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.FWIW, mine spiral and aren’t kinked.
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).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.
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.
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.. Spin rate should be in the 300-400 rpm range, minimum
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?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.
Fin breakages and ballistic events no longer seem to be occurring.
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.Our next all new model will be BT-55 for easier viewing on video.
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.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?
Thank you for your very welcome post!Actual numerical data.... awesome.
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.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.
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.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.
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.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.
You shouldn't need much, like the stitches on a baseball.Whatever else these tubes do, they add very noticeable weight and drag
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.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.
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.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'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.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.)
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.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.
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.May the Force be with You!
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