He's being VERY thoroughThe OP is likely trying to mitigate anything he can think of before flight (usually by asking the forum).
Small fins are only one component required for coning. Typically, you'll see it with small fins, an over stable rocket, low thrust, and some wind. It's not as simple as small fins = coning. You may even see it at times on a rocket with normal sized fins....I was told it would cone because of the small fins.
I did use 4 fins for the rocket. I used OR and RASAero for the sim.I want to say I recall that 3-fins have more risk of coning than 4 due to lateral asymmetry. Its a great example of reducing one negative and introducing a different one. Welcome to real optimization.
Got into a discussion about coning/spiral behavior and "trajectory damping" with a guy once. Apparently Rocksim has some damping simulation that OpenR doesn't.
[damping related to the angle-of-attack oscillations]
The OP is likely trying to mitigate anything he can think of before flight (usually by asking the forum).
Why is coning a concern to you?
Well i thought either coning would reduce the altitude by alot or the rockt would go off-course.He didn't ask "why will it cone?" He asked, "Why are you concerned?" IOW, so what? What's the worry?
Oh ok. I do have small fins but my stability is only around 2 cal. My thrust to weight ratio is about 50:1.He's being VERY thorough
Small fins are only one component required for coning. Typically, you'll see it with small fins, an over stable rocket, low thrust, and some wind. It's not as simple as small fins = coning. You may even see it at times on a rocket with normal sized fins....
Regardless of the reason of your concern (from loss of altitude to destruction of rocket), you can learn more about coning from this publication (link below). Their damping solutions are beyond the scope of this forum, but it may help you visualize the issues.
You may need a math professor and an aerospace engineer (or both) to explain it in detail (I know I would). :eyepop:
BTW, IMHO this stuff is at the deeper end of the pool of rocket science.
I think this phenomena is somewhat related to coupling dynamics, here is a link to a NASA publication in the subject:
The first two link were a bit too advanced for me, so i checked out the last one, which helped shed some light on the issue. Thanks!
I agree. I'll check it out.IMHO, the fins are too small. But I noticed the length to diameter ration is similar to the Nike Smoke (which is about 13.8 for the Nike).
The fin span (and perhaps area, but not necessarily the fin plan form) for this rocket should be something like the Nike Smoke with regard to fin span to airframe ratio (which is in 1.31). You might cut the fin span down some off that ratio, but I'm not sure I would go less than 90%.
This is the where you have to decide is stability more important or is drag. This is the trade-off. Too much drag hurts altitude, whereas too little stability hurts you getting it back in one piece.
View attachment 315892
I have an ASP Scale WAC I fly on 38mm two grain motors, commercial and research and have never seen the rocket cone. I have skins on the fins that are supposed to make it more "scale-like". I got another one to build as my second one, stupidhead here forgot the charge size to use with the MAD apogeeI stand corrected, maybe he did ask the right question, but it was so far above my head that I didn't recognize it.
I will say that I have a small Estes WAC Corporal (clone). It is straight as an arrow until it starts to coast, then it corkscrews. Every time. I don't know why, but at the speeds it flies, it is not a problem.
In the case of the OP, I can see where coning or corkscrewing could be a concern at the velocity.
I'll shut up now, as I realize this discussion is beyond my knowledge.