The Zero-Power Flight Computer

March 23, 2026 by Al Williams 8 Comments

In the early days of aviation, pilots or their navigators used a plethora of tools to solve common navigation and piloting problems. There was definitely a need for some kind of computing aid that could replace slide rules, tables, and tedious dead-reckoning computations. This would become even more important during World War II, when there was a massive push to quickly train young men to be pilots.

The same, but different. A Pickett slide rule (top) and an E6B slide rule (bottom). (Own Work).

Today, we’d whip up some sort of computer device, but in the 1930s, computers weren’t anything you’d cram on a plane, even if they’d had any. For example, the Mark 1 Fire Control Computer during WW2 was 3,000 pounds of gears and motors.

The computer is made to answer flight questions like “how many pounds of fuel do I need for another hour of flying time?” or “How do I adjust my course if I have a particular crosswind?”

History

There were a rash of flight computers starting in the 1920s that were essentially specialized slide rules. The most popular one appeared in the late 1930s. Philip Dalton’s circular slide rule was cheap to produce and easy to use. As you’ll see, it is more than just an ordinary slide rule. Keep in mind, these were not computers in the sense we think of today. They were simple slide rules that easily did specialized math useful to pilots.

Dalton actually developed a number of computers. The popular Model B appeared in 1933, and there were refinements leading to additional models. The Mark VII was very popular. Even Fred Noonan, Amelia Earhart’s navigator, used a Mark VII. Continue reading “The Zero-Power Flight Computer” →

The Rise And Fall Of Free Dial Up Internet

March 18, 2026 by Al Williams 45 Comments

In the early days of the Internet, having a high-speed IP connection in your home or even a small business was, if not impossible, certainly a rarity. Connecting to a computer in those days required you to use your phone. Early modems used acoustic couplers, but by the time most people started trying to connect, modems that plugged into your phone jack were the norm.

The problem was: whose computer did you call? There were commercial dial-up services like DIALOG that offered very expensive services, such as database searches via modem. That could be expensive. You had a fee for the phone. Then you might have a per-minute charge for the phone call, especially if the computer was in another city. Then you had to pay the service provider, which could be very expensive.

Even before the consumer Internet, this wasn’t workable. Tymnet and Telenet were two services that had the answer. They maintained banks of modems practically everywhere. You dialed a local number, which was probably a “free” call included in your monthly bill, and then used a simple command to connect to a remote computer of your choice. There were other competitors, including CompuServe, which would become a major force in the fledgling consumer market.

While some local internet service providers (ISPs) had their own modem banks, when you saw the rise of national ISPs, they were riding on one of several nationwide modem systems and paying by the minute for the privilege. Eventually, some ISPs reached the scale that made dedicated modem banks worthwhile. This made it easier to offer flat-rate pricing, and the presumed likelihood of everyone dialing in at once made it possible to oversubscribe any given number of modems.

The Cost

Once consumer services like CompuServe, The Source, and AOL started operations, the cost was less, but still not inexpensive. Some early services charged higher rates during business hours, for example. There was also the cost of a phone line, and if you didn’t want to tie up your home phone, you needed a second line dedicated to the modem. It all added up.

By the late 1990s, a dial-up provider might cost you $25 a month or less, not counting your phone line. That’s about $60 in today’s money, just for reference. But the Internet was also booming as a place to sell advertising.

Continue reading “The Rise And Fall Of Free Dial Up Internet” →

Preparing To Fire Up A 90-Year-Old Boiler After Half A Century

March 17, 2026 by Maya Posch 4 Comments

Continuing the restoration of the #1 Lancashire boiler at the Claymills Pumping Station in the UK, the volunteers are putting on the final touches after previously passing the boiler inspection. Although it may seem that things are basically ready to start laying down a fire after the boiler is proven to hold 120 PSI with all safeties fully operating, they first had to reassemble the surrounding brickwork, free up a seized damper shaft and give a lot of TLC to mechanisms that were brand new in the 1930s and last operated in 1971.

Removing the ashes from a Lancashire boiler. (Credit: Claymills pumping station, YouTube)

The damper shaft is part of the damper mechanism which controls doors that affect the burn rate, acting as a kind of throttle for the boilers. Unfortunately the shaft’s bearings had seized up completely, and no amount of heat and kinetic maintenance could loosen it up again. This forced them to pull it out and manufacture a replacement, but did provide a good look at how it’s put together. The original dial indicator was salvaged, along with some other bits that were still good.

Next was to fit the cast-iron ash boxes that sit below the boiler and from where ash can be scraped out and deposited into wheelbarrows. The automatic sprinkler stokers are fitted above these, with a good look at their mechanism. The operator is given a lot of control over how much coal is being fed into the boiler, as part of the early 20th-century automation.

The missing furnace doors on the #1 boiler were replaced with replicas based on the ones from the other boilers, and some piping around the boiler was refurbished. Even after all that work, it’ll still take a few weeks and a lot more work to fully reassemble the boiler, showing just how complex these systems are. With some luck it’ll fire right back up after fifty years of slumbering and decades of suffering the elements.

