Loyd Searle High Tech Promotions Inc. SPECTRUM IEEE #0018-922-0060 SEPTEMBER 1989 The bombsight war: Norden vs. Sperry As the Norden bombsight helped write World War II’s aviation history, The less-known Sperry technology pioneered avionics for all-weather flying Contrary to conventional wisdom, Carl L. Norden - inventor of the classified Norden bombsight used in World War I! - did not invent the only U.S. Bombsight of the war. He invented one of two major bombsights used, and his was not the first one in combat.
That honor belongs to the top secret product of an engineering team at Sperry Gyroscope Co., Brooklyn, N. The Sperry bombsight out did the Norden in speed, simplicity of operation, and eventual technological significance. It was the first bombsight built with all-electronic servo systems, so it responded faster than the Norden's electromechanical controls. It was much simpler to learn to master than the Norden bombsight and in the hands of a relatively inexperienced bombardier its targeting was at least as accurate. And the autopilot that made it work so effectively became the basis for decades of commercial and military aircraft. Yet although the U.S. Government authorized Sperry to construct a 186,OOO-square-meter plant in Great Neck on New York's Long Island to manufacture the bombsight and autopilot, the Army canceled the Sperry contracts less than a year after the plant's opening and handed the business to Norden and other companies.
Furthermore, declassified documents, plus recollections from some of the principals, show that the design of the final Norden bombsight‹for which a patent was applied for in 1930 but not issued until 1947 incorporated many of the central improvements pioneered by engineers at Sperry. How were the Norden and Sperry bombsights invented, and how did they compare?
If both bombsights were classified, why did the Norden become so famous during World War II that it was even featured in popular movies while the Sperry was comparatively little known? What factors caused the Army's sudden reversal, even with the Sperry device's advantages? Recent synthesis from scattered documents and interviews with some of the surviving principals lend some insight into these questions. The precision-bombing problem Before the Norden and Sperry bombsights, accurate high altitude bombing was considered impossible.
Strategists thought of bombers as unstable artillery gun platforms. In the 1930s, comparatively simple mechanisms guaranteed fair accuracy in hitting targets from altitudes below 5000 feet (1.5 kilometers). But at heights above the effective range of antiaircraft guns, aircraft moved too fast for normal calculations of firing data. The problem of calculating in real time the proper point for releasing a bomb was formidable for the equipment then in use. A bomber traveled rapidly in three dimensions and rotated about three axes, and was often buffeted by air turbulence. The path of the dropped bomb was a function of the acceleration of gravity and the speed of the plane, modified by altitude wind direction, and the ballistics of the specific bomb. The bombardier's problem was not simply an airborne version of the artillery-gunner's challenge of hitting a moving target; it involved aiming a moving gun with the equivalent of a variable powder charge aboard a platform evading gunfire from enemy fighters.
Originally, bombing missions were concluded by bombardier-pilot teams using pilot-director indicator (PDI) signals. While tracking the target, the bombardier would press buttons that moved a needle on the plane's control panel, instructing the pilot to turn left or right as needed. The pilot had to maintain straight and level flight at the precise altitude and airspeed the bombardier had predetermined for the mission. If the pilot allowed those factors to vary, it would upset the bombardier's efforts to track the target; similarly, if the bombardier operated the azimuth tracking of the bombsight unsteadily, the wavering PDI signals would cause the pilot to fly the plane inaccurately. It took expert pilots and expert bombardiers working in harmony to target a bomb accurately. And in the heat of combat, that ideal combination was the exception rather than the rule. Norden takes up the challenge Carl L.
Norden began studying bombing problems in 1921 as a consultant to the U.S. He had been a Navy consultant on different projects since 1915.
For the four years before that, he was an engineer working on ship gyrostabilizers with the newly formed Sperry Gyroscope Co., and continued as a consultant to Sperry through World War I. In 1923, Norden went into partnership with another Navy consultant, a former Army colonel named Theodore H.
Barth, who provided valuable know-how in sales. Over the next five years, Norden designed bombsights, and Barth built and tested prototypes from Norden's top secret drawings. In 1928, Norden and Barth received their first order from the Navy for 40 bombsights. At that point the two incorporated as Car!
The Norden company delivered its first prototype of its Mark XV bombsight to the Navy in 1931. To make the bombsight's telescope independent of the buffeting of the plane, it was hung from gimbals (ring-shaped bearings that allowed the telescope to point in any direction and remain level when the plane banked). Inside the sight were two dc-powered gyroscopes one for vertical orientation and one for azimuth reference. Both spun at 7800 revolutions per minute.
