Here is a video showing a bomb run using the restored Norden bomb sight in the B-25 Miss Mitchell. This run was using data from our actual speed and altitude. It took a long time to set the sight up for the run, and that is using the benefit of an Iphone calculator to find the tangent of the dropping angle, and modern Garmin airplane GPS to find ground speed and altitude. I cant imagine how difficult it was to do this in WWII with pencil, paper, and mechanical computers, all while the enemy is attacking you with airplanes and anti aircraft ground fire. Here is a synopsis of what is involved in setting up the bomb sight. To set up the run, the Bombing Table document is referred to for the type of bomb used in the airplane (in this case 100 pound practice). The table gives you a value of trail (the distance covered by the airplane from the moment of bomb impact, airplane travel past that point), which in this case for 5500 foot altitude was 111 mils. This is entered into the horizontal circular component on the right side of the sight. Next the sights disk speed is set using the bombing tables. In this case 288 RPM, based on a ground speed of 250 miles per hour and altitude of 5,500 feet. A tachometer (inserted into the spinning adapter) is used to make fine adjustments to the large drum on the right until the value is obtained. The disk speed does waiver slightly so it is necessary to make constant checks. In WWII the process to obtain true ground speed involved several mechanical computers, instrument measurements, and calculations. Next, the dropping angle is set using the vertical rectangular window. The bombing tables indicate the correct dropping angle for this altitude is 50 degrees, but the sights window is set in tangents. So the bombardier would need to calculate this number, which is 1.19. This value is set by placing the right finger in the index window to the correct tangent. Next the bombardier needs to level the bomb sight scope by using the two bubble levels in the left circular window. If the sight head is not perfectly level, the dropping angle calculation will be completely off. Every time the plane moves, the sight head (stabilized by a gyro) moves so it is necessary to constantly adjust this component. Next the bombardier sights in the target. When the sight points to the target, an electrically connected indicator in the cockpit moves telling the pilot where to steer the plane. Or, if the plane has the C1 autopilot, the bombardier can steer the plane (Miss Mitchell does not have this autopilot). If a crosswind is present, the bombardier must kill this by making adjustments to the sight (the two interconnected handles under the big speed drum on the right). When drift is killed the bombardier begins the run when the cross hairs intersect the target, which is where this video begins. This is done by engaging a clutch, which engages a motor that drives the mirror at a speed that matches ground speed. When looking through the telescope, the cross hairs remain stationary on the target when the correct motor speed is set. This process happens very fast while at this low of an altitude. I bet I had 20 minutes of prep time to get the sight set up before the clutch was engaged. When the correct dropping angle is obtained (the two fingers touching), the arming lever drops and the bomb intervelometer is engaged. This sends electrical pulses to each bomb release station in the bomb bay, at the number selected on the unit. It also drops them at a rate selected for bomb spacing on the ground. Now you know how a Norden bomb sight works, and hopefully have more of an appreciation for what these brave men had to do. If even one of the above steps is in error, the bombs will miss. And all that was done while the airplane was being engaged by the enemy. For this video, nothing was dropped out of the bomb bay - it was full of our luggage, on the way to the Memphis air show.
Posted on: Sun, 02 Nov 2014 13:16:30 +0000
Trending Topics
Recently Viewed Topics
© 2015