A Peek Inside A 747 Fuel Gauge

It isn’t that often that we civilians get the chance to closely examine the fantastic internals that make up the modern marvels of avionic engineering. Luckily for us, [Glen] got his hands on a 747 fuel gauge and tore it down for our benefit. Not only does he tear it down, but he also builds a controller to display values.

Unlike your typical automotive fuel gauge that reports the distance from the top of the tank to the fuel level, this gauge reports the number of pounds of fuel. The fact that the indicator pictured above can go all the way to 95,000 pounds of fuel hits home the sheer scale of the fuel tanks on a 747 compared to your Volvo. Of course, where this gets interesting is the teardown with the metal sleeve removed. A 400 HZ AC servo motor moves the pointer and counter through the gearing with the help of a feedback potentiometer. The resistance tolerance is only 3%, as there are adjustment knobs on the back. But the linearity spec is only 0.06%, putting this part in a different grade from most pots.

One of the indicators was in worse shape than the others, so [Glen] got to work tapping into the internals of the gauge to drive the motor directly. A custom AC power supply repurposed from another project provided power, and a Raspberry Pi Pico was the PID controller. For [Glen], it isn’t all roses. Unfortunately, a noisy spot around 22,500 prevents accurate placement around there.

The code is up on GitHub, and we love having a gauge on the desk to show whatever value we like. If you are curious about more 747 instruments, this retro control unit might interest you.

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Virgin Orbit’s First UK Launch Attempt: What Went Wrong

A month ago there was disappointment as Virgin Orbit’s first attempt at a space launch from the United Kingdom using its converted Boeing 747 airliner platform failed to achieve orbit. Now with the benefit of a lot of telemetry analysis the company have released their findings, which conclude that a fuel filter within the second stage became dislodged. The resulting fuel starvation was enough to cause the engine to receive insufficient cooling and overheat, bringing the mission to a premature end.

As we said at the time, the interesting part of the launch, midair from the 747, appears to have gone flawlessly. Space exploration is hard, and we are confident that they’ll fix any fuel filter mounting issues on future launches and be placing payloads in orbit for their customers soon afterwards. The whole program has seen significant news coverage in the UK where the craft has its base, and those of us in that environ will no doubt see it portrayed locally as a matter of national pride. The truth however will be that it flies on the talents of engineers from all corners of the world. We’ll be watching out next time, and look forward to a successful mission.

Header: Österreichisches Weltraum Forum, CC BY-SA 4.0.

Virgin Not-Quite-Orbit-Yet

A country’s first orbital satellite launch from home soil is a proud moment, even when as is the case with Virgin Orbit, it’s not from the soil itself but from a Boeing 747 in the stratosphere over the sea. The first launch of the under-wing rocket took place yesterday evening, and pretty much every British space enthusiast gathered round the stream to watch history being made somewhere over the Atlantic south of Ireland. Sadly for all of us, though the launch itself went well and the rocket reached space, it suffered an anomaly in its second stage and failed to reach orbit.

No doubt we will hear more over the coming days as we’re sure they have a ton of telemetry data to work through before they find a definitive answer as to what happened. Meanwhile it’s worth remembering that the first launch of a new platform is a test of a hugely complex set of systems, and this one is certainly not the first to experience problems. It’s the under-wing launch that’s the interesting bit here, and in that we’re glad to see that part of the mission as a success. We know there will be a secomd launch and then many more, as not just the UK’s but Europe’s first launch platform from native soil becomes a viable and hopefully lower-cost launch option than its competitors.

People with very long memories will remember that this wasn’t the first time a British satellite launch attempt failed at the second stage and then went on to launch successfully, but Black Arrow launched Prospero back in 1971 from the Australian outback rather than the chilly North Atlantic.

Header: Österreichisches Weltraum Forum, CC BY-SA 4.0.