bomb were not subject to drag, its path would be purely ballistic and it would impact at an easily calculable point, the vacuum range. In practice, drag means that the impact point is short of the vacuum range, and this real-world distance between dropping and impact is known simply as the range. The difference between the vacuum range and actual range is known as the trail because the bomb appears to trail behind the aircraft as it falls. The trail and range differ for different bombs due to their individual aerodynamics and typically have to be measured on a bombing range. The main problem in completely separating the motion into vertical and horizontal components is the terminal velocity. Bombs are designed to fly with the nose pointed forward into the relative wind, normally through the use of fins at the back of the bomb. The drag depends on the angle of attack of the bomb at any given instant. If the bomb is released at low altitudes and speeds the bomb will not reach terminal velocity and its speed will be defined largely by how long the bomb has been falling. Finally, consider the effects of wind. The wind acts on the bomb through drag and is thus a function of the wind speed. This is typically only a fraction of the speed of the bomber or the terminal velocity, so it only becomes a factor if the bomb is dropped from altitudes high enough for this small influence to noticeably affect the bomb's path. The difference between the impact point and where it would have fallen if there had been no wind is known as drift, or cross trail. The bombsight problem In ballistics terms, it is traditional to talk of the calculation of aiming of ordnance as the solution. The bombsight problem is the calculation of the location in space where the bombs should be dropped in order to hit the target when all of the effects noted above are taken into account. In the absence of wind, the bombsight problem is fairly simple. The impact point is a function of three factors, the aircraft's altitude, its forward speed, and the terminal velocity of the bomb. In many early bombsights, the first two inputs were adjusted by separately setting the front and back sights of an iron sight, one for the altitude and the other for the speed.