Retrotechtacular: Supersonic Transport Initiatives

In the early days of PBS member station WGBH-Boston, they in conjunction with MIT produced a program called Science Reporter. The program’s aim was explaining modern technological advances to a wide audience through the use of interviews and demonstrations. This week, we have a 1966 episode called “Ticket Through the Sound Barrier”, which outlines the then-current state of supersonic transport (SST) initiatives being undertaken by NASA.

MIT reporter and basso profondo [John Fitch] opens the program at NASA’s Ames research center. Here, he outlines the three major considerations of the SST initiative. First, the aluminium typically used in subsonic aircraft fuselage cannot withstand the extreme temperatures caused by air friction at supersonic speeds. Although the Aérospatiale-BAC Concorde was skinned in aluminium, it was limited to Mach 2.02 because of heating issues. In place of aluminium, a titanium alloy with a melting point of 3,000°F is being developed and tested.

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Retrotechtacular: Ma Bell’s Advanced Mobile Phone Service (AMPS)

This gem from the AT&T Archive does a good job of explaining the first-generation cellular technology that AT&T called Advanced Mobile Phone Service (AMPS). The hexagon-cellular network design was first conceived at Bell Labs in 1947. After a couple of decades spent pestering the FCC, AT&T was awarded the 850MHz band in the late 1970s. It was this decision coupled with the decades worth of Bell System technical improvements that gave cellular technology the bandwidth and power to really come into its own.

AT&T’s primary goals for the AMPS network were threefold: to provide more service to more people, to improve service quality, and to lower the cost to subscribers. Early mobile network design gave us the Mobile Service Area, or MSA. Each high-elevation transmitter could serve a 20-mile radius of subscribers, a range which constituted one MSA. In the mid-1940s, only 21 channels could be used in the 35MHz and 150MHz band allocations. The 450MHz band was introduced in 1952, provided another 12 channels.

repeated channelsThe FCC’s allocation opened a whopping 666 channels in the neighborhood of 850MHz. Bell Labs’ hexagonal innovation sub-divided the MSAs into cells, each with a radius of up to ten miles.

The film explains quite well that in this arrangement, each cell set of seven can utilize all 666 channels. Cells adjacent to each other in the set must use different channels, but any cell at least 100 miles away can use the same channels. Furthermore, cells can be subdivided or split. Duplicate frequencies are dealt with through the FM capture effect in which the weaker signal is suppressed.

Those Bell System technical improvements facilitated the electronic switching that takes place between the Mobile Telephone Switching Office (MTSO) and the POTS landline network. They also realized the automatic control features required of the AMPS project, such as vehicle location and automatic channel assignment. The film concludes its lecture with step-by-step explanations of inbound and outbound call setup where a mobile device is concerned.

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Retrotechtacular: The Construction of Wooden Propellers

During World War I, the United States felt they were lagging behind Europe in terms of airplane technology. Not to be outdone, Congress created the National Advisory Committee for Aeronautics [NACA]. They needed to have some very large propellers built for wind tunnel testing. Well, they had no bids, so they set up shop and trained men to build the propellers themselves in a fantastic display of coordination and teamwork. This week’s film is a silent journey into [NACA]’s all-human assembly line process for creating these propellers.

Each blade starts with edge-grained Sitka spruce boards that are carefully planed to some top-secret exact thickness. Several boards are glued together on their long edges and dried to about 7% moisture content in the span of five or so days. Once dry, the propeller contours are penciled on from a template and cut out with a band saw.

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Retrotechtacular: The (Long, Arduous) Birth of a Tank

Throughout the 1950s and early 1960s, the United States Army provided regular status reports to both its interior members and the American public through a half-hour documentary television show called The Big Picture. Since the program was produced by the government, every episode immediately entered the public domain. This particular report tells the story of the T-48 project that culminated in the 90mm M48 Patton tank.

