What are aerodynamics benefits of using unloaded wingtips (zero lift)? does unloaded wingtip make inner parts of wing more efficient?
(I know that unloaded wingtip reduces bending moment,so structural weight can be lower, thus reduction in L/D and higher net wing lift (lift minus wing weight), but you can connect wingtip with wire and use elliptical distribution..so..)
Twofold (at least): firstly it results in less energy going into the tip vortices, secondly, is the reduction in lift is gradual towards the wingtip then it tends to reduce the spin tendency - the angle of attack of the tip is typically lower than at the root and so it will stall later than the root. In a slow-flying aircraft such as a paraglider the airspeed may be significantly lower at the tip when turning, and so the angle of attack for a given sink rate will be higher, increasing the risk of a spin.
I don't think any kinds of external wires are going to affect the aerodynamic properties of the zero-lift tip, they will just add their own independent effects.
For a straight wing the benefits are as already described. You note minimal root stress, hence light weight, hence minimal induced drag. A previous answer notes improved stall characteristics at slow speeds or in tight turns.
For a swept wing the benefits are more profound. The most visible difference is that it acts like a "tail at the end of the wings" to confer pitch stability and control, so the wing can be tailless. It also improves directional stability so that for a pure flying wing (an all-wing), no tail fin is needed either (yaw control is then effected by "drag rudders" located outboard near each wing tip). Then, the lift over the tip section is mostly a little above zero. Due to its washout and the upflow induced by the inboard wing sections, its lift vector is tilted forwards, which can lead to negative induced drag, i.e. a small amount of thrust. This not only makes the wing more efficient, but also in the turn it creates proverse aileron yaw, which is a tendency for the plane to swing into the turn. Adverse yaw, the tendency to swing the nose out of the turn, is a problem with constant-angle (zero washout) wings and, especially when swept, can lead to Dutch roll and other unpleasantnesses.
