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Single bladed propellers certainly do work, look around for old outdoor freeflight designs on how to do it.
From a theoretical point of view, a single bladed propeller can be more efficient.
The bonus is intended to be real, whether it is worth the 25%, the rules writers don't actually know. That's intentionally left to the students experiments to prove or not.

As an example of our thinking, a number of years ago in helicopter the bonus was for a 'chinook' style helicopter, one with the rotors NOT on a common axis. Again, the rules writers knew it should be doable, but hadn't done it themselves. Turned out it was very doable, and the bonus made it the winning strategy. But it took thousands of students across the country to figure it out.

Jeff Anderson
Livonia, MI

Just wondering about the chinook style- has anyone made it? I feel on a GOOD ceiling (rip NJ and whatever other state that has had controversy) that it would be plausible, and be eligible for a 75% bonus. With 3 motors how would you wind it all? I assume you could try making a truss design to hold the extra tension (woo towers) and then have a triangle like winding mechanism where you wind one first and then the other one? It seems really interesting! At that rate, just getting 1:30 would yield a 3 minute time.

When we had the chinook bonus, the working solutions used two rotors. I've never seen, nor heard of a three rotor solution. Though I hope to some day, that's why its been left in the rules and gets a pretty good bonus.
Two works because the rotors can counter rotate and meet Newton's equal and opposite requirement so the whole thing doesn't spin. You can theoretically do that with three rotors, but somehow you have to make two rotors offset the third exactly (or at least close).
The min mass was also larger, I think 4.0 gm.
Oh, and the bonus was pretty big, I don't remember how much off the top of my head.

The solution was pretty much what you said. Two shorter rotor sticks held together with a light frame (doesn't take a lot of load for the frame, not a lot of force from the rotors) to separate them. Two matching, counter rotating rotors. Two half motors, carefully matched and carefully wound to same torque and winds. I think all the ones I saw were wound off the copter individually. All that matching stuff was to ensure the rotors counteracted each other closely enough for the whole thing to fly well and without spinning, much.

And I like the way you are thinking. Is the bonus worth the trip. Exactly what we were trying to motivate. Though I will say you should master the basic WITHOUT bonus first.

Jeff Anderson
Livonia, MI

jander14indoor wrote:When we had the chinook bonus, the working solutions used two rotors. I've never seen, nor heard of a three rotor solution.

Really? I remember seeing several posts in the 2012 forums about three and four-rotor designs; I thought I read of one team that had two sets of rotors side by side, and another team who built three in a triangle (pretty sure one of them was Troy and the other was Ward Melville, but I can't remember for sure).

http://scienceglitz.blogspot.com/2011/0 ... d-fly.html

I think this design would be really cool It seems viable just replacing the rotors with all single bladed rotors and attaching one to the base- though I don't know if rules allow the metal part that powers the side rotor. Extending the long shaft to accommodate more winds and removing the fluff parts to cut mass seems viable too. Adding a counter balance on the other side would finish balancing it? It would be quite impressive if that worked as well as it would seem to

If there have been three rotor designs I'm disappointed to have missed them. Four rotors wouldn't be much harder than a chinook, easy to counterbalance all the forces.

On that helicopter you pointed to, the challenge would be getting the weight down to make it competitive.

Jeff Anderson
Livonia, MI

Dang that heli looks cool but yeah, getting it structurally strengthened to withstand 150 winds on 15:1 would be challenging- but that's what bonuses are for... I feel that one could possibly go for a 3 rotor config by putting two rotors on top, one on the bottom and just have them attached to hooks at the other end, not necessarily a rotor? And somehow have one person wind and one person hold to allow all three to be wound... weight and balance would be an issue but that's one way to do it I guess so kinda like a Chinook?

Hit 2:17 for first place in Ohio yesterday! Ceiling was about 30', but venue was quite bad; lots of obstructions, but we managed to avoid them on our first flight besides brushing the curtain on the descent. Probably could have gotten a few more seconds if it had gone down untouched by obstacles.

dhdarren wrote:Hit 2:17 for first place in Ohio yesterday! Ceiling was about 30', but venue was quite bad; lots of obstructions, but we managed to avoid them on our first flight besides brushing the curtain on the descent. Probably could have gotten a few more seconds if it had gone down untouched by obstacles.

Mentor's second flight was 2:33 but (fortunately for many teams) the flight was not counted. I heard that the 2:33 flight didnt count because the rotating disk on the top of the heli fell out.
I've seen this happen to Mentor once before at Solon and am surprised they didn't change this design flaw.

AlbatrossTree wrote:

dhdarren wrote:Hit 2:17 for first place in Ohio yesterday! Ceiling was about 30', but venue was quite bad; lots of obstructions, but we managed to avoid them on our first flight besides brushing the curtain on the descent. Probably could have gotten a few more seconds if it had gone down untouched by obstacles.

Mentor's second flight was 2:33 but (fortunately for many teams) the flight was not counted. I heard that the 2:33 flight didnt count because the rotating disk on the top of the heli fell out.
I've seen this happen to Mentor once before at Solon and am surprised they didn't change this design flaw.

This actually happened to us on our second flight as well; it hit one vertical girders and snapped off, but our heli continued flying for 2:25 if I remember correctly; probably could have gone a bit longer if it had descended without hitting obstructions. I think this issue is part of the nature of the rotating disk design. It's just very fragile, especially considering its low density and thickness balsa that shears very easily.