The down force is unrelated the jets. They said the car could have up to 10 jets and none of those were pointed upwards. The car has some fans that suck the air out from under that car which then sucks the car down onto the road. It’s nearly 60 years old technology that was first used in F1 to great effect. There’s a car currently in production that uses it. Porsche very recently unveiled something like that too.