Through an electromechanical servo mechanism similar to those that operated ship stabilizers, the Loyd Searle High Tech Promotions Inc. SPECTRUM IEEE #0018-922-0060 SEPTEMBER 1989 azimuth gyro steadied the bombsight optics in the horizontal plane so the crosshairs could be synchronized with the plane's approach.
The Norden design had at least four significant problems. First, the carbon dc brushes wore out and had to be replaced frequently; moreover, carbon dust from the wearing brushes would settle into the sensitive gimbal bearings, increasing friction, and necessitating the repeated cleaning and oiling of the precision bearings. Second, accurate leveling of the vertical gyro was a tricky procedure' especially in rough air, as it required manual setting of two liquid levels like the bubble in a carpenter's level. The process took 510 seconds, a significant fraction of the bombing run. Third, both the azimuth and range operating knobs were on the right hand side of the bombsight, making simultaneous two-hand sighting on a target almost impossible. Fourth, the angular freedom of the vertical gyro was such that in rough air the gyro would hit the limits and tumble off its axis of rotation, losing the bombing run. In spite of the Norden bombsight's imperfections, it performed so much better than any other sight available in the early 1930s that it was quickly adopted by the Navy for all its bombers.
Furthermore, the Navy designated Carl L. As a dedicated source‹meaning the Navy purchased bombsights exclusively from Norden, and Norden supplied bombsights only to the Navy. In effect, this made the Norden company a manufacturing arm of the Navy under the Norden name.
Meanwhile, Sperry Gyroscope Co., which had been founded by Elmer Sperry in 1909, had begun designing and building bombsights as a natural outgrowth of its development of gyroscopes for commercial and military aircraft and ships. As early as 1914, when Norden had been on the payroll for three years, Sperry's company had built and was granted a patent for a vertically stabilized bombsight that relied on a vertical gyro assembly driven with dc power. The company went on to develop improved models of this first synchronized sight in 1915, 1918, 1924, 1927, 1929, 1930, and 1933, culminating in a model called the Sperry O-1.
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But as in the Norden sight, the Sperry gyros had significant problems. Moreover, there was no market for the Sperry bombsights until the Army began having procurement problems with the Norden company in 1936.
The politics of procurement In the 1930s, the U.S. Army was building up its own airborne fighting arm, known as the General Headquarters (GHQ) Air Force, which had been established in 1922.
The Army was structured so thee the GHQ Air Force had to arrange training and procure supplies through another arm, the Army Air Corps. The GHQ Air Force, as impressed with the Norden bombsight as the Navy, made it standard equipment on its own bombers by 1934. But because the Norden company was a dedicated ource to the Navy, the only way the Army Air Corps could get Norden bombsights was by ordering them through the Navy, a pass-along arrangement that complicated design development and delivery. Since the Norden bombsight had been developed primarily for the medium altitudes and slow speeds of small Navy flying boars, such as the PBY bombers, it needed to be modified for the higher speeds and extremely high and low altitudes of the heavy, long–range Army GHQ Air Force bombers.
For Air Force purposes, the Norden's optical field of the telescope was too limited, giving insufficient forward and thwartship vision. The Norden bombsight also did not allow bombs to be accurately targeted if the plane were descending in a glide a maneuver preferred to level flight during bombing runs because changing altitude made the bomber a more elusive target for antiaircraft guns and its trail settings were too limited to accommodate the wind resistance encountered by the faster Air Force planes. These shortcomings could only be overcome if Air Force bombardiers fudged the data they entered into the bombsight by levers and knobs. The design problems became moot, however, when despite the pressure from both Navy and Army, Carl L. Could not deliver. One reason may have been the fact that the firm relied on old-world artisans in its various plants to manufacture he bombsight had to determine in real time both the range and the course of the plane so as to calculate the proper moment for releasing a bomb. It had to compensate for air resistance, which caused the bomb to trail behind the plane (top), and cross winds, which made it drift downwind to the side of the plane's path (bottom).
Other factors included the bombs ballistics and the target's altitude, which affected, the time of fall. Loyd Searle High Tech Promotions Inc. SPECTRUM IEEE #0018-922-0060 SEPTEMBER 1989 Norden Mark XV by hand, fitting the parts according to qualitative tolerances as free-running fit, no play. In January 1936, the Navy suspended all deliveries of the Norden sight to the Army Air Corps until the Navy's own requirements were satisfied.
