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jander14indoor wrote:In addition, the single bladed rotor had to be powered to rotate by the rubber band. It couldn't be free rotating in the airstream. It had to provide lift.

Note that this does not necessarily prohibit the single stationary rotor and single mobile rotor approach used by many competitors with multi-bladed rotors. Rotation of the a rotor fixed to the motor carriage is powered by the rubber motor.

retired1 wrote:if you had 2 connected to the same prop shaft , they could not rotate independently.

Sounds like you're describing rotors that are rigidly connected. The top two blades pictured would not count as two single-bladed rotors:

retired1 wrote:If you put 1 on top and 1 on the bottom there is also no place to to have a rubber powered 3rd one.

Don't need to have rotors as top and bottom; balsa Chinook helicopters can have two rotors rotating in the same plane about non-coincident parallel axes.

The statement was that there is no way to have 3 single blade rotors--And you proved that.

retired1 wrote:The statement was that there is no way to have 3 single blade rotors--And you proved that.

In which statement am I "proving" that it is not possible?

Three single bladed rotors is certainly as possible as three multi bladed rotors. Three independent motor sticks linked by a horizontal triangular frame. This is similar to the Chinook concepts flown a couple of years back. Three motors, each a third of the max (though I should probably make sure to reread the rules to make sure that is OK). A single bladed rotor on each motor stick. Probably wouldn't work too well if all three spun the same way. Some rotation if two of three spun one way, and the third the other.

Practical or effective, all I can say is I haven't seen one yet...

Jeff Anderson
Livonia, MI

There is no limit on the mass of the rubber motor in the 2017 Helicopter rules. Determining the optimum mass of the rubber motor for a given helicopter will require significant experimentation (and record keeping).

I am happy with the changes to the 2011 and 2012 Division C Helicopter rules.

A diagram for Helicopters is posted on the national website: https://www.soinc.org/sites/default/fil ... iagram.pdf.

In several of the old Wright Stuff threads, the technique of using a jig to enable you to build a propeller with a curved shape, to minimize drag. Would this be a viable technique in Helicopters?

andrew lorino wrote:In several of the old Wright Stuff threads, the technique of using a jig to enable you to build a propeller with a curved shape, to minimize drag. Would this be a viable technique in Helicopters?

In my experience (which is basically just looking at some Helicopters in 7th and 8th grade) that would certainly be possible; I've seen many Helicopters with curved wings, and the concept seems to me like it would transfer well to helicopters. The most common way I've seen it be done is with the lower and upper whatever-they're-called both attached to the central axis, but with an angle in between, and several connectors; it basically looked like a normal wing at the end, and became closer to vertical near the axis.

andrew lorino wrote:In several of the old Wright Stuff threads, the technique of using a jig to enable you to build a propeller with a curved shape, to minimize drag. Would this be a viable technique in Helicopters?

Yes, you can bucket form framed blades and blades made from sheets. Of course you can also go without helical pitch. For my next helicopter, I'll be using blades that are just like wings for planes, just smaller.

I have built and flown about 15 - 20 SO helicopters since it first became an event in 2011. I have tried helicopters with flat blades and blades that have flat undersides and air foil shaped upper sides (but no twist). None of them has flown as well as helicopters with helical blades. Has anyone else achieved different results?

Real helicopters have blades with very little twist, but most are designed to fly forward at over 100 mph. SO helicopters simply fly vertically to the ceiling, and then come down vertically when the torque of the rubber motor has diminished to the point that the lift of the rotors is insufficient to support the weight of the helicopter.

I predict that 90 - 95% of competitors in the 2017 Helicopters event across the nation will simply build the 2017 FFM kit following the instructions and fly those helicopters in the regional, state and National SO competitions. If you decide not to build the FFM kit, the goal is to design a rubber powered helicopter that meets the current SO rules and consistently produces the longest flight times in a typical high school gym. All the theoretical discussion and mathematical calculations in the world can't replace actual test flights of real rubber powered helicopters with different blade configurations. FFM produces excellent kits and designs. However, since 2005 the gold medal winners in both WS and Helicopters in the very large regional SO competition in my area are almost always custom designs.