The E6B flight computer is a form of circular slide rule used in aviation . It is an instance of an analog calculating device still being used in the 21st century.
171-539: The Course Setting Bomb Sight ( CSBS ) is the canonical vector bombsight , the first practical system for properly accounting for the effects of wind when dropping bombs. It is also widely referred to as the Wimperis sight after its inventor, Harry Wimperis . The CSBS was developed for the Royal Naval Air Service (RNAS) in order to attack submarines and ships . It was introduced in 1917, and
342-414: A gimbal system to keep the bombsight pointed roughly downward during maneuvering or compensating for windage had been pursued for some time. Experiments as early as the 1920s had demonstrated that this could roughly double the accuracy of bombing. The US carried out an active program in this area, including Estoppey sights mounted to weighted gimbals and Sperry Gyroscope 's experiments with US versions of
513-502: A *, as in the Mk. IX A*. Prior to the war a major redesign of the CSBS was underway. The new Mk. X replaced the vertical slider used for altitude adjustment with a horizontally-moving backsight at the top of the device, and the entire foresight and drift wire area was made considerably smaller. The calculator and wind drift settings, formerly mounted on top and in front of the large compass at
684-482: A 125-by-375 foot target with 15 bombs dropped from 800 meters. In spite of early examples like Scott's prior to the war, during the opening stages of the First World War bombing was almost always carried out by eye, dropping the small bombs by hand when the conditions looked right. As the use and roles for aircraft increased during the war, the need for better accuracy became pressing. At first this
855-442: A 25 miles per hour (40 km/h) wind the bomb will move about 1,350 ft (410 m) due to the wind's effect on the aircraft's ground speed. In comparison, the effect of the wind after leaving the aircraft would be only 300 ft (91 m). At the rear of the CSBS is a large compass with a slip ring carrying a rotating compass rose known as the bearing plate . The bearing plate has lines on it that are used to represent
1026-406: 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
1197-577: A calculator would allow the bomb aimer to dial in the basic aircraft parameters – speed, altitude, direction, and known atmospheric conditions – and the bomb sight would use tacheometrically-based trigonometry to automatically calculate the proper aim point in a few moments. Some of the traditional inputs, like airspeed and altitude, could even be taken directly from the aircraft instruments, eliminating operational errors, and allowing constant recalculation of essential target-tracking and bomb release parameters. Although these developments were well known within
1368-510: A conventional scientific calculator. The graphic nature of the flight computer also helps in catching many errors which in part explains their continued popularity. The ease of use of electronic calculators means typical flight training literature does not cover the use of calculators or computers at all. In the ground exams for numerous pilot ratings, programmable calculators or calculators containing flight planning software are permitted to be used. Many airspeed indicator (ASI) instruments have
1539-421: A fixed 20 miles or greater. Compounding this inaccuracy is that it is made using the instrument's airspeed indication, and as the airspeed in this example is about 10 times that of the wind speed, its 5% error can lead to great inaccuracies in wind speed calculations. Eliminating this error through the direct measurement of ground speed (instead of calculating it) was a major advance in the tachometric bombsights of
1710-402: A large knob known as the milled head was placed directly behind the compass and drove this shaft independently of the compass face, allowing calculations to be carried out without changing the bombsight settings. The rotating shaft ran to the wind bar located in front of the body of the gunsight. The rotation of this bar to the selected angle mechanically represented the wind vector relative to
1881-421: A long run into the target, and which would allow the aircraft to manoeuvre throughout the bomb run. The solution to this problem was well understood within the industry: use gyroscopes to provide a level platform to mount the bombsight so it did not move relative to the ground even if the aircraft moved. Today these are known as an inertial platform . However, the large physical size of the CSBS series, especially
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#17327809185542052-468: A long straight run before dropping the bombs to accommodate windage) led to the development of bombsights based on the field of tacheometry . Unlike a vector bombsight, which merely offered a bombardier a launch point for a desired bomb trajectory, tachometric bombsights tracked the bomb target and recalculated the release point based on input that included horizontal deviations induced by minor aircraft maneuvering or wind drift. In their most advanced form
2223-477: A marketing name of "E6-B" (note the moved hyphen). An aluminium version was made by the London Name Plate Mfg. Co. Ltd. of London and Brighton and was marked "Computer Dead Reckoning Mk. 4A Ref. No. 6B/2645" followed by the arrowhead of UK military stores. During World War II and into the early 1950s, The London Name Plate Mfg. Co. Ltd. produced a "Height & True Airspeed Computer Mk. IV" with
2394-487: A movable ring built into the face of the instrument that is essentially a subset of the flight computer. Just like on the flight computer, the ring is aligned with the air temperature and the pressure altitude, allowing the true airspeed (TAS) to be read at the needle. In addition, computer programs emulating the flight computer functions are also available, both for computers and smartphones. Instructions for ratio calculations and wind problems are printed on either side of
2565-480: A new vector bombsight, the Mk. XIV . The Mk. XIV featured a stabilizing platform and aiming computer, but worked more like the CSBS in overall functionality – the bomb aimer would set the computer to move the sighting system to the proper angle, but the bombsight did not track the target or attempt to correct the aircraft path. The advantage of this system was that it was dramatically faster to use, and could be used even while
2736-400: A plane crash with a student practicing spins. He, with P. V. H. Weems , invented, patented and marketed a series of flight computers. Dalton's first popular computer was his 1933 Model B, the circular slide rule with true airspeed (TAS) and altitude corrections pilots know so well. In 1936 he put a double-drift diagram on its reverse to create what the U.S. Army Air Corps (USAAC) designated as
2907-400: A second might be considered the best possible. In this case, the error is simply the ground speed of the aircraft over this time, or about 30 feet. All of these are well within the lethal radius of the bomb. The wind affects the accuracy of the bomb in two ways, pushing directly on the bomb while it falls, as well as changing the ground speed of the aircraft before the drop. In the case of
3078-462: A separate adjustment for trail , the deceleration of the bomb due to drag . At low speeds and altitudes the time between drop and impact was too short for the bombs to reach terminal velocity so the trajectory of the bombs was roughly parabolic. At higher altitudes or forward speeds the bombs would reach terminal long before impact, which had the effect of making the last portion of the flight path more vertical. The trail adjustment, set by dialling in
3249-481: A separate line of development was leading to the first reliable mechanical computers . These could be used to replace a complex table of numbers with a carefully shaped cam -like device, and the manual calculation though a series of gears or slip wheels. Originally limited to fairly simple calculations consisting of additions and subtractions, by the 1930s they had progressed to the point where they were being used to solve differential equations . For bombsight use, such
3420-404: A series of increasingly sophisticated bombsight designs dedicated to high-altitude level bombing. Bombsights were first used before World War I and have since gone through several major revisions. The earliest systems were iron sights , which were pre-set to an estimated fall angle. In some cases, they consisted of nothing more than a series of nails hammered into a convenient spar, lines drawn on
3591-406: A significant portion of a minute falling through the air. Those effects can be minimized by reducing the fall time by low-level bombing or by increasing the speed of the bombs. Those effects are combined in the dive bomber . However, low-level bombing also increases the danger to the bomber from ground-based defences, so accurate bombing from higher altitudes has always been desired. That has led to
