I work for CJ Youngblood Ent, a remote control helicopter and quad-copter design company based out of Texas. A few months ago we released the Stingray 500, a full collective-pitch quad-copter for the r/c industry. There were a lot of good responses to the model, and a lot of people wanted to see a nitro version. We have completed our single-motor internal combustion collective-pitch quad-copter prototype: The MantaRay.
The MantaRay is a proof of concept, and is not necessarily intended to be produced in this exact configuration, however we feel this model is leaps and bounds ahead of the industry and will help pave the way for a lot of great technology in large-scale stable flight.
We hope you find this interesting and would love some feedback on interest.