Pic illustrating field adjustable model rocket geometry. Does this kink in the tube facilitate spiraling? Reader theories are welcome.
Horizontal Spin Recovery - with Magnus Effect?
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Verrrrrrry interrrrresting! (Also cool.)
Just came confirming, does a rocket that doesn’t spiral, CONSISTENTLY not spiral? As in with different motors or other conditions? Conversely, do spirallers ALWAYS spiral?
My first thought when mine spiraled (I think all of mine did, but it’s been a bit) was that it made sense, the generated lateral Magnus force would be different for the fin can than for the body tube (we’ll assume nose con contribution is negligible.)
I’m NOT sure that the fin can force would be HIGHER (due to larger effective diameter) or far LOWER (due to breakup of laminar flow, the pilots and RC guys will probably say this is wrong term, “spoiler”?). But seems likely the fin can would be DIFFERENT, and the asymmetry would tend to force one end to turn harder than the other.
But that begs the question, why do some NOT spiral? So I’m back to “I dunno.”
Just came confirming, does a rocket that doesn’t spiral, CONSISTENTLY not spiral? As in with different motors or other conditions? Conversely, do spirallers ALWAYS spiral?
My first thought when mine spiraled (I think all of mine did, but it’s been a bit) was that it made sense, the generated lateral Magnus force would be different for the fin can than for the body tube (we’ll assume nose con contribution is negligible.)
I’m NOT sure that the fin can force would be HIGHER (due to larger effective diameter) or far LOWER (due to breakup of laminar flow, the pilots and RC guys will probably say this is wrong term, “spoiler”?). But seems likely the fin can would be DIFFERENT, and the asymmetry would tend to force one end to turn harder than the other.
But that begs the question, why do some NOT spiral? So I’m back to “I dunno.”
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FWIW, mine spiral and aren’t kinked.
Of your models which do spiral all the time, what is the length to diameter ratio? What is the fin area compared to the tube area? Where is the CG as measured with an expended motor in place? Your models are not kinked, but how carefully have you measured? We find that a kink of as little as 0.150" may be enough to have an affect on spiraling a BT-50 model of 42". Other factors such as wind may be important.
We made a tool, usable in the field, to carefully measure the kink.
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I am not on the same planet with you in build quality or documentation for anything, including Horizontal Spin Recovery (HSR.)
But glean what you can from the following.
https://www.rocketryforum.com/threa...r-wide-body-bt-80-horizontal-recovery.166124/
https://www.rocketryforum.com/threa...-previously-squirt-no-recovery-system.165609/
Video is useless , but IIRC it was a loose spiral. I think my 6-shooter fin cans are heavier than yours, they spiral but the horizontal part is a bit tail down, which I think is a mass issue.
https://www.rocketryforum.com/threads/perfect-24-gap-staging-see-last-post.45863/
May have been my first @hornetdriver was still active on this forum. Horizontal Spin Recovery is awesome for long gap staging non-electronic booster recovery.
https://www.rocketryforum.com/threa...flight-3-dog-night-post-12.64307/#post-693030
https://www.rocketryforum.com/threa...flight-3-dog-night-post-12.64307/#post-693030
No video. But booster DOES recover HSR.
https://www.rocketryforum.com/threa...-horizontal-spin-booster.149667/#post-1856679
Crummy video, BUT I do remember booster recovered nearby, so doubt it back-slid
And I think Bail Out Bill may have been a design that piqued your interest early on
https://www.rocketryforum.com/threa...tal-spin-recovery-rocket.147210/#post-2117449
Building with low mass is I believe a major key to GOOD HSR, as I believe the key to descent rate is roughly proportional to lateral surface area divided by mass. So a thin walled SuperRoc seems optimal, and I think your plastic thin walled fins are a plus for strength vs weight over balsa, although you have said robust attachment is problematic . Low mass is probably also helpful in rapid “spooling up” as it has lower inertia/ resistance to rotation.