The film opens by providing a brief history of tanks and the lessons learned about them between WWI and the Korean War. The Army sought a more robust vehicle that could handle a wide variety of climates and terrain, and so the process of information gathering began. After a series of meetings at the Pentagon in which all parties involved explored every facet, the project was approved, and a manila folder was officially designated to the project and labeled accordingly.

vesselsWe then tour the R&D facility where new tank materials and components are developed and tested. It is here that the drive gears are put through their paces on a torsion machine. Air cleaners are pitted against each other to decide which can filter out the finest dust and sand. After careful analysis, different tank shell materials are test welded together with various, well-documented electrodes, and these panels are taken outside so their welds can be directly fired upon.

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Retrotechtacular: How to Teletypewriter

This week, you’re going to learn the ins and outs of the AN/GRC-46 thanks to this army training film from 1963. What is the AN/GRC-46, you ask? Why it’s a complete mobile-tactical sheltered radio-teletypewriter rig capable of CW, voice, and teletype transmission.

The film covers the components that make up the AN/GRC-46, their functions, the capabilities of the system, and proper operation procedures. There’s a lot going on in the tiny 1400lb. steel shelter, so each piece will be introduced from the ground up.

You’ll become familiar with the voltage distribution system and the AN/GRC-46’s included accessories. This introduction will be followed by a short course in RF signal transmission and the Frequency-Shift Keying (FSK) that is performed by the modulator. The ranges of both the transmitter and receiver are discussed, along with the capabilities mentioned before: CW operation using the keyer, voice operation, teletype operation, and reperforation of teletype tape.

Finally, you’ll observe a seasoned operator make contact and send a teletype message with movements so careful and deliberate that they border on mesmerizing. When he’s not sending messages or taking long walks on the beach, he can usually be found cleaning and/or lubricating the transmitter filter.

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Retrotechtacular: The Jet Story

A plane from Britain is met in the US by armed security. The cargo? An experimental engine created by Air Commodore [Frank Whittle], RAF engineer air officer. This engine will be further developed by General Electric under contract to the US government. This is not a Hollywood thriller; it is the story of the jet engine.

The idea of jet power started to get off the ground at the turn of the century. Cornell scholar [Sanford Moss]’ gas turbine thesis led him to work for GE and ultimately for the Army. Soon, aircraft were capable of dropping 2,000 lb. bombs from 15,000 feet to cries of ‘you sank my battleship!’, thus passing [Billy Mitchell]’s famous test.

The World War II-era US Air Force was extremely interested in turbo engines. Beginning in 1941, about 1,000 men were working on a project that only 1/10 were wise to. During this time, American contributions tweaked [Whittle]’s design, improving among other things the impellers and rotor balancing. This was the dawn of radical change in air power.

Six months after the crate arrived and the contracts were signed, GE let ‘er rip in the secret testing chamber. Elsewhere at the Bell Aircraft Corporation, top men had been working concurrently on the Airacomet, which was the first American jet-powered plane ever to take to the skies.

In the name of national defense, GE gave their plans to other manufacturers like Allison to encourage widespread growth. Lockheed’s F-80 Shooting Star, the first operational jet fighter, flew in June 1944 under the power of an Allison J-33 with a remarkable 4,000 pounds of thrust.

GE started a school for future jet engineers and technicians with the primary lesson being the principles of propulsion. The jet engine developed rapidly from this point on.

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Retrotechtacular: Fire Control Computers in Navy Ships

Here is a two-part Navy training film from 1953 that describes the inner workings of mechanical fire control computers. It covers seven mechanisms: shafts, gears, cams, differentials, component solvers, integrators, and multipliers, and does so in the well-executed fashion typical of the era.

Fire control systems depend on many factors that occur simultaneously, not the least of which are own ship’s speed and course, distance to a target, bearing, the target’s speed and course if not stationary, initial shell velocity, and wind speed and direction.

The mechanisms are introduced with a rack and pinion demonstration in two dimensions. Principally speaking, a shaft carries a value based on revolutions. From this, a system can be geared at different ratios.

Cams take this idea further, transferring a regular motion such as rotation to an irregular motion. They do so using a working surface as input and a follower as output. We are shown how cams change rotary motion to linear motion. While the simplest example is limited to a single revolution, additional revolutions can be obtained by extending the working surface. This is usually done with a ball in a groove.

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