Lifting capacity of helium balloons...

Helium Balloon Lift Test

For initial testing I have decided to keep the prototyping simple - helium balloons, balsa wood, and the occasional lego...

I purchased six 16" helium balloons to get an experimental verification of lifting capability. With a payload mass of 82 g the system is just about neutrally buoyant. Using weight instead of mass, we can state that the 6 helium balloons are providing 0.8 N of lift.

Of course we can calculate what the theoretical lift should be using the standard definition of buoyancy and a static analysis of the system. To simplify things, let's assume that the balloons can be approximated as spheres with a diameter of 0.4 m. The calculation is then...

So the analysis yields a lifting estimate of about 1.1 N minus the weight of the actual balloons. Of course, it didn't dawn on me to get some extra empty balloons while I was at the party store so that I could weigh them, but I would say that experiment and theory are in good agreement...

So where does that put our system?

Well the picture below shows what 82 g of payload look like...

This isn't too bad but the legos represent the extra components: 9V battery, balsa wood structure, wires and some LED's and resistors. 

The base configuration of the Syma S107 has a mass of 40 g which corresponds to a weight of 0.39 N. There are a number of components that are not critical to its operation as a thruster for the blimp-bot such as the plastic cowling, the tail assembly and the landing gear. Removing these components may get the system weight down to about 0.3 N.

The reverse engineering project that I worked on at TCNJ yielded thrust data for these small helicopters. The thrust data was collected using a simple but accurate thrust stand and data was collected for about 20 helicopters. One such data set is shown below - the majority of the tests yielded similar results with the helicopter being able to generate a net lift of 500 mN at full throttle. With a thrust of 0.5 N and a weight of 0.3 N, the helicopter can provide the system with an extra 0.2 N of lift - this extra lift corresponds to 20 g increase in payload capacity. 

This should bring the total payload mass up to a maximum of 100 g. Though this assumes that everything is "perfect", I am planning on a design the is no more than 90 g.

In looking at my options I decided to check the mass differential between my Arduino Duemilanove board and the SparkFun RedBoard that comes in their Inventor's kit. The RedBoard is 18 g which is 10 g less than the Arduino board. Excellent...

Okay - now its time to get back to my balloons...