The F-14's Central Air Data Computer, also abbreviated as CADC, computes altitude,

vertical speed Vertical is a geometric term of location which may refer to: * Vertical direction, the direction aligned with the direction of the force of gravity, up or down * Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...

air speed In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: * Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system; * Calibrated a ...

, and

mach number Mach number (M or Ma) (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Moravian physicist and philosopher Ernst Mach. : \mathrm = \frac ...

from sensor inputs such as pitot and

static pressure In fluid mechanics the term static pressure has several uses: * In the design and operation of aircraft, ''static pressure'' is the air pressure in the aircraft's static pressure system. * In fluid dynamics, many authors use the term ''static pres ...

and temperature. Earlier

air data computer An air data computer (ADC) or central air data computer (CADC) computes altitude, vertical speed, air speed, and Mach number from pressure and temperature inputs. It is an essential avionics component found in modern aircraft. This computer, rath ...

systems were

electromechanical computer A mechanical computer is a computer built from mechanical components such as levers and gears rather than electronic components. The most common examples are adding machines and mechanical counters, which use the turning of gears to increment outp ...

s, such as in the

F-111 The General Dynamics F-111 Aardvark is a retired supersonic, medium-range, multirole combat aircraft. Production variants of the F-111 had roles that included ground attack (e.g. interdiction), strategic bombing (including nuclear weapons ca ...

. From 1968 to 1970, the first CADC to use custom digital

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s was developed for the

F-14 The Grumman F-14 Tomcat is an American carrier-capable supersonic, twin-engine, two-seat, twin-tail, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experimental (VFX) program after the ...

History

The CADC was a multi-chip integrated flight control system developed by

Garrett AiResearch Garrett AiResearch was a manufacturer of turboprop engines and turbochargers, and a pioneer in numerous aerospace technologies. It was previously known as Aircraft Tool and Supply Company, Garrett Supply Company, AiResearch Manufacturing Compa ...

and used in early versions of the

US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...

F-14 Tomcat The Grumman F-14 Tomcat is an American carrier-capable supersonic aircraft, supersonic, twinjet, twin-engine, two-seat, twin-tail, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experi ...

fighter. It is notable for early use of

MOS MOS or Mos may refer to: Technology * MOSFET (metal–oxide–semiconductor field-effect transistor), also known as the MOS transistor * Mathematical Optimization Society * Model output statistics, a weather-forecasting technique * MOS (filmm ...

custom integrated circuits and has been claimed as the first

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

. The first microprocessor existing on a single chip was the contemporary

Intel 4004 The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. Sold for US$60, it was the first commercially produced microprocessor, and the first in a long line of Intel CPUs. The 4004 was the first signific ...

. However, 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. The CADC was designed and built by a team led by Steve Geller and

Ray Holt Raymond M. Holt is a computer designer and businessman in Silicon Valley. From 1968 to 1970, Ray and his brother Bill Holt were on the Garrett AiResearch's small design team that developed the world's first microprocessor chip set, the 20-bit Ce ...

, and supported by the startup

American Microsystems onsemi (stylized in lowercase; legally ON Semiconductor Corporation; formerly ON Semiconductor until August 5, 2021) is an American semiconductor supplier company, based in Phoenix, Arizona and ranked #483 on the 2022 ''Fortune'' 500 based on it ...

. Design work started in 1968 and was completed in June 1970, beating out a number of

electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...

systems that had also been designed for the F-14. It was classified by the Navy until 1998. Ray Holt's story of this design and development is presented in his autobiography ''The Accidental Engineer''. The CADC consisted of an

A-to-D converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provid ...

, several

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

pressure sensors, and a number of MOS-based

microchips An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Transistor count, Large ...

. 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 primary flight controls, wing sweep, the F-14's leading edge "glove", and the flaps. The MP944 ran at 375 kHz. It contained six chips used to build the CADC, all based on a 20-bit fixed-point-fraction

two's complement Two's complement is a mathematical operation to reversibly convert a positive binary number into a negative binary number with equivalent (but negative) value, using the binary digit with the greatest place value (the leftmost bit in big- endian ...

number system. They were the parallel multiplier unit (PMU) in a 28-pin DIP, the parallel divider unit (PDU) (28-pin DIP), the random-access storage (RAS) (14-pin DIP), the

read-only memory Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing sof ...

(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. In 1971, Holt wrote an article about the system for ''Computer Design'' magazine, but the Navy classified it, and finally released it in 1998. For this reason, the CADC and MP944 remain fairly obscure in spite of their historical importance.

References

External links

First Microprocessor
{{AlliedSignal Avionics computers Computer-related introductions in 1970 Flight control systems Military computers

History

References

Further reading

External links