Without waiting for the full report, I can reveal one of our (preliminary) key findings. After establishing a baseline series of six launches at 50:1, we recorded another series of launches at 40:1. Both series were 100% successful in achieving HSR. Both series achieved essentially the same descent time. Whatever may have been lost in Magnus effect, the shorter tube seems to have made up in less weight and drag. In other words, it went a bit higher before beginning its descent.
”) altitude.
My suspicion is variable magnus effect of body tube vs fin can (although I can’t tell why some fin cans do and others don’t, so not sure this helps.)
More or less, yes. Each individual rocket seems to have its own personality and behave the same way each time.. The experimental rocket with the interchangeable tubes and fin cans we are working with right now likes to make a half-spiral descent with either 50" length or 40" length. The distance it lands from the pad is almost as far as the altitude achieved. We have another model that spirals more tightly. It may go up 700' yet land only 100' from the pad. Quite a lot more experimentation is needed. It may be that subtle variation (defects) in tube straightness and nose cone alignment plays a significant role.
Agreed. In scratch building models with a changing variety of shapes, sizes, materials and build processes, variation will occur. Damage and degradation will occur over an unpredictable number of flights. In holding and glueing fins, we are mostly using the Estes fin alignment jig. The precise way in which we align and clamp the fins in the jig is evolving and improving towards a standardized process. But still we make mistakes and find variation. Sometimes the jig is oriented vertically and sometimes horizontally. The type of glue changes quite a lot depending upon the materials. I find CA is more unforgiving, but a heavy use of curved plastic fins (not easy to clamp in the Estes jig) prohibits slow setting white glue. We are currently trying a greater reliance on original Gorilla glue, being more forgiving during installation but leaving somewhat ugly bumps and bubbles.Physics doesn't care about handedness., but we bring artifacts of it into what we create.
The FBI can tell the handedness of the unknown bomber long before they have any other details.
My point is that if it shows a preference, it has to do with a bias in the way you held and glued the fins
You do know that the curvature of the fin makes a big difference on spin-rotation/stabilization/effect. I see your height and width measurements but no radia or curvature measurements….if i am to assume that it is 3” dia div by 4 to calc the curve then ok.
Glad to have your input. Thank you! I have no schooling in spin-rotation/stabilization/effect. Any helpful technical references would be greatly appreciated.
Generally on a curved fin the stabilization forces are stronger towards the area where the fins connect to the body tube and lesser as they move out towards the fin tip…kind of common sense I know. What makes the real difference is the amount of area there the fin has and this can be controlled by the radius of that specific area….plus the height of that fin…the larger the diameter (cut in 4 or 3 pieces) provides this force. So, a 4” diameter tube cut down to 4 sections/fins will have more stabilizing surface area where it counts compared to a 3” dia. The actual mathematics can be done to determine what size you would need depending on your roc weight, length, CG/CP tube dia, etc. in this case bigger is better for larger roc’s…that’s just to keep it stabile going up and you can count on the spin/force to help correct by 1x - 5x depending on these calcs too….that’s what I have found through my experimentation….but I usually error on the more stabile than less stabile approach. This may not be what you want with the effect you are going for though.
The fin may be indestructible. Given a chain is only as long as it’s weakest link, the next “at risk” components are the joint and the body tube itself. So you may simply shift the damage to another location.
Agreed. I'm phasing out my 1/2 box fin design on the grounds that it tends to descend by zooming away from the launch site in a single direction, while the curved fin tends much more to spiraling safely nearer to the pad. NOTE: The latest refined observation of the spin rate is a solid 420 rpm.
Absolutely yes. But major drawbacks are weight and cost.
interesting that the box fins descend straight and the part tube fins spiral (although you haven’t specified if this is universal, I.e some box fins may spiral and some curved fins glide.)
By careful computer analysis on his high-end cellphone camera video, my associate was able to gradually refine the rpm from an estimated 250-500 rpm on most of the fleet to the confident figure we have for the Magnus Opus model and its variants. We are trying to gradually do more and better experiments on what started last year as an exotic amusement. We seldom have all the time and weather we need to proceed steadily, let alone rapidly on what is turning into hard rocket science. Stay tuned and build a few of your own! BT-5 sizes with 1/2A motors are quick and cheap to build and don't go too far, yet they can demonstrate the effect quite elegantly. We need all the help we can get in rowing this little boat in the Magnus Ocean.
My videographer spends most of his time in Oregon and Montana, so his time is hard to come by. I'll try to get a video out this week.
YouTube
The motor is taped firmly into the tube. If it popped out at ejection, the ejection "blow-over" event may not be strong enough to send the model gyrating and for the fins to catch crosswind air and start the spinning before the model went ballistic.
In case you care (probably not), those Latin words do not agree. Magnum Opus is a great work.
@Dotini, I searched this thread, and, if I missed it, I apologize.... do your rockets eject the nose cone, or does it stay attached during the recovery phase?
It stays attached, ejection charge goes out the hole in the side, just below the nose cone.
Correct. There is a single 1/4" punched hole immediately below the base of the nose cone (which is permanently fixed in place).
Hey Dotini!
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