Scramjet Engines on the Long Road to Mach 5

When Charles “Chuck” Yeager reached a speed of Mach 1.06 while flying the Bell X-1 Glamorous Glennis in 1947, he became the first man to fly faster than the speed of sound in controlled level flight. Specifying that he reached supersonic speed “in controlled level flight” might seem superfluous, but it’s actually a very important distinction. There had been several unconfirmed claims that aircraft had hit or even exceeded Mach 1 during the Second World War, but it had always been during a steep dive and generally resulted in the loss of the aircraft and its pilot. Yeager’s accomplishment wasn’t just going faster than sound, but doing it in a controlled and sustained flight that ended with a safe landing.

Chuck Yeager and his Bell X-1

In that way, the current status of hypersonic flight is not entirely unlike that of supersonic flight prior to 1947. We have missiles which travel at or above Mach 5, the start of the hypersonic regime, and spacecraft returning from orbit such as the Space Shuttle can attain speeds as high as Mach 25 while diving through the atmosphere. But neither example meets that same requirement of “controlled level flight” that Yeager achieved 72 years ago. Until a vehicle can accelerate up to Mach 5, sustain that speed for a useful period of time, and then land intact (with or without a human occupant), we can’t say that we’ve truly mastered hypersonic flight.

So why, nearly a century after we broke the sound barrier, are we still without practical hypersonic aircraft? One of the biggest issues historically has been the material the vehicle is made out of. The Lockheed SR-71 “Blackbird” struggled with the intense heat generated by flying at Mach 3, which ultimately required it to be constructed from an expensive and temperamental combination of titanium and polymer composites. A craft which flies at Mach 5 or beyond is subjected to even harsher conditions, and it has taken decades for material science to rise to the challenge.

With modern composites and the benefit of advanced computer simulations, we’re closing in on solving the physical aspects of surviving sustained hypersonic flight. With the recent announcement that Russia has put their Avangard hypersonic glider into production, small scale vehicles traveling at high Mach numbers for extended periods of time are now a reality. Saying it’s a solved problem isn’t quite accurate; the American hypersonic glider program has been plagued with issues related to the vehicle coming apart under the stress of Mach 20 flight, which heats the craft’s surface to temperatures in excess of 1,900 C (~3,500 F). But we’re getting closer, and it’s no longer the insurmountable problem it seemed a few decades ago.

Today, the biggest remaining challenge is propelling a hypersonic vehicle in level flight for a useful period of time. The most promising solution is the scramjet, an engine that relies on the speed of the vehicle itself to compress incoming air for combustion. They’re mechanically very simple, and the physics behind it have been known since about the time Yeager was climbing into the cockpit of the X-1. Unfortunately the road towards constructing, much less testing, a full scale hypersonic scramjet aircraft has been a long and hard one.

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Low Tech High Safety and the NYC Subway System

The year is 1894. You are designing a train system for a large city. Your boss informs you that the mayor’s office wants assurances that trains can’t have wrecks. The system will start small, but it is going to get big and complex over time with tracks crossing and switching. Remember, it is 1894, so computing and wireless tech are barely science fiction at this point. The answer — at least for the New York City subway system — is a clever system of signals and interlocks that make great use of the technology of the day. Bernard S. Greenberg does a great job of describing the system in great detail.

The subway began operation in 1904, well over 30 years since the above-ground trains began running. A clever system of signals and the tracks themselves worked together with some mechanical devices to make the subway very safe. Even if you tried to run two trains together, the safety systems would prevent it.

On the face of it, the system is very simple. There are lights that show red, yellow, and green. If you drive, you know what these mean. But what’s really interesting is the scheme used at the time to make them light.

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Electrifying A Vintage Outboard Motor

Clamped or bolted to the stern of the boat, outboard motors offer a very easy and (relatively) economical way of powering small craft. The vast majority of these outboards are gasoline powered, with electric models generally limited to so-called “trolling motors” which are often used to move slowly and quietly during fishing. That might be fine for most people, but not [Olly Epsom].

