lakeroadster
When in doubt... build hell-for-stout!
What is the difference?
A tube fin is a much more restrictive area and channels the air flow in that tight area.
What is the difference?
I believe the nearest thing to an "official" definition of a ring fin would be something that is coaxial with the airframe.What is the difference?
That pretty much coincides with my own gut feel.The top one would probably work for that, the bottom one probably not.
The open round things don't encircle the body, so tube fins, despite the small L:D.
The (mostly) open round things do encircle the body, so ringtails. But something of a grey area, since each one, as interrupted by the others, does not encircle the body, just like mine don't. But unlike mine, that interruption is not by the body. So it's grey, but I'd have to say light grey if ringtails are white; clearly (to me) more ringtail than tube fin. Maybe these intersecting ring designs are just a thing unto themselves.
Thanks! I'm in the process of finishing up one model and starting another while some critical parts are on the way for a third. For this current fin tube build, I'd like to work with a BT-55 tube. But I'd like to make the ring segments from 0.020" PETG flat stock, so I'll need the cut length that when formed describes the desired arc.I can do the calculations for you soon. As show, the central circle is 2 inches in diameter, and the truncated circles are 1¾, or an 8:7 ratio. So if you use a BT-55 (33.7 mm OD) and BT-52 (29.9 mm OD for Apogee's version) fins you'd have a 1.127:1 ratio, which is almost perfect. Then I or someone can compute the part of the fin tubes to remove. If you want a different size, just name the tubes and someone will generate the numbers. (BT-80 and BT-70, for example, gives you 1.173:1
But I can't do it right now.
Incidentally, I was thinking of a bias cut on the leading edge of each fin tube. But of course you can do what you like with it.
Here is a model I'm completing now, shown in its infancy. I cut a strip of plastic, joined the ends and it formed a circle. It is very flexible.Can do.
EDIT: 1.987 inches (so call it 2) along the outside of the curve.
How do you plan to bend the sheet into a circular arc and attach it in just that shape?
Yup, you are right. I made a quick and dirty test article, and the results weren't the best. My methods and materials are not up to this task, so it's back to kit bashing for me.I'm less confident that they'll become circular arcs, rather than, say, parabolae, cycloids, or some such other thing. Maybe I'm all wet and worrying about nothing.
In the example above, you've got the angle where the ends meet (zero) constrained, and my concern is that that's crucial for my design. I know it's crucial in the case above. Imagine bringing the two ends together with no overlap; they'd come to a point. My thinking is that you'd get circular arcs if you can constrain the angles at the ends, but something else of you don't.
On the other other hand, parabolae, cycloids, or some such other thing might be just fine anyhow. (The the first other hand is the one where all wet.)
I haven't touched a clear payload tube in... oh, 40+ years. I'm suddenly having an idea that maybe I built an X-ray back in the day, but can't be sure.What you can do is use BT-52 or BT-50 size clear payload tubes. Cut away the unwanted section, and what you've got is preformed in the circular arc that you want.
Have you got a name in mind? Truncated Tube Fin?Yes, I expect that'd probably work, if my mind sim is any good.
Nope. And if I do it, I'll stick to the original notion of circular arcs, which give a much sleeker look, imo.
You haven’t added the third dimension, length.Inspired by the above, and many other intersecting ring fins such as this, I wonder about truncated tube fins. Sort of like "What if ring fins actually intersected the body tube?" Here are some way less than half baked possibilities for aft views of what I'm talking about. I like the last one best, but I'm not sure if there's enough open space in the partial rings to make it stable. (Well, stable without an ungainly amount of nose weight; I'm confident the CP will be shifted aft somewhat.) RS allows for tube fins, but with the tubes partially buried in the body I doubt it will calculate and simulate correctly. I'd have to build and test.
View attachment 479178
View attachment 479179
View attachment 479180
You haven’t added the third dimension, length.Inspired by the above, and many other intersecting ring fins such as this, I wonder about truncated tube fins. Sort of like "What if ring fins actually intersected the body tube?" Here are some way less than half baked possibilities for aft views of what I'm talking about. I like the last one best, but I'm not sure if there's enough open space in the partial rings to make it stable. (Well, stable without an ungainly amount of nose weight; I'm confident the CP will be shifted aft somewhat.) RS allows for tube fins, but with the tubes partially buried in the body I doubt it will calculate and simulate correctly. I'd have to build and test.
View attachment 479178
View attachment 479179
View attachment 479180
Indeed not. I guess "half baked" is putting it generously in this case; I just thought this would look sleek and cools and I wonder if it could work.You haven’t added the third dimension, length.
Absolutely. And, lest anyone forget, I was teasing Neil a bit, and he's totally welcome to post ideas here if he wants to.i believe everyone (except Neil) is welcome to share new ideas??
Van Milligan has said tube fins are no more draggy than standard fins of the same area, but are less efficient.Indeed not. I guess "half baked" is putting it generously in this case; I just thought this would look sleek and cools and I wonder if it could work.
View attachment 479825
View attachment 479826
I dashed something together a few years back out of paper towel tubes. Always intended to go back and make something similar out of fiberglass.Indeed not. I guess "half baked" is putting it generously in this case; I just thought this would look sleek and cools and I wonder if it could work.
For l:I was indeed thinking of about 3:1, knowing that there is a maximum length for tube fins to work, so if 2:1 is more effective then so be it. I was also thinking of beveling the leading edge at something in the ballpark of 30° from the body tube wall, and the trailing edge in the ballpark of 75° degrees. My gut says the critical length for the L would be almost the outboard length where the tube is fully closed, since the flow restriction may be somewhat effective a little bit before that. Perhaps Kraken's designer can shed some light on that.
As I think more, of the leading face of the tube is beveled to such an angle, the root edges would end up really long with outer measure being three times the diameter, so more like 2:1 might look batter after all.
View attachment 479825
View attachment 479826
Of course, these plane trapezoids are rough stand ins for the actual shapes.
Absolutely. And, lest anyone forget, I was teasing Neil a bit, and he's totally welcome to post ideas here if he wants to.
I really like that third one. Funky.
Different sleekness/coolness aesthetic. No claim of outright superiority.Too uncool, not sleek enough?
Au contraire !Different sleekness/coolness aesthetic. No claim of outright superiority.
Also, unless I'm mistaken, the mechanism at work with a tube fin is sufficiently different from that of a conventional fin that comparisons like this are not valid.
I've seen "pylons". I don't think I use any single consistent name for them myself, I just call them whatever pops into my head at the moment.@neil_w or anyone in peanut gallery, is there any recognized name for the ring rocket attachments to the main body? I guess you could call them struts or spokes, but when they are long and thin (basically just like regular fins, except somebody glued a ring on the end), they have two effects.
"Pylons", I believe.@neil_w or anyone in peanut gallery, is there any recognized name for the ring rocket attachments to the main body?
I like Pylons!"Pylons", I believe.
Enter your email address to join: