They know exactly what the air density and gravity is and tested for the exact conditions. It it makes to the surface in one piece it will fly.
Tethers are cheap but don't really allow free flight. Parabolic flights only give you a few seconds in fairly cramped space, and getting the low air density inside a plane sounds tough. A large spinning laboratory in space that can be spun up to simulate the desired gravity would be a solution, but we don't have that.
They could do something like that.
It nearly killed him. I don't think anyone actually liked it, and I bet a lot of people in risk assessment went hard on the "nixon needs to prepare the death letter" story.
Nit: the Lunar Lander Research Vehicle actually used a CF700 turbofan[0], not a rocket, to partially counter-act gravity.
That will be somewhat more tricky (or impossible) to emulate on earth.
Unfortunately, everything is trivial in theory.
So far the fastest winds observed on Mars are about 30m/s.
So, the thin air that makes it hard to fly on Mars makes it safe to stay on the ground.
Running the worst case numbers, 1000 10um particles per cm^3 adds up to about 1/3 the air density. Realistically it's maybe 10% of density increase.
“The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive. This occurs because the molar mass of water (18 g/mol) is less than the molar mass of dry air.”
(Not sure I like the language above but that’s how Wikipedia says it)
Is this potential effect accounted for in your numbers? I.e. What happens to the molar mass of Martian atmosphere when Martian dust is suspended in it?
At any rate, dust is bad for the moving parts of flying machines.
Dust doesn't have a meaningful vapour pressure and can't influence air density this way.