An engineer focusing on renewable energy by profession, [Olly] wanted to equip his small inflatable dinghy with a suitably powerful “green” propulsion system. Deciding nothing on the market quite met his requirements, especially for what manufacturers were charging, he decided to convert an old gas outboard to electric. Not only did he manage to do it for less money than a turn-key system would have cost, but he ended up with a system specifically geared to his exact requirements. Something he says will come in handy if he ever gets around to converting the dinghy to remote control so he can use it as a wildlife photography platform.

Put simply, an outboard motor consists of a gasoline engine with a vertical shaft that’s coupled to a right-angle gearbox with a propeller on the end. Beyond that they’re a fairly “dumb” piece of gear, so replacing the engine on top with something else should be (at least in theory) a pretty simple job. Especially on the small older model that [Olly] decided to use as a donor unit. The 1974 Johnson 2 HP motor didn’t have any tricky electronics in it to contend with; the thing didn’t even have a clutch.

Once [Olly] had removed the old gas engine from the top of the outboard, he designed an adapter plate in OnShape and had it cut out of aluminum so he could mount a beefy 1 kW 48 V brushless electric motor in its place. Connecting the new electric motor to the carcass of the outboard actually ended up being simpler than putting the original motor on, as this time around he didn’t need to reconnect the cooling pumps which would usually pull water from down by the propeller and recirculate it through the engine.

While the mechanical aspects of this project are certainly cool, we’re especially interested in the control system for this newly electric outboard. It uses a 3.2 inch Nextion color touch screen and Arduino Nano to provide a very slick looking digital “dashboard” which can convey motor status and other information at a glance. Unfortunately, [Olly] says the details on that part of the project will be saved for a future post, leaving us with only a single picture of the system’s interface for us to drool over until then.

We’ve seen the occasional seafaring project that made use of an electric trolling motor, and we’ve even seen an electric drill put in some overtime spinning a prop in the water. Converting gasoline boat over to electric is however a rarity. But much like electric car conversions, such projects may become more common as the cost and complexity of powerful electric propulsion systems continues to fall.

[Thanks to Alex for the tip.]

A Quartet of Drills Put The Spurs To This Electric Utility Vehicle

Low-slung body style. Four-wheel drive. All electric drivetrain. Turns on a dime. Neck-snapping acceleration. Leather seating surface. Is it the latest offering from Tesla? Nope; it’s a drill-powered electric utility vehicle, and it looks like a blast to drive.

Surprisingly, this isn’t a just-for-kicks kind of build. There’s actually a practical reason for the low form factor and long range of [Axel Borg]’s little vehicle. We’ll leave the back story to the second video below, but suffice it to say that this will be a smaller version of the crawler NASA used to roll rockets out to the launch pad, used instead to transport his insanely dangerous looking manned-multicopter. The running gear on this vehicle is the interesting bit: four hefty electric drills, one for each of the mobility cart wheels. The drills are powered by a large series-connected battery pack putting out 260V at full charge. The universal motors of the drills are fine with DC, and the speed of each is controlled via the PWM signals from a pair of cordless drills. The first video below shows [Axel] putting it through its paces; he didn’t hold back at all, but the vehicle kept coming back for more.

We know this cart is in service to another project, but we’d have a hard time concentrating on anything if we had the potential for that much fun sitting in the shop. Still, we hope that multirotor gets a good test flight soon, and that all goes well with it.

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Adaptive Infotainment Plays Tunes To Match Your Dangerous Driving

Part of the fun of watching action movies is imagining yourself as the main character, always going on exciting adventures and, of course, being accompanied by the perfect soundtrack to score the excitement and drama of your life. While having an orchestra follow you around might not always be practical, [P1kachu] at least figured out how to get some musical orchestration to sync up with how he drives his car, Fast-and-Furious style.

The idea is pretty straightforward: when [P1kachu] drives his car calmly and slowly, the music that the infotainment system plays is cool and reserved. But when he drops the hammer, the music changes to something more aggressive and in line with the new driving style. While first iterations of his project used the CAN bus, he moved to Japan and bought an old Subaru that doesn’t have CAN. The new project works on something similar called Subaru Select Monitor v1 (SSM1), but still gets the job done pretty well.

