Background

So this design was really marking the switch from what people imagine a ‘drone’ to look like, to one more in line with the requirements of a long-range delivery drone. A VTOL drone allows us to effectively glide and greatly increase our range, like a traditional fixed wing drone, yet the vertical take-off allows the drone to be installed almost anywhere, with minimal infrastructure.

Design Process

Although we had decided we needed a VTOL drone, VTOL is an incredibly broad field and we had to settle on a design. Since simplicity is one of our goals, we decided to go for a tail-sitter design.

Most other designs either involved additional propellers on the top for upward flight, which requires additional power, increases cost, and induces greater drag. 

Another option were pivoting propellers, which would move the drone up, then rotate and act like traditional plane propellers. This design would increase complexity, and the existence of more moving parts would also reduce the longevity of each drone.

Finally, we settled on a tail-sitter, where the drone would sit vertically, take off, and roll 90 degrees to transition into fixed wing flight. We chose this because most of the complexity lies in the software, which we can existing open-source solutions for, and the only mechanical difference is the presence of a winglet to prop it up, which has the added benefit of preventing air from mixing at the tips of the wings, removing the need for vortex generators.

As for the design of the body itself, this initial version served more as a crude proof of concept. The airfoil was automatically generated by a program (airfoiltools) based on certain constraints, and the drone followed a generally aerodynamic shape, but there were no special considerations made to the detail of the design itself.

Simulations

The steady state simulation was performed by Naman using Autodesk CFD. This helped give a general idea of whether the design would work and gave positive results. The CFD also helped recognize the unintended effect of the winglet - it prevented the air from above and underneath from mixing.