akg1486 wrote:What is mentioned is that the blades can be asymmetrically tilted during revolution to provide torque to move sideways. I wouldn't be surprised if the shape is optimized for that.
That characteristic is traditional helicopter technology; the pitch on each individual blade is cyclicly (ie at a particular point on the revolution) changed so that the disc formed by all blades tilts in the dynamically desired direction.
The blade shape and twist will be optimised for the atmosphere in which they operate, and they look strange because no Earth-bound helicopter has operated in such low gas (atmospheric) pressure. Hence the significantly more rapid rotor speed, wider chord, and greater twist.
As PPL theory from Bernoulli tells us for a wing (hence any aerofoil, including a rotor blade):
Lift = 1/2 x rho x v(squared) x S x CL
rho = atmospheric density
v = airspeed (ie blade speed at a particular point along the blade in a nil wind hover)
S = aerofoil area (linked to chord, naturally)
CL = Lift coefficient ( driven by local aerofoil shape)
rho is very, very low by Earth terms, hence everything else needs to be higher even given an extremely light airframe hence low lift force requirement.
There is no real Earth precedent for performance at this level.
So higher rotational speed (> V), greater blade chord (> S) and unusual aerofoil with greater twist and AoA (>CL). The exaggerated twist is I suspect likely due to the higher speed and lower density hence unusual (for Earth) aerodynamic lift distribution along the blade.
The technicalities of it make it an even more impressive achievement than even it superficially seems, to my mind. JPL and NASA are rightfully ecstatic and deserve every ounce of the pride they must be feeling today.