Horizontal Spin Recovery - with Magnus Effect?

jhill9693

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Yes, very interesting - and your paint scheme looks very good, too. I've long thought about adding a booster to one of my HSR rockets, especially in the attempt to go over the one minute descent time mark. I have several boosters on hand. But I've hesitated because (#1) I've wanted to make the best possible sustainer first, and (#2) because the altitude attainable might easily get the model lost to sight and video. Accordingly, I've tried to get the diameter of my models up to the bigger tube sizes for improved visibility. Unfortunately, the bigger the tube size it seems some of the problems also get bigger, and experience teaches me BT-5 and BT-20 are the best sizes to experiment with and not get too carried away with expense and lost models. From the looks of your sustainer, it seems as though it may have come in ballistically. The 100% absolute reliability of the ejection event which starts the horizontal spin descent mode is probably not attainable. I have a model in which the event went perfectly 13 times in a row, but the 14th time the rocket went ballistic and the tube crumpled on impact. I'm still trying to wrap my mind around the physics and technology of this most crucial phase of the mission with the goal of near-perfect reliability. Sometimes I question the variability inherent in the Estes motors, in particular the consistency of the ejection event. Are some Estes motors statistically more reliable than others? I wonder about that. Keep up the good work!
Perhaps airspeed at the time of the event is a factor. Airspeed could be higher after staging, and it could be higher after a long delay and ballistic descent has already begun.

I’m toying with a HPR dual deploy upscale of one of these and using a sideways 1/2A or 1/4A forward thruster to trigger the roll. This could be very reliable with the right igniter.
 

Dotini

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Perhaps airspeed at the time of the event is a factor. Airspeed could be higher after staging, and it could be higher after a long delay and ballistic descent has already begun.

I’m toying with a HPR dual deploy upscale of one of these and using a sideways 1/2A or 1/4A forward thruster to trigger the roll. This could be very reliable with the right igniter.
Agreed, airspeed at the time of the event is a major factor. I've found short delays and plenty of speed at the event are safer than longer delays and a slowing rocket.
 

jhill9693

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Agreed, airspeed at the time of the event is a major factor. I've found short delays and plenty of speed at the event are safer than longer delays and a slowing rocket.
Oh, interesting. So probably my 1/2A3-4T wasn’t the best choice for the sustainer.
 

BABAR

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I've built and flown about ten HSR rockets in all tube sizes from BT-5 to BT-55. Most in the 50:1 ratio, but some at 40:1

My best performer, a BT-20 seen below, has spiraled four complete circles from apogee in a 1 mph wind.

View attachment 531611
Rear tube is taped to straight edge. Gap of about 1/8" exists at front of front tube. Note opposite misalignment of nosecone. These variations from design specification resulted from accidental mistakes in the build.

My current and near-future HSR models will have tube curvature deliberately built-in to compare with otherwise similar straight tube models. I'm also investigating other means of controlling body tube diameter/eccentricty in preferential sections of the airframe.

Edit: I guess my hypothesis is that the kinked horizontally spinning rocket develops unevenly distributed aerodynamic (Magnus) forces along the length of the tube, constantly pulling the rocket away from a single direction.
Maybe I am losing it, but I don't see/appreciate the "misalignment" of the nose cone.

My theory on spiral effect is slightly different from yours. Almost absolutely secondary to unevenly distributed Magnus force, but I would expect the greatest variability would be with the fin can segment. Again, not certain if the LARGER and MORE IRREGULAR spinning fins generate MORE or Less Magnus than the SMALLER and SMOOTH body tube (larger size makes me think more, but irregularity makes me think spoiled lift. @Rktman wanna render an opinion here?)

In any case, I would suspect significant difference. what surprises me is that they ALL don't spiral, my hypothesis is that with smaller fins and greater length to diameter the body tune Magnus force dominates, and the tail variation (whether less or more) is negligible, thus rocket BackSlides straight. With shorter rockets and or bigger fins, the tail component asymmetry dominates and spirals.

slightly disappointed with idea that HSR may be susceptible to the same problem as dedicated Back Slide, namely that occasionally the random post ejection “puff” orientation is near vertical nose down. I think HSR is LESS susceptible than BSR, but if post puff it is IN this near vertical nose down position, when it starts to fall the fins “catch” ballistically rather than start to rotate. I think this susceptibility can be MINIMIZED although likely not eliminated by long light weight body tubes, very light nose cones, light paint jobs (keep CG as far back as possible, although still at least one caliber ahead of Barrowman CP). The goal is that the initial fall post ejection charge puff is a tumble (which fin orientation will convert to a positive vicious cycle spine) rather than a negative vicious cycle ballistic redovery.
 

jhill9693

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Maybe I am losing it, but I don't see/appreciate the "misalignment" of the nose cone.

