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Dualing Magnus vs Backspin
- Thread starter BABAR
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BT-20 mount
BT-50 Body Tube
BT-5 Tube fins
(Shorter tube fins are sturdier)
8 fins leaves a small gap
9 fins requires a bit of elliptical compression. But it gives me more surface area.
I'll go with 9
BT-50 Body Tube
BT-5 Tube fins
(Shorter tube fins are sturdier)
8 fins leaves a small gap
9 fins requires a bit of elliptical compression. But it gives me more surface area.
I'll go with 9
It looks quite sturdy enough to take a beating upon landing. I've had plenty of landing mishaps in this research, and I'm taking steps to mitigate that. If you want to beef it up even more, Apogee is now marketing a 4" long external tube doubler for BT50. With this, there is no need for the external splines or internal motor mount extension I've been using.
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Well the videos didn't come out very well and I won't bother to post them but I can post the results.
The Magnus rocket with the nine BT-5 cut fins around the BT-50 core flew a great stable upward flight on B6-4
On decent, interestingly, it came in roughly tail first. I would estimate 10-20 degrees off vertical. It So it came down fast even though it came down backwards. That crimped the body tube just forward of the fin can.
Fix the crimp of the two by putting a second piece of BT 50 tube around the area that was cramped and taped it on. Looked pretty straight to me. Then swapped out the fin can for the nine complete uncut tube fins for the anti-Magnus non-spin version. Interestingly, this Rocket was completely unstable off the pad, sky rock Skyroom as soon as it left the rod. Otherwise uneventful, landed perhaps 30 feet away (flew this also on B6-4 motor).
it MAY have had a slight bend it the body tube, I didn’t try it again.
so, regarding the Magnus version, weird. Basically this was spinning, but it was NOT horizontal, it was almost as if the tail weight was the overwhelming force and came down nearly stable tail FIRST. That shouldn’t happen by the laws of physics as I understand them, but I HAVE seen it before with long gap (18”) boosters with ring fins cut for spin before. Obviously something I am missing. I INTENTIONALLY left off the e-bay with the pseudo altimeter nose weight BECAUSE I was afraid, after ejection, that it would be like a NORMAL rocket and nose over and come in ballistic. Seems like current situation was the opposite, the tail was too heavy. Really not intuitive, because in the up flight the tail at launch was even heavier (still had full propellant, delay, ejection charge in the casing) and it WAS stable NOSE first. I figured the WORST possible case after ballistic would be backsliding, definitely not intuitive to me that it would fall TAIL first and very steep at that.
The Magnus rocket with the nine BT-5 cut fins around the BT-50 core flew a great stable upward flight on B6-4
On decent, interestingly, it came in roughly tail first. I would estimate 10-20 degrees off vertical. It So it came down fast even though it came down backwards. That crimped the body tube just forward of the fin can.
Fix the crimp of the two by putting a second piece of BT 50 tube around the area that was cramped and taped it on. Looked pretty straight to me. Then swapped out the fin can for the nine complete uncut tube fins for the anti-Magnus non-spin version. Interestingly, this Rocket was completely unstable off the pad, sky rock Skyroom as soon as it left the rod. Otherwise uneventful, landed perhaps 30 feet away (flew this also on B6-4 motor).
it MAY have had a slight bend it the body tube, I didn’t try it again.
so, regarding the Magnus version, weird. Basically this was spinning, but it was NOT horizontal, it was almost as if the tail weight was the overwhelming force and came down nearly stable tail FIRST. That shouldn’t happen by the laws of physics as I understand them, but I HAVE seen it before with long gap (18”) boosters with ring fins cut for spin before. Obviously something I am missing. I INTENTIONALLY left off the e-bay with the pseudo altimeter nose weight BECAUSE I was afraid, after ejection, that it would be like a NORMAL rocket and nose over and come in ballistic. Seems like current situation was the opposite, the tail was too heavy. Really not intuitive, because in the up flight the tail at launch was even heavier (still had full propellant, delay, ejection charge in the casing) and it WAS stable NOSE first. I figured the WORST possible case after ballistic would be backsliding, definitely not intuitive to me that it would fall TAIL first and very steep at that.
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So I may try it again with the fully repaired body tube (just cut the crimped segment, about two inches, out. The fin cans for the Magnus, AntiMagnus, and Devil’s Triangle are interchangeable (the 3 of the 4 Devil’s Triangle flights, one before tube cutting and three after, went spectacularly, two on B6-4 and one on C6-5 that I almost lost, the last on A8-3 was barely adequate simply because it didn’t get that high.)
I will add the e-bay, with a dummy altimeter payload. This will make it longer and nose heavier, if anything that will make it more likely to go ballistic and currently I have the opposite problem it’s almost ballistic TAIL-first.
I will add the e-bay, with a dummy altimeter payload. This will make it longer and nose heavier, if anything that will make it more likely to go ballistic and currently I have the opposite problem it’s almost ballistic TAIL-first.
I had a similar issue with my backslider, X2C - it backslid alright, but it wanted to come in hot and heavy, ultimately suffering tube crimping. I attributed that to the small(?) fin area bequeathed by the adapted Estes E2X fin unit. Soon, I'll have a new backslider, hopefully with belt-and-suspenders overkill.
