Mars's lower gravity, lower-density atmosphere, and different speed of sound (atmosphere mixture & temperature) happen to combine to similar aerodynamics in the

Mars's lower gravity, lower-density atmosphere, and different speed of sound (atmosphere mixture & temperature) happen to combine to similar aerodynamics in the high-subsonic region as the stratospheric region around 40 km altitude on Earth. I.e., a plane that can fly up there on Earth could fly on Mars at low altitude. Because gravity times travel distance is constant for constant aerodynamic efficiency and constant engine ISP, and Mars is both smaller than Earth and has significantly lower gravity, a hydrolox fuel-cell (driving electric props) flying wing should be able to do a "half-way around the planet" trip with reasonable cargo, followed by re-fueling oxygen, and flying back to the other place, before running out of hydrogen. (Alternatively, at less than 50% cargo capacity loss, it could collect the water exhaust from the fuel cell, to recover the hydrogen.) The main issue of such a plane would be that the lift-off speed on the runway would be about half the speed of sound. Maybe use the electric motors to drive fuel pumps and run hydrolox rocket engines for lift-off? Sounds like that could allow VTOL.