The drouge chute method could work. I spent 20 years in the Air Force as an Aircraft Weapons guy, there was a towed target that was used for shooting at with other aircraft. They were towed aloft attached securely under the wing, then released and the cable reeled out to the proper distance. They looked like big silver darts. I am not sure how stable they were longitudinally. The bigggest issue with the drouge is the very high drag, releasing or bringing the unit back and I believe longitudinal stability. I am sure these could be overcome with some experimentation.Based on my experience, I have pursued two types of towed vehicle.
Type 1, lifting surface, this type has a large wing area and flies high above the towed plane with the video looking down on the tow plane. I like this video the best as compared to looking up at the towed plane. For the most part so far to achieve longitudinal stability, the towed platform has had to be controlled ( with reciever and live control surfaces). So far, I have balanced these vehicles and set the CG so they will glide back to earth. So far, this type releases itself from the tow plane and tow line, leaving the tow line trailing behind the tow aircraft. Landing with this type is difficult thusfar because the lifting property of the vehicle wants to lift the tail of the landing plane. Even with the big hawk, this has happened the two times we tried to land connected. The goal for me is to have this towed vehicle stop flying just before the towed vehicle does so it will not cause the nose overs and yet still keep the tow line taught and land stably behind the tow plane. My goal is to build a large lifting surface vehicle that is not controlled, that way one person can do the flying.
Type 2. The trailing type has very little lifting (wing) area and trails below the towing aircraft. This type so far has been very simple in that I have not used "Live" control surfaces. Longitudinal stability is an issue, but not as bad as the larger winged vehicles. The CG is not so critical on these types so far, but as I get a better compromise between a winged lifting type and a trailing type, I believe the Cg will be more important.Thusfar, this type is towed and still attached at landing with the trailing vehicle touching down on the runway and losing lift before the towing plane does. The last test, I installed a release mechanism on the tow vehicle to release the tow line in case of emergency and to see if I could get the trailing vehicle to land softly enough to prevent damage to the vehicle and video camera. The trailing types are also much easier to build. Using the foam pool noodle, the camera slides nice and snugly into the hole and the foam protects the video camera.
One critical design consideration is the location of the tow line connection to the towed vehicle in the vertical. Connecting it too low makes too high of an angle of attack for the lifting surfaces, somewhere just at center or slightly lower seems to be the best location.
Denny