Blair tells me fin angle of attack is best.

 

[BABAR]

Very interesting project which I will follow closely. I'm learning a lot and having loads of fun, already working on X-2 and beyond, seeking the Holy Grail of Magnus Effect. How will you induce spin in your model? There are several ways - I don't know how many - but my friend Blair tells me fin angle of attack is best.

I too would like to see a rocket that truly recovers via Magnus effect, but given Magnus force is always perpendicular to airflow, I can't see a way to generate it from the airflow created by a falling rocket.

Angle of attack can certainly generate spin, canted fins have been used both on real sounding rockets (to reduce weathercocking, I believe), also used "just cuz" on model rockets. And I seem to recall it being used in some rocket gliders, I think because the tend to weathercock as well. It was also used in the StovePipe, the cylindrical glider would glide as long as it spun, the forward edge was weighted symmetrically to provide inertial mass to prolong the spin (the motor and body and nose were ejected out the back.)

BackSpin will have 6 radially evenly space tube fins, with the clockwise lateral 1/3 to 1/2 cut out. Fins remain parallel to flight path as long as rocket flies nose first (boost phase.) When falling truly horizontally, viewed from nose, at any given time the fins on the right are concave to airflow (think "cups") will those on the left are convex to airflow (think Mosquito rocket nose cone.)

Key event is ejection gas from unilateral nose port kicking the nose sideways. (Note: @Dotini this is also a possible source of crimping of the tube.)

Initially starts a random fall and the race is for which force kicks in first, tail drag or rotation. @neil_w, this is where the cardboard cut out test trumps the barrowman and sim programs, the latter two do not apply to a randomly falling object (basically high angle of attack.)

So the idea is that on boost with near zero angle of attack, OpenRocket applies. But if we can either stop the rocket completely or more likely at least START an initially uncontrolled tumble, cardboard cut out trumps Open Rocket (BackSlider theory.) If we can add SPIN we tip the scales to get the rocket to fall horizontal, to some extent we can even overcome cardboard cut out. This gets us to AT LEAST max drag (rocket falling horizontally, 90 degrees off ballistic.) At this point I don't completely understand how this can "glide." Even if it does go horizontal, spinning rapidly, and not only falling vertically but also traveling "backwards" parallel to axis, the Magnus Force will STILL not be in an upward direction, but lateral to both the descent vector AND the axis of rotation (the vector ALONG the longitudinal axis.) So physics says the Magnus force will pull the rocket LATERALLY. This doesn't help slow the rocket's fall (does not hurt, either).

 

[BABAR]

I think a longitudinally spinning rocket (like a backslider) doesn't produce any Magnus Effect lift. It would if it were flying sideways (or falling vertically) while spinning. And I think the larger the diameter of your ring tail, the more lift it would produce, again assuming it's falling flat and spinning (larger surface area to affect airflow).

I initially disagreed with your statement, the quibble is with the term "lift." An airplane flying upside own may still produce "lift" even if the vector for that lift is DOWN. Positively airfoiled fins (as opposed to neutral or symmetrical airfoiling) also produce "lift" with the force causing longitudinal rotation around the long axis. A spinning rocket does provide potentially plenty of Magnus Force, which can be termed "lift", unfortunately it is (from a recovery standpoint) useless lift because it is lateral, it doesn't slow the rocket down.

 

[Rktman]

Since your spinning Bail Out Bill rocket did successfully soft recover, perhaps that may be evidence that there was some amount of Magnus Effect involved? Anyhoo, if your bird is set up to the proportions of the Alway Bros. backslider (long and thin with a vent hole as far forward as possible and the CG set where advised) it will "glide" (nothing record-setting or with the duration of a traditional glider of course) but it'll definitely cover more distance horizontally than vertically. Unknown whether the spinning will extend duration though since it'll be spinning longitudinally. Again, my hunch is that the spinning primarily contributes to its stability, the same way rifling stabilizes a spinning bullet. Hope my hunch is incorrect though and that the spinning DOES make for a longer glide time.

Glad you decided to investigate what I feel is a fascinating phenomenon that has unfortunately gone largely unexplored. This should be a fascinating experiment to watch unfold.

 

[Dotini]

Since your spinning Bail Out Bill rocket did successfully soft recover, perhaps that may be evidence that there was some amount of Magnus Effect involved? Anyhoo, if your bird is set up to the proportions of the Alway Bros. backslider (long and thin with a vent hole as far forward as possible and the CG set where advised) it will "glide" (nothing record-setting or with the duration of a traditional glider of course) but it'll definitely cover more distance horizontally than vertically. Unknown whether the spinning will extend duration though since it'll be spinning longitudinally. Again, my hunch is that the spinning primarily contributes to its stability, the same way rifling stabilizes a spinning bullet. Hope my hunch is incorrect though and that the spinning DOES make for a longer glide time.