Continue reading “Preparing To Fire Up A 90-Year-Old Boiler After Half A Century” →

Fictional Moon: Reality TV And SciFi Don’t Mix

March 17, 2026 by Al Williams 33 Comments

It is a safe bet that nearly all Hackaday readers like to at least imagine what it would be like to build and live in an orbital station, on the moon, or on another planet. Moon bases and colonies show up all the time in fictional writing and movies, too. For the Hackaday crowd, some of these are plausible, and others are — well — a bit fanciful. However, there’s one fictional moonbase that we think might have been too realistic: Moonbase 3.

If that didn’t ring a bell, we aren’t surprised. The six-episode series was a co-production between Twentieth Century Fox and the BBC that aired in 1973. To make matters worse, after the initial airings in the UK, Australia, and New Zealand, the video master tapes were wiped out. Until 1993, there were no known copies of the show, but then one turned up in a US television station.

The show had many links to Dr. Who and, in fact, if you think the spacesuits look familiar, they made later appearances in two Dr. Who episodes.

Continue reading “Fictional Moon: Reality TV And SciFi Don’t Mix” →

The Shockley 4-Layer Diode In 2026

March 14, 2026 by Jenny List 10 Comments

The physicist William Shockley is perhaps today best known for three things: his role in the invention of the transistor, his calamitous management of Shockley Semiconductor which led to a mass defection of employees and precipitated the birth of the Silicon Valley we know, and his later descent into promoting eugenics. This was not the sum of his work though, and [David Prutchi] has been experimenting with a now-mostly-forgotten device that bears the Shockley name (PDF), after finding one used in an early heart pacemaker circuit. His findings are both comprehensive and fascinating.

The Shockley diode, or 4-layer diode as it later became known, is as its name suggests a two terminal device with a 4-layer NPNP structure. It can be modeled as a pair of complementary transistors in parallel with a reverse biased diode, and the avalanche breakdown characteristics of that diode when a particular voltage is applied to it provide the impetus to turn on the two transistors. This makes it a voltage controlled switch, that activates when the voltage across it reaches that value.

The PDF linked above goes into the Shockley diode applications, and in them we find a range of relaxation oscillators, switches, and logic circuits. The oscillators in particular could be made with the barest minimum of components, important in a time when each semiconductor device could be very expensive. It may have faded into obscurity as it was superseded by more versatile 4-layer devices such as the PUJT or silicon-controlled switch and then integrated circuits, but he makes the point that its thyristor cousin is still very much with us.

This appears to be the first time we’ve featured a 4-layer diode, but we’ve certainly covered the genesis of the transistor in the past.

The “Tin Blimp” Was A Neither Tin Nor A Blimp: The Detroit ZMC-2 Story

March 10, 2026 by Tyler August 31 Comments

That fireball was LZ37. Nobody wanted to see repeats post-war.
Image: “The great exploit of lieutenant Warnefort 1916 England” by Gordon Crosby, public domain.

After all the crashing and burning of Imperial Germany’s Zeppelins in the later part of WWI – once the Brits managed to build interceptors that could hit their lofty altitude, and figured out the trick of using incendiary rounds to set off the hydrogen lift gas – there was a certain desire in airship circles to avoid fires. In the USA, that mostly took the form of replacing hydrogen with helium. Sure, it didn’t lift quite as well, but it also didn’t explode.

Still, supplies of helium were– and are– very much limited, and at least on a rigid Zeppelin, the hydrogen wasn’t even the most flammable part. As has become widely known, thanks in large part to the Mythbusters episode about the Hindenburg disaster, the doped cotton skin in use in those days was more flammable than some firestarters you can buy these days.

That’s a problem, because, as came up in the comments of our last airship article, rigid airships beat blimps largely on Rule of Cool. Who invented the blimp? Well, arguably it was Henri Griffard with his steam-driven balloon in 1857, but not many people have ever heard his name. Who invented the rigid airship? You know his name: Ferdinand Adolf Heinrich August Graf von Zeppelin. No relation. Probably. Well, admittedly most people don’t know the full name, but Count Zeppelin is still practically a household name over a century after his death. His invention was just that much cooler.

That unavoidable draw of coolness led to the Detroit Airship Company and their amazing tin blimp. The idea was the brainchild of a man named Ralph Upton, and is startling in its simplicity: why not take the all-metal, monocoque design that was just then being so successfully applied to heavier-than-air flight, and use it to build an airship? Continue reading “The “Tin Blimp” Was A Neither Tin Nor A Blimp: The Detroit ZMC-2 Story” →

Hiding A Bomb In Plain Sight

March 7, 2026 by Al Williams 38 Comments

You are at war. Trains are key to keeping your army supplied with fuel, ammunition, food, and medical supplies. But, inexplicably, your trains keep blowing up. Sabotage? Enemy attack? There’s no evidence of a bomb or overt enemy attack. This is the situation the German military found itself in during World War II. As you can see in the video below, the hidden bomb was the brainchild of a member of Britain’s SOE.

The idea was to put plastic explosive inside a fake plastic lump of coal. They hand-painted each one, and the color had to match the exact appearance of local coal. Paint and coal dust helped with that. The bomb had to weigh the correct amount as well.

The coal was safe until it got quite hot, so resistance fighters could easily carry the coal and surreptitiously drop the bomb anywhere coal is stored. Eventually, it will be put in a boiler, and at the right temperature, it will do its job. There’s some actual footage of a test in the second video below.

Continue reading “Hiding A Bomb In Plain Sight” →