My theory on spiral effect is slightly different from yours. Almost absolutely secondary to unevenly distributed Magnus force, but I would expect the greatest variability would be with the fin can segment. Again, not certain if the LARGER and MORE IRREGULAR spinning fins generate MORE or Less Magnus than the SMALLER and SMOOTH body tube (larger size makes me think more, but irregularity makes me think spoiled lift. @Rktman wanna render an opinion here?)

In any case, I would suspect significant difference. what surprises me is that they ALL don't spiral, my hypothesis is that with smaller fins and greater length to diameter the body tune Magnus force dominates, and the tail variation (whether less or more) is negligible, thus rocket BackSlides straight. With shorter rockets and or bigger fins, the tail component asymmetry dominates and spirals.

slightly disappointed with idea that HSR may be susceptible to the same problem as dedicated Back Slide, namely that occasionally the random post ejection “puff” orientation is near vertical nose down. I think HSR is LESS susceptible than BSR, but if post puff it is IN this near vertical nose down position, when it starts to fall the fins “catch” ballistically rather than start to rotate. I think this susceptibility can be MINIMIZED although likely not eliminated by long light weight body tubes, very light nose cones, light paint jobs (keep CG as far back as possible, although still at least one caliber ahead of Barrowman CP). The goal is that the initial fall post ejection charge puff is a tumble (which fin orientation will convert to a positive vicious cycle spine) rather than a negative vicious cycle ballistic redovery.
If you’re correct, it could be eliminated with multiple programmable attitude thrusters near the forward end, either remotely controlled or with onboard electronics. (If the first charge results in a ballistic orientation, fire another. Repeat as needed.)

On that note, vectoring the ejection charge to encourage spin may also help. This may be difficult to accomplish in small diameter models.
 

Dotini

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Maybe I am losing it, but I don't see/appreciate the "misalignment" of the nose cone.

My theory on spiral effect is slightly different from yours. Almost absolutely secondary to unevenly distributed Magnus force, but I would expect the greatest variability would be with the fin can segment. Again, not certain if the LARGER and MORE IRREGULAR spinning fins generate MORE or Less Magnus than the SMALLER and SMOOTH body tube (larger size makes me think more, but irregularity makes me think spoiled lift. @Rktman wanna render an opinion here?)

In any case, I would suspect significant difference. what surprises me is that they ALL don't spiral, my hypothesis is that with smaller fins and greater length to diameter the body tune Magnus force dominates, and the tail variation (whether less or more) is negligible, thus rocket BackSlides straight. With shorter rockets and or bigger fins, the tail component asymmetry dominates and spirals.

slightly disappointed with idea that HSR may be susceptible to the same problem as dedicated Back Slide, namely that occasionally the random post ejection “puff” orientation is near vertical nose down. I think HSR is LESS susceptible than BSR, but if post puff it is IN this near vertical nose down position, when it starts to fall the fins “catch” ballistically rather than start to rotate. I think this susceptibility can be MINIMIZED although likely not eliminated by long light weight body tubes, very light nose cones, light paint jobs (keep CG as far back as possible, although still at least one caliber ahead of Barrowman CP). The goal is that the initial fall post ejection charge puff is a tumble (which fin orientation will convert to a positive vicious cycle spine) rather than a negative vicious cycle ballistic redovery.
In re the misalignment of the nose cone, see below:
DSC00701.jpg
The rear tube is taped firmly to the straight edge. There is a clear gap at the front tube, and a reduced gap under the nosecone.

DSC00702.jpg
The nosecone is slightly larger in OD than the tube, and is misaligned - see raw balsa; see gap. Lazy workmanship for sure, but mistakes sometimes lead to a trail of questions and answers.

I welcome all your theoretical and practical ideas. What I need most is ideas for practical experiments I can do to clear up the questions.

