[HOW TO LEVEL THE BOMBSIGHT]
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Year Published: 1943
Format: 16mm
Description: One of a series of classified films made for the Army Air Forces during WWII about the Norden Bombsight, this film focuses on the importance of properly leveling the device so as to minimize the error of deflection. During the entire war the Norden was considered a top secret piece of equipment and normally when it was shown in training films, it was hidden behind a piece of canvas or otherwise "blacked out". This series of films provides a rare look at the operation of the bombsight as it was presented to bombardiers. The Norden Mk. XV, known as the Norden M series in Army service, was a bombsight used by the United States Army Air Forces (USAAF) and the United States Navy during World War II, and the United States Air Force in the Korean and the Vietnam Wars. It was the canonical tachometric design, a system that allowed it to directly measure the aircraft's ground speed and direction, which older bombsights could only measure inaccurately with lengthy in-flight procedures. The Norden further improved on older designs by using an analog computer that constantly calculated the bomb's impact point based on current flight conditions, and an autopilot that let it react quickly and accurately to changes in the wind or other effects. Together, these features seemed to promise unprecedented accuracy in day bombing from high altitudes; in peacetime testing the Norden demonstrated a circular error probable (CEP)[a] of 23 metres (75 ft), an astonishing performance for the era. This accuracy allowed direct attacks on ships, factories, and other point targets. Both the Navy and the AAF saw this as a means to achieve war aims through high-altitude bombing; for instance, destroying an invasion fleet by air long before it could reach US shores. To achieve these aims, the Norden was granted the utmost secrecy well into the war, and was part of a then-unprecedented production effort on the same scale as the Manhattan Project. Carl L. Norden, Inc. ranked 46th among United States corporations in the value of World War II military production contracts. In practice it was not possible to achieve the expected accuracy in combat conditions, with the average CEP in 1943 of 370 metres (1,200 ft) being similar to Allied and German results. Both the Navy and Air Forces had to give up on the idea of pinpoint attacks during the war. The Navy turned to dive bombing and skip bombing to attack ships, while the Air Forces developed the lead bomber concept to improve accuracy, while adopting area bombing techniques by ever larger groups of aircraft. Nevertheless, the Norden's reputation as a pin-point device lived on, due in no small part to Norden's own advertising of the device after secrecy was reduced late in the war.
Complete Record:
Transcription
[Music] you are about to make Time cadet who is no longer with it a sad case but nevertheless instructed pilot to Bombardier [Music] pilot the bomber there ramadhir [Music] instructed a pilot Bombardier bubble happy return to face local well that was an extreme case just the same those bubbles can be a headache to anyone of you if you don't know what they're saying naturally they've been put there to tell you the position of the axis of the vertical gyro that is whether it's maintaining a true vertical reference line or whether it's tipped to one side so that you'd get an error in deflection like this now here is an experienced Bombardier leveling his vertical gyro what does he know about the relation of the bubbles to the gyro that the cadet didn't know or that you don't know let's review it you know that the gyro axis maintains its position no matter what the movement of its mounting you know to how the leveling system operates when you press in the lateral precessing knob you cause the gyro to precess if pressure or torque is applied to the left the gyro precesses to the right and vice versa the inner knob is for making large Corrections and the auto knob is for slight correction to change the far enough position of the axis torque is applied through the carton bearing against the housing of the gyroscope that's how on the pilot levels the airplane the Bombardier in turn levels the gyroscope but even at the plane level the bubbles also respond to the slightest change in the forward motion or attitude of the airplane any such change acceleration going skidding and so forth will affect the bubbles but none of these motions in any way affects the general axis itself but then how does the Bombardier know whether he's correcting for the movement of the airplane or for the position of the gyro suppose the lateral bubble is acting like this well you can be very sure it's caused by the motion of the airplane and not by any movement of the gyro axis so you wait before you attempt a level to see if the bubble will come to rest and then bring it back under the centreline if it doesn't come to rest perhaps because of a flutter condition and you must estimate the point around which it is oscillating and move the precessing knob until that point is under the centreline but when you first look at the bubbles and see one of them apparently still don't assume it's at rest it may have just finished moving in one direction and be about to return [Music] take plenty of time a gyroscope one bubbles length of the vertical causes an error of 17.5 mils which at 10,000 feet can mean get in the habit of taking a time get your bubble on dead center and you're set for this [Music] you [Music] you
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