“Pure” HSR (no nose cone ejection or other configuration change aside from burned propellant) definitely needs a relatively extremely high length to diameter ratio, as you need to shift from Barrowman Stability realm to Center of Lateral Area Stability (aka cardboard cut out) realm. “Dirty” HSR (where you “cheat” by ejecting nose weight, e.g., either nose cone with chute or streamer or an upper stage) is pretty easy, in fact the shorter the better, as post ejection without the nose weight the rocket tends to be unstable anyway, which is ideal for this phase of flight.
But glean what you can from the following.
https://www.rocketryforum.com/threa...r-wide-body-bt-80-horizontal-recovery.166124/
https://www.rocketryforum.com/threa...-previously-squirt-no-recovery-system.165609/
Video is useless , but IIRC it was a loose spiral. I think my 6-shooter fin cans are heavier than yours, they spiral but the horizontal part is a bit tail down, which I think is a mass issue.
https://www.rocketryforum.com/threads/perfect-24-gap-staging-see-last-post.45863/
May have been my first @hornetdriver was still active on this forum. Horizontal Spin Recovery is awesome for long gap staging non-electronic booster recovery.
https://www.rocketryforum.com/threa...flight-3-dog-night-post-12.64307/#post-693030
https://www.rocketryforum.com/threa...flight-3-dog-night-post-12.64307/#post-693030
No video. But booster DOES recover HSR.
https://www.rocketryforum.com/threa...-horizontal-spin-booster.149667/#post-1856679
Crummy video, BUT I do remember booster recovered nearby, so doubt it back-slid
And I think Bail Out Bill may have been a design that piqued your interest early on
https://www.rocketryforum.com/threa...tal-spin-recovery-rocket.147210/#post-2117449
Building with low mass is I believe a major key to GOOD HSR, as I believe the key to descent rate is roughly proportional to lateral surface area divided by mass. So a thin walled SuperRoc seems optimal, and I think your plastic thin walled fins are a plus for strength vs weight over balsa, although you have said robust attachment is problematic . Low mass is probably also helpful in rapid “spooling up” as it has lower inertia/ resistance to rotation.
“Pure” HSR (no nose cone ejection or other configuration change aside from burned propellant) definitely needs a relatively extremely high length to diameter ratio, as you need to shift from Barrowman Stability realm to Center of Lateral Area Stability (aka cardboard cut out) realm. “Dirty” HSR (where you “cheat” by ejecting nose weight, e.g., either nose cone with chute or streamer or an upper stage) is pretty easy, in fact the shorter the better, as post ejection without the nose weight the rocket tends to be unstable anyway, which is ideal for this phase of flight.
Surely spin is the most important single factor in achieving a spiral HSR descent. Spin rate should be in the 300-400 rpm range, minimum. Right hand spiraling or left hand is determined by the direction the fins are installed. For a 1" diameter tube, we feel 12 square inches minimum fin area is needed, with 16 square inches providing more spirals (4 as opposed to 2).
The more we test, the more confident we are of the Cyclops nose cone port ejection method for reliability as well as performance. The correct CG must always be born in mind and measured with care. We find 69% to 71% from the nose cone to the expended motor works well.
We are still evaluating L/W ratios between 42:1 and 52:1.
We are still evaluating kinks of various magnitudes in the tube.
Fin breakages and ballistic events no longer seem to be occurring.
Our next all new model will be BT-55 for easier viewing on video.
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lakeroadster
When in doubt... build hell-for-stout!
Actual numerical data.... awesome.