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#17327809185543762-412: A simple system that greatly eased the measurement of the wind. By observing their movement over the ground, the aircraft would first determine the direction of the wind. The aircraft would then turn to fly at right angles to this wind direction so that the wind was pushing the aircraft sideways. Observing the sideways drift of the aircraft by comparing the motion of objects on the ground to a metal rod along
3933-702: A square box by a knob. He applied for a patent in 1936 (granted in 1937 as 2,097,116). This was for the Model C, D and G computers widely used in World War II by the British Commonwealth (as the "Dalton Dead Reckoning Computer"), the U.S. Navy , copied by the Japanese, and improved on by the Germans, through Siegfried Knemeyer 's invention of the disc-type Dreieckrechner device, somewhat similar to
4104-409: A stabilized platform. This allowed the sights to be used even while the aircraft was maneuvering, and required only 10 seconds to settle. Together, these changes dramatically simplified the task of maintaining an accurate bombsight setting. On the downside, it required the addition of a new crew member to operate the system. This was not a minor problem as most aircraft had no room for them. This led to
4275-402: Is V w . d , a and w are angles. V g , V a and V w are consistent units of speed. π {\displaystyle \pi } is approximated as 355/113 or 22/7) Wind Correction Angle: True ground speed: Wind Correction Angle, in degrees, as it might be programmed into a computer (which includes conversion of degrees to radians and back): True ground speed
4446-483: Is an adaptation of the method used with the Drift Sight. Prior to approaching the target, the bomb aimer would have the pilot turn onto the expected wind line, and dials in zero wind speed and due north wind direction, which points the drift bar straight forward. With the bar in this position, the bomb aimer uses the drift wires to tune out any sideways drift and thereby find the exact wind direction. The bearing plate
4617-418: Is calculated as: Although digital E6Bs are faster to learn initially, many flight schools still require their students to learn on mechanical E6Bs, and for FAA pilot written exams and checkrides pilots are encouraged to bring their mechanical E6Bs with them for necessary calculations. The device's original name is E-6B, but is often abbreviated as E6B, or hyphenated as E6-B for commercial purposes. The E-6B
4788-412: Is from the hole, to the wind correction angle portion of the slide's grid. The true ground speed is determined by matching the center hole to the speed portion of the grid. The mathematical formulas that equate to the results of the flight computer wind calculator are as follows: (desired course is d , ground speed is V g , heading is a , true airspeed is V a , wind direction is w , wind speed
4959-400: Is known as the range , it is a function of the speed and the time to fall, the latter a function of altitude. The bomber attempts to manoeuvre along a line toward the target and then drop the bombs at the instant they are that distance, the range, from the target. The location at that instant is known as the drop point or point of release . Simple trigonometry can calculate the angle that
5130-419: Is left is the calculation of the time of fall, which, multiplied by the ground speed, gives the range. The CSBS solves this through the height bar , which extends vertically from the center of the device where the compass section meets the drift bar. Turning a knob at the top of the height bar (or using a slip fitting on earlier models) moves the height slider up or down to set the aircraft's altitude. Once set,
5301-429: Is rotated to the compass heading and locked, thereby recording the wind direction for future reference. The pilot then turned 90 degrees to one side or the other, placing the wind directly off the side of the aircraft. The bomb aimer then rotated the milled head to the same 90 degrees. At this point the wind speed knob is adjusted, pushing the drift bar sideways until objects on the ground could be seen moving directly along
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5472-481: Is used for wind triangle calculations using a rotating scale and a sliding panel. The other side is a circular slide rule . Extra marks and windows facilitate calculations specifically needed in aviation. Electronic versions are also produced, resembling calculators , rather than manual slide rules. Aviation remains one of the few places that the slide rule is still in widespread use. Manual E6Bs/CRP-1s remain popular with some users and in some environments rather than
5643-585: The AN/APQ-13 and AN/APQ-7 used on the Boeing B-29 Superfortress . These early systems operated independently of any existing optical bombsight, but this presented the problem of having to separately calculate the trajectory of the bomb. In the case of Oboe, these calculations were carried out before the mission at the ground bases. But as daylight visual bombing was still widely used, conversions and adaptations were quickly made to repeat
5814-730: The B-17 Flying Fortress . In tests, these bombsights were able to generate fantastic accuracy. In practice, however, operational factors seriously upset them, to the point that pinpoint bombing using the Norden was eventually abandoned. Although the US put the most effort into development of the tachometric concept, they were also being studied elsewhere. In the UK, work on the Automatic Bomb Sight (ABS) had been carried on since
5985-683: The Luftwaffe developed the Lotfernrohr 7 . The basic mechanism was almost identical to the Norden, but much smaller. In certain applications the Lotfernrohr 7 could be used by a single-crew aircraft, as was the case for the Arado Ar 234 , the world's first operational jet bomber. During the war the RAF had the need for accurate high-altitude bombing and in 1943 introduced a stabilized version of
6156-434: The disastrous raid on Wilhelmshaven in 1939, the RAF was forced to abandon daylight attacks and move to night bombing. The Mk. X proved to have very poor visibility at night, and it would be difficult to modify it to correct this problem. The Mk. X had to be abandoned, and Mk. VII's and Mk. IX's hurriedly re-fit to aircraft. Thus the older versions of the CSBS soldiered on long after they were due to be replaced, and remained
6327-574: The 1930s and 40s. Finally, consider errors of the same 5% in the equipment itself, that is, an error of 5% in the setting of the range angle, or a similar 5% error in the levelling of the aircraft or bombsight. For simplicity, consider that 5% to be a 5 degree angle. Using simple trigonometry, 5 degrees at 20,000 feet is approximately 1,750 feet, an error that would place the bombs far outside their lethal radius. In tests, accuracies of 3 to 4 degrees were considered standard, and angles as high as 15 degrees were not uncommon. Given
6498-606: The 1930s, mechanical computers with the performance needed to solve the equations of motion started to be incorporated into the new tachometric bombsights, the most famous of which is the Norden . Then, in World War II , tachometric bombsights were often combined with radar systems to allow accurate bombing through clouds or at night. When postwar studies demonstrated that bomb accuracy was roughly equal either optically or radar-guided, optical bombsights were generally removed and
6669-616: The ABS was even larger than the CSBS, and the demands for new bombsights to be stabilized would make it even larger and meant it would take some time before it could be brought into service. Something was needed in the meantime. The physicist and scientific advisor Patrick Blackett took up the challenge of fixing all of these problems at once, producing the Blackett sight with the Royal Aircraft Establishment . First,
6840-487: The Automatic Bomb Sight was dusted off and mounted to new stabilization platform, producing the Stabilized Automatic Bomb Sight . This complex device was available only in very small numbers from late 1943 on, and used only by specific groups within the RAF. The following description is based on the Mk. IX as described in A.P.1730A, but will be separated into sections on the basic operation and
7011-413: The CSBS mounted to a gyroscopically -stabilized inertial platform . These same developments led to the introduction of the first useful autopilots , which could be used to directly dial in the required path and have the aircraft fly to that heading with no further input. A variety of bombing systems using one or both of these systems were considered throughout the 1920s and 30s. During the same period,
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7182-657: The E-1, E-1A and E-1B. A couple of years later he invented the Mark VII, again using his Model B slide rule as a focal point. It was hugely popular with both the military and the airlines. Fred Noonan , Amelia Earhart 's navigator on her attempted circling of the globe, used one on their last flight. Dalton felt that it was a rushed design, and wanted to create something more accurate, easier to use, and able to handle higher flight speeds. So he came up with his now famous wind arc slide, but printed on an endless cloth belt moved inside
