Ancillary Aircraft Equipment
Ancillary equipment covers individual units or devices which are parts of larger set of equipment necessary for the aircrew or aircraft to complete its mission.
AN/APG-41 radar was located above the B-47 tail gun turret. It was used for tracking and targeting incoming enemy aircraft and provided data to the gunner. The performance of the prototype B-47 was projected to be so good that the bomber would be as fast as fighters then on the drawing board thus the only defensive armament was to be a tail turret with two .50 cal AN/M2 Browning machine guns, (later two 20 mm cannons) which would in principle be directed by an automatic fire-control system. The aircraft was designed to carry a crew of three in a pressurized forward compartment: a pilot and copilot, in tandem, in a long fighter-style bubble canopy, and a navigator/bombardier in a compartment in the nose. The copilot doubled as tail gunner (using a remotely controlled, radar-directed tail gun), and the navigator as bombardier.
The tail gun on the B-47 was housed in a remotely operated turret known as the M24A1. This turret was mounted at the extreme rear of the aircraft's fuselage and was armed with two machine guns or cannons. The B-47 Stratojet and its tail turret were significant assets during the early years of the Cold War when the United States needed a long-range strategic bomber capable of delivering nuclear weapons. But the system was limited by relatively primitive radar capabilities of the time, improved capabilities of enemy aircraft and changing tactics. As the Cold War progressed, newer strategic bombers, such as the B-52 Stratofortress, replaced the B-47 in the USAF's inventory. These newer aircraft relied more on speed, altitude, and electronic countermeasures for defense rather than traditional tail gunners.
The closest the RB-47 came to combat, was flying thousands of " ferret" missions - reconnaissance missions designed to locate Soviet radar stations. In case war broke out with the USSR, which appeared increasingly possible at that feral juncture of history, the data gathered on such flights would be critical. At least five aircraft were fired upon and three were shot down. The RB-47s returned fire with their tail turrets, although it is uncertain if they scored any kills; these were the only shots fired in anger by any B-47. On 1 July 1960, a MiG-19 shot down an RB-47H reconnaissance aircraft in the international airspace over the Barents Sea. The co-pilot reported that the MiG-19 jammed ("whited-out") his MD-4 FCS scope (the radar which aimed the tail guns), rendering the RB-47H defenseless, highlighting a weakness.
The AN/ART-13 radio transmitter was developed by Collins Radio Company in the 1930s. It was designed for military use and was introduced in the late 1930s, just prior to World War II and quickly became the standard HF (High-Frequency) radio transmitter used by the U.S. military. The AN/ART-13 was versatile and could be used for both voice and telegraphy (Morse code) communications. It had a wide frequency range, allowing it to operate on different HF
bands. The AN/ART-13 was commonly installed in military aircraft, including bombers and transport planes. It provided essential communication capabilities for aircraft in various roles, including strategic bombing missions. The AN/ART-13 was known for its reliability and ruggedness, making it a valuable tool for maintaining communication in challenging combat conditions. The AN/ART-13 is known for its distinctive, large tuning dial and analog controls. After World War II, the AN/ART-13 continued to be used by the U.S. military and was also adopted by other countries. As technology evolved, the AN/ART-13 was eventually phased out in favor of more modern and efficient communication systems. It was gradually replaced by solid-state and digital radio equipment.
The AN/ART-13 operated in CW (code), MCW and AM (voice) modes and covered LF, MF and HF frequencies up to 18.1 MHz. It had ten autotuned VFO tuned channels that could be preset. Power output was approximately 100 watts using an 813 vacuum tube as the final amplifier. Under favorable atmospheric conditions communications could be established between aircraft and ground stations separated by thousands of miles. The Russians made nearly exact copies of the AN/ART-13 transmitter (called RSB-70 and R-807) for use on their military aircraft. It is thought that they obtained AN/ART-13 units from battle damaged B-29 bombers that landed in Russia during World War II. It was well known that the Russians copied the B-29 bomber calling their version the Tu-4.
BC-375-E Radio Transmitter
The BC-375-E US Army Radio Transmitter (here sitting above a TU-7-B transmitter tuning unit) was manufactured by General Electric and installed WWII-era bomber planes such as the B-17 and the B-24. The design was based off of the BC-191F ground based radio, but modified to optimize it for use in planes. Commonly used on B-17s, the SCR-287 (the combination of BC-375 and BC-348 receiver) set-up was found on thousands of those bombers. On the B-17, the transmitter was usually located under the radioman's table while the receiver was on top of the table. Other installations had the transmitter on the opposite side of the fuselage from the radioman's position. Installations did vary from plane to plane but it illustrates the importance of the receiving operation versus the transmitting function. Most BC-375 transmissions were very short - a word or two was all that was necessary. Nearly all transmissions were in CW. Now simply called "CW", radio communication by Morse code
was the only way to communicate for the first decade or more Voice was rarely used. The BC-275-E was used as a liasion radio by the bombers to communicate with command bases on the ground. Additionally, only those items necessary for operation on the specified frequencies were taken on a bombing mission. On other types of airplanes, such as transports or search and rescue types, more equipment may have been taken along since the mission might require more specialized communications than the typical bombing run would.