At that point, the commander of the GHQ Air Force, Major General Frank M. Andrews, expressed his concern in a memo to the Chief of the Air Corps and to the Navy. He then openly encouraged the Sperry Gyroscope Co. To develop the O-1 bombsight to meet Air Force specifications. On The Drawing board By this time, 1937, a new type of gyroscope had been developed by Orland E.
Esval, one of Sperry's foremost electrical engineers. Since the gyroscopic effect is due to the moment of inertia of the wheel, the greatest effect is obtained by a massive gyro spinning fast.
Esval's new gyro had twice the mass of the one used in the then-current Sperry O-1 bombsight, and about the same weight as the vertical gyro in the Norden Mark XV. However, Esval's gyro was designed to spin at 30 000 rpm nearly four times faster than the Norden's gyros.
The increased gyroscopic effect overcame friction in the gimbal bearings that was a source of precession (a slow gyration of the rotation axis) and failure. Carl Frische, then a young development engineer who years later became Sperry's president, assisted Esval in developing the first self-erecting system for the new vertical gyro. When engaged, the self-erecting system would automatically find the exact vertical, eliminating the necessity for a pilot and bombardier to spend time in a bombing run aligning liquid levels. Esval and Frische designed the self-erecting system so that it could be turned off during banking maneuvers, so as not to precess the gyro to a false vertical; when switched on again after the aircraft returned to level flight, it would again automatically seek the true vertical. Esval's high-speed gyro and Frische's self-erecting system, along with an optical gyro-balancing machine that speeded manufacture, dramatically improved the vertical tracking accuracy of Sperry's O-1 bombsight, later designated the S-1.
Next, they turned a second gyro wheel assembly on its side to make an azimuth gyro. Esval and Frische also decided to treat the azimuth gyro as a sensor only, to eliminate the physical linkage that in the Norden bombsight was a source of friction. To do this, they mounted an electromagnetic pickoff on a nonspinning ring that was centered on the spinning rotor and was controlled by the azimuth servo motor. When aircraft movements caused the slightest angular deviation of the gyro's from the plane's axes, the E-pickoff generated electric signals that, when amplified, controlled a servomechanism that compensated for the plane's movement and thus stabilized the bombsight optics in azimuth. This may have been the first use of closed-loop amplifiers. Esval's new gyros were self-lubricating and induction- powered, eliminating the dc brushes that caused carbon dust.
Norden Bombsight For Sale
This innovation, however, required the new gyro to have its own ac power source, because in the late 1930s U.S. Airborne instrumentation ran only on dc power or on vacuum suction generated through venturi tubes mounted outside the cockpit. The Army Air Corps was so inspired by the performance of the Sperry bombsight that it soon adopted induction electrical systems for aircraft, which later facilitated radio instrumentation. The Air Corps settled on a 400-hertz electrical system that, accordingly, spun the new gyros at a somewhat reduced rate of 24 000 rpm.
Although there was some loss in gyroscopic momentum, the instrument still spun more than three times faster than the Norden Mark XV's gyros. In 1940 and 1941, the Norden XV bombsight was installed in Air Corps B-17 bombers. The Sperry S-1 was installed in B24Es used by the 15th Air Force in the Mediterranean area and in lendlease B-24s supplied to the British Royal Air Force (RAF), since the Navy refused to release Norden sights to foreign governments. A modified Sperry O-1 bombsight first saw combat on April 30, 1941 from a British bomber, more than six months before the United States entered the war with its Norden-equipped planes.
The target was a heavily armed yet small Nazi supply ship of 700-800 tons near Tyboron, Denmark, recalled John Mallinson, a former RAF wing commander who flew on that first mission. Our squadron was the 220 Coastal Command based at Thornaby, Yorkshire. The Sperry had been installed in a Lockheed Hudson Mk V, and we made our approach at 8000 ft 2.4 km. The German supply ship looked like a tiny speck from 8000 ft, but with the Sperry bombsight, our bombardier and Wing Commander Charles Dann dropped only one salvo, and our bombs hit squarely across the ship's stern on the first pass.