7353-671: The E-1. The "B" simply meant it was the production model. The designation "E-6B" was officially marked on the device only for a couple of years. By 1943 the Army and Navy changed the marking to their joint standard, the AN-C-74 (Army/Navy Computer 74). A year or so later it was changed to AN-5835, and then to AN-5834 (1948). The USAF called later updates the MB-4 (1953) and the CPU-26 (1958), but navigators and most instruction manuals continued using
7524-720: The Mark I sight as soon as supplies were available, and by April 1918 were also fully converted to this type. For his work on the CSBS and the Drift Sight Wimperis was awarded £2,100 by the Royal Commission on Awards to Inventors. In the post-war era, work on new bombsights was seriously curtailed, and little new development had taken place by 1930. Several minor variations of the CSBS had been introduced during this period to adapt to higher speeds, higher or lower altitudes, and new types of bombs. These also included
7695-419: The RAF found in the training schools that it was all too common for the bomb aimers to dial in an incorrect setting, or forget to update one when conditions changed. It was planned that many of these problems would be solved on the Automatic Bomb Sight (ABS), which had been under development from before the war, and used very simple inputs from the bomb aimer to carry out all the needed calculations. Unfortunately,
7866-530: The Sperry T-1. It did not offer the level of accuracy of tachometric bombsights like the Norden or ABS, but for night area bombing from medium altitude as practiced by RAF Bomber Command this was not an issue. The Mk. XIV remained in RAF use until 1965. Later in the war the development of the Tallboy and Grand Slam earthquake bombs demanded accuracy that even the Mk. XIV could not supply. For this role,
8037-469: The UK market, they can be used to perform the added conversions of Imperial to Metric units. The wheel on the back of the calculator is used for calculating the effects of wind on cruise flight . A typical calculation done by this wheel answers the question: "If I want to fly on course A at a speed of B, but I encounter wind coming from direction C at a speed of D, then how many degrees must I adjust my heading, and what will my ground speed be?" This part of
8208-410: The aircraft into the general direction of the wind and then observing motion of objects on the ground and adjusting the flight path side to side until any remaining sideways drift due to wind was eliminated. The speed over the ground was then measured by timing the motion of objects between two given angles as seen through the sight. One of the most fully developed examples of such a sight to see combat
8379-432: The aircraft needs to turn to the left until the portion of its airspeed equal to the wind speed cancels out the drift. The resulting direction is represented by the yellow arrow in the diagram above. On the CSBS each of these arrows has a mechanical equivalent in the bombsight. The direction of the yellow arrow is that of the aircraft itself, represented in the bombsight by its mounting to the aircraft fuselage. The length of
8550-444: The aircraft was flying in the right direction to take it directly over the drop point, with zero sideways velocity. The bomb aimer (or pilot in some aircraft) then sighted through the attached iron sights to time the drop. The CSBS was introduced into service in 1917 and quickly replaced earlier sights on aircraft that had enough room – the CSBS was fairly large. Versions for different speeds, altitudes and bomb types were introduced as
8721-538: The aircraft was manoeuvring, only a few seconds of straight-line flying were needed before the drop. Facing a lack of production capability, Sperry was contracted to produce the Mk. XIV in the US, calling it the Sperry T-1. Both the British and Germans would later introduce Norden-like sights of their own. Based at least partially on information about the Norden passed to them through the Duquesne Spy Ring ,
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#17327809185548892-418: The aircraft with it. This momentum is countered solely by drag, which starts to slow the forward motion. As the forward motion slows, the drag force drops and this deceleration diminishes. The forward speed is never reduced entirely to zero. If the 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
9063-471: The aircraft's path during the bomb run, whether due to difficulty turning and a tendency to oscillate after levelling induced by the Dutch roll or evasive maneuvers forced by the enemy, bomb trajectory calculations had to be set up again. There simply was not time to do so with the bombsights and mechanical computers of the day. One solution was to stabilize the bombsight independent of the aircraft. The use of
9234-444: The aircraft, or visual alignments of certain parts of the structure. They were replaced by the earliest custom-designed systems, normally iron sights that could be set based on the aircraft's airspeed and altitude. These early systems were replaced by the vector bombsights, which added the ability to measure and adjust for winds. Vector bombsights were useful for altitudes up to about 3,000 m and speeds up to about 300 km/h. In
9405-417: The aircraft. At the end of the wind bar is the wind screw knob , which is used to set the wind speed. As the knob is rotated, a plate inside the wind bar moves fore and aft along the direction of the bar. Connected to and extending from the front of the main bombsight housing is the drift bar , normally forming over half the overall length of the device. The drift bar is pivoted at its base, just in front of
9576-449: The altitude measurement with a radar altimeter for low-altitude use, but these Mk. XV and Mk. XVII were not used operationally. The Mk. XIV was a major advance over the Mk. IX, but service entry was slow. It was not until January 1942 that it was given priority. This was aided by Sperry Gyroscope , who re-designed the system to U.S. production methods. They sub-contracted construction to A.C. Spark Plug who built tens of thousands as
9747-439: The angle between backsights on the height slider and foresights on the ground speed slider indicates the proper range angle, no lookups required. The bomb aimer then sights along this angle and waits for the target to appear, dropping the bombs when it appears under a notch in the backsight. Although a bomb's trajectory is roughly parabolic, when the bomb is dropped from high altitudes it may reach terminal velocity before hitting
9918-421: The approach direction. His new Course Setting Bomb Sight featured a large compass at the rear that could be used for making general calculations of wind speed or solving navigational problems. In most cases these could be ignored; the bomb aimer dialled in the wind direction on the compass, then wind speed, airspeed and altitude on different knobs. Through internal mechanisms, these adjustments carried out all of
10089-411: The bar was indexed in seconds, corresponding to the measurement made of the times using the stopwatch. The cursor slid along the wind bar and was set to that measurement. A small scale on the cursor allowed for the conversion of indicated air speed to true air speed, which differs depending on altitude. A small ring on the right side of the cursor was used to accurately place markings on the compass using
10260-403: The basic vector calculator system and drift wires, differing primarily in form and optics. As bombers grew and multi-place aircraft became common, it was no longer possible for the pilot and bombardier to share the same instrument, and hand signals were no longer visible if the bombardier was below the pilot in the nose. A variety of solutions using dual optics or similar systems were suggested in
10431-429: The basic vector math in a mechanical system. The vectors that would normally be drawn by hand were duplicated in a series of screws, gears and sliding components. By dialling in the four inputs, altitude, airspeed, wind speed and wind direction, the mechanism moved the aiming pippers so they directly represented the required heading and range angle for the current airspeed and altitude. The wind will also have an effect on
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#173278091855410602-408: The bomb after it leaves the aircraft. As bombs are generally well streamlined and have high density , this effect is much smaller in magnitude than the effects of the wind on the aircraft itself. For instance, consider a bomber at 20,000 feet (6,100 m) altitude dropping a stick of AN-M65 500 lb general-purpose bombs. These bombs will take approximately 37 seconds to reach the ground. In
10773-620: The bomb aimers would forget to reset it to the proper angle for bombing when things got busy. These same measurements could be made with the Auxiliary Bar, leaving the main drift bar in the proper position. Later versions used by RAF Coastal Command and the Royal Navy also included a further adjustment, the Fourth Vector , for attacking moving targets. This was primarily intended for use against ships and submarines . This
