External Cargo Proposal (Slung Load)
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Proposal for simulating External Cargo on helicopters (Slung Loads/ Container)
Helicopters can be simulated quite realistic in FlightGear. With the bo105, the Aircrane, Bell UH-1 and EC130 B4 with some descent helicopters with realistic and plausible fdm. Helicopters are used for rescue missions on sea and in the mountains, transporting cargo from one point to another; or used to extinguish fire by dropping water loads. This is a major feature of helicopters in RL and a real challenge for pilots and ground crew.
The challenge is due the often hardly predictable motion of the slung loads, as it behaves like harmonic oscillation. Reacting to any movements of the helicopter, but also influecning the movements of the helicopter due to the weight, impulse and aerodynamic drag and lift of the cargo.
Until now all this isn't possible in FlightGear.
Attempts to change this
Attempt by Wayne Bragg 2014
This is a current attempt to simulate External Cargo. An AI Aircraft scenario is loaded. The flightplan defines the spot where the cargo is waiting to be picked up and an AI aircraft as this cargo. Then a nasal script looks up for the distance to the cargo, and creates a scripted ballistic ai model.
While with this an AI Object can be defined and actually be carried and dropped, it doesn't simulate weight, aerodymanic drag and other forces yet. So we don't have any swing motions between helicopter and cargo. Applying physics for this is on his To-Do-List. The approach is a noticeable attempt, nethertheless the author seems not aware of a much earlier attempt, as his stuff could be much easier achieved. The earlier attempt will be described next:
Attempt by Maik Justus and Vivian Meazza 2007/08
Maik Justus is the author behind the Helicopter-Physics and the aerotowing/winch simulation in YASim. Inspired by an animation used on a helicopter-model in FlightGear he asked Vivian Meazza, author of the ballictic AI code, if external forces could be added to it. And indeed, within few days Vivian Meazza extended the code so external forces can be added to ballistic AI objects.
An ballistic AI object is created (load-demo.xml)which defines weight, inertia and aerodynamic drag and the location where the object can picked up. External forces can be applied which moves the object, winch and aerotows can be locked to the AI object as well. It is also affected by wind. The external force is defined in terms of: Magnitude (lbf), Azimuth (deg, North = O), Elevation (deg, up = 90). 
Unfortunately some problems occured which could't be solved at this time. But they left us the most important file to play again with: data/AI/load_demo.xml