[danielrpa]

It's more complex than that. There factors other than drag. Planes wouldn't be more efficient if they simply used roads at 60mph all the way to the destination (no takeoff)! Fuel is expensive so they do a lot of work to figure out the optimal speed.

[lonelygirl15a]

Use roads at 60mph? I guess they're most efficient if they don't start the engines at all and you put the plane on a boat or a train.