Using transform.Rotate to rotate my airplane is not smooth

Various rotation of enemy is so hard to me.I used "transform.Rotate",but it not smooth.Who can help me.

Make sure you multiply against Time.deltaTime.

Javacript

var amount: float = 5.0F;
function Update()
{
    transform.Rotate(Vector3.up * Time.deltaTime * amount);
}

C#

float amount = 5.0F;
void Update()
{
   transform.Rotate(Vector3.up * Time.deltaTime * amount);
}