The BC-375 rapidly became outdated for aircraft use, especially towards the end of WWII. Certainly the decision to build 100,000 transmitters was based on the planned requirements early in the war. Towards the middle of WWII, the radio engineers at Collins Radio Company had introduced their famous and very modern ATC/ART-13. These transmitters produced more RF power in smaller packages and didn't require several tuning units for frequency mobility. Additionally, the ATC/ART-13 would autotune itself and had superb audio. These new transmitters were installed on the newest types of bombers while BC-375s were still being delivered. Near the end of WWII, crates of BC-375s were left unopened because the military viewed the transmitter as obsolete. However, that view was for bombers. The military still used the BC-375 in transports and in "search and rescue" planes well after WWII. They weren't the "latest and greatest" but they were reliable and worked well in those areas.
B-52 MD-1 Astro Navigator
Before GPS, a primary navigation method for ships, aircraft, spacecraft and missiles was celestial tracking, also known as astronavigation. The basic approach is to sight on the sun or a particular star and calculate the position of the aircraft, missile or ship from the sighting angles to the star. The calculation is based upon highly accurate data about the positioning of the sun and certain reference stars at various time and locations. For modern applications, the star tracking location is used to calibrate and update an inertial navigation system.
Early Air Force aircraft such as early B-52 bombers relied on a human using a sextant through a bubble in the top of the plane. Some time in the late '60s, manual sighting was replaced on the E and F models by this automatic astro tracker mechanism and its associated analog computer. At some point, the astro navigator was replaced by GPS. Our device has a maintenance tag dated 1983, so the system was used at least until then.
Similar "star trackers" were and are used on many other planes such as the SR-71 and RC-135 reconnaissance aircraft, the B-58 bomber, and the P-3 Orion patrol plane. Of special interest is the fact that the most modern USAF plane, the B-2 bomber, still has a automatic star tracker navigation system. Many missiles, including some currently operational ones, also use automated start tracker navigation: the Polaris, Poseidon, Trident, MX, SM-62 Snark and the AGM-28 Hound Dog, and others.
Astro navigator (top removed for display)
B-52 Polar Converter
The Polar Converter is a specialized analog computer designed to convert rectangular coordinates into polar coordinates swiftly and accurately. It is part of the B-52 bombing navigational system, AN/ASB-15, and is integrated into the aircraft's navigation and targeting systems, ensuring seamless communication between different components of the aircraft.
In aviation, particularly during bombing missions, knowing the precise location of the target is vital for success and minimizing collateral damage. However, aircraft typically gather information in terms of vertical and horizontal distances from their position to the target, often represented in rectangular coordinates. These rectangular coordinates, while essential for calculations, can be cumbersome to work with, especially during high-pressure situations. Converting them into polar coordinates simplifies the navigation and targeting processes and enhances the pilot's ability to make quick and accurate decisions. Polar coordinates take the earth's curvature into account. Constantly corrected values of airspeed, aircraft heading, distance to target and wind velocity are passed to the Polar Converter by the tracking computer. As a result of solving the bombing problem, the computer will display time to go before bomb release and heading error to the pilot and to the operator, supply heading error to the autopilot for automatic steering to the bomb release point, open the bomb doors at the correct time, and release the weapon at the correct time.
Polar Converter cut-a-way
B-52 Tracking Computer
The tracking computer is part of the AN/ASB-15 bomb/nav system. It contains the mechanical computing mechanisms that are used to determine data that used in the solution of navigational and bombing problems. The tracking computer contains constantly corrected values of airspeed, aircraft heading, distance to target and wind velocity. It then passes solutions to bombing and navigational problems to ballistics control which adds any offsets required before passing the signals to the polar converter. As a result of solving the bombing problem, the computer will display time to go before bomb release and heading error to the pilot and to the operator, supply heading error to the autopilot for automatic steering to the bomb release point, open the bomb doors at the correct time, and release the weapon at the correct time.
K-3 computing gun sight:
The Sperry K-3 is a computing gun sight used in used in Sperry upper gun turrets used on the B-17 bomber. The K-4 is the same device with a different mount used in the Sperry lower gun turrets on the B-17. Figure 1 shows our two K-3's plus a computing element from a third. The other pictures show various views of these devices. Figure 9 shows a page from the Gunner's Information File illustrating the lower turret with the K-4 sight right in the middle.
The gunner inputs range information by estimating the size of the plane and adjusting its image in the attached optical sight so that the image fits withing reticles. The gunner then tracks the target with the optical sight by moving the K-3 (mounted on a movable head) keeping the plane image centered in the reticles. The sight movements cause the computing unit, which, based on the range information and built-in ballistics data, to calculates the deflection, or lead, for aiming the guns and moves the turret accordingly.
K-3 computing gun sight
Gun sight in turrret
Norden M series in U.S. Army service, is a bombsight that was used by the United States Army Air Forces (USAAF) and the United States Navy during World War II, and the United States Air Force in the Korean and the Vietnam Wars. It was an early tachometric design that directly measured the aircraft's ground speed and direction, which older bombsights could only estimate with lengthy manual procedures. The Norden further improved on older designs by using an analog computer that continuously recalculated the bomb's impact point based on changing flight conditions, and an autopilot that reacted quickly and accurately to changes in the wind or other effects.
Under combat conditions the Norden did not achieve its expected precision, yielding an average CEP in 1943 of 1,200 feet (370 m) (a CEP of 1200 feet means 50% of all bombs dropped land within 1200 feet of the target), similar to other Allied and German results. Both the Navy and Air Forces had to give up using pinpoint attacks. The Navy turned to dive bombing and skip bombing to attack ships, while the Air Forces developed the lead bomber procedure to improve accuracy, and adopted area bombing techniques for ever-larger groups of aircraft.