Delco Carousel IV

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The Delco Carousel IV was a widely used inertial navigation system (INS) from the US manufacturer Delco Electronics and the first INS to be installed ex works in commercial aircraft. It made it possible to navigate to waypoints that were only defined by their geographic coordinates, without resorting to a navigator or radio navigation .

history

Cockpit of an Air France Boeing 747-100 with three versions of the Delco Carousel IV: One control unit each for the commander and the first officer in the front center console and a third unit in the rear center console.

Navigation over long distances had not changed much in the period after the end of the Second World War: In addition to the use of a navigator , navigation using ground-based rotating and circular radio beacons was common in civil aviation. The costly facilities required for this were not always available or not always reliable in structurally weak regions and developing countries; They could not be realized on long overwater flights either. At the same time, the increase in global air traffic meant that more reliable solutions had to be found with regard to safe flight operations and compliance with the separation . The Doppler navigation represented a first foray in this direction, but was cautiously received compared to the later market penetration of the Carousel IV.

In 1966, Pan Am was the first civilian operator to test an inertial navigation system, the Sperry SGN10 . Although Sperry could not prevail with the SGN10 and Pan Am did not order any units after the end of the trial operation, the aircraft manufacturer Boeing took up the subject of an inertial navigation system as part of the design process for its 747 and placed the order for the development and construction of such a system in February 1967 after tendering to Delco Electronics , a subsidiary of General Motors . Delco Electronics had also previously provided the inertial navigation system for NASA's Apollo program , and some components were reused to create the Delco Carousel IV for civil aviation.

After completion of the tests on board a Douglas DC-8 of Finnair in February 1969 and approval, the Carousel IV went into regular service from December of the same year. The Boeing 747 was the first commercial aircraft to be fitted with a Delco Carousel IV at the factory, and it was also the first civilian aircraft to be fitted with an inertial navigation system at the factory. The machine could be used worldwide with approval and control waypoints solely on the basis of their geographic coordinates without having to carry a navigator, which was a novelty at the time. The cost of the Carousel IV at this point was approximately $ 75,000. Delco secured exclusive rights from Boeing to equip the first 200 Boeing 747s with the Carousel IV.

In the course of time, further sub-versions and improvements of the system emerged, such as the Carousel IV-A, which offered the possibility of position updates in flight and of waypoint input via a card reader. The Carousel IV-C, on the other hand, was a Carousel version specially developed for the Concorde , which also worked reliably beyond the speed of sound, while the Carousel IV-E had been modified for military purposes.

The Delco Carousel IV and its control unit may appear primitive - measured against today's flight management systems and their GNSS -based RNAV implementation . Nevertheless, the system marked a significant step in the development of modern navigation solutions. Although the limited storage space for only nine waypoints often made it necessary to enter additional waypoints in flight and, due to the increasing inaccuracies over time, a complicated procedure for updating the position was necessary, which - if executed incorrectly - rendered the entire inertial navigation system useless, the Delco Carousel enjoyed one great popularity. Despite competition from the Litton LTN-51 and an initially weak MTBF, it spread to machines such as the Boeing 707 , 727 , 737 , 747, the McDonnell Douglas DC-10 and the Lockheed L-1011 .

Structure and operation

Components

Control and Display Unit of a Delco Carousel IV-A: In the two upper liquid crystal displays the current position of the INU, which corresponds to the geographic coordinates of Frankfurt Airport.

The Delco Carousel IV consisted of four central elements:

  • The Inertial Navigation Unit , INU for short , contained the heart of the unit with the acceleration sensors and gyrometers in fully cardanic , gyro-stabilized suspension: In contrast to today's rigid solutions, the acceleration sensors mounted on a platform were always aligned horizontally to the earth's surface. Means Aufintegrieren the sensor readings over time, the spatial position of the machine has, starting from an initial position to be reconstructed (see also: inertial navigation system # basic principle ) . This part of the Delco Carousel also housed the digital processor and an analog-digital converter for communication with the other systems of the aircraft. The latter enabled a connection to the autopilot for the purpose of flying a programmable waypoint sequence as well as the display of carousel information in the aircraft's horizontal situation indicator .
  • The Control and Display Unit , or CDU for short , represented the interface for the pilots. The approximately 14.5 × 11.5 cm control element housed three liquid crystal displays, the numeric keys for entering coordinates and waypoints, further function keys, status lights and two rotary switches, with which additional information about the flight path and the operation of the Delco Carousel could be called up.
  • The Mode Selector Unit , MSU for short , enabled switching between the operating modes of the Delco Carousel (Off, Standby, Align, Navigation, Attitude) and also included lamps to indicate readiness for use and to indicate emergency power operation. This unit could optionally be installed directly above the CDU but also elsewhere in the cockpit.
  • The Battery Unit , or BU for short , guaranteed an independent, self-sufficient DC power supply for up to 15 minutes. It was used when the system was switched on and in emergency situations - in other words, when a sufficient power supply could no longer be guaranteed by the aircraft itself and the 115 volt primary voltage fell below a certain value. The activation of the BU was acknowledged by the lighting up of a red warning light in the MSU. By installing an extension, the emergency power supply could be guaranteed for up to 30 minutes.

