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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Retrotechtacular: Blue Collar, Red Nightmare

This week’s presentation is a well-cast piece of anti-Communist propaganda perpetrated by a division of the DoD that you’ve probably never heard of: the Directorate for Armed Forces Information and Education.

It’s narrated by Jack Webb of Dragnet and Adam-12 fame. He tells us of a fake American town located somewhere behind the Iron Curtain. It’s full of young comrades who sock hop and bebop while studying and playacting the bourgeoisie activities of the American economy and way of life. After introducing this, Webb pulls back the cushy, velvet curtain to profile a typical American household led by one [Jerry Donavan].

[Jerry] has it all: a wise-cracking wife played by Jeanne Cooper (most notably of The Young and the Restless), a son with a healthy interest in war games, a young daughter with pretty blond hair, and a beautiful older daughter who would go on to fame up the road at Petticoat Junction. After some unsettling news from this daughter at the dinner table, Jerry heads up to bed early to catch a few Zs.

Jack Webb denies [Jerry] any visions of sugar plums and instead drops him in the middle of Fakesville, USSR for a vivid nightmare of an America reconstructed by Communism. Watch as he figures out what’s going on and what the new regime means for him and his good-looking family.

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Retrotechtacular: Core Competencies

As the dashing officer shown above will tell you, early data processing machines and ADP systems employed two types of magnetic cores for memory and other purposes. This 1961 U.S. Army training film is an introduction to the properties of ferrite cores, which are commonly made from nickel alloy and other magnetic materials. As this is only part one of a series, the metallic ribbon type of magnetic core is covered in some other segment we have yet to locate.

The use of magnetic cores for random access memory was built upon transformer theory and provided a rugged and low-power solution until the semiconductor came into vogue. Before that time, the humble ferrite core served many uses and did so very well. The Apollo Guidance Computer had erasable magnetic core memory, and much of its software was stored in core rope memory.

binary 1The film covers a lot of theory and does so clearly and concisely. It begins by explaining what a magnetic core is and why it’s used, and then moves on to describe how the cores are used to store bits and the method by which they can transfer information to other cores. Along the way, it provides background on bi-stable devices and provides explanation of magnetization behavior in terms of magnetizing force and flux density.

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