Model Z is the most efficient airplane we have designed so far thanks to its winglets, high taper ratio or aerodynamic fuselage among other design features.
Lift to drag ratio
Lift force divided by the drag force (L/D) is the most common way to measure the aerodynamic efficiency of any airplane, this value is numerically equal to the glide ratio. L/D is not constant, this value varies with the angle of attack,see picture below. Maximum L/D will be always at the same angle of the attack. This point, the optimum for the airplane allows you to flight reducing to the mínimum the drag
Eclipson EBW-160 CL/CD vs Alpha graph
Wingtip vortices occur when a wing is generating lift. Air from below the wing is drawn around the wingtip into the region above the wing by the lower pressure above the wing, causing a vortex to trail from each wingtip, these vortices generate induce drag therefore reducing the maximum lift to drag ratio of the airplane.
Eclipson model Z has the lowest induce drag thanks to:
-High taper ratio, reduce the chord of the wing tip reducing the size of the vortices
-Winglets, block the airflow reducing the size of the vortices.
Nevertheless Eclipson Model T has the greatest induce drag due to its rectangular wing, the huge chord of the tip creates big vortices as you can see in the picture.
4 main forces acting on a airplane
Model T CFD simulation
Wingtip vortex increases drag
Model Z CFD simulation
Small vortices thanks to winglets