Edit: When this rocket takes off at launch, a vicious corkscrewing is briefly visible.
 
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BABAR

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Oh, interesting. So probably my 1/2A3-4T wasn’t the best choice for the sustainer.
Long delays are gonna be bad. If the rocket is ALREADY on an established downward ballistic trajectory, the puff may be insufficient to knock it off course. Conversely, EARLY ejection isn‘t so bad, if the rocket is still vertical at time off puff, it will start to fall tail first, go unstable, start to tumble, start to spin, and Bob’s your uncle transition to HSR.

Unfortunately I believe that ejection charge at or near apogee ”puff” results in a random orientation (I don’t think there is any way to control or predict it, but I would love to be wrong.)
 

BABAR

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I welcome all your theoretical and practical ideas. What I need most is ideas for practical experiments I can do to clear up the questions.

Edit: When this rocket takes off at launch, a vicious corkscrewing is briefly visible.
I like your idea of experimenting with smaller rockets. Only downside especially with BT-5 is the mass to diameter ratio for the tube is higher, so the longer rocket has a more forward CG just due to relatively heavier tube.

My suggestion for experiments for spiraling is compare longer rockets with minimal fin length and diameter (enough for boost stability and HSR initiation) to shorter rockets with larger fin area.

For increased probability of success, consider using lighter nose cones (maybe the thin blow molded ones, although I don’t know how well they will handle ejection charge diversion) lighter tubes and couplers and stay light on paint and maximize length to diameter.

I think these are commonalities between HSR and BSR.
 
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Maybe I am losing it, but I don't see/appreciate the "misalignment" of the nose cone.

My theory on spiral effect is slightly different from yours. Almost absolutely secondary to unevenly distributed Magnus force, but I would expect the greatest variability would be with the fin can segment. Again, not certain if the LARGER and MORE IRREGULAR spinning fins generate MORE or Less Magnus than the SMALLER and SMOOTH body tube (larger size makes me think more, but irregularity makes me think spoiled lift. @Rktman wanna render an opinion here?)

In any case, I would suspect significant difference. what surprises me is that they ALL don't spiral, my hypothesis is that with smaller fins and greater length to diameter the body tune Magnus force dominates, and the tail variation (whether less or more) is negligible, thus rocket BackSlides straight. With shorter rockets and or bigger fins, the tail component asymmetry dominates and spirals.

slightly disappointed with idea that HSR may be susceptible to the same problem as dedicated Back Slide, namely that occasionally the random post ejection “puff” orientation is near vertical nose down. I think HSR is LESS susceptible than BSR, but if post puff it is IN this near vertical nose down position, when it starts to fall the fins “catch” ballistically rather than start to rotate. I think this susceptibility can be MINIMIZED although likely not eliminated by long light weight body tubes, very light nose cones, light paint jobs (keep CG as far back as possible, although still at least one caliber ahead of Barrowman CP). The goal is that the initial fall post ejection charge puff is a tumble (which fin orientation will convert to a positive vicious cycle spine) rather than a negative vicious cycle ballistic redovery.
In a perfectly aligned HSR, the rocket in its entirety is spinning at the same rate, so the Magnus Force should be equal across the body tube. The only deviations I can think of are the aforementioned kinked tube or misaligned nose cone which might introduce vortices or airflow disturbances that create enough drag to pull one end of the rocket away from a straight line backslide, causing it to circle instead.

When I built my backslider, I wanted it to circle my launch position so I wouldn't lose it, and so I wouldn't have to walk so far to recover it. So I purposely canted one of the fins about 3 degrees. What I didn't expect was that it would cause my backslider to spin pretty furiously. While it DOES have a bit of a curved trajectory back down to the ground, it was nothing like what I had hoped; it curves maybe about 30°, but definitely does not complete even one 360° circuit around my launch position. It's since developed a kink in the tube near the aft end, so it should be interesting to see if it'll cause it to spiral/circle more now than before.
 
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BABAR

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Eric, while I agree that slightly bent tubes or curves or a slightly askew nose cone would potentially cause variances of Magnus force, seems like these would be MINISCULE compared with the fin can. Again I am not sure whether the fin can would produce more or less force (argument for greater is the far larger effective diameter, argument for lesser [ which I think is stronger] is the severe discontinuity which I think would likely negate any effective force at all.)

