Will The Lilium Jet Work? A Deep-Dive Into The Physics Behind EVTOL Aircraft

June 22, 2023 by 26 Comments

The Lilium Jet is a proposed eVTOL (electric Vertical Take Off and Landing) aircraft that the German company Lilium GmbH has claimed it will bring to the market ‘soon’, which would made it the first eVTOL aircraft in the world to enter into commercial service. As anyone who has any experience with VTOL knows, it’s a tricky subject to engineer, let alone when you want to do it fully electric. In a deep-dive video on the Lilium Jet and eVTOL in general, [John Lou] goes through the physics behind VTOL take-off, landing and flight, as well as range and general performance.

It is clear that Lilium’s presented aircraft concept has many issues, some of which are due to new and unproven technologies, while others seem to be founded in over-promising and likely under-delivering. With Lilium having signed a number of contracts to deliver the first Pioneer Edition Lilium Jets and commercial service promised by 2025, it’s hard to ignore that the first full prototype of the 7-seater Lilium Jet is supposed to fly this year.

Although as [John] points out in the video, eVTOL is not an impossible concept, it is important to remain realistic about what is physically possible, and not seek to push the boundaries. When the UK introduced its first mass-produced VTOL jet in the form of the Harrier, it too faced an uncomfortable time as bugs got ironed out. As these eVTOL aircraft would be carrying real human passengers, it’s a good place to realize that although you can pick a fight with physics, you will never come out on the winning side.

Hopefully Lilium realizes this too, and these sleek, battery-powered aircraft will truly take to the skies in a few years.

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An HP9863C partially disassembled on a workbench

Repairing A $25,000 HP Workstation To Run Pac-Man

June 20, 2023 by 21 Comments

The microcomputer revolution of the 1970s and 1980s turned computers from expensive machines aimed at professionals into consumer products found in the average household. But there always remained a market for professional users, who bought equipment that was so far ahead of consumer gear it seemed to belong in a different decade. While a home computer enthusiast in 1981 might fork out a few hundred dollars for an 8-bit machine with 64 KB of memory, a professional could already buy a 32-bit workstation with 2.8 megabytes of RAM for the price of a brand-new sports car. [Tech Tangents] got his hands on one of those machines, an HP Series 200 9863C from 1981, and managed to get it up and running.

The machine came in more-or-less working condition. The display cable turned out to be dodgy, but since it was just a straight-through sub-D cable it was easily replaced. Similarly, the two 5.25″ floppy drives were standard Tandon TM100-2As which [Tech Tangents] had some experience in repairing, although these specific units merely needed a thorough cleaning to remove forty years’ worth of dust. Continue reading “Repairing A $25,000 HP Workstation To Run Pac-Man“ →

Teardown Of An Aircraft Video Symbol Generator

June 19, 2023 by 17 Comments

[Adrian Smith] recently scored an avionics module taken from a British Aerospace 146 airliner and ripped it open for our viewing pleasure. This particular aircraft was designed in the early 1980s when the electronics used to feed the various displays in the cockpit were very different from modern designs. This particular box is called a ‘symbol generator’ and is used to generate the various real-time video feeds that are sent to the cockpit display units. Various instruments, for example, the weather radar, feed into it, and it then reformats the video if needed, mixing in any required additional display.

Top view of the symbol generator instrument rack

There are many gold-plated chips on these boards, which indicates these may be radiation-hardened versions of familiar devices, most of which are 54xx series logic. 54xx series logic is essentially the same functionally as the corresponding 74xx series, except for the much wider operating temperature range mandated by military and, by extension, commercial aviation needs. The main CPU board appears to be based around the Intel 8086, with some Zilog Z180 compatible processors used on the two video display controller boards. We noted the Zilog Z0853604, which is their counter/timer/GPIO chip. Obviously, there are many custom ASICs produced by Honeywell as well as other special order items that you’ll never find the datasheet for. Now there’s a challenge!

Finally, we note the standard 400 Hz avionics-standard power supply, which, as some may know, is the standard operating frequency for the AC power system used within modern aircraft systems. The higher frequency (compared to 50 or 60 Hz) means the magnetic components can be physically smaller and, therefore, lighter for a given power handling capability.

We see a lot of avionics teardowns, likely because they’re fascinating. Here’s some more British military gear, an interesting RF distance measuring box from the 1970s, and finally, some brave soul building their own avionics gear. What could possibly go wrong?

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Ham Pairs Nicely With GMRS

June 17, 2023 by 37 Comments

Ignoring all of the regulations, band allocations, and “best amateur practices,” there’s no real fundamental difference between the frequencies allocated to the Family Radio Service (FRS), the General Mobile Radio Service (GMRS), the Multi-Use Radio Service (MURS), and the two-meter and 70-centimeter bands allocated to licensed ham radio operators. The radio waves propagate over relatively short distances, don’t typically experience any skip, and are used for similar activities. The only major difference between these (at least in the Americas or ITU region 2) is the licenses you must hold to operate on the specific bands. This means that even though radios are prohibited by rule from operating across these bands, it’s often not too difficult to find radios that will do it anyway.