10944-429: The bomb has time to build up speed. Later models of the CSBS, starting with the Mk. VII, used a cam that was driven by both the altitude setting and the trail screw in order to automate the calculation of this effect. Additionally, each aircraft has a slightly different way of measuring altitude that needs adjustment, the CSBS accounted for this effect by including two altitude scales, a linear scale of altitude in orange on
11115-430: The bomb trajectory in real time , as the aircraft manoeuvres, and add the ability to adjust for weather, relative altitude, relative speeds for moving targets and climb or dive angle. That makes them useful both for level bombing, as in earlier generations, and tactical missions, which used to bomb by eye. The drag on a bomb for a given air density and angle of attack is proportional to the relative air speed squared. If
11286-451: 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
11457-404: 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 . 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
11628-399: The bomber is to approach a target located at the tip of the green arrow, compared to its current position at the base of the arrow. A powerful wind is blowing from just off the port wing of the aircraft, blowing towards about 120 degrees. If the aircraft simply points toward the target, along the green arrow, the wind will cause it to drift to the right. In order to approach the target properly,
11799-415: The bombsight so it pointed out from the fuselage. Prior to the bomb run, the bomber would fly at right angles to the bomb line, and the bomb aimer would look past the rod to watch the motion of objects on the ground. He would then adjust the wind speed setting until the motion was directly along the rod. This action measured the wind speed, and moved the sights to the proper angle to account for it, eliminating
11970-420: The bombsight, as a reference location and spots past them through the drift wires. Although these are now angled several degrees to the right, the wind to the right is pushing the aircraft so its final motion is along the wires. When initially set up the aircraft would likely be flying a course close to the green arrow, so the bomb aimer would see the targets drifting to the left relative to the wires. He would call
12141-404: The brunt of the bombing role. A bombsight has to estimate the path the bomb will take after release from the aircraft. The two primary forces during its fall are gravity and air drag , which make the path of the bomb through the air roughly parabolic . There are additional factors such as changes in air density and wind that may be considered, but they are concerns only for bombs that spend
12312-579: The calculations needed to set the approach and range angle. Through these calculations the CSBS allowed bombing from any direction, freeing the aircraft from the wind line for the first time. In testing in December 1917 at the Scilly Isles air station, in eight bomb runs the CSBS scored two direct hits, and near-misses on all six other runs. Production quickly followed, and by 1918 about 720 had been produced. The Royal Flying Corps (RFC) started using
12483-402: The calculator consists of a rotatable semi-transparent wheel with a hole in the middle, and a slide on which a grid is printed, that moves up and down underneath the wheel. The grid is visible through the transparent part of the wheel. To solve this problem with a flight computer, first the wheel is turned so the wind direction (C) is at the top of the wheel. Then a pencil mark is made just above
12654-503: The changing velocities as the bombs fell. Even as the Drift Sight was being introduced, Wimperis was working on a new bombsight that helped solve these calculations and allow the effects of wind to be considered no matter the direction of the wind or the bomb run. The result was the Course Setting Bomb Sight (CSBS), called "the most important bomb sight of the war". Dialling in the values for altitude, airspeed and
12825-407: The compass area, allowing it to rotate to the left or right. On top of the wind bar, connecting the wind bar to the drift bar, is the ground speed slider . A pin passing vertically through the wind bar's internal slider to slotted plates in the drift bar and ground speed slider translate the motion of the wind bar into components along and across the axis of the drift bar. Motion across the axis pushes
12996-434: The computer for reference and are also found in a booklet sold with the computer. Also, many computers have Fahrenheit to Celsius conversion charts and various reference tables. The front side of the flight computer is a logarithmic slide rule that performs multiplication and division. Throughout the wheel, unit names are marked (such as gallons, miles, kilometers, pounds, minutes, seconds, etc.) at locations that correspond to
13167-521: The constants that are used when going from one unit to another in various calculations. Once the wheel is positioned to represent a certain fixed ratio (for example, pounds of fuel per hour), the rest of the wheel can be consulted to utilize that same ratio in a problem (for example, how many pounds of fuel for a 2.5-hour cruise?) This is one area where the E6B and CRP-1 are different. Since the CRP-1s are made for
13338-469: The correct angles, as on the earlier CSBS models, but then fed them directly into a remote sighting unit, the sighting head . This provided practically instant updates of the sighting angles. The wire sights of the earlier models were replaced by reflector sights indicating the location the bombs would hit if dropped at that instant. As the sighting head lacked the vector computer it was much smaller than earlier models, which allowed it to be easily mounted on
13509-421: The direct effects on the bomb, a measurement that has a 5% error, 1.25 mph, that would cause a 5% error in the drift, which would be 17.5 feet. However, that 1.25 mph error, or 1.8 fps, would also be added to the aircraft's velocity. Over the time of the fall, 37 seconds, that would result in an error of 68 feet, which is at the outside limit of the bomb's performance. The measurement of
13680-439: The drag are: where C is the coefficient of drag, A is the cross-sectional area, and ρ is the air density. These equations show that horizontal velocity increases vertical drag and vertical velocity increases horizontal drag. These effects are ignored in the following discussion. To start with, consider only the vertical motion of a bomb. In this direction, the bomb will be subject to two primary forces, gravity and drag ,
13851-410: The drift relative to the aircraft without having to rotate the main drift bar and thereby possibly leave the sight in an incorrect setting. To use the system, the bomb aimer would lower the auxiliary bar and rotate it until objects were moving along its single wire. This provided a measurement relative to the current setting, say +10. The aimer could then update the wind bar to the correct setting. Next,
14022-432: The drift wires. The wind speed is now known and set, and the aircraft can then manoeuvre as it wants with only the milled head needing adjustment. A later modification to the CSBS, and supplied with most of the Mk. VII and Mk. IX examples, was the auxiliary drift bar . This was attached at the front of the main drift bar and consisted of a single drift wire mounted on a rotating fixture. This allowed relative measurements of
14193-472: The drop point before impact, for a trail of about 305 m (1,001 ft) from the vacuum range, and impact with a velocity of 351 m/s (1150 fps) at an angle of about 77 degrees from horizontal. A 42 km/h (26 mph) wind would be expected to move the bomb about 91 m (299 ft) during that time. The time to fall is about 37 seconds. Assuming errors of 5% in every major measurement, one can estimate those effects on accuracy based on
14364-427: The earlier ABS, the hand-built Stabilized Automatic Bomb Sight (SABS). It was produced in such limited numbers that it was at first used only by the famed No. 617 Squadron RAF , The Dambusters. In the pre-World War II era there had been a long debate about the relative merits of daylight versus night-time bombing. At night the bomber is virtually invulnerable (until the introduction of radar ) but finding its target
14535-412: 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
14706-419: The effects of drag and wind during the fall will be so small that they can be ignored. In this case only the forward speed and altitude have any measurable effect. One of the earliest recorded examples of such a bombsight was built in 1911 by Lieutenant Riley E. Scott, of the U.S. Army Coast Artillery Corps . This was a simple device with inputs for airspeed and altitude which was hand-held while lying prone on
14877-427: The electronic ones because they are lighter, smaller, less prone to break, easy to use one-handed, quicker and do not require electrical power. In flight training for a private pilot or instrument rating, mechanical flight computers are still often used to teach the fundamental computations. This is in part also due to the complex nature of some trigonometric calculations which would be comparably difficult to perform on
