you have to overcome a certain amount of drag

你得要克服一定大小的拖曳力
and the propeller spins at a speed

而以一定速度旋转的螺旋桨
that will provide that force to move forward.

会提供前进运动的力
That seems, if not a complete description,

看上去即便这不是一个完整的说明
that seems like a pretty adequate description of how you move ahead.

也足以说明飞行时怎样才能向前走
How do you get off the ground and maintain off the ground,

那你怎么从地面起飞并且不坠地
maintain your height off the ground?

保持有一定高度不至于坠地呢
In order to do that, you have to overcome this

为此你必须要克服
constant force of gravity which is pulling you back.

恒定的将你向下拉的重力
That's the main problem with flight,

这是飞行中的主要问题
overcoming the force of gravity

那就是克服重力的问题
and in airplanes that's done through design of wings.

而在飞机中通过设计机翼来解决