What are the advantages of airplanes flying so high?

Question

If it’s because of wind tunnels that helps push the planes faster, how much slower would they be if they weren’t in those wind tunnels?
If the average flight from NY to London is 7H and 10M what would the flight time be?

In: Physics

Answer 1

While engines are less efficient at high altitudes. Lower air density reduces drag at higher altitudes which is more than enough to overcome the inefficiencies.

Which is why each model has their own optimal cruising altitude for lowest fuel usage.