@Dotini and @lakeroadster , got experiment for you if either of you have a lathe and a small fan.

Put a body tube on a lathe. Put fan either directly below or directly above. Take a crepe paper streamer (for safety purposes, if it gets caught in fan or lathe tears paper, not hand!) and hold it to left side and right side. If i remember the Bernoulli's principle right, on the side where the tube surface is spinning TOWARD the fan (airstream) the pressure should be higher as the flow is slowed, pressure is higher so streamer should be pushed outward away from the tube. On the ”spinning away” side the flow is faster, so should be lower pressure and “pull” the streamer toward the tube.

Most likely the fan flow will overwhelm the Magnus effect and will be inconclusive.


if it DOES however work, next would be to try it with a fin can with fins rotating at same speed, and see if effect is more or less pronounced. My guess is less, I think it will be so turbulent it will cancel Magnus effect.

Anyway, if you get bored building rockets (unlikely) something to try. I don’t have a lathe and if don’t have clamps to hold my drill in place, so I can’t do it.
 

Dotini

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Eric, while I agree that slightly bent tubes or curves or a slightly askew nose cone would potentially cause variances of Magnus force, seems like these would be MINISCULE compared with the fin can. Again I am not sure whether the fin can would produce more or less force (argument for greater is the far larger effective diameter, argument for lesser [ which I think is stronger] is the severe discontinuity which I think would likely negate any effective force at all.)

@Dotini and @lakeroadster , got experiment for you if either of you have a lathe and a small fan.

Put a body tube on a lathe. Put fan either directly below or directly above. Take a crepe paper streamer (for safety purposes, if it gets caught in fan or lathe tears paper, not hand!) and hold it to left side and right side. If i remember the Bernoulli's principle right, on the side where the tube surface is spinning TOWARD the fan (airstream) the pressure should be higher as the flow is slowed, pressure is higher so streamer should be pushed outward away from the tube. On the ”spinning away” side the flow is faster, so should be lower pressure and “pull” the streamer toward the tube.

Most likely the fan flow will overwhelm the Magnus effect and will be inconclusive.


if it DOES however work, next would be to try it with a fin can with fins rotating at same speed, and see if effect is more or less pronounced. My guess is less, I think it will be so turbulent it will cancel Magnus effect.

Anyway, if you get bored building rockets (unlikely) something to try. I don’t have a lathe and if don’t have clamps to hold my drill in place, so I can’t do it.
Speaking as a layman with no formal education in fluid dynamics, I would imagine the fin can as having zero Magnus effect or force. The fins falling through the air are the "engine" which turns the body tube at ~400 rpm, and themselves provide only the drag which spins the bare tube, which is the lifting body, and source of the Magnus effect. You could think of the spinning fins as analogous to the engine and propeller on a Piper Cub which pulls the wing through the air, providing lift though the Bernoulli effect.

I'm thinking of an experiment which would prove or disprove the existence of the Magnus effect as a source of vertical lift:
I would fly one rocket in two otherwise identical configurations, one in the horizontal spin mode with curved fins, and also in the backslider mode with flat fins and no spin. This entails the use of the interchangeable fin can, as employed on the Magus Opum model featured earlier in this thread. If the descent rate is identical, there is no vertical Magnus effect. If the descent rate is not identical, then there must be some vertical Magnus effect. Please criticize this experiment.
 

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@Dotini and @lakeroadster , got experiment for you if either of you have a lathe and a small fan.

Put a body tube on a lathe. Put fan either directly below or directly above. Take a crepe paper streamer (for safety purposes, if it gets caught in fan or lathe tears paper, not hand!) and hold it to left side and right side. If i remember the Bernoulli's principle right, on the side where the tube surface is spinning TOWARD the fan (airstream) the pressure should be higher as the flow is slowed, pressure is higher so streamer should be pushed outward away from the tube. On the ”spinning away” side the flow is faster, so should be lower pressure and “pull” the streamer toward the tube.

Most likely the fan flow will overwhelm the Magnus effect and will be inconclusive.


if it DOES however work, next would be to try it with a fin can with fins rotating at same speed, and see if effect is more or less pronounced. My guess is less, I think it will be so turbulent it will cancel Magnus effect.