Glad you decided to investigate what I feel is a fascinating phenomenon that has unfortunately gone largely unexplored. This should be a fascinating experiment to watch unfold.

My own experiments continue, as well. X-2 will feature improved resistance to damage upon landing, and hopefully be robust enough to perform a series of tests to determine just how far below 50 to one it can get before reduced performance sets in. Another test will be of alternate methods of inducing spin.

 

[Rktman]

My own experiments continue, as well. X-2 will feature improved resistance to damage upon landing, and hopefully be robust enough to perform a series of tests to determine just how far below 50 to one it can get before reduced performance sets in. Another test will be of alternate methods of inducing spin.

If it's any help, my backslider tends to crimp just forward of the fins (probably from touchdowns aft-first). That might be an area you might want to consider reinforcing with a coupler and/or CA. In my case, I had to add weight to the aft end anyway to get the CG where indicated in the Alway Brothers backslider plans.

 

[rharshberger]

Somebody actually wrote a article on backsliding rockets at one point iirc. Cant remember who but it might have been Peter Alway.

Edit: It was Peter and the OP had already linked it in post #1.

 

[BABAR]

If it's any help, my backslider tends to crimp just forward of the fins (probably from touchdowns aft-first). That might be an area you might want to consider reinforcing with a coupler and/or CA. In my case, I had to add weight to the aft end anyway to get the CG where indicated in the Alway Brothers backslider plans.

I love it when one part can accomplish 2 or more functions. The mass reinforcing the rear may help bring CG back. I guess I need to build a regular back slider on addition to the BackSpin.

One problem I see is launch sites. Not sure that experiments with rockets where the question is, " Ballistic or Not" mix well with public sites.

This is one reason I am starting with BT 5 models and I may use @jqavins idea of a nerd dart for a nose cone.


Edit: Nerf dart, not Nerd Dart. Stupid spell check....

 

[BABAR]

Probably a relatively uncommon fin can. Need to sand down the cut off edges closest to center. I used white glue, which is what I usually use for paper to paper.

Don't want to start a glue thread, but anybody got a good paper to paper glue recommendation that stands well?

 

[BABAR]

Nose cone options

One is a Nerf Dart (with bonus whistle, my Hope's for audible sound are not high!) Other is a BT-5 CONE. I got 50 for a song from Apogee Rockets a decade ago.

Single standard hole punch hole

 

[BABAR]

Cleaned up edges and hardened with thin CA. sanded as much as I could.

Should have put in launch lugs later, covered the areas of placement. Can't get a rolled up Sandpaper in to clean that.

Thanks to @Mugs914 for the tube fin idea, I think it will work really well. Even if it doesn't spin recover, it makes a cool fin can

 

[BABAR]

I used two small launch lugs. Additional drag really isn’t an issue, mainly I use two small lugs with less mass than a single large lug. I didn’t want the extra asymmetric weight to throw the spin off any more than necessary.

just hit it with first coat of prime, I really like the look of the cut tube fins.

I’m going with a swappable forward body tube, one with the Nerf Dart nose, the second with the plastic nose. I figure if experiment fails and it comes in ballistic, I am better off with a short flat soft nose than a pointy hard plastic one, mass is really low, this will easily boost on an A10-3, may go smaller if I have any in my stash.

 

[BABAR]

I never got around to posting a build thread for it.

I'm guessing the spinning doesn't contribute as much to lift as it does to stability, like those old Whamo! Turbo Tube toys that you threw like a football.
Here's what the Alway brothers had to say about it: http://www.lunar.org/docs/LUNARclips/v9/v9n4/superroc.shtml

I think a longitudinally spinning rocket (like a backslider) doesn't produce any Magnus Effect lift. It would if it were flying sideways (or falling vertically) while spinning. And I think the larger the diameter of your ring tail, the more lift it would produce, again assuming it's falling flat and spinning (larger surface area to affect airflow). Just my conjecture.

Any pics of your backslider bird?

 

[Rktman]

Any pics of your backslider bird?

For some reason this is the only thing in my fleet I've never snapped a pic of. So here you go, fresh off my camera's SDHC card.

 

[BABAR]

Very nice!

is it reliable? I’m kind of wondering, it things like backsliding recovery and horizontal spin (and possibly a combination of both) are consistently reliable, seems like these would be popular birds. If you have a motor hook, prep time is like, shove a motor in, sticking an igniter, throw it on the pad, clear the area and punch it. No wadding, no streamer or chute, no worries about cone too tight.

did you have to play with balancing it at all? Nose or tail weight?

 

[Rktman]

Very nice!

is it reliable? I’m kind of wondering, it things like backsliding recovery and horizontal spin (and possibly a combination of both) are consistently reliable, seems like these would be popular birds. If you have a motor hook, prep time is like, shove a motor in, sticking an igniter, throw it on the pad, clear the area and punch it. No wadding, no streamer or chute, no worries about cone too tight.

did you have to play with balancing it at all? Nose or tail weight?

