P6-112 Fire Support: Ballistic Flight Paths

Quick primer on ballistic flight paths

In order to understand some of the calculations you are going to be doing, we must understand what effect the different factors have on a flight path. Those factors are called fire elements and are as follows:

The effects of changing ELEV and Charge will now be shown visually. 

Note: The following curves are not realistic curves in an atmosphere, as they do not consider drag, the wind forces acting on the projectile in flight. But the principles stay the same.

ELEV:

In the above picture you can see 3 flight paths with different elevations, while the charge is staying the same. ELEV changes the height of the curve and as a secondary effect the distance. Note: 800 mils corresponds to 45° and is the optimal ELEV to achieve the longest range with a given charge.

Charge

In the above picture you see 3 flight paths, all shot at 800 mils and only the charge changing. Charge changes the distance of the flight path and has a secondary effect on the height of the curve.

Angle groups
 

In ballistic flight paths we must differentiate between two different angle groups:

• Higher angle group are all flight paths fired at over 800 mils. 

• Lower angle group are all flight paths fired at under 800 mils

Generally speaking a mortar will fire in the higher angle group only. Artillery can do both.

The reason this is important is that the angle group determines the way one has to calculate corrections for height differences between the fire position (read: the mortar) and the target.

Higher angle group

From the above graph one can see that in order to hit a target which is the same measured distance away on the map, but at a different altitude, different ELEV are required. T2 shows the case where the fire position and the target are on the same altitude. This is going to be the ELEV you will read of your range card in the ELEV column. Now if the target’s altitude is higher than the fire position (T1). The ELEV has to be reduced compared to T2.

The opposite is true for a target whose altitude is lower than the fire position (T3). The ELEV has to be increased compared to T2. This might seem counterintuitive at first, but another way of thinking about it is that these three flight paths do cross each other near their highest point. They cross before they hit the target.

Remember: Fire position higher than target ADD ELEV. Fire position lower than target SUBSTRACT ELEV.

Lower angle group
 

From the above graph one can see that in order to hit a target which is the same measured distance away on the map, but a different altitude, different ELEV are required. T2 shows the case where the fire position and the target are on the same altitude. This is going to be the ELEV you will read of your range card in the ELEV column. Now if the target’s altitude is higher than the fire position (T1). The ELEV has to be increased compared to T2. The opposite is true for a target whose altitude is lower than the fire position (T3). The ELEV has to be decreased compared to T2. Another way of thinking about this is that the flight paths will only cross far down their flight path. They cross after they hit the target. (Not shown on graph) 

Remember: Fire position higher than target SUBSTRACT ELEV. Fire position lower than target ADD ELEV.