Quiet Supersonic Technology

SpaceNut · 2018-11-21 17:05:07

NASA's Quiet Supersonic Technology Project passes major milestone

https://www.nasa.gov/feature/the-quesst-for-quiet

article content:

NASA has officially committed to a development timeline that will lead to the first flight of its X-59 Quiet Supersonic Technology (QueSST) aircraft in just three years.

This critical milestone comes after a rigorous review, Key Decision Point-C (KDP-C), that confirmed NASA's continued support of the X-59, in terms of funding, and established an achievable development timeline for NASA's first piloted, full-size X-plane in more than three decades.

"This aircraft has the potential to transform aviation in the United States and around the world by making faster-than-sound air travel over land possible for everyone," said NASA Administrator Jim Bridenstine. "We can't wait to see this bird fly!"

KDP-C commits NASA to the full X-59 development effort through flight-testing in 2021. The cost and schedule commitments outlined in KDP-C align the project with program management best practices that account for potential technical risks and budgetary uncertainty beyond the project's control.

"This is a monumental milestone for the project," said Jaiwon Shin, NASA's associate administrator for aeronautics. "I'm extremely proud of the team for its hard work getting to this point, and we all look forward to watching this aircraft take shape and then take flight."

The X-59 QueSST is shaped to reduce the loudness of a sonic boom to that of a gentle thump, if it's heard at all. The supersonic aircraft will be flown above select U.S. communities to measure public perception of the noise - data that will help regulators establish new rules for commercial supersonic air travel over land.

Management of X-59 QueSST development falls under the Low Boom Flight Demonstrator project, part of the Integrated Aviation Systems Program in NASA's Aeronautics Research Mission Directorate.

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This would be comparable to the concord being replaced

GW Johnson · 2018-12-01 10:49:13

Supersonic flight will always be more expensive than subsonic flight. This is because supersonic drag is far higher than subsonic drag, no matter the shape of the vehicle.

You might reduce a drag coefficient a few percent using some novel shape, but the dynamic pressure is factor upon factor higher at higher speeds. Dyn. press. q = 0.5 gamma P M^2: a quadratic variation with speed! Physics. No way around that.

As for the sonic boom noise heard on the ground, there are three ways to eliminate this from any supersonic airplane:

(1) Slow down to subsonic (what we have been doing the last 3 decades).

(2) Fly very, very high, so that the shock wave has weakened to inaudibility by the time it reaches the ground. This has been known since the 1950's. I saw an SR-71 in the sky above Dallas-Ft.Worth back in 1962. It was very high up, and very fast: crossing from horizon to horizon in a matter of seconds. I heard absolutely nothing, with the "usual" high speed mission being Mach 3 to 3.3 at just about 85 kft.

(3) Spend gobs of money on a new gravy train program trying to reduce wave strength and drag just a little bit, by investigating novel shapes (which actually just trace directly to Whitcomb's area rule from about 1950). Then just fly your design at very high altitude, at whatever speed you think you can afford, because it will NEVER be an inaudible sonic boom wave, if you fly at lower altitudes! THAT is what the government is doing here, with this program.

What this program might (or might not) do is eliminate or weaken the second boom from the recompression shock that happens in the wake just behind ANY aircraft. That ridiculously-long nose might slightly (SLIGHTLY !!!) weaken the bow shock wave (the first boom you hear in the double boom, the second being the wake recompression shock). But the bow shock CANNOT be eliminated, or even very significantly weakened, it's just physics that one has to be there! Physics. No way around that.

As for the inherent expense of supersonic flight, you can only fly as fast as you can afford, assuming you have propulsion available. The dynamic pressure at Mach 1.5 is 3.1 times higher than at Mach 0.85, at ANY altitude. At Mach 2 it is 5.5 times higher. At Mach 3, it is 12.5 times higher. (And there are no gas turbines for flying much faster than Mach 3 to 3.3.) Transonic drag coefficients are at most factor 2 higher at Mach 1.1 than subsonic, or well-supersonic (Mach 2 to 3). Reducing drag coefficient with a novel shape by a few percent makes no real difference to that picture.