15048-413: The entire drift bar assembly to the right. When all of the adjustments are complete, the bombsight and airspeed shaft mechanically represent the yellow arrow, the wind bar represents the blue arrow, and the green arrow is formed by the drift wires providing direction, and the foresight is positioned at the tip of the green arrow. Once set, the bomb aimer uses the rear sights, or any other convenient part of
15219-503: The entire process of correcting the flight path was greatly extended. In the aftermath of the Wilhelmshaven raid on 3 September 1939, it was found that the lengthy setup and bomb run demanded by the CSBS made its aircraft extremely vulnerable to fighters and anti-aircraft artillery . At a pre-arranged meeting on 22 December 1939, Air Chief Marshal Sir Edgar Ludlow-Hewitt made a request for a new bombsight that did not require such
15390-401: The entire wind bar to the left or right, indicating the proper heading to fly to cancel out the wind drift. Motion along the axis pushes the ground speed slider fore or aft, accounting for the difference between air and ground speed. The ground speed slider also carries the pin-shaped foresights, so as they move they adjust the sighting angle in order to drop the bombs early or late to account for
15561-474: The eventual E6B's backside compass rose dial in general appearance, but having the compass rose on the front instead for real-time calculations of the wind triangle at any time while in flight. These are commonly available on collectible auction web sites. The U.S. Army Air Corps decided the endless belt computer cost too much to manufacture, so later in 1937 Dalton morphed it to a simple, rigid, flat wind slide, with his old Model B circular slide rule included on
15732-538: The final accuracy of the drop. It is useful to consider a single example of a bomb being dropped on a typical mission. In this case we will consider the AN-M64 500 lbs General-Purpose Bomb, widely used by the USAAF and RAF during World War II, with direct counterparts in the armouries of most forces involved. Ballistic data on this bomb can be found in "Terminal Ballistic Data, Volume 1: Bombing". Against men standing in
15903-417: The final conversion. The accuracy of the drop is affected both by inherent problems like the randomness of the atmosphere or bomb manufacture as well as more practical problems like how close to flat and level the aircraft is flying or the accuracy of its instruments. These inaccuracies compound over time, so increasing the altitude of the bomb run, thereby increasing the fall time, has a significant impact on
16074-408: The first constant, and the second varying with the square of velocity. For an aircraft flying straight and level, the initial vertical velocity of the bomb will be zero, which means it will also have zero vertical drag. Gravity will accelerate the bomb downwards, and as its velocity increases so does the drag force. At some point (as speed and air density increase), the force of drag will become equal to
16245-415: The force of gravity, and the bomb will reach terminal velocity . As the air drag varies with air density, and thus altitude, the terminal velocity will decrease as the bomb falls. Generally, the bomb will slow as it reaches lower altitudes where the air is denser, but the relationship is complex. Now consider the horizontal motion. At the instant it leaves the shackles, the bomb carries the forward speed of
16416-579: The grease pencil. The face of the compass was then rotated to the aircraft heading, which caused the dot to move. The resulting position indicated the wind speed and direction. A holder for the pencil and a sharpener blade were attached on the left side of the case. Bombsight A bombsight is a device used by military aircraft to drop bombs accurately. Bombsights, a feature of combat aircraft since World War I , were first found on purpose-designed bomber aircraft and then moved to fighter-bombers and modern tactical aircraft as those aircraft took up
16587-542: The ground before takeoff) to aid in calculating fuel burn, wind correction, time en route, and other items. In the air, the flight computer can be used to calculate ground speed, estimated fuel burn and updated estimated time of arrival. The back is designed for wind vector solutions, i.e., determining how much the wind is affecting one's speed and course. They are frequently referred to by the nickname "whiz wheel". Flight computers are usually made out of aluminum, plastic or cardboard, or combinations of these materials. One side
16758-417: The ground speed was measured by timing objects as they passed through any two sets of small beads on the main drift bar using a stopwatch. To calculate the resulting wind speed and direction, systems with the auxiliary bar were also equipped with the wind gauge bar . This was normally stowed folded against the back of the height bar, but could be rotated down and to the rear to lie over the compass. The top of
16929-405: The ground speed. The motion of the wind bar and wind screw knob accounts for two of the three vectors involved in the windage calculation. The last is the airspeed of the bomber – its absolute direction can be ignored if everything is measured in terms of the direction to the target, as in the case of the CSBS. The length of this vector is set by the air speed drum , found on the right side of
17100-468: The ground. The bombsight is then set to indicate that angle. The bombs are dropped when the target passes through the sights. The distance between the aircraft and target at that moment is the range, so this angle is often referred to as the range angle , although dropping angle , aiming angle , bombing angle and similar terms are often used as well. In practice, some or all of these calculations are carried out using angles and not points in space, skipping
17271-418: The ground. This affects the final trajectory in a non-linear fashion, generally making the line of fall more vertical. To account for this a trail screw was added starting with the Mk. II version of the CSBS, which rotated the height bar forward. This had the effect of reducing the range angle, which accounted for the more vertical trajectory of the bombs. This effect only comes into play for high altitudes when
17442-406: The hole, at a distance representing the wind speed (D) away from the hole. After the mark is made, the wheel is turned so that the course (A) is now selected at the top of the wheel. The ruler then is slid so that the pencil mark is aligned with the true airspeed (B) seen through the transparent part of the wheel. The wind correction angle is determined by matching how far right or left the pencil mark
17613-404: 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
17784-490: The incorporated sophisticated optics, data derived directly from the aircraft's flight instruments, compact mechanical computers , and autopilot to guide the aircraft to a its target and automatically release its bombs. Once the operator of a Norden M-1 , the most famous of all tachometric bombsights, was able to identify a target the bombsight was able, in perfect conditions, to fly the plane to it. In battle, complicated by anti-aircraft defenses, crosswinds and clouds, and
17955-588: The industry, only the US Army Air Corps and US Navy put any concerted effort into development. During the 1920s, the Navy funded development of the Norden bombsight while the Army funded development of the Sperry O-1 . Both systems were generally similar; a bomb sight consisting of a small telescope was mounted on a stabilizing platform to keep the sighting head stable. A separate mechanical computer
18126-426: The introduction of newer sighting systems with great advantages over the CSBS, and even newer versions of the CSBS that failed to be used for a variety of reasons. The later versions of the CSBS, eventually reaching the Mark X, included adjustments for different bombs, ways to attack moving targets, systems for more easily measuring winds, and a host of other options. The limitations of vector bombsights (which required
18297-404: The later additions. The bombsight problem is the need to determine the exact spot in the air where the bombs should be dropped to hit a target on the ground. Due to the acceleration of gravity, bombs follow a roughly parabolic path, the steepness being defined by the forward speed of the aircraft at the instant of release. The distance the bombs travel between being dropped and hitting the ground
18468-420: The long drift bar, made it difficult to mount successfully on a platform. A compromise solution was designed as the Mk. XI , which mounted a single drift wire and iron sight on the front of a gyroscope taken from a Sperry artificial horizon that was already common in RAF use. This provided stabilization in the roll axis, which greatly eased the problem of sighting while maneuvering. In order to make it fit on
