Axe... I have recently learned the helicopter manuever, so I feel honored to offer you the lessons of my experience.
Do you already have the balls to actually try to spin? If so, you've won most of the battle... I think the thing that disqualifies many people from the joys of the helicopter is the fear of committing to the spin. It's a big, mysterious step.
Until recently, there has been very little available in the way of technical instruction resources for this kind of stuff. Ask those who routinely pull off 3's and 7's and beyond how they do it and you are likely to get a response like... "uhhhhh, I don' know, dude. I just, like, spin around, you know?" So, there is a certain intangible component to spinning... there has to be a certain amount of "just do it" in ya. After all, it is a very simple trick mechanically. The helicopter has always been on the back burner of my dream-stove... I'm glad it's recent semi-return to fashion came along to inspire me.
As an instructor, it occurs to me that we should be able to teach to people anything that passes through the skiing world. There has to be a scientific and logical set of facts and conditions for everything. From here, we can develop a progression for learning. So, I offer the "helicopter progrssion" for your perusal, enjoyment, entertainment and experimenting. (Axe, sorry if you are already past this point in your progrssion, but hang out a while, I got more stuff for you later.)
Learning the Helicopter. Technical skills progression.
1) Skiing backward with skis parallel. Slide forward at moderate speed and skid the skis 180 degrees, focusing on turning the head to watch where you're going. Maintain fairly narrow stance and gradually increase speeds and duration of backward travel as comfort level gets higher. Ski it out after spending a little time in the strange and exciting world of backward skiing. So, you are doing 360's on the snow with a little delay in the middle. When you are comfortable with a longish backward slide at moderate speeds, shorten the delay and eventually take it out altogether so you are spinning seamless 3's on the snow. Play around with different speeds.
2) Replace skidding 180 degrees with a small hop to 180, again focusing on turning the head to spot the landing. As comfort level increases, increase speed, duration and slope. Your prerequisite to progressing onward is to develop the ability to hop a 180, land and "ski it out" as soon as possible.
Of course, you are so obsessed with the 360 that you are doing dryland training at nite. On flat ground, jump into the air and spin around. Keep yer feets close, you spin easier that way. Keeps your axis intact. When body parts start flailing around, you throw off the integrity of your axis. Use your arms to drive the spin. Start with right hand low and left hand high. Swing right arm up and across yer bod. The left arm is trickier: you have to throw it sort of downward and across your low back. Try to keep your shoulders level. They need to stay outta the way of your head, because your head carries your eyes in it, and you're gonna need your eyes to see where you're gonna land. Your head gots to stay up, but yer eyes gots to look down to find that spot. As you progress, start jumping off from small heights, like a foot or so high and increasing to 2 or maybe 3 feet.
Do you spin to the left? I do, so these instructions need to be reversed if you go right.
By now, your on snow training will have taken you to doing little 180's off of small lips at "game" speed. You're comfortable landing backwards and your dry land training is preparing you for the big moment.
Having said all that, there's still that "just do it" component and I fear that's one of those things that can be learned, but not taught. Lesson's pretty much over, but a couple closing thoughts before you go try it: check out figure skaters doing those crazy spins - the faster they want to spin, the closer together they keep all their appendages and attachments. To slow the spin, they make themselves wider. So, approach the jump with a narrow stance and commit to keeping it that way. Try to time the spin so it starts just as the entire length of your ski leaves the snow. That means your arm swing should start just a tiny little bit before you become totally airborne. Takes a pretty sharp focus and a little patience. Lots of prospective spinners start the action just a wee bit too soon.
After the arm swing, try to tuck 'em in as close as you can, just like the figger skaters do. Apply the spinning force calmly and gradually, so you've got some left for the darkest side of the rotation, that last 90 degrees. If you spin frantically right at the start, you run outta gas before the trip is over.
Some smart-asses out there might do all this progression in one day, but it took me about 300 years. Shit, it was fun! Fell a lot, so I think that's a reality that has to be considered in one's decision to try the 3.
Someday maybe I'll try to write this into a more concise language. You can call me a lot of things, but you can't call me late for dinner, so that'll hafta wait. The 360 is one of those things that "everyone" has a little mantra for, but I think anyone would do well to remember that it's a whole-body move and the fact is, it takes a lotta "just doin'". It's very believable science though, so it can be learned.