Anyway, if you get bored building rockets (unlikely) something to try. I don’t have a lathe and if don’t have clamps to hold my drill in place, so I can’t do it.

I'll give this experiment a shot out in the barn today on my JET wood lathe.
  • What size tubing are you thinking? BT-50'ish or something like BT-60 or 80?
  • The wood lathe RPM range is 550 to 3000, I'm assuming you'll want the lowest RPM to make it more real world?
  • As to the fin can experiment, I could use my Ahpla, it's the only rocket I have in the arsenal that is a simple 3FNC.... it is a BT-55 with TTW 3 ply basswood fins so no worries of breaking off a fin. And/or I could use the Ahpla's ring fin booster? Your thoughts?
001.JPG
 
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jmasterj

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I'm making a BT-5 one with @jhill9693's fin style. I'm going to paper some 1/16" balsa because that's what I have on hand. One 18" body tube and a nose cone gets me about 36:1. No couplers, just an engine block, nose cone, and the three 2" x 1" fins. I'll let you know how it goes. Thanks for the work and inspiration, @Dotini!
 
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Eric, while I agree that slightly bent tubes or curves or a slightly askew nose cone would potentially cause variances of Magnus force, seems like these would be MINISCULE compared with the fin can. Again I am not sure whether the fin can would produce more or less force (argument for greater is the far larger effective diameter, argument for lesser [ which I think is stronger] is the severe discontinuity which I think would likely negate any effective force at all.)

@Dotini and @lakeroadster , got experiment for you if either of you have a lathe and a small fan.

Put a body tube on a lathe. Put fan either directly below or directly above. Take a crepe paper streamer (for safety purposes, if it gets caught in fan or lathe tears paper, not hand!) and hold it to left side and right side. If i remember the Bernoulli's principle right, on the side where the tube surface is spinning TOWARD the fan (airstream) the pressure should be higher as the flow is slowed, pressure is higher so streamer should be pushed outward away from the tube. On the ”spinning away” side the flow is faster, so should be lower pressure and “pull” the streamer toward the tube.

Most likely the fan flow will overwhelm the Magnus effect and will be inconclusive.


if it DOES however work, next would be to try it with a fin can with fins rotating at same speed, and see if effect is more or less pronounced. My guess is less, I think it will be so turbulent it will cancel Magnus effect.

Anyway, if you get bored building rockets (unlikely) something to try. I don’t have a lathe and if don’t have clamps to hold my drill in place, so I can’t do it.
Tom, was I misunderstanding what you and Dotini were referring to by "spiraling"? I took it to mean that some of Dotini's HSRs circle around their launch location on their way down (the way you can intentionally get a glider to do).

If so, I guess I didn't clarify that I believe the circling was due more to uneven or increased drag along certain parts of the rocket, caused by a kinked tube or off-centered nose cone (or the fins depending on shape/size). Any difference in drag anywhere along the rocket body could very well get it to circle, especially if it’s close to either the forward or aft ends.

My thought is that if a kink or misalignment could affect the rotation rate of the rocket, it would do so for the whole rocket, as it’s impossible for just one area of the rocket to spin faster or slower than the rest. As such, the Magnus force would remain equal across the entire length of the rocket and wouldn't be the cause of it circling.

Hope I’m not again misunderstanding the question or nomenclature.
 
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BABAR

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First, thanks you for doing this, I thought it was a lot to ask.

second, I think there area of the streamer to concentrate on is the part just PAST (in this case below) the rotating object. Purely subjective test, but to me it appeared with all object the streamer below the object was pushed AWAY from the lathe on the FAR side, which based on lathe direction was the UP side of the surface rotation. The streamer curled TOWARD the lathe side on the NEAR side, which would be the DOWN side of the surface rotation.

so I believe you effectively demonstrated Magnus effect.

third, SUBJECTIVELY challenging. I think the finding was most pronounced with the large ring fin, which is to be expected. Wasn’t sure with the actual Ahpla fin can, but seemed to me more pronounced there as well, although there is a lot of wishful thinking/bias on my part (however pre-test I expected the opposite, I figured too much turbulence. But a very rapidly spinning fin can (and @Dotini has documented that these puppies are really twirling fast) is definitely going to generate some rotating airflow, perhaps even MORE than a smooth tube or ring.