[Greg], aka [K4HSM], was experimenting with a TIDRADIO H8 meant for GMRS, which in North America is a service used for short-range two-way communication. No exams are required, but a license is still needed. GMRS also allows for the use of repeaters, making it more effective than the unlicensed FRS. GMRS radios, this one included, often can receive or scan frequencies they can’t transmit on, but in this case, the limits on transmitting are fairly easy to circumvent. While it isn’t allowed when programming the radio over Bluetooth, [K4HSM] found that programming it from the keypad directly will allow transmitting on the ham bands and uses it to contact his local two-meter and 70-cm repeaters as a proof-of-concept.

The surprising thing about this isn’t so much that the radio is physically capable of operating this way. What’s surprising is that this takes basically no physical modifications at all, and as far as we can tell, that violates at least one FCC rule. Whether or not that rule makes any sense is up for debate, and it’s not likely the FCC will break down your door for doing this since they have bigger fish to fry, but we’d definitely caution that it’s not technically legal to operate this way.

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Tree Planting Festivals, Air Cannons, Self-Burying Seeds, And The Complexities Of Reforestation

June 8, 2023 by 20 Comments

At first glance the problem of how to plant trees would seem to be a straightforward one: take a seed, jam it into the soil and let nature take its course. Or alternatively do much the same with a sapling that already got a start in a nice, comfortable greenhouse before leaving it to its own devices. To the average person this is generally the point where it’s considered a ‘done deal’, but one only has to take a look at the average survival rate of saplings out in the wild to perish that thought.

Each environment offers its own set of challenges when it comes to reforestation, which can perhaps be considered ironic as many of these trees are being planted where forests used to be, albeit centuries ago in many cases. There are the easy spots, such as flat fields, with rich soil, ample rain and mild weather, to the challenging terrain of Iceland, or mountainous terrain. Here the logistics are challenging and where once rich forests flourished, the very landscape seems adamant to reject this botanic intrusion.

Further complicating matters here are the myriad of reasons why we’re looking at planting so many new trees that it has even become an internet thing, as with the 2019 ‘Team Trees’ 20 million new trees challenge. So how did we get here, why exactly are we doing all of this, and how much of these attempts do bear fruit?

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Bike Rides Played Back Via Aircraft Altitude Indicator

June 3, 2023 by 7 Comments

Any good bike ride should have a big climb to push your fitness, and a nice descent for the joy of careening down at high speed. [Glen Akins] has been recording his altitude during his mountain biking expeditions, and has now built a way to play them back on an aircraft altitude indicator.

A Python script is used to parse a recorded GPX file, which stores position and elevation data captured from a GPS device during [Glen]’s rides. The elevation data is then output to a Raspberry Pi Pico, which drives a set of three Microchip MCP4802 DACs and three TI OPA584 op-amps in order to create the necessary 400 Hz AC waveforms to drive the aircraft altitude indicator. One DAC and op-amp are used to generate 400 Hz AC to simply power the device, while the other two are used to generate synchro signals to actually drive the dial as needed. The maths involved is worth checking out, particularly if you’re into old-school instrumentation from the 20th century.

We’ve seen similar tinkering efforts from [Glen] before, too.

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A blue work tricycle (single front wheel with platform between two rear wheels) sits on an asphalt path with trees and wildflowers in the background. A boxy, white camper with a front overhanging the bike seat is attached to the platform. It has a yellow stripe and curtains like many campers did in the 1970s. One white male is exiting the door of the camper while his brother is standing to the left of the camper by the bike seat.

Bike Camper With Retro Flair

May 23, 2023 by 33 Comments

As we’re approaching summer here in the Northern Hemisphere, thoughts naturally turn toward road trips. While most people do this in their car, the [Dangie Bros] built a 500 lb bike camper for their own take on the great American Road Trip.

Taking a maximalist approach not seen in most bike campers, this behemoth has a working sink, propane stove, seating area, and an upstairs sleeping area. A small window in the front of the camper opens to let the passenger inside converse with the person pedaling, and a solar panel charges a small battery for lights and a roof fan.

While the camper is very ’70s retro-chic, its lack of assist (other than the passenger getting out to push) meant that on the second day of their road trip they resorted to towing the camper behind a second bike in a pseudo-tandem arrangement. The fold out bed takes some design cues from RVs, but clearly needed more reinforcement since it collapsed partway through the night. With an e-assist and some refinements, this could be comfortable (albeit slow) way to go bike glamping.

If you’d like to try your own hand at a bike camper but do it more aerodynamically and attached to an assisted bike, checkout this teardrop trailer or this bike camper.

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