Now, I just gave you the answers you need about quiet, affordable supersonic flight, without spending one dime of anybody's money!!!

Think there might be some dishonesty in aerospace technology marketing? And some ignorance or incompetence in the various government labs that fund these idiocies?

GW

PS - that 1962 SR-71 sighting over DFW was a UFO sighting I could not explain until 1964, when the airplane's existence was publicly revealed by LBJ.

Last edited by GW Johnson (2018-12-01 10:58:33)

elderflower · 2018-12-02 04:20:06

Subsonic aircraft are limited in how high they can go due to their running out of lift. The height at which this happens depends on the wing design- assuming that the engines can develop sufficient thrust at altitude. Therefore any SST must exceed Mach 1 at a limited altitude before climbing to its very high cruising altitude, unless it can develop additional lift.
I recall sailing off the French coast as Concorde accelerated through the speed of sound. I damn near fell overboard as there were no notices about live firing in the area!

GW Johnson · 2018-12-04 10:19:57

OK, there’s a band of feasible dynamic pressures within which you must fly, to have lift nearly equal to weight without stalling. That’s true. There are also definable speeds for best rate of climb and best angle of climb. But, there is not a single definable speed for best lift/drag ratio in cruise.

Those climb speeds are set within the band of feasible dynamic pressures by the interaction of thrust characteristics with weight and with aerodynamic characteristics. Up in the thin air, thrust and drag are low, while weight is not. When thrust is too low to have any significant acceleration pushing on the weight, that’s when you can’t go faster and you can’t climb any higher.

Most supersonic-capable aircraft climb at high subsonic speed, accelerating into supersonic speed as (or after) they pull over level near their intended cruise altitude. The same is true of subsonic aircraft: acceleration to desired cruise happens more-or-less after a slower climb, to arrival near desired altitude. Nothing says you can’t adjust speed and altitude after you begin cruise, especially as weight slowly burns off. In fact, that is exactly what they do.

Your intended cruise speed should be fast enough and high enough for you to operate at or very near what the aerodynamics say is best lift/drag ratio at the speed you wish to fly (a definite value of lift coefficient, which in turn is a definite value of angle of attack). That gets you the longest cruise range for the fuel you burn. It needs to be up higher in the thinner air if you want best L/D for supersonic flight. That’s set by lift coefficient (angle of attack) for lift = weight.

Now if you do that for a supersonic cruise, keep in mind that while drag coefficients get somewhat smaller from transonic to hypersonic, that’s a minor effect. The Mach-number-squared effect on dynamic pressure is far stronger than the thin-air low-pressure effect, and certainly stronger than the decreasing-drag-coefficient effect.

Thus drag will inevitably be very much higher for a supersonic cruise, than a subsonic cruise. (That’s true for choice of subsonic cruise speeds, too, just not as exaggerated). You have to fight higher drag with a larger fuel burn. It’s just physics, there is no “clever-shape” way around that.

Clever shapes are just a minor adjustment, once you have met Whitcomb’s area rule to lower wave drag. That has been known for over half a century now.

Meanwhile, subsonic airliners slowed from Mach 0.90-0.95 cruise at 35-45 kft to Mach 0.75-0.80 cruise at 30-35 kft to save fuel: an economics thing as fuel prices rose. Supersonic airliners will have the same “as fast as you can afford” choice of speeds, just at higher altitudes. Those will likely be above 50 kft, maybe approaching 70 kft, for the higher cruise speeds. It was ~60 kft for the Mach 2 Concorde.

Higher altitudes in thinner air greatly weaken the strength perceived at the ground, of the bow and wake-recompression shocks a supersonic airplane inherently produces. As I observed in 1962, a Mach 3 airplane at around 85 kft was utterly silent to me standing in the front yard watching it.

It really shouldn’t be hardly noisy at all for Mach 2 at ~60 kft. Even for a modest Mach 1.5 design, that ought to be somewhere around 50 kft. If you need to climb supersonic at low altitudes, you did a bad job designing your airplane: no one will ever be able to afford to fly it. It shouldn’t go supersonic until reaches nearly cruise altitude. Concorde violated that, but it was the first of its kind, too. And it proved a money-loser.

