Scioly.org

So did anybody make a helicopter over summer vacation or think about a new of design?

I still can't seem to think of a design that is more efficient (as well as easy enough to build) as the counter-rotating design with curved rotors (helical rotors). I was planning on building some over the summer, but of course I didn't =P

which is more efficient? a counter rotater with a fixed bottom rotor or a dual rotation where both rotors spin freely?

I always preferred two free-rotating rotors over a fixed one on the bottom because I felt it was the most efficient. That said, I've seen successful teams do well using one fixed rotor. Perhaps there's an expert here that would like to share some info with the rest of us?

My attempts at dual rotation helicopter were never nearly as successful as my fixed rotor ones, but that was probably just me failing at actually building it. I'll try again this year.
My problem in the past has been with stability/balance, so I'm going to try a split motor stick, which I didn't have time to make last year. I've heard that often helps, since it's easier to put the rotors on the same axis. Can you make a split motor stick with a fixed rotor (I think you can, but I don't remember)?

I have always done better with a fixed bottom rotor, due to ease of building and releasing for flight. Once Jeff Anderson gets back on here, maybe he can give us some helpful advice.

You're implying I left.

As usual though, no straight answer.

Fixed and free rotor. With usual design (single stick) you have two spinning objects tied together at the axle with different centers of gravity and axes of spin. That's unbalanced, thus it WILL wobble. Wobble PROBABLY means more drag, lower duration.

Two free rotors, the rotors have common centers of gravity and spin as long as the axes line up and shouldn't wobble (I'm assuming you balanced your rotors). Of course that assumes perfect bearings or perfecly match bearings so the stick doesn't follow one rotor or the other. Not entirely true, but probably good enough to significantly reduce wobble. Course now you have two bearings, increased friction there and again lower duration. I suspect a small effect if your bearings are good, large if not. Oh, and you have slightly harder build.

Split motor stick (or perhaps even better, rolled/hollow motor stick with rubber running down the center) if designed properly, can line up the centers of gravity and spin axes eliminating wobble with only one bearings worth of friction. Theoretically the best choice, but the build is definitely harder.

We've all seen successful versions of each though so what's that mean? I suspect it means that these things (unless the wobble is totally out of control) are at best second order effects. Only important after you get the first order stuff like weight, and pitch/rubber match right FIRST.

Jeff Anderson
Livonia, MI

You know Mr. Anderson, I should start a Wiki page quoting all of your posts... That'd be so helpful.

This seems like an interesting event. I hope they will have this next year

Under the Scoring section of this year's rules, part c has a sizeable time bonus for "Chinook-style" helicopters (recorded flight time is multiplied by 3!), which I believe weren't even allowed under last year's rules. That's probably going to lead to some interesting designs... time for some experimenting