The hardware uses an Asus Tinkerboard and a Raspberry Pi with the 7″ screen, and a shield that can interface with CAN (and later with SSM1). The new music is selected by sensing pedal position, allowing him to more easily trigger the aggressive mode that his previous iterations did. Those were done using vehicle speed as a trigger, which proved to be ineffective at producing the desired results. Of course, there are many other things that you can do with CAN bus besides switching up the music in your car.

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Improved Controller For E-Skateboards

[Timo] recently purchased himself a Acton Blink Qu4tro electric skateboard. Performance-wise, the board was great, but the controller left a lot to be desired. There were issues with pairing, battery displays, and just general rideability. Like any good hacker, he decided some reverse engineering was in order, and got to work.

Initial results were disheartening – the skateboard relies on various chips of Chinese origin for which documentation proved impossible to come by. However, as it turned out, the board and controller communicated using the common NRF24L01+ transceiver.

Initial work focused on understanding the pairing process and message protocol. With that done, [Timo] decided the best course of action was to redevelop a controller from scratch, using an Arduino Nano and NRF24L01+ to do the job. [Timo]’s Open esk8 controller improves driveability by removing delays in message transfer, as well as improving on the feel of the controller with a 3D printed chassis redesign.

[Timo] now has a much more usable skateboard, and has racked up over 200 miles in testing since the build. However, if you fancy converting your existing board to electric, check out this project.

Rebuilding an Extremely Rare Twin Mustang Fighter

Towards the end of the Second World War, as the United States considered their options for a possible invasion of Japan, there was demand for a new fighter that could escort long range bombers on missions which could see them travel more than 3,200 kilometers (2,000 miles) without refueling. In response, North American Aviation created the F-82, which essentially took two of their immensely successful P-51 fighters and combined them on the same wing. The resulting plane, of which only 272 were built, ultimately set the world record for longest nonstop flight of a propeller-driven fighter at 8,129 km (5,051 mi) and ended up being the last piston engine fighter ordered by the United States Air Force.

Today, only five of these “Twin Mustangs” are known to exist. One of those, a prototype XP-82 variant, is currently in the final stages of an epic decade-long rebuilding process directed by warbird restoration expert [Tom Reilly]. At the end of this painstaking restoration, which makes use of not only original hardware but many newly produced components built with modern technology such as CNC milling and 3D printing, the vintage fighter will become the only flyable F-82 in the world.

CNC milled replacement brake caliper

The project provides a fascinating look at what it takes to not only return a 70+ year old ultra-rare aircraft to fully functional status, but do it in a responsible and historically accurate way. With only four other intact F-82’s in the world, replacement parts are obviously an exceptional rarity. The original parts used to rebuild this particular aircraft were sourced from literally all over the planet, piece by piece, in a process that started before [Tom] even purchased the plane itself.

In a way, the search for parts was aided by the unusual nature of the F-82, which has the outward appearance of being two standard P-51 fighters, but in fact utilizes a vast number of modified components. [Tom] would keep an eye out for parts being sold on the open market which their owners mysteriously discovered wouldn’t fit on a standard P-51. In some cases these “defective” P-51 parts ended up being intended for the Twin Mustang project, and would get added to the collection of parts that would eventually go into the XP-82 restoration.

For the parts that [Tom] couldn’t find, modern manufacturing techniques were sometimes called in. The twin layout of the aircraft meant the team occasionally had one component but was missing its counterpart. In these cases, the original component could be carefully measured and then recreated with either a CNC mill or 3D printed to be used as a die for pressing the parts out of metal. In this way the team was able to reap the benefits of modern production methods while still maintaining historical accuracy; important on an aircraft where even the colors of the wires used in the original electrical system have been researched and faithfully recreated.

We’ve seen plenty of restorations here at Hackaday, but they tend to be of the vintage computer and occasionally Power Wheels variety. It’s interesting to see that the same sort of techniques we apply to our small scale projects are used by the pros to preserve pieces of history for future generations.

[Thanks to Daniel for the tip.]