Today I did something a little bit unusual, and definitely more difficult than flying around with a camera. A possible commercial customer asked to see a demonstration of a helicopter flying with a 2.5kg sensor. This sort of thing is commonly done for magnetometer surveys for mining exploration. The sensitive sensor must be hung from a long line in order to get it away from the magnetic interference from the UAV. This could also be done for water or gas sampling.
The big helicopter has no problem with flight control despite the hanging weight. It just requires some special piloting to control the swinging, basic pendulum dynamics.
These sorts of surveys require many tight passes at low speed, so it takes a long time to cover a large area. It's an ideal job for a gas powered helicopter UAV. This one can fly for an hour easily.
It would be possible to create a payload management system which would measure the position of the sensor via the angle of the rope, and automatically control the UAV to control the swinging (basically, the reverse of a balance bot). Something I would love to work on in the future.