Automatic cannon aiming

I tried JS version and its working in Unity 5.3.4. I'm not quite sure what`s wrong with C# version. My C# skill isn`t good enough. Maybe you didn`t enter Target, grenadePrefab, fireRate manually in Editor?

I remember I had a similar problem, i manually added greater angle. float shootAng = ang + 15; // you can add any angle After ElevationAngle function calculates minimum (like on your second picture) angle required to hit target

 function ElevationAngle(Target: Transform): float {
   // find the cannon->target vector:
   var dir = Target.position - transform.position;
   // create a horizontal version of it:
   var dirH = Vector3(dir.x, 0, dir.y);
   // measure the unsigned angle between them:
   var ang = Vector3.Angle(dir, dirH);
   // add the signal (negative is below the cannon):
   return ang;
 }

And after that. BallisticVel function calculates required velocity for the grenade with my desire angle (shootAng).

 function BallisticVel(Target: Transform, angle: float): Vector3 {
     var dir = Target.position - transform.position;  // get target direction
     var h = dir.y;  // get height difference
     dir.y = 0;  // retain only the horizontal direction
     var dist = dir.magnitude ;  // get horizontal distance
     var a = angle * Mathf.Deg2Rad;  // convert angle to radians
     dir.y = dist * Mathf.Tan(a);  // set dir to the elevation angle
     dist += h / Mathf.Tan(a);  // correct for small height differences
     // calculate the velocity magnitude
     var vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 * a));
     return vel * dir.normalized;
 }

Maybe this small explanation with help you with your code.

 var Target: Transform;
     var grenadePrefab: Transform;
     var fireRate = 10;
     var attackRange = 20.0; 
     var Damping = 6.0; 
     private var Distance : float; 
     private var nextFireTime = 0.0; 
 
     function Start () 
     { 
            Target = PlayerTransform.playerTransform; 
        } 
        function Update()
        { 
            Distance = Vector3.Distance(Target.position, transform.position);
            if (Distance < attackRange) 
            { 
                Fire (); 
            } 
        } 
        function BallisticVel(Target: Transform, angle: float): Vector3 {
         var dir = Target.position - transform.position;  // get target direction
          var h = dir.y;  // get height difference
          dir.y = 0;  // retain only the horizontal direction
         var dist = dir.magnitude ;  // get horizontal distance
          var a = angle * Mathf.Deg2Rad;  // convert angle to radians
          dir.y = dist * Mathf.Tan(a);  // set dir to the elevation angle
          dist += h / Mathf.Tan(a);  // correct for small height differences
          // calculate the velocity magnitude
          var vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 * a));
          return vel * dir.normalized;
      }
        function ElevationAngle(Target: Transform): float {
            // find the cannon->target vector:
            var dir = Target.position - transform.position;
            // create a horizontal version of it:
            var dirH = Vector3(dir.x, 0, dir.y);
            // measure the unsigned angle between them:
           var ang = Vector3.Angle(dir, dirH);
            // add the signal (negative is below the cannon):
            return ang;
      } 
 
        function Fire () 
        { 
            if (Time.time > fireRate + nextFireTime)
            { 
                nextFireTime = Time.time; 
                FireOneShot(); 
            }
        } 
 
        function FireOneShot ()
        { 
            var ang = ElevationAngle(Target);
            var shootAng = ang +15; //
            shootAng = Mathf.Clamp(shootAng, 0, 360); 
            transform.eulerAngles.z = -shootAng - 15; 
            var grenade: Transform = Instantiate(grenadePrefab, transform.position, transform.rotation); 
            var shoot = BallisticVel(Target, shootAng); 
            shoot = Vector3(Random.Range((shoot.x - 20),(shoot.x + 5)), shoot.y, shoot.z); grenade.GetComponent.<Rigidbody2D>().velocity = shoot; //
            BallisticVel(Target, shootAng); // pass the angle and the target transform 
        }

+++

And still nothing :/

Fine, it´s finally done! Thx for your patience and for piece of your own script...