I have been working on a crop/golf course dusting Hex AgCopter. I am using a DJI S800 with DIY APM as the controller. We did some preliminary test using a simple spray rig to test the feasibility. It was a good test and now I'm working on a better spray rig that can attach and detach quickly so that you could us it on multiple vehicles.
Below are some pictuers;
This is the S800 with the spray rig...
Below is a YouTube link of a video of the HexCopter flying and spraying
I am doing similar work but focusing on solids (seed and granular products) at this time.
Such a concept can work but your end product must be mindful of the leglislation that you will have to work under and the products you ultimately want to distribute. The effects of the spray particularly fine particles as shown in the downdraft are also worth noting and would suggest going to a 120 deg air induction nozzle at lower pressures (2-4 bar ).
Are you using a pre compressed mixture in the canister as on backpack sprayers or a pump? I have considered both systems and the power/ weigh benifits for both.
I was using a pre-compressed canister for the simplicity and demonstration purposes but the final product will utilize a pump and a circular ring distribution removable yoke with variable pressure setting and nozzles for specific applications. I'm currently working on the ring and trying to com up with usable system, weight is an issue and certainly a big factor...