[cirrus3]

> how much does it decrease the fuel economy of the towing plane

Probably a lot, but I'd assume it is by less than the fuel that 1-2x more planes would use, otherwise there wouldn't be a point to doing this.

[gervwyk]

I did a masters on design a autopilot to optimize fuel consumption in formation flight. What is interesting about the aerodynamics is that if placed in the upwash wake of the leader, you are essentially increasing the wing aspect ratio of the system, resulting in gains for both the leader and the follower aircraft. Feels very unintuitive but basically the donut spool is larger and the combined wing is bigger in the spool.

[hermitcrab]

Apparently that is part of the reason geese fly in formation.

[sysguest]

could you provide a link for this? I'm interested but I'm not sure what to google for