so my GUESS is that the fin can generates more Magnus effect than the body tube.

my problem with this conclusion is that it then begs the question, if the fin can generates more force than the rest of the tube, given it is radically far from the CG, my expectation would be that ALL HSR rockets should spiral (BTW, Eric @Rktman , for me and I think @Dotini , by spiral we really mean the rocket is rotating roughly around it‘s CG as it falls straight down, not “flying” in a concentric circle like a well designed rocket glider. Technically I think would be better described as a helix rather than a spiral. Maybe not, because I think a spiral is a 2 D concept, and a true spiral expands outward. Anyhoo, for my spiral HSR the rocket trajectory is roughly straight down, the rocket nose and tail are rotating around the fall axis. The Alway brothers DID describe some of their rockets as initially spinning AND backsliding presumably straight, then returning to ballistic path when they stopped spinning.

so I may have reversed the question, it isn’t “why do HSR rockets sometimes descend helically or rotating horizontally around CG? but rather why don’t ALL HSR rockets do this?“. My best guess remains that with longer rockets with smaller fins (which kind of describes Back Sliders), the fin can exaggerated force is minimal co pared to the much longer body tube.

i would love to play with this, but I haven’t found a good rocket field around Vancouver Wa yet:mad:

@Dotini , again presumptuous of me, but I think the test would be build two rockets, as straight as possible and with no nose cone weirdness, one relatively long and one as short as you have reliably recovered with HSR. My hypothesis is the longer rocket will be LESS likely to rotate. Alternative would be same length, but one with the smallest fins capable of stable boost and the other much larger. Hypothesis is the smaller finned rocket will be LESS likely to rotate.

again @lakeroadster , thanks for doing this! Let me know when you finish the wind tunnel!
 

Dotini

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First, thanks you for doing this, I thought it was a lot to ask.

second, I think there area of the streamer to concentrate on is the part just PAST (in this case below) the rotating object. Purely subjective test, but to me it appeared with all object the streamer below the object was pushed AWAY from the lathe on the FAR side, which based on lathe direction was the UP side of the surface rotation. The streamer curled TOWARD the lathe side on the NEAR side, which would be the DOWN side of the surface rotation.

so I believe you effectively demonstrated Magnus effect.

third, SUBJECTIVELY challenging. I think the finding was most pronounced with the large ring fin, which is to be expected. Wasn’t sure with the actual Ahpla fin can, but seemed to me more pronounced there as well, although there is a lot of wishful thinking/bias on my part (however pre-test I expected the opposite, I figured too much turbulence. But a very rapidly spinning fin can (and @Dotini has documented that these puppies are really twirling fast) is definitely going to generate some rotating airflow, perhaps even MORE than a smooth tube or ring.

so my GUESS is that the fin can generates more Magnus effect than the body tube.

my problem with this conclusion is that it then begs the question, if the fin can generates more force than the rest of the tube, given it is radically far from the CG, my expectation would be that ALL HSR rockets should spiral (BTW, Eric @Rktman , for me and I think @Dotini , by spiral we really mean the rocket is rotating roughly around it‘s CG as it falls straight down, not “flying” in a concentric circle like a well designed rocket glider. Technically I think would be better described as a helix rather than a spiral. Maybe not, because I think a spiral is a 2 D concept, and a true spiral expands outward. Anyhoo, for my spiral HSR the rocket trajectory is roughly straight down, the rocket nose and tail are rotating around the fall axis. The Alway brothers DID describe some of their rockets as initially spinning AND backsliding presumably straight, then returning to ballistic path when they stopped spinning.

so I may have reversed the question, it isn’t “why do HSR rockets sometimes descend helically or rotating horizontally around CG? but rather why don’t ALL HSR rockets do this?“. My best guess remains that with longer rockets with smaller fins (which kind of describes Back Sliders), the fin can exaggerated force is minimal co pared to the much longer body tube.

i would love to play with this, but I haven’t found a good rocket field around Vancouver Wa yet:mad:

@Dotini , again presumptuous of me, but I think the test would be build two rockets, as straight as possible and with no nose cone weirdness, one relatively long and one as short as you have reliably recovered with HSR. My hypothesis is the longer rocket will be LESS likely to rotate. Alternative would be same length, but one with the smallest fins capable of stable boost and the other much larger. Hypothesis is the smaller finned rocket will be LESS likely to rotate.

again @lakeroadster , thanks for doing this! Let me know when you finish the wind tunnel!
It's definitely fun to perform rocket science experiments - then figure out what in the hell we've actually done. It's turning into a good summer for HSR rocketry! I'm really digging it. My genius engineer friend is back in town next week, and we'll do some more building and experimenting at 60 Acres.
 