Flown 5X, worked perfectly each time. Semi-retired at the moment due to the crimp just forward of the fins. Built exactly to the specs in the Alway Bros. backslider plans (except I didn't make the fin can removable, thereby omitting the weight of a 3" coupler. In retrospect, maybe if I had included it, there might not be a crimp in the body tube where there is one now ).

Affirmative, some rebalancing was necessary. That slug of weight in the photos just aft of the fins was necessary to get the CG exactly where specified in the plans.

 

[Rktman]

...seems like these would be popular birds. If you have a motor hook, prep time is like, shove a motor in, sticking an igniter, throw it on the pad, clear the area and punch it. No wadding, no streamer or chute, no worries about cone too tight.

I'm guessing they're not more popular because, like super rocs, they're prone to bending and crimping because of their length and thinness. They're a problem to store and transport (unless you use a coupler so you can break them down between flights). That said, I really like mine because of its unique type of recovery and it's always an attention getter.

 

[BABAR]

I'm guessing they're not more popular because, like super rocs, they're prone to bending and crimping because of their length and thinness. They're a problem to store and transport (unless you use a coupler so you can break them down between flights). That said, I really like mine because of its unique type of recovery and it's always an attention getter.

I will have to see how mine go. I am starting with the same relative super length. I am wondering if the spin addition will allow me to work with shorter length.

I think you nailed it with the coupler idea. I read somewhere that that is how many transport their Mean Machines.

Was yours according to plans, built BT-20?

 

[Rktman]

Was yours according to plans, built BT-20?

Yes BT-20. Never got around to trying a 13mm size since this one is already hard to track as it descends.

 

[BABAR]

Yes BT-20. Never got around to trying a 13mm size since this one is already hard to track as it descends.

Hybrid might be interesting. Eject the nose with a streamer which is just enough to keep the nose from dragging the rocket ballistic. Still attached to body, which backslides. I have seen this on a number of my asymmetric fin models, rockets that recover well on streamers despite their size, at least in part because they turn horizontal.

 

[TomBroad]

You can make a model rocket glide backward for recovery, sometimes with it spinning also. This is patentable? SERIOUSLY? I discovered this accidentally 50 years ago when flying modrocs, especially with long thin models with tube fins, BT-20 & BT-50 (D-powered). Spit the none on a streamer and the body glides back. Always amazing to watch.

 

[Bruce]

Maybe add small wings to increase the glide ratio too?

 

[BABAR]

Thought about Eric's (@Rktman ) idea of coupler, and since obviously the toughest part of the bird is the fin can, put the split there. Since this is BT_5, there really isn't that much extra link to work with. The blue is a stubby nose cone actually a Nerf dart and will be the first flight just to make sure the backspin concept works. I don't know if you can see it here but there is a piece of cellophane tape along the forward edge of the fincan unit and along the trail edge of the body tubes.
This allows me to tape the units together and exchange them. (The tape protects the underlying cardboard and paint so I can put an outer layer of tape on and take it off with relative impunity.) I will be able (assuming the initial flights are successful) to at least try one piece cutting it shorter and shorter and seeing how short I can get this to work.

 

[BABAR]

I'm guessing they're not more popular because, like super rocs, they're prone to bending and crimping because of their length and thinness. They're a problem to store and transport (unless you use a coupler so you can break them down between flights). That said, I really like mine because of its unique type of recovery and it's always an attention getter.

Since you and Frank @burkefj seem to be the current glider gurus (@georgegassaway has branched out into drone recovery and other cool pursuits), wondering about backslide recovery. Is it REALLY gliding (I guess I define “gliding” as “forward movement generating vertical (away from earth’s core) lift”) or is the rocket simply falling horizontally so really all that is going on is the rocket is held in a high drag profile?

the first I would call true gliding, the second, to quote Woody referring to Buzz Lightyear in Toy Story, I would call “falling with style.”

Assuming my model works, I would not expect a crimp from impact, as the fins don’t stick out very far, they actually will flex a bit. A more worrisome source of crimp is the ejection charge going out the lateral port. This causes an intentional lateral “kick” to get again of attach way off zero. It likely also cause lateral stress emphasized at the tube fin can junction. I am wondering if a second similar or smaller hole bored in the body tube on opposite lateral side wall of the body tube would counter the stress, you are kicking the nose to the right, the tail to the left, theoretically no net stress on the rocket tube.

????

also wondering if the holes will whistle?

do pigs fly?

according to @hcmbanjo, they do. Hey Chris, would you sell a reliable BackSlider?

@jadebox

 

[Rktman]

...wondering about backslide recovery. Is it REALLY gliding (I guess I define “gliding” as “forward movement generating vertical (away from earth’s core) lift”) or is the rocket simply falling horizontally so really all that is going on is the rocket is held in a high drag profile?

I vote for “falling with style.”
Without any airfoiled surfaces, I can't see how a backslider would generate any lift at all.