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Not arguing, just curious since you haven’t posted the data. You had rockets with less than 300 rpm spin that came in ballistic? Alternative is that BECAUSE the were not horizontal, they didn’t achieve max spin. I still theorize the spin starts SLOWLY, when the ejection puff alters the rocket from negligible (near 0) angle of attack (nAoA) m, where Barrowman stability calcs apply to significant angle of attack (say over 10 degrees) sAoA, where Barrowman fails and Center of Lateral Area (CLA, aka Cardboard CutOut) applies. The puff failure mode is if after the puff the rocket’s vertical velocity shifts to zero (basically apogee OR if post apogeecyclops nose puff reverses descent) [let’s call this Vertical Velocity Apogee Zero VVA0] AND the rocket’s orientation is near vertical nose down. Think of a sphere with a South Pole circular ice cap. The diameter of the cap is in someway inversely proportional to the L/D ratio. So long as the orientation of the rocket at VVA0 is OUTSIDE the ice cap, the rocket is UNSTABLE (which in this case is GOOD), as it fails it will TUMBLE, as it TUMBLES the rotationally “cupped” fins start to “catch” air and induce rotation, at first slow. The rotation starts to induce force as the rocket falls gradually shifting the rocket perpendicular to the fall vector (in this case horizontal.). This is a POSITIVE feedback loop, as the more horizontal, the better the fins “catch” air, the more rotational force, the faster the rotation, the more horizontal the rocket gets, until finally the rocket is essentially perfectly horizontal.
I wonder that perhaps your measurement of rotation rate when the rocket is already horizontal is measuring effect, not cause. Unless of course you observed and measured spinning rockets coming in ballistic, but even then still potentially would be effect not cause.
My experience is certainly far less than yours, but I believe the key failure mode for HSR recovery is near nose down orientation at VVA0. The orientation is completely random at this time, can be represented by a sphere, the center is tail position, the surface is potential nose tip positions. So long as these are OUTSIDE the South Pole “ice cap” HSR succeeds. The smaller the “ ice cap” the higher the probability of success.
Higher L/D ratios are good as they effectively shrink the cap (or more properly they INCREASE the range of SUCCESFUL orient, which results in a smaller range of unsuccessful orientations.) more efficient fins would also do this. Another option would be to put a spin tab on so some rotation would be initiated during boost. I believe you have considered a rotation component to the puff, and maybe feel (as I do) that it would add too much complexity and not be reliable.
with 16 square inches providing more spirals (4 as opposed to 2).
I think the spiral itself is a manifestation of Magnus force. In this case asymmetric. The lateral pulling force of the tail section is either greater than or less than that of the body. ( I really am not sure which, is the larger effective diameter causing INCREASED force or the fin extrusions SPOILING the force. I dunno.). Interesting that it seems to be accentuated by fin surface area. I’m still surprised they don’t ALL spiral.
I love the Cyclops method. It is so simple, so NON-intuitive. I theeeenk it is also LESS likely to torque or kink the rocket. This is also counterintuitive. Maybe @perfessor can correct me if needed. With the Cyclops, the ejected mass is coming out of the nose. The pressure CHAMBER in this case is the whole length of the rocket, with the lowest pressure at the nose. So is the nose now PUSHING the rocket tailward or is the higher internal pressure of the tail pushing the rocket tailward?
Put another way, in a standard motor, where is the action of the rocket force being FIRST applied to the rocket? Is it in the NOZZLE or the FORWARD END of the motor chamber?
In HSR it makes a difference, as if the (I am word searching, not fulcrum, for now will use bulkhead) bulkhead of force is at the tail end of the rocket (now force backwards) there is no potential torquing force on the rocket body.
Of course, even if nose cone WAS now “pushing” the rocket backwards, at least now it is aligned with the axis, so less likely to kink than a lateral puff port.
I expected a minimum CG from nose, but this suggests a maximum as well. What is the issue with OVER 71%? Instability on boost? Too tail heavy? (I think I have had issues with the latter.)
I’d have guessed aside from structural issues longer/higher would always be better.
So the unpainted tubes are tough enough? Are they bouncing on impact? Are you still using augmented “cheaters” for fin to body tube attachment? Are you using epoxy for plastic fin to cardboard tube attachment?
FWIW , BT-80 works (Turbinator), and at a far lower L/D ratio. I think because I used numerous small fins, it was optimally UNstable by CLA calcs despite the suboptimal L/D ratio.