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Okay, here is where physics experts (maybe @prfesser or @ksaves2 ) may kick in.

I have argued that while Horizontal Spin Recovery (HSR) definitely GENERATES a Magnus force, the force is LATERAL to the downward gravitationally induced trajectory of the descending (essentially falling) rocket and therefore doesn’t generate any lift.

Technically I believe this is true.

HOWEVER, the goal of HSR is to slow the descent rate for safe recovery. A major (if not sole component) of this is the horizontal orientation of the rocket itself, rockets fall slower sideways than pointy end down. The Magnus force is laterally to the fall vector, so doesn’t directly slow the rocket. But the Magnus Force does induce either a lateral acceleration and thus velocity or a lateral spin, which does eventually reach equilibrium when the rate of lateral velocity or lateral spin matches the air resistance from the velocity outside the fall plane. The ENERGY for this acceleration HAS to come from SOMEWHERE (TANSTAAFL*, for those Heinlein fans out there). So the POTENTIAL energy the rocket has from its mass and altitude has to be distributed into the following

1. kinetic energy of the falling rocket (bad)

2. kinetic energy required to induce the RAPID rotation (neutral vs good)

3. kinetic energy from either lateral translation or lateral ROTATION (the spiral or helical phenomenon) [neutral vs good]

of course, I still think the major component slowing the rocket descent is the markedly increased drag due to horizontal position. However, any energy “stolen” from the kinetic energy above (robbing Peter to pay Paul) by processes 2 and 3 should (I theeeeeeenk) result in slowing the rocket descent, maybe not a lot, but somewhat. Not sure if quantifiable, may be negligible.

opinions?




*TANSTAAFL: There Ain’t No Such Thing As A Free Lunch, first quoted from the Moon is a Harsh Mistress by Robert Heinlein.
 

Dotini

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Okay, here is where physics experts (maybe @prfesser or @ksaves2 ) may kick in.

I have argued that while Horizontal Spin Recovery (HSR) definitely GENERATES a Magnus force, the force is LATERAL to the downward gravitationally induced trajectory of the descending (essentially falling) rocket and therefore doesn’t generate any lift.

Technically I believe this is true.
Well, the title of this thread is Horizontal Spin Recovery - with Magnus Effect?, emphasis here on the question mark. We've made a lot pf progress, but we still have questions. Simply for the sake of discussion and experiment, I will respectfully suggest the affirmative hypothesis that there is Magnus force and that it does generate some vertical lift. I also propose an experiment to prove or disprove this hypothesis to everyone's general satisfaction.
 

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Here are the new components for the latest round of Magnus effect experiments. It's a BT-20, 50:1, with three interchangeable fin cans.
DSC00706.jpg
Left to right: (1) Styrene fins, flat and straight, (2) PETG fins, two oriented for left rotation, two for right rotation - so hopefully no net spin, (3) Our usual PETG fins for spin. All fin cans have the same area and weight.

Paint goes on tonight, with testing to resume at 60 Acres on Thursday.
 

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Here are the new components for the latest round of Magnus effect experiments. It's a BT-20, 50:1, with three interchangeable fin cans.
View attachment 532923
Left to right: (1) Styrene fins, flat and straight, (2) PETG fins, two oriented for left rotation, two for right rotation - so hopefully no net spin, (3) Our usual PETG fins for spin. All fin cans have the same area and weight.

Paint goes on tonight, with testing to resume at 60 Acres on Thursday.
Something tells me the flights of one and two will not end well. Again, a case I hope to be proven wrong.
 

Dotini

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Something tells me the flights of one and two will not end well. Again, a case I hope to be proven wrong.
I agree #2 is a bit off the beaten path. But what would you doubt about #1? The intention of this configuration is a flight without spin, i.e., a backslider.