18639-441: The main case (or at the back of the device on earlier versions). Turning the air speed knob that pushes the tube carrying the wind direction shaft fore or aft. A housing at the end of this tube carries the wind bar, so rotating the airspeed drum moves the entire wind speed calculation fore and aft to account for increasing or decreasing airspeed. Once set, the combination of the air speed, wind direction and wind speed provided all of
18810-401: The manual calculator was replaced by an external box operated by a new crew member. The box contained the inputs needed to drive the vector calculator, as well as copies of the various aircraft instruments displaying the required information. The operator simply had to keep the input dials set so their indicators overlapped those on the instruments. Turning the dials drove the machine to calculate
18981-447: The measured terminal velocity for the bombs being dropped, used a cam to move the height bar forward away from the vertical, reducing the range angle and thereby reducing the range to account for this effect. Many thousands of CSBSs were sold around the world, and many other sights were developed from the basic idea. In the mid-1930s, the basic CSBS concept was largely universal for production bombsights. During its development prior to
19152-402: The methodology and tables in the guide. A 5% error in altitude at 20,000 feet would be 1,000 feet, so the aircraft might be anywhere from 19 to 21,000 feet. According to the table, this would result in an error around 10 to 15 feet. A 5% error in airspeed, 10 mph, would cause an error of about 15 to 20 feet. In terms of drop timing, errors on the order of one-tenth of
19323-440: The mid-1930s in an effort to replace the CSBS. However, the ABS did not include stabilization of the sighting system, nor the Norden's autopilot system. In testing the ABS proved to be too difficult to use, requiring long bomb runs to allow the computer time to solve the aim point. When RAF Bomber Command complained that even the CSBS had too long a run-in to the target, efforts to deploy the ABS ended. For their needs they developed
19494-523: The movement was timed. A great upgrade to the basic concept was introduced by Harry Wimperis , better known for his later role in the development of radar in England. In 1916 he introduced the Drift Sight , which added a simple system for directly measuring the wind speed. The bomb aimer would first dial in the altitude and airspeed of the aircraft. Doing so rotated a metal bar on the right side of
19665-744: The need for aircraft to stay in formation to avoid collisions, results were less ideal but as good as could be achieved with the technology under the circumstances. Two real-world considerations accelerated the development of tachometric bombsights: the introduction of monoplane bombers made manual adjustments to keep a plane on target more difficult. Large monoplanes suffered from an effect known as " Dutch roll ", and were not able to slip-turn to correct for it as easily as their biplane predecessors. Also, intense ground-based anti-aircraft defenses and improved interceptors made it impossible to sustain long straight-and-level bombing runs without excessive loss of aircraft and their valuable crews. If anything changed
19836-643: The need for separate calculations. A later modification was added to calculate the difference between true and indicated airspeed , which grows with altitude. This version was the Drift Sight Mk. 1A, introduced on the Handley Page O/400 heavy bomber. Variations on the design were common, like the US Estoppey bombsight . All of these bombsights shared the problem that they were unable to deal with wind in any direction other than along
20007-518: The night mission. As " the bomber will always get through ", these forces were strategic in nature, largely a deterrent to the other force's own bombers. However, new engines introduced in the mid-1930s led to much larger bombers that were able to carry greatly improved defensive suites, while their higher operational altitudes and speeds would render them less vulnerable to the defences on the ground. Policy once again changed in favour of daylight attacks against military targets and factories, abandoning what
20178-544: The one from the earlier Drift Sight. Like the Drift sight, simply taking a measure of the wind using the sight itself provided all of the unknown variables needed to completely calculate the bombing approach. Unlike the Drift Sight, the new design not only calculated the effect on the distance the bombs travelled, but also indicated the proper direction to fly to approach the target so the aircraft reached it with no residual sideways motion – thereby cancelling any drift no matter
20349-465: The open, the 500 lbs has a lethal radius of about 107 m (351 ft), but much less than that against buildings, perhaps 27 m (89 ft). The M64 will be dropped from a Boeing B-17 flying at 322 km/h (200 mph) at an altitude of 20,000 feet in a 42 km/h (26 mph) wind. Given these conditions, the M64 would travel approximately 10,000 feet (3,000 m) forward from
20520-475: The opening of World War II , the CSBS added several new features. A simple modification found on pre-war models was the Auxiliary Drift Bar attachment. This consisted of a single drift wire in a C-shaped clamp that could be moved along the main drift wires, and rotated in relation to them. Previously, the bomb aimer would use the main drift bar as a tool to measure wind speed, but it was found that
20691-527: The order of 35 yards, much better than any optical bombsight. The introduction of the British H2S radar further improved the bomber's abilities, allowing direct attack of targets without the need of remote radio transmitters, which had range limited to the line-of-sight. By 1943 these techniques were in widespread use by both the RAF and USAAF, leading to the H2X and then a series of improved versions like
20862-511: The original E-6B name. Many just called it the "Dalton Dead Reckoning Computer", one of its original markings. After Dalton's death, Weems updated the E-6B and tried calling it the E-6C, E-10, and so forth, but finally fell back on the original name, which was so well known by 50,000 World War II Army Air Force navigator veterans. After the patent ran out, many manufacturers made copies, sometimes using
21033-520: The path of travel. That made them effectively useless against moving targets, like submarines and ships . Unless the target just happened to be travelling directly in line with the wind, their motion would carry the bomber away from the wind line as they approached. Additionally, as anti-aircraft artillery grew more effective, they would often pre-sight their guns along the wind line of the targets they were protecting, knowing that attacks would come from those directions. A solution for attacking cross-wind
21204-466: The pilot and ask him to turn to the left and then watch the results. In some aircraft, a pilot direction indicator would be used. Several corrections are normally required before the aircraft is flying along the yellow line and the residual drift is entirely cancelled out. Although the CSBS automated the calculation of the effects of the wind, it did not automate the measurement of the wind itself. The bombsight manual describes several ways to do this. One
21375-422: The pilot free to fly the plane. None of these sights had a way to calculate drift , the sideways motion of the bombs due to wind. This meant the aircraft had to attack their targets directly along the wind line. Even in this direction, the wind would cause the bombs to fall long or short. To correct for this, the bomb aimer would first measure their speed over the ground using a stopwatch . They would next look up
21546-544: The pilot had to hold out of the cockpit in one hand while flying the aircraft with the other. The Central Flying School Sight replaced this in 1915, but was difficult to install in the cockpit. The CFS was in turn replaced by the Equal Distance Sight (EDS) designed in 1916 by F. W. Scarff, better known for the development of the Scarff ring . The EDS allowed the bomb-run parameters to be entered once and then left
21717-456: The platform, all of the mechanical calculator portions of the sight were removed. Instead, the bomb aimer had to use manual slide rule calculators to find the drift and bombing angles, and then set the bombsight to these values. The bombsight was unable to quickly adapt to changes in direction or altitude, and in this case was even slower to calculate such changes. Very few of the Mk. XI designs were produced. As if these problems were not enough,
21888-478: The post-war era, but none of these became widely used. This led to the introduction of the pilot direction indicator , an electrically driven pointer which the bomb aimer used to indicate corrections from a remote location in the aircraft. Vector bombsights remained the standard by most forces well into the Second World War , and was the main sight in British service until 1942. This was in spite of
22059-425: The primary British bombsights into 1942. The Mk. VII was widely found on slower aircraft and training schools, while the Mk. IX was used in higher speed aircraft. Another problem with all of the existing CSBS designs was that it could only be read correctly with the aircraft absolutely level. This was true especially during the run-up to the drop point, when the sight was used to correct the direction of flight through
