I understood it perfectly. You are the genius who thinks that the plane would not be moving forward because of the treadmill. Maybe the OP thought the same thing. You both could not be more wrong.
Your brain is tied to the misconception that the plane is propelled by it's wheels, like a car would be..
Think of this.....
You have a Corvette on a treadmill, and both the wheel speed and the treadmill speed are perfectly offsetting each other, so there is no relative movement. Then.....They pull off the tarp off the back of the car revealing a 15,000 lb. thrust jet engine. Somebody turns on the great big freakin' jet engine attached to the back of the corvette. So you think that the car would still not move forward relative to the treadmill?
.
Heck, even think of this....as the jet engine thrust increases, take the car out of gear. Now the car's wheels are mechanically disconnected from the new drivetrain (jet engine) Increase the thrust and the car will move forward - the wheels will spin faster and faster as the thrust is increased and the relative car speed increases.