DSC00707.jpg

Fluorescent yellow, pink and orange paints applied. Tomorrow comes the gloss black.
 
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BABAR

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I agree #2 is a bit off the beaten path. But what would you doubt about #1? The intention of this configuration is a flight without spin, i.e., a backslider.
Brain fart on my part IF the rockets have extremely long body tubes. I wasn’t even thinking of BSR AS AN OPTION for your rockets. You have FAR more experience here WITH HSR but I think HSR works with medium to long rockets, where-as BSR works ONLY with long to really long rockets. Perhaps better put, the failure window/probability is higher with BSR Than HSR for a given body length. I was thinking all your rockets were HSR, and fin cans 1 and 2 are highly unlikely to spin. probability of successful BSR is likely the same for 1 and 2.

The plastic fins are actually a good choice for BSR like HSR. To my knowledge you are the first to try it with both, as the landing forces are rough on non-streamer or non-parachute rockets.

my BSRs used asymmetric fins so the contact point was with the strongest part of the fin or the body tube, as my fins were balsa. A suggestion for a plastic fin BSR would be a reverse delta trail edge, more likely to slide a bet rather than come down pointy end first and jolt to a sudden stop.

I’ve either gotta find a local flying field or start shipping you rockets to try at 60 acres!
 

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Brain fart on my part IF the rockets have extremely long body tubes. I wasn’t even thinking of BSR AS AN OPTION for your rockets. You have FAR more experience here WITH HSR but I think HSR works with medium to long rockets, where-as BSR works ONLY with long to really long rockets. Perhaps better put, the failure window/probability is higher with BSR Than HSR for a given body length. I was thinking all your rockets were HSR, and fin cans 1 and 2 are highly unlikely to spin. probability of successful BSR is likely the same for 1 and 2.

The plastic fins are actually a good choice for BSR like HSR. To my knowledge you are the first to try it with both, as the landing forces are rough on non-streamer or non-parachute rockets.

my BSRs used asymmetric fins so the contact point was with the strongest part of the fin or the body tube, as my fins were balsa. A suggestion for a plastic fin BSR would be a reverse delta trail edge, more likely to slide a bet rather than come down pointy end first and jolt to a sudden stop.

I’ve either gotta find a local flying field or start shipping you rockets to try at 60 acres!
Including the half inch the motor hangs out the back, our new model is 39" long. At .74" diameter, the ratio is 52.7 to one.

How far are you from the tide flats? I've launched at low tide from my beach cabin. You should get online to search for local parks and fields. If you want to launch at 60 Acres, why not drive very early in the morning when there's virtually no traffic on the roads? Even on soccer practice days we have been launching between 7 and 9 AM.
 
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Including the half inch the motor hangs out the back, our new model is 39" long. At .74" diameter, the ratio is 52.7 to one.

How far are you from the tide flats? I've launched at low tide from my beach cabin. You should get online to search for local parks and fields. If you want to launch at 60 Acres, why not drive very early in the morning when there's virtually no traffic on the roads? Even on soccer practice days we have been launching between 7 and 9 AM.
Over 50 to 1 should have high prob of backsliding.

This may be a good way of testing for Magnus lift presence or absence.

All other things being equal, (same size, length, fin size), if HSR falls slower than BSR, it is probably Magnus effect. Converse may NOT be true, as BSR glide may proved some lift. Eric (@Rktman ) may have input here, does BACKSLIDE work simply due to high drag from horizontal position or is there a true wing lift from the non-air foiled fins?
 
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Over 50 to 1 should have high prob of backsliding.

This may be a good way of testing for Magnus lift presence or absence.

All other things being equal, (same size, length, fin size), if HSR falls slower than BSR, it is probably Magnus effect. Converse may NOT be true, as BSR glide may proved some lift. Eric (@Rktman ) may have input here, does BACKSLIDE work simply due to high drag from horizontal position or is there a true wing lift from the non-air foiled fins?
I don't believe even the Alway bros. touched on possible lift generation from either the fins or the horizontal position of the BSR. http://web.archive.org/web/20071015035108/http://members.aol.com/petealway/srrg.htm
Interestingly they did note that a SPINNING BSR tends to be more significantly successful at backsliding. "We found that models that spin on recovery can fall sideways or glide over a larger part of the predicted range BCP-CG-CLA relationships".
 
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