Hope this post is more helpful than annoying.
We always paint the tubes, but now never apply paint to the clear flexible plastic fins because of embrittlement. The models seem to settle or bounce once upon landing, ceasing rotation immediately. The long, soft, well-tended grass at 60 Acres is just perfect for landings. The "cheaters" - actually strips cut from Apogee BT-50 airframe sleeves - seem superbly suited to beefing up the fin attachment. We initially tack the fin in place with CA, but finally apply JB Weld 15 Minute epoxy for the full fillet.
We'll take up the other questions in due course.
Thank you for your very welcome post!
If I'm not mistaken, you have the skills and tools to wet-form balsa. I imagine that a formed and papered balsa fin could make for an exceptionally functional HSR model rocket.
My mindsim says this is correct. The Magnus effect exerts a lateral force on the body tube. So, perhaps a number of stringers along the outside of the body tube would enhance the effect. If they were placed only on the aft (or forward) half of the rocket, the spiral could be controlled.
That's an interesting thought: make the surface friction of the front and rear of the rocket different. To a certain extent that is already true with the fins, but that doesn't seem to cause spiraling on its own. Stringers on half the rocket seems like a good experiment.
Provided, of course, that something like this hasn't already been tried.
Obviously we have been intrigued from the beginning by the question of Magnus effect. Alas, we have been unable to prove it. We haven't entirely given up, but are not focusing on the question at this time.
Below, two examples of drag, friction or turbulence generating tubes.
Whatever else these tubes do, they add very noticeable weight and drag.
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You shouldn't need much, like the stitches on a baseball.
Since I am lazy, I would start with adding pin stripes made from narrow strips of electrical tape, or similar.
In an effort to actually reduce drag and weight at the front, we tried using two(!) balsa transitions in one rocket.
This model is of three diameters and has forward facing ejection ports just ahead of the fin can. The ejection works just fine but tests were cut short by fin damage.
This model is of three diameters and has forward facing ejection ports just ahead of the fin can. The ejection works just fine but tests were cut short by fin damage.
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I believe you proved the Magnus effect very early on, when you had a model in video clearly translating laterally while falling in a horizontal attitude.
I think the laws of physics dictate that the Magnus effect will always be lateral to the main direction, in this case lateral to the direction of fall. Unfortunately that means the Magnus effect will NOT slow the descent rate as was hoped. I don’t think there is any way in this universe to alter that.
A baseball spin has the same effect, it doesn’t slow or speed up the ball, but makes it makes the ball deviate transverse to the major velocity vector. For the ball this may be right, left, up, or down, depending on the orientation of the spin. If it varies, you get a classic “screwball.”
If that is so, then perhaps the spiraling can be finally attributed to an uneven distribution of pressure along the length of the tube, with the fins modifying the effect relative to the opposite end. So enlarging the fins or altering the length may change the effect.
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An unanswered question is the effect of the fin can on the Magnus effect.
Maybe close observation of the rocket orientation relative to the spiral maaaaay be helpful.
I’m confident that the spiral phenomenon itself is due to asymmetric Magnus effect. If so, the rocket pole (nose or tail) with the greater Magnus force should point slightly inside the radius of the spiral curvature and the weak pole outward. This should be more obvious on more tightly spiraling rockets.
Your paint schemes have been done to video rotation speed. You may want to paint so you can easily tell nose from tail, although it may be obvious otherwise, I dunno.
I figure fin can must either magnify Magnus due to larger diameter, or nullify it due to turbulence.
A clearly defined method of varying Magnus effect is your transitions, a larger forward diameter with a smooth surface will increase Magnus AND increase CLA post ejection instability (if you keep it light.)
Unless you use a stuffer tube however (which screws up CG), you have a higher volume and less force for a Cyclops of forward lateral puff port.
I believe I have come up with a scientific test to determine if the fin can creates an INCREASE in Magnus or DECREASE.
control rocket: standard minimum diameter HSR rocket.