Both INU and BU were installed outside the range of the pilots and thus outside the cockpit in the electronic and equipment section (E & E Bay) of the aircraft. In the event of retrofitting, there was later the option of accommodating the system on a pallet basis in the cargo hold of a Boeing 707, for example.

service

Cockpit process trainer of a Lockheed L-1011 TriStar in the National Airline History Museum, Kansas City, with three installed Carousel IVs and their control units in the front area of ​​the center console.

The actual operation of the Carousel IV was preceded by an initialization phase in Align mode lasting ten to fifteen minutes, which, depending on the geographical latitude, could take a longer period and in which the aircraft was not allowed to be moved. The start position entered here formed the basis for the subsequent integration of the measured values; The Carousel IV's acceleration sensors and gyroscopes initialized and the system subjected the emergency power supply to a self-test.

Up to nine waypoints could be entered into the memory of the Carousel IV during the initialization and later operation. After completing the initialization and switching to the central navigation mode, the unit was ready for operation - all changes made to the spatial aircraft position from this point on were recorded by the INU and the position of the carousel updated with every movement. When flying the entered flight plan in automatic mode, the Carousel IV automatically switched to the next waypoint. If the machine then flew over the ninth waypoint, which at the same time represented the limit of the internal memory, the system switched back to the first waypoint, so that the crew had to continuously reprogram flight plans with more than nine waypoints. Apart from this, one of the nine waypoints could also be flown to directly from the current position by using the waypoint change button, intermediate points could be skipped or any connecting segment between two waypoints could be controlled in order to continue from there in the flight plan.

Like all inertial navigation systems, the Delco Carousel IV was also exposed to a significant problem: a deviation from the actual aircraft position that increased over time ("drift") due to the constant integration of smaller measurement errors. A few months after the introduction, the British airline BOAC reported a maximum drift of 0.57 NM / operating hour in 50% of all cases and a maximum drift of 1.35 NM / operating hour in 95% of all cases. Although these values ​​turned out to be relatively good, they exceeded the expectations of the airlines and Delco's own guarantee of a maximum of 2 NM drift per operating hour in a positive sense, but they still wanted to be able to improve them. As of version IV-A, it was therefore possible to periodically specify and update the position in flight via the reception of radio beacons with connected distance measuring equipment . After manually entering the coordinates of the distance measuring equipment and their altitude, the carousel unit was not available for the actual navigation or activation on the autopilot for the duration of the update process, which lasted a few minutes, while the accumulated drift was reversed. Apart from this measure, it was also possible to increase the position accuracy in machines with a triple carousel design - regardless of the carousel version installed in each case - by interpolating and comparing all three device signals. A dimensionless performance index display, accessible via the MSU rotary selector switch, informed the crew at any time of the current system accuracy.

Individual evidence

  1. ↑ a b c B. J. Calvert: Carousel IV in the 747 . In: Flight International . tape 100 , no. 3251 . IPC Business Press, July 1, 1971, ISSN  0015-3710 , p. 16-17 (English).
  2. ^ A b Mike Hirst: Ten years of airline INS . In: Flight International . tape 114 , no. 3519 . IPC Business Press, July 29, 1978, ISSN  0015-3710 , p. 347 (English).
  3. ↑ a b Carousel IV-A Inertial Navigation System - On Airplane Reference Handbook . Delco Electronics, Milwaukee July 1975, p. 14 (English).
  4. ^ Inertial Navigation Means Help Is on the Way . In: The MAC Flyer . Military Airlift Command , United States Air Force, Scott Air Force Base March 1976, p. 9-10 (English).
  5. ↑ Chris Binns: Aircraft Systems: Instruments, Communications, Navigation and Control . John Wiley & Sons, Hoboken 2018, ISBN 978-1-119-25954-1 , pp. 51 (English).
  6. ^ Digital avionics - experience and prediction . In: Flight International . tape 107 , no. 3435 . IPC Business Press, January 9, 1975, ISSN  0015-3710 , p. 40 (English).
  7. ↑ a b Carousel IV Inertial Navigation System - Operations Manual . AC Electronics, Milwaukee June 1, 1971 (English).
  8. ↑ Cordt-Christian Rossow, Klaus Wolf, Peter Horst: Handbuch der Luftfahrzeugtechnik . Carl Hanser, Munich 2014, ISBN 978-3-446-42341-1 , p. 660 .