A Canuck wrote:
If one was to be asked to design an UltraLight that would be able to
fly on Mars, what would have to change?

Make it much, much bigger.

Would the wingspan have to change significantly?

It depends.

As the air density is so much lower (around 1% of that on earth) a
standard ultralight moving at the same speed it does on earth will
generate about 1% of the lift.
Or due to the lower gravity, about 3% of the lift needed to keep it
at a stable altitude.
You need to fly about 6 times as fast as on earth in order to push enough
air downwards to generate enough lift to keep up.
So, a typical ultralight with a speed of 25m/s (around 50mph) might
need to fly at 150m/s (300mph).
Of course, you'd need a long prepared strip to take off and land at this
speed.
For a proper "ultralight", landing at a similar sort of speed to one on
earth, you'll need to make the wing area 30 times larger.
Challenging.

Engines are of course another challenge. Propellors work just fine, but
there is no oxygen to burn, so you need to take it with you.