Test: add transition with INCREASED diameter to noseward 1/3 length. So you are INCREASING forward Magnus.
If control spirals, and Test spirals TIGHTER, the fin can causes DECREASED, nulled, or stalled Magnus, likely due to turbulent flow, I.e., the control in terms of Magnus force was already “nose heavy”, increasing forward Magnus made it MORE nose heavy in terms of Magnus force, so fin can weakens Magnus force.
If control spirals, and test does NOT or spiral is wider or reverses, the fin can has POSITIVE Magnus (greater than the minimum diameter body tube.)
Maybe close observation of the rocket orientation relative to the spiral maaaaay be helpful.
I’m confident that the spiral phenomenon itself is due to asymmetric Magnus effect. If so, the rocket pole (nose or tail) with the greater Magnus force should point slightly inside the radius of the spiral curvature and the weak pole outward. This should be more obvious on more tightly spiraling rockets.
Your paint schemes have been done to video rotation speed. You may want to paint so you can easily tell nose from tail, although it may be obvious otherwise, I dunno.
I figure fin can must either magnify Magnus due to larger diameter, or nullify it due to turbulence.
A clearly defined method of varying Magnus effect is your transitions, a larger forward diameter with a smooth surface will increase Magnus AND increase CLA post ejection instability (if you keep it light.)
Unless you use a stuffer tube however (which screws up CG), you have a higher volume and less force for a Cyclops of forward lateral puff port.
I believe I have come up with a scientific test to determine if the fin can creates an INCREASE in Magnus or DECREASE.
control rocket: standard minimum diameter HSR rocket.
Test: add transition with INCREASED diameter to noseward 1/3 length. So you are INCREASING forward Magnus.
If control spirals, and Test spirals TIGHTER, the fin can causes DECREASED, nulled, or stalled Magnus, likely due to turbulent flow, I.e., the control in terms of Magnus force was already “nose heavy”, increasing forward Magnus made it MORE nose heavy in terms of Magnus force, so fin can weakens Magnus force.
If control spirals, and test does NOT or spiral is wider or reverses, the fin can has POSITIVE Magnus (greater than the minimum diameter body tube.)
I'm thinking along the same lines. But I'm gone tomorrow and the rest of the team is gone for a week. So it'll be a while before we can do new tests.
Edit: Email contact with the team resulted in a decision to swiftly test the idea it's the nose doing the turning. However, for sake of ease and CG control, our first test will likely be with a reduced diameter nose section. Another idea we may implement is to follow the rocket with a drone.
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Increase diameter rearward (but forward of fin can) should increase rear Magnus force, although with less “moment” given will be closer to CG.
So compared to a control uniform diameter HSR, three possibilities
1. Spiraling is tighter/exaggerated
Means fin can Magnus is POSITUVE.
2. Spiraling is looser. Means spin can nulls or spoils Magnus force.
3. No change. Indeterminate.
Above presumes that the ONLY effect of larger diameter rocket rear is on Magnus. It may alter CG and other factors.
So compared to a control uniform diameter HSR, three possibilities
1. Spiraling is tighter/exaggerated
Means fin can Magnus is POSITUVE.
2. Spiraling is looser. Means spin can nulls or spoils Magnus force.
3. No change. Indeterminate.
Above presumes that the ONLY effect of larger diameter rocket rear is on Magnus. It may alter CG and other factors.
We have new models on the drawing board/build table which will test both the enlarged nose cone tube and the smaller nosecone tube for their effect on spiraling.
We have two new HSR models ready to test, each with very similar length, weight, CG and fin area. The big difference is where the bulk of the surface area is, fore or aft. We think this may have an affect on a desired spiraling descent.
We hope to launch Friday.
We hope to launch Friday.
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May the Force be with You!
Well, we launched, but to little effect. Our session was abbreviated by several issues unrelated to the test question. So no conclusion could be drawn, although we did get the best spiral from the model with the larger diameter nose tube. More testing is needed, and will come.
