WTC Collapse and Air Resistance.

In a recent discussion with a truther regarding the collapse of the towers the topic of air resistance came up. An analogy was made about sticking your hand out of a car window moving at speed and feeling the force exerted on your hand.

Now my math may be a little rusty but I figure an object that’s been falling in a vacuum for 10 seconds is going about 350 km/h, a speed that’s going to exert a considerable force due to wind resistance.

I search around for info on this and all I could find on a non CT site was F Greening’s paper which stated that air resistance “is not a significant factor”

Is Greening right ? should the air resistance offered to a flat object travelling at several hundred km/h simply be discounted and if so , how come ?