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Mark Ollig
“A miniature electronic flying brain for jet speed,” is how one newspaper described it.
In 1951, at the request of the US Air Force, a program was started to design a new digital computer to be installed in the military’s supersonic jets. This computer would be used for navigation, targeting, and other flight computations.
March 14, 1955, Bell Telephone Company announced they had developed a new airborne digital computer to be used by the US Air Force in their military jets flying above supersonic speeds of 767.2 mph.
TRADIC (TRAnisitor DIgital Computer) was the name given for the computer.
Bell Telephone’s version of the “flying brain” is the first airborne digital computer using point-contact transistors and no vacuum tubes. It was designed and built by Jean H. Felker.
The transistor was invented in 1947 at the Bell Telephone Laboratories as a replacement for equipment requiring a vacuum tube for controlling electronic radio/voice signaling.
Transistors are more efficient, take less space and power to operate, are highly reliable, and are not susceptible to overheating failures as are vacuum tubes.
The airborne digital computer used was known as TRADIC Phase Two.
This computer used dials and switches for input commands, not punched tape or electric typewriter keystrokes. Its data output would be visual operational signals and informational numerals.
Three years earlier, the TRADIC Phase One computer was built inside Bell Labs, where it underwent electronic component, instruction command, and calculation performance testing. This binary digital computer was synchronous operating using a clocking signal.
The TRADIC electronic components includes 800 transistors, 11,000 electronic germanium diodes for one-way current switching, 6,000 resistors, 4,000 capacitors, and 1,000 power transformers.
The 1955 TRADIC used compact 684 Bell Labs-manufactured removable component module cartridges to hold the transistors and diodes. Each cartridge is plugged into an assigned slot on a mounting strip panel inside the computer.
Before TRADIC, US Airforce jet aircrafts’ electronic computing systems were exceptionally vulnerable to overheated vacuum tubes, which failed and needed to be replaced.
Because of its use of transistors, the TRADIC requires less than 100 watts of power to operate its processing capabilities, which is one-twentieth the power needed to operate a similar computer design using vacuum tubes.
Of course, space aboard a supersonic jet is at a premium.
The airborne TRADIC computer occupied three cubic feet, which is equivalent to a moving box measuring 18 1/8-inches by 18-inches by 16-inches.
The airborne TRADIC performed 62,500 basic computations per second using its 1 MHz processor clock.
The TRADIC operated the jets transistorized radar, onboard encoding and decoding devices, its decimal display devices, the jet’s instruments, and navigation equipment.
Its command instructions are coded in single address memory blocks along with other data and are stored in the computer’s internal memory magnetic drum registers.
Although it was 65 years ago, the familiar computer input, output, memory, arithmetic, and control functions were designed into this all-transistor digital computer.
I read a 1955 report by J.H. Felker, titled “Performance of TRADIC Transistor Digital Computer.”
In the report, I noted the diodes used in the TRADIC were manufactured by the Hughs Organization, not Western Electric, which at the time was the equipment manufacturing arm of the Bell Telephone System.
Felker said the transistorized digital computer required a unique diode that could recover rapidly.
“We were delighted when they came out. Western does not make a diode that would do our job,” Felker wrote.
He stated there are five or six different types of diodes used with the TRADIC and was happy “the Hughs people were willing and anxious to make diodes to our specifications.”
Felker preferred wire-wrapping instead of soldering within the TRADIC. He felt wire-wrapping provided a better physical connection.
He also talked about his interest in “printed circuit cables,” which probably seemed a bit futuristic 65 years ago.
In 1945, after having served in the US Army during WWII, Felker worked on computer circuitry at the Bell Telephone Military Systems Laboratory in Whippany, NJ.
The National Academy of Engineering elected Felker to membership in 1973, citing him for "design of the first transistorized digital computer and for the engineering of digital systems."
In 1962, he became a founding director of Bellcomm, Inc., an engineering organization working with NASA.
Bellcomm, Inc. was directly responsible for systems engineering, analysis, and overall spacecraft integration for the Apollo moon landing program.
Jean H. Felker passed away on Feb. 27, 1994, in Durham, PA.
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| Tail section of an Air Force plane. The cargo door is open and inside is the TRADIC computer with three men, in suits, looking at manuals |
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| TRADIC computer inside the tail section of an Air Force jet. |
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| Transistor is inserted into one of TRADIC's "memory" packages. |