This balloon helicopter is a neat toy, tool for teaching basic flight physics, and very nice case study in design and experimentation that could be useful in the undergraduate or high school teaching lab.

Notes on flying:
Current best configuration: 16mm blades (blade_16.stl), 13 degree rotor (rotor_13.stl).

Short flying video clip located here: http://youtu.be/mo7PvU1rNRc

Before you build: Unfortunately, it does not yet perform as well as commercial versions, if you are interested in a set of commercial balloon helicopters, consider one of these https://www.amazon.ca/s/ref=as_li_ss_tl?url=search-alias=toys&field-keywords=balloon+helicopter&linkCode=sl2&tag=themakerman-20&linkId=0109f7a43091d24fbd75bf792add82c6&language=en_CA or this set seemed rather good https://www.amazon.ca/s/ref=as_li_ss_tl?url=search-alias=toys&field-keywords=balloon+helicopter&linkCode=sl2&tag=themakerman-20&linkId=0109f7a43091d24fbd75bf792add82c6&language=en_CA

Once printed, insert the three blades into the rotor. Insert the nozzle long ways into a balloon and fill the balloon. Insert the nozzle into the rotor while pinching off the balloon, try to ensure that it is straight. Throw. Try different techniques, I found a little spin can help get it going.

Notes on making:
[See instructions for full details] All the components should be printable and all you need in addition is a nice balloon. The helicopter was developed using PLA on one MakerBot Replicator 2, but hopefully you can tell me if it works on yours or others. One key element is the need for a very flat build plate since it requires very thin (0.1mm) films to reduce the weight.

Notes on design:
I really enjoy design for 3D print and this was a nice case study with interesting constraints. I have included the SolidWorks design files for the latest and greatest version. This has gone through 5 major revisions to date in order to get it to fly as well as it does, but it still needs improvement. To get the weight down, I experimented with various surface profiles, wall thicknesses, geometry, build parameters, etc. My hope is others may try to improve it and we can collectively identify the optimal design.

I conducted some basic experiments on variants and have posted STL's for different blades and rotors in case you want to do some of those experiments for yourself. The design files are not well documented but if you have some basic skills with SolidWorks, it should be no problem to figure out.