The first all-electronic autopilot The precision targeting made possible by the bombsights demanded a higher level of precision in maintaining a plane's course, attitude, altitude, and trim-far beyond what could be attained with a bombardier-pilot team or commercial autopilot. Some of the B-17s in the late 1930s came equipped with a Sperry A-3 commercial autopilot. The gyros in the A-3 sensed only simple angular displacement of the aircraft from the desired course. It used pneumatic hydraulic servo systems that were sluggish, and since there was no measure of velocity or acceleration, the system tended to overcompensate in rough air and thus oscillate. The Norden company developed an autopilot called the stabilized bombing approach equipment (SBAE), also based upon the earlier displacement only signal technology of commercial auto pilots. The Norden SBAE's mechanically sliding trolley-contact electric servos had simple dashpots or shock absorbers that produced negative clamping to eliminate oscillations, but this also showed response either to wind buffeting or to commands from the bombsight. The result was flight control no better than that of the Sperry A-3 commercial autopilot.
For the new Sperry S-l bombsight, Frische invented the first all-electronic autopilot, the A-5. It was based on three dual element vacuum tube amplifiers, each corresponding to a different axis in the aircraft's control system: roll, pitch, and yaw.
Norden Bombsight Theory
The tubes had been subjected to accelerated life testing, temperature cycling, and vibration to ensure unprecedented reliability. Each tube amplified the weak signal measured from the autopilot's own set of sensors on the high-speed induction gyros.
More important, in addition to the displacement-error signal, the A-5 autopilot adjusted for the first and second time derivatives (the velocity and acceleration with which the aircraft departed from the base reference signal). The amplified signals controlled independent electro hydraulic servomechanisms, providing fast response for stabilizing the aircraft. This resulted in a system that was critically damped, thus allowing for the aircraft's inertia, and was much more responsive than the electromechanical technology to wind gusts and command signals from the bombsight. Loyd Searle High Tech Promotions Inc.
SPECTRUM IEEE #0018-922-0060 SEPTEMBER 1989 Controls for the Sperry S-1 bombsight were electrically connected to the A-5 autopilot. Once the bombing run was begun, the pilot turned the aircraft over to the bombardier, who then flew the bomber by tracking the target through the bombsight. When the bombsight determined that the release point had been reached, it alerted the bombardier and dropped the bomb. The combination of Norden Mark XV bombsight (above' had all its controls on the right-hand side, slowing the bombardier's adjustments, while the Sperry S-1 bombsight (below) had controls on both sides, allowing range and course to be adjusted simultaneously. The Norden's top section, dubbed the football, was removable; it contained the vertical gyro while the azimuth gyro was housed in the stabilizer. In the Sperry the azimuth gyro not shown) was in a box bolted to the far side. The Sperry bombsight was mounted on shock absorbers to prevent vibration from the plane's engines from shaking the telescope optics; the Norden was not.
Again “history” repeated itself For a bombing attack in formation things need to be discussed before, and every one must know what to do in a given situation. Although I had it in my head how it should be done, I learne d allot from those early attempts.
Looking all over the net for a good bomb ing manual, I haven’t found one suited to our needs. There are some great ones, but none of them shows how to do a manual bomb release (in satisfactory detail) which is necessary for level bombing in formation. Also seeing how people react when they see me on UKD2 server, and want to join me on my bombing runs – I decided to do it myself. This manual is written to help anyone who wants to level bomb. Hopefully there will be more organized bombing runs after this. As we fl y on UK D2 mo st ly (u nt il UK D3 go es pu bl ic ), th es e pi lo ts wi ll ge t an advantage over “ad-hoc” pilots, meaning they will get better positions inside formation.
Of course, any one is invited to fly with us. We always welcome good bomber pilots.
Lots of things have been discussed before, about what formation we'll use, what's the best tactic and what should be done in certain situations. After some time spent in flying together, we’ve gathered experience to do it right. All that we learned I’m now going to put together, with some of my findings also. M a n u a l c o n s i s t s o f t h e f o l l o w i n g p a r t s: p a g e n o. For UKD servers (UKD2 namely and upcoming UKD3) I think that limit on bomber numbers should be set from 9 to 10 planes (depending on the formation). More than that provides us without efficient fighter cover. Charts are also drawn for those pilots who didn’t sign up, named “ad-hoc” pilots.
If, by any chance, more than 9(10) bombers assemble, they will be placed on special positions. These positions are colored in gray – for occasions when all bomber positions are full. Since that won’t be happening every day, positions should be filled by certain order depending on bomber numbers, 1 = 9(10). First I will address smaller flights (3 to 4 planes). Small flight consisted of three planes flying in close formation, called an Element formation, and was a basic unit in all formations. Later in war another plane was added, and so Element consisted of four planes.
A three plane Element flew.