Air-Breathing Rocket Engine Promises Future Space Planes

If you are a certain age, you probably remember the promise of supersonic transports. The Concorde took less than 4 hours to go across the Atlantic, but it stopped flying in 2003 and ended commercial supersonic passenger flights  But back in the 1970s, we thought the Concorde would give way not to older technology, but to newer. After all, man had just walked on the moon and suborbital transports could make the same trip in 30 minutes and — according to Elon Musk — go between any two points on the Earth in an hour or less. A key component to making suborbital flights as common as normal jet travel is a reasonable engine that can carry a plane to the edge of space. That’s where the UK’s Sabre engine comes into play. Part jet and part rocket, the engine uses novel new technology and two different operating modes to power the next generation of spaceplane. The BBC reports that parts of the new engine will undergo a new phase of testing next month.

The company behind the technology, Reaction Engines, Ltd, uses the engine in an air-breathing jet mode until it hits 5.5 times the speed of sound. Then the same engine becomes a rocket and can propel the vehicle at up to 25 times the speed of sound.

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Shushing Sonic Booms: NASA’s Supersonic X-Plane to Take Flight in 2021

The history of aviation is full of notable X-Planes, a number of which heralded in new generations of flight. The Bell X-1 became the first aircraft to break the speed of sound during level flight in 1947 with the legendary Charles “Chuck” Yeager at the controls. A few years later the X-2 would push man up to Mach 3, refining our understanding of supersonic flight. In the 1960’s, the North American built X-15 would not only take us to the edge of space, but set a world speed record which remains unbroken.

Compared to the heady post-war days when it seemed the sky was quite literally the limit, X-Planes in the modern era have become more utilitarian in nature. They are often proposed but never built, and if they do get built, the trend has been towards unmanned subscale vehicles due to their lower cost and risk. The few full-scale piloted X-Planes of the 21st century have largely been prototypes for new military fighter jets rather than scientific research aircraft.

But thanks to a commitment from NASA, the Lockheed Martin X-59 might finally break that trend and become another historic vehicle worthy of the X-Plane lineage. Construction has already begun on the X-59, and the program has recently passed a rigorous design and timeline overview by NASA officials which confirmed the agency’s intent to financially and logistically support the development of the aircraft through their Low Boom Flight Demonstrator initiative. If successful, the X-59 will not only help refine the technology for the next generation of commercial supersonic aircraft, but potentially help change the laws which have prevented such aircraft from operating over land in the United States since 1973.

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GE’s Engine to Reignite Civil Supersonic Flight

On October 24th, 2003 the last Concorde touched down at Filton Airport in England, and since then commercial air travel has been stuck moving slower than the speed of sound. There were a number of reasons for retiring the Concorde, from the rising cost of fuel to bad publicity following a crash in 2000 which claimed the lives of all passengers and crew aboard. Flying on Concorde was also exceptionally expensive and only practical on certain routes, as concerns about sonic booms over land meant it had to remain subsonic unless it was flying over the ocean.

The failure of the Concorde has kept manufacturers and the civil aviation industry from investing in a new supersonic aircraft for fifteen years now. It’s a rare example of commercial technology going “backwards”; the latest and greatest airliners built today can’t achieve even half the Concorde’s top speed of 1,354 MPH (2,179 km/h). In an era where speed and performance is an obsession, commercial air travel simply hasn’t kept up with the pace of the world around it. There’s a fortune to be made for anyone who can figure out a way to offer supersonic flight for passengers and cargo without falling into the same traps that ended the Concorde program.

With the announcement that they’ve completed the initial design of their new Affinity engine, General Electric is looking to answer that call. Combining GE’s experience developing high performance fighter jet engines with the latest efficiency improvements from their civilian engines, Affinity is the first new supersonic engine designed for the civil aviation market in fifty five years. It’s not slated to fly before 2023, and likely won’t see commercial use for a few years after that, but this is an important first step in getting air travel to catch up with the rest of our modern lives.

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Supersonic Speed Measurement With A Sound Card

You might think that if you have a need to measure the speed of a projectile that is too fast for your high-speed camera, you would have to invest in some significantly expensive equipment.

That was the problem facing [Nick Moore], and the solution he arrived at is extremely elegant in its simplicity. He’s arranged a pair of foil tapes in the path of the projectile, as it passes through them they break, and he measures the time between those breaks. The clever bit though lies not in the tapes, but in how he measures the timing. Instead of relying on a lab stuffed with equipment, he’s using his computer sound card. The outputs send a tone through each tape to the inputs, and using Audacity he can capture both tones and measure the time between the end of each one on left and right channels.

In the video below the break he demonstrates measuring the speed of a supersonic particle at 496.5 metres per second, which for such relatively simple equipment is rather an achievement. He could certainly improve his resolution by increasing the sampling frequency, but we are guessing that the choice of 48 kHz owes much to the quality of his sound card. Still, to achieve this with such a relatively basic piece of equipment is a neat achievement.

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Why No Plane Parachutes? And Other Questions.

This week I was approached with a question. Why don’t passenger aircraft have emergency parachutes? Whole plane emergency parachutes are available for light aircraft, and have been used to great effect in many light aircraft engine failures and accidents.

But the truth is that while parachutes may be effective for light aircraft, they don’t scale. There are a series of great answers on Quora which run the numbers of the size a parachute would need to be for a full size passenger jet. I recommend reading the full thread, but suffice it to say a ballpark estimate would require a million square feet (92903 square meters) of material. This clearly isn’t very feasible, and the added weight and complexity would no doubt bring its own risks.

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Retrotechtacular: Don’t Balk at Pitch-Up in the McDonnell F-101 Voodoo

The McDonnell aircraft corporation’s F-101 Voodoo was a lean, mean, supersonic machine capable of going from tarmac to 40,000 feet in about two minutes. But for all its innovation and engineering, the Voodoo had a common problem of pitch-up. That is, the swept-back wings of the Voodoo created a tendency for the plane to nose upward very sharply, negating the pilot’s control.

McDonnell assures Voodoo pilots that this problem is easily overcome with a cool head and a solid foundation of know-how about the issue. This training film is meant to provide that foundation, exploring the causes of pitch-up and the prescribed methods for recovery with and without deployment of the drag chute.

The drag chute is always the recommended route to help correct the craft. This is especially true for a full-scale pitch-up situation. Recovery is possible without the drag chute, however. The altitude lost in recovery is proportional to the altitude at the time that pitch-up occurs. That is, the lower the altitude of the craft when pitch-up occurs, the less altitude is lost in getting back to straight and level flight.

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Retrotechtacular: Supersonic Transport Initiatives

In the early days of PBS member station WGBH-Boston, they in conjunction with MIT produced a program called Science Reporter. The program’s aim was explaining modern technological advances to a wide audience through the use of interviews and demonstrations. This week, we have a 1966 episode called “Ticket Through the Sound Barrier”, which outlines the then-current state of supersonic transport (SST) initiatives being undertaken by NASA.

MIT reporter and basso profondo [John Fitch] opens the program at NASA’s Ames research center. Here, he outlines the three major considerations of the SST initiative. First, the aluminium typically used in subsonic aircraft fuselage cannot withstand the extreme temperatures caused by air friction at supersonic speeds. Although the Aérospatiale-BAC Concorde was skinned in aluminium, it was limited to Mach 2.02 because of heating issues. In place of aluminium, a titanium alloy with a melting point of 3,000°F is being developed and tested.

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