View source for F-14 CADC

{{Short description|Early flight control computer using MOS}}
[[File:Garrett F-14A dual channel CADC.png|thumb|A Garrett-manufactured F-14A dual channel central air data computer (CADC)]]
The '''F-14's Central Air Data Computer''', also abbreviated as '''CADC''', computes altitude, [[vertical speed]], [[air speed]], and [[mach number]] from sensor inputs such as [[Pitot-static_system#Pitot_pressure|pitot]] and [[Pitot-static_system#Static_pressure|static pressure]] and temperature.<ref>{{cite book|title=Dictionary of Military and Associated Terms|date=Oct 1, 1987|publisher=DIANE Publishing|isbn=9780941375108|page=63}}</ref> From 1968 to 1970, the first CADC to use custom digital [[integrated circuit]]s was developed for the [[Grumman_F-14_Tomcat|F-14]].<ref name=holt>{{cite book |first1=Raymond |last1=Holt |first2=Leo |last2=Sorge |title=The Accidental Engineer |date=2017 |publisher=Lulu.com |isbn=9781387313488 |page=36 |url=https://books.google.com/books?id=_r47DwAAQBAJ&pg=PA15 |accessdate=2 June 2020 |archive-date=26 December 2020 |archive-url=https://web.archive.org/web/20201226121448/https://books.google.com/books?id=_r47DwAAQBAJ&pg=PA15 |url-status=live }}</ref>
==History==
The CADC was a multi-chip integrated flight control system developed by [[Garrett AiResearch]] and used in early versions of the [[US Navy]]'s [[F-14 Tomcat]] fighter. It is notable for early use of [[metal–oxide–semiconductor|MOS]] custom integrated circuits and has been claimed as the first [[microprocessor]].<ref name=holt/> The first commercial microprocessor was the contemporary [[Intel 4004]]. The 4004 did not have nearly the computing power or interfacing capability required to perform the functions of the CADC. At the time, the best integrated circuit (chip) technology available lacked the scale (number of transistors per chip) necessary to build a single-chip microprocessor for a flight control system.
[[File:F-14 Tomcat preparing to refuel.jpg|thumb|The MP944 chip set was the core of the CADC used to control the swing wings of the [[F-14 Tomcat]] naval interceptor.]]
The CADC was designed and built by a team led by Steve Geller and [[Ray Holt]], and supported by the startup [[American Microsystems]]. Design work started in 1968 and was completed in June 1970, beating a number of [[electromechanical]] systems that had also been designed for the F-14.  It was classified by the Navy<ref>{{cite book |first1=Sudhir |last1=Dixit |first2=Ramjee |last2=Prasad |title=Human Bond Communication: The Holy Grail of Holistic Communication and Immersive Experience |date=2017 |publisher=9781119341338 |page=211 |isbn=9781119341338 |url=https://books.google.com/books?id=UW4lDgAAQBAJ&dq=%22ray+holt%22+%22microprocessor%22+classified&pg=PA211 |accessdate=2 June 2020 |archive-date=26 December 2020 |archive-url=https://web.archive.org/web/20201226121449/https://books.google.com/books?id=UW4lDgAAQBAJ&pg=PA211&dq=%22ray+holt%22+%22microprocessor%22+classified |url-status=live }}</ref> until 1998.  Ray Holt's story of this design and development is presented in his autobiography ''The Accidental Engineer''.<ref name=holt/>
The CADC consisted of an [[Analog-to-digital converter|A-to-D converter]], several [[quartz]] pressure sensors, and a number of MOS-based [[microchips]]. Inputs to the system included the primary flight controls, a number of switches, static and dynamic air pressure (for calculating stall points and aircraft speed) and a temperature gauge. The outputs controlled the wing sweep and the maneuver flaps and slats and limited allowable control inputs.<ref>{{cite book |title=NATOPS Flight Manual Navy Model F-14D Aircraft |date=15 Jan 2004 |publisher=Department of the Navy |pages=11-1,20-6,14-42 |url=https://info.publicintelligence.net/F14AAD-1.pdf}}</ref>
The CADC's MP944 chip set ran at 375 kHz, executing 9375 instructions per second. It contained six chips used to build the CADC, all based on a 20-bit [[Fixed-point arithmetic|fixed-point]]-fraction [[two's complement]] number system. They were the parallel multiplier unit (PMU) in a 28-pin [[Dual in-line package|DIP]], the parallel divider unit (PDU) (28-pin DIP), the random-access storage (RAS) (14-pin DIP), the [[read-only memory]] (ROM) (14-pin DIP), the special logic function (SLF) (28-pin DIP), and the steering logic unit (SLU) (28-pin DIP). The complete system of 28 circuits consists of 1 PMU, 1 PDU, 1 SLF, 3 RASs, 3 SLUs, and 19 ROMs, enabled by 74,442 transistors.<ref>{{Cite web|title=Ray Holt and the history of MP944/Cadc @ Rome Technopole, 2017 - YouTube|url=https://www.youtube.com/watch?v=3GROYRkWvxc&feature=youtu.be&t=1343|access-date=2020-11-06|website=www.youtube.com|archive-date=2020-12-26|archive-url=https://web.archive.org/web/20201226121449/https://www.youtube.com/watch?v=3GROYRkWvxc&feature=youtu.be&t=1343|url-status=live}}</ref>
In 1971, Holt wrote an article about the system for ''Computer Design'' magazine.<ref>[https://firstmicroprocessor.com/wp-content/uploads/2020/02/ap1-26-97.pdf 1971 paper on the CADC (which was classified and never published)]</ref> The Navy [[Classified information in the United States|classified]] it, and released it in 1998.
==References==
{{Reflist}}
=== Further reading ===
*[https://www.wired.com/story/secret-history-of-the-first-microprocessor-f-14/ The Secret History of the First Microprocessor, the F-14, and Me]
*[https://www.youtube.com/watch?v=YpruA5mC7wg The World's First Microprocessor: F-14 Central Air Data Computer]
==External links==
* [https://firstmicroprocessor.com/ First Microprocessor]
{{AlliedSignal}}
[[Category:Avionics computers]]
[[Category:Computer-related introductions in 1970]]
[[Category:Flight control systems]]
[[Category:Military computers]]