ProjectileTrailScript.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

//Attached to the cannon ball projectile - produces a trail to show the projectile path.
public class ProjectileTrailScript : MonoBehaviour {

    private GameObject trailParticle;       //the particle that makes up the projectile path       
    public float deltaTime = 0.1f;         //The time difference between trail particles
    private float nextTime;             //the next time that a trail particle should be formed

    // a list of all the trail particle gameobjects for easy destruction
    public List<GameObject> particles = new List<GameObject>();
    
	// Use this for initialization
	void Start () {
        trailParticle = Resources.Load("TrailParticle") as GameObject;
        nextTime = Time.time + deltaTime;
	}
	
	// Update is called once per frame
	void FixedUpdate () {
		if(Time.time > nextTime)
        {
            GameObject particle = Instantiate(trailParticle) as GameObject;     //create the trail particle
            particle.transform.position = transform.position;                   //position it where the cannon ball is
            particles.Add(particle);                                            //add it to the list of particles
            nextTime = Time.time + deltaTime;                                   //update the next time a trail particle is formed
        }
	}

    //loops through all the trail particles created and destroys them
    public void DeleteTrailParticles()
    {
        for(int i=0; i<particles.Count; i++)
        {
            Destroy(particles[i].gameObject);
        }
    }
}