Drag is associated with the movement of the aircraft through the air, so drag depends on the velocity of the air. Like lift, drag actually varies with the square of the relative velocity between the object and the air.

Does drag coefficient depend on size?

The drag coefficient will change with size because the Reynolds number will change and the ratio of viscous and inertial forces will be different. One can sometimes alter the fluid conditions so that a scale model will have a Reynolds number near that of the actual body and the drag coefficient will be more meaningful.

Does drag coefficient change with scale?

Drag coefficient is the same for two bodies of exact shape but different sizes. In other words, scaling does not affect a model’s coefficient of drag as long as the model and the full scale object are of the same exact shape.