22230-469: The radar and radio systems. In the case of the Canberra, the optical system only existed due to delays in the radar system becoming available. E6B They are mostly used in flight training , because these flight computers have been replaced with electronic planning tools or software and websites that make these calculations for the pilots. These flight computers are used during flight planning (on
22401-523: The radar signal in the existing bombsights, allowing the bombsight calculator to solve the radar bombing problem. For instance, the AN/APA-47 was used to combine the output from the AN/APQ-7 with the Norden, allowing the bomb aimer to easily check both images to compare the aim point. Analysis of the results of bombing attacks carried out using radio navigation or radar techniques demonstrated accuracy
22572-405: The rear of the earlier models, was moved to the left side of the device and changed in form to make it smaller as well. The compass, no longer containing pointers and dials, was replaced with a smaller unit. The result was a version of the CSBS that was much smaller than earlier versions. About 5,000 of the new Mk. X were built and awaiting fitting to aircraft at the opening stages of the war. After
22743-522: The reverse. He called this prototype his Model H; the Army called it the E-6A. In 1938 the Army wrote formal specifications, and had him make a few changes, which Weems called the Model J. The changes included moving the "10" mark to the top instead of the original "60". This "E-6B" was introduced to the Army in 1940, but it took Pearl Harbor for the Army Air Forces (as the former "Army Air Corps"
22914-424: The right side of the bar, and any number of white scales on the back that could be clipped onto the sight. The two were used in combination to make adjustments for the altitude of the target over sea level. The operation of the CSBS is best understood using a simple example. For this the windage triangle shown in the section above will be used, combined with the operational description from AP1730. The problem for
23085-413: The role passed to dedicated radar bombsights. Finally, especially since the 1960s, fully computerized bombsights were introduced, which combined the bombing with long-range navigation and mapping. Modern aircraft do not have a bombsight but use highly computerized systems that combine bombing, gunnery, missile fire and navigation into a single head-up display . The systems have the performance to calculate
23256-404: The seriousness of the problem, systems for automatic levelling of bombsights was a major area of study before World War II, especially in the US. All of the calculations needed to predict the path of a bomb can be carried out by hand, with the aid of calculated tables of the bomb ballistics. However, the time to carry out these calculations is not trivial. Using visual sighting, the range at which
23427-410: The side of the bombsight, the drift could be seen. Using a knob, the rod was angled away from the side of the aircraft until objects could be seen moving directly along the line of the rod. A gear in the knob that adjusted the rod angle also drove the sights fore or aft, moving them to account for the wind speed. This eliminated the need for a stopwatch to measure the ground speed. However, the Drift Sight
23598-420: The speed and direction of the wind rotated and slid various mechanical devices that solved the vector problem. Once set up, the bomb aimer would watch objects on the ground and compare their path to thin wires on either side of the sight. If there was any sideways motion, the pilot could slip-turn to a new heading in an effort to cancel out the drift. A few attempts were typically all that was needed, at which point
23769-408: The speed. Terminal velocity, which extends the fall time, can be accounted for by raising the effective altitude by an amount that is based on the bomb's measured ballistics. When windage is accounted for, the calculations become more complex. As the wind can operate in any direction, bombsights generally break the windage into the portions that act along the flight path and across it. In practice, it
23940-487: The target is first sighted remains fixed, based on eyesight. As aircraft speeds increase, there is less time available after the initial spotting to carry out the calculations and correct the aircraft's flight path to bring it over the proper drop point. During the early stages of bombsight development, the problem was addressed by reducing the allowable engagement envelope, thereby reducing the need to calculate marginal effects. For instance, when dropped from very low altitudes,
24111-405: The target would appear when the aircraft was at the drop point. This is known as the range angle or drop angle , and was typically looked up from a set of pre-computed tables or using a simple mechanical calculator . The bombsight is then set to that angle, and the bomb aimer drops the bombs when the target passes through the sights. In the presence of a cross-wind, as the aircraft flies forward
24282-454: The telescope to keep the target in view had the side effect of fine-tuning the windage calculations continuously, and thereby greatly increasing their accuracy. For a variety of reasons, the Army dropped their interest in the Sperry, and features from the Sperry and Norden bombsights were folded into new models of the Norden. The Norden then equipped almost all US high-level bombers, most notably
24453-441: The time it would take the bombs to reach the ground from their current altitude using a pre-computed table. Then, using both values, they would look up the proper angle for the sights, the so-called range angle , and set the sights to that angle. This solution was far from practical, and prone to error. In 1916, Harry Wimperis started the design of a new bombsight, working in collaboration with Scarff. This new Drift Sight included
24624-521: The time taken to hit the ground, and then a pointer in the sight was set to an angle looked up on a table. The bomb aimer then watched the target in the sight until it crossed the pointer, and dropped the bombs. Similar bombsights were developed in France and England, notably the Michelin and Central Flying School Number Seven bombsight. While useful, these sights required a time-consuming setup period while
24795-404: The ultimate development of the series, the Mk. XIV. This version replaced the manual input dials with ones powered by air suction bled from the engines. Before the mission, the bomb aimer entered basic information about the target altitude and the bombs being dropped, and periodically updated the wind speed and direction. Everything else was fully automated. Versions were also developed that replaced
24966-420: The use of the drift wires. The biplane bombers the CSBS had been developed for had the ability to slip-turn using the rudder only, which made it simple for the pilot to adjust their heading without affecting the aim too much. Modern monoplanes were subject to an effect known as dutch roll that makes them oscillate for a time after turning to a new heading. During this time the drift wires were difficult to use, so
25137-422: The vector inputs, and the angle of the drift bar and position of the foresight formed the output. The drift wires running down either side of the drift bar were used to measure the drift once calculated, to ensure the aircraft was flying along the correct heading to zero out any wind drift. The bombsight solution is now almost complete, having calculated the ground speed and zeroed out any sideways drift. All that
25308-410: The vertical component of the velocity is denoted by v v {\displaystyle v_{v}} and the horizontal component by v h {\displaystyle v_{h}} then the speed is v v 2 + v h 2 {\displaystyle {\sqrt {v_{v}^{2}+v_{h}^{2}}}} and the vertical and horizontal components of
25479-445: The war progressed. After the war, the CSBS continued to be the main bombsight in British use. Thousands were sold to foreign air forces and numerous versions were created for production around the world. A number of experimental devices based on a variation of the CSBS were also developed, notably the US's Estoppey D-1 sight, developed shortly after the war, and similar versions from many other nations. These "vector bombsights" all shared
25650-403: The wind direction during manual calculations. The top of the bearing plate was designed to be drawn on with a chinagraph pencil so it could serve as a general navigation calculator as well. On early models, rotating the compass face also rotated a shaft that ran forward under the main body of the bombsight and through a metal tube running out the lower front of the main housing. On later models,
25821-522: The wind speed is a more serious concern. Early navigation systems generally measured it using a dead reckoning procedure that compares measured movement over the ground with the calculated movement using the aircraft instruments. The Federal Aviation Administration 's FAR Part 63 suggests 5 to 10% accuracy of these calculations, the US Air Force's AFM 51-40 gives 10%, and the US Navy's H.O. 216 at
25992-451: The wind will push it sideways, away from the drop point. The solution is to calculate the angle that the aircraft should fly in order to cancel out this drift, the difference between the course and the heading . Calculating the proper drift angle is a simple task of basic vector addition , and is commonly carried out on a circular slide rule like the E6B. This is a somewhat time-consuming process. The CSBS solved this problem by reproducing
26163-423: The winds aloft and then the course made good. These calculations are identical to those needed to properly account for the effects of winds on the bombing approach. The problem was that these calculations were complex, time-consuming and error prone. Wimperis decided to attack the calculation problem by incorporating a similar vector calculator directly into the bombsight, combining it with a drift measure similar to
26334-432: The wing of the aircraft. After considerable testing, he was able to build a table of settings to use with these inputs. In testing at College Park, Maryland , Scott was able to place two 18 pound bombs within 10 feet of a 4-by-5 foot target from a height of 400 feet. In January 1912, Scott won $ 5,000 for first place in the Michelin bombing competition at Villacoublay Airfield in France, scoring 12 hits on
26505-417: The yellow arrow is set by rotating the air speed drum, carrying the windage calculator with it. The milled head is used to rotate the wind bar to the same angle as the wind, in this case about 120 degrees. This would leave the wind bar almost at right angles to the drift bar, with the wind speed knob easily accessible on the left. Finally, the wind speed would be dialled into the wind speed knob, which would push
26676-482: Was a fairly complex system of rotating rings and sliders that allowed the bomb aimer to dial in the relative course of the target and its estimated speed. This moved the backsight directly fore and aft, and turning the heading dial adjusted how much the speed dial moved the backsight. As the resulting mechanism was fairly large and complex, the sights were also available with the Fourth Vector removed, denoted with
26847-422: Was a major problem. In practice, only large targets such as cities could be attacked. During the day the bomber could use its bombsights to attack point targets, but only at the risk of being attacked by enemy fighters and anti-aircraft artillery . During the early 1930s the debate had been won by the night-bombing supporters, and the RAF and Luftwaffe started construction of large fleets of aircraft dedicated to
27018-454: Was accomplished by sighting off parts of the aircraft, such as struts and engine cylinders, or drawing lines on the side of the aircraft after test drops on a bombing range. These were useful for low altitudes and stationary targets, but as the nature of the air war expanded, the needs quickly outgrew these solutions as well. For higher altitude drops, the effect of wind and bomb trajectory could no longer be ignored. One important simplification
27189-503: Was an expert on the topic, and would later write a well-known book about it. To aid in the necessary calculations, it was common to use a simple mechanical calculator that combined a slide-rule like calculator on one side with a vector calculator on the other. The best-known modern example is the E6B , which remains a basic part of every pilot and navigator's toolkit. Using the vector calculator and basic measurements, one can easily calculate
27360-725: Was considered a cowardly and defeatist night-bombing policy. In spite of this change, the Luftwaffe continued to put some effort into solving the problem of accurate navigation at night. This led to the Battle of the Beams during the opening stages of the war. The RAF returned in force in early 1942 with similar systems of their own, and from that point on, radio navigation systems of increasing accuracy allowed bombing in any weather or operational conditions. The Oboe system, first used operationally in early 1943, offered real-world accuracies on
27531-587: Was developed in the United States by Naval Lt. Philip Dalton (1903–1941) in the late 1930s. The name comes from its original part number for the U.S Army Air Corps , before its reorganization in June 1941 . Philip Dalton was a Cornell University graduate who joined the United States Army as an artillery officer, but soon resigned and became a Naval Reserve pilot from 1931 until he died in
27702-563: Was essentially equal for the two systems – night time attacks with Oboe were able to hit targets that the Norden could not during the day. With the exception of operational considerations – limited resolution of the radar and limited range of the navigation systems – the need for visual bombsights quickly disappeared. Designs of the late-war era, like the Boeing B-47 Stratojet and English Electric Canberra retained their optical systems, but these were often considered secondary to
27873-575: Was eventually replaced in British service by more advanced designs like the Mark XIV bomb sight and the Stabilized Automatic Bomb Sight . Other services used vector bombsights throughout the war. Prior to the introduction of the CSBS, bombsights were generally very simple systems of limited accuracy suitable only for low-level use. The primary pre-war device in RNAS service was the Lever Sight, which
28044-476: Was generally simpler to have the aircraft fly in such a way to zero out any sideways motion before the drop, and thereby eliminate this factor. This is normally accomplished using a common flying techniques known as crabbing or sideslip . Bombsights are sighting devices that are pointed in a particular direction, or aimed. Although the solution outlined above returns a point in space, simple trigonometry can be used to convert this point into an angle relative to
28215-581: Was renamed on June 20, 1941) to place a large order. Over 400,000 E-6Bs were manufactured during World War II, mostly of a plastic that glows under black light (cockpits were illuminated this way at night). The base name "E-6" was fairly arbitrary, as there were no standards for stock numbering at the time. For example, other USAAC computers of that time were the C-2, D-2, D-4, E-1 and G-1, and flight pants became E-1s as well. Most likely they chose "E" because Dalton's previously combined time and wind computer had been
28386-424: Was sorely needed. Calculating the effects of an arbitrary wind on the path of an aircraft was already a well-understood problem in air navigation , one requiring basic vector mathematics . Wimperis was very familiar with these techniques, and would go on to write a seminal introductory text on the topic. The same calculations would work just as well for bomb trajectories, with some minor adjustments to account for
28557-435: Was still useful only for bomb runs along the wind line. When an aircraft flies in the presence of wind, its flight path over the ground is a function of the aircraft's airspeed, heading, and the speed and direction of the wind. These are combined using basic vector addition to return the course made good or track . These calculations are a basic part of air navigation and dead reckoning , taught to all aviators. Wimperis
28728-665: Was such a great advance over earlier designs that it was quickly adopted by the Royal Flying Corps , and the Independent Air Force . It has been called "the most important bomb sight of the war". After the war the design found widespread use around the world. A US version of the CSBS was used by Billy Mitchell on his famous attack on the Ostfriesland in 1921 . The basic design was adapted by almost all air forces and used well into World War II . It
28899-519: Was the German Görtz bombsight , developed for the Gotha heavy bombers . The Görtz used a telescope with a rotating prism at the bottom that allowed the sight to be rotated fore and aft. After zeroing out sideways motion the sight was set to a pre-set angle and then an object was timed with a stopwatch until it was directly below the aircraft. This revealed the ground speed, which was multiplied by
29070-414: Was to ignore the terminal velocity of the bomb, and calculate its average speed as the square root of the altitude measured in feet. For instance, a bomb dropped from 10,000 feet would fall at an average rate of 400 fps, allowing easy calculation of the time to fall. Now all that remained was a measurement of the wind speed, or more generally the ground speed. Normally this was accomplished by flying
29241-411: Was used to calculate the aim point. The aim point was fed back to the sight, which automatically rotated the telescope to the correct angle to account for drift and aircraft movement, keeping the target still in the view. When the bombardier sighted through the telescope, he could see any residual drift and relay this to the pilot, or later, feed that information directly into the autopilot . Simply moving
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