I don’t think you’ll see any practical transonic designs, either. From Mach 0.95 to about Mach 1.1, that’s where drag coefficients are highest, and (more importantly) where shock-wave/boundary layer interactions make all planes the least controllable. When people “bust Mach”, they always take it higher than about Mach 1.2. Those transonic problems are exactly why.

GW

kbd512 · 2018-12-13 20:17:06

GW,

Given what you stated, is Elon Musk correct when he posits that one of the best ways to fly at high speed between two points separated by significant distances on Earth is to use rockets to follow a suborbital ballistic trajectory to the destination?

Apart from the noise of liftoff and landing, which I don't find overly objectionable, I could live with a little regular thunder from a spaceport. Maybe it's just personal perspective that comes from living aboard aircraft carriers, but all of us enjoyed the rare supersonic fly-by and sights and sounds of a F-14 breaking Mach.

If the propellants used were LOX/LH2 and manufactured using solar panels or nuclear reactors, would anyone care about putting a little more water vapor into the atmosphere? Basically, would the EPA declare airborne H2O a pollutant as they did with CO2, even if little to no CO2 was emitted to produce the propellant required?

GW Johnson · 2018-12-14 10:59:23

Hi Kbd512:

Musk is correct to point at exo-atmospheric ballistic high-speed travel instead of high-supersonic or hypersonic cruise down in the atmosphere. High speed flight in the atmosphere is energetically very expensive, and requires a steady-state solution to the heat protection problem. There is no way around that requirement. It’s just physics.

Ascent and entry heating transients do not require steady state-heat protection solutions. The steady-state heat protection problem is orders-of-magnitude more difficult to solve, something ignored by most who debate this topic, and has been (for multiple decades now) deliberately glossed over by the big favored contractors to sell gravy train programs to the government.

There are far more lies than truths circulating out there on this issue, same as with space radiation.

As for hydrogen-oxygen “pollution” designations by the EPA, there’s no accounting for what an over-politicized agency staffed dominantly by lawyers will do. EPA didn’t start out that way, but the rot set in early, with byzantine regulations that are deliberately written in turgid prose no ordinary human can deal with.

I know, I have tried, in a couple of jobs I did, after the defense plant closure decades ago ended my employment in aerospace defense work.

You can tell that the population of scientists and other non-lawyers who still work there at EPA is quite small, because of the overwhelming predilection for enforcement court cases versus any attempts to help people understand how exactly to comply.

Even if it were methane-LOX instead of LH2-LOX, it would still be rather clean, in any practical terms whatsoever. Even run slightly rich as all rocket engines are, there is very little soot in the exhaust plume, quite unlike kerosene-LOX. PM2.5 soot particulate is a known human health hazard. Kerolox produces quite a bit of it. Methane-LOX, not so much. LH2-LOX, not at all.

The only problem I see with suborbital ballistic travel is that one cannot tell a transport from an ICBM, from the trajectory shape alone (radar tracking). They are, in fact, exactly the same trajectories. Positive ID would require estimating radar cross sections out in space, plus active transponders on the transports. None of that radio-based stuff works during entry, though.

Another issue is that while ICBM hardware and warhead hardware are not radar stealthy, things like Musk’s BFR/BFS transport really is semi-stealthy, because it’s not generally metallic construction. That’s why I said the far-larger transport needs an active transponder: otherwise its radar return will be similar to that of an ICBM upper stage and its small cloud of warheads and decoys.

We wouldn’t want the start of such ballistic travel to accidentally trigger a nuclear war, after all. This issue is just another valid thing to think about, that I have never seen mentioned in all the decades since Heinlein proposed such travel in his science fiction.

And, Merry Christmas to you and yours. And all the guys and gals on the forums.

GW

SpaceNut · 2018-12-14 17:48:25

Air friction and speed do not mix....

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#1 2018-11-21 17:05:07

Quiet Supersonic Technology

#2 2018-12-01 10:49:13

Re: Quiet Supersonic Technology

#3 2018-12-02 04:20:06

Re: Quiet Supersonic Technology

#4 2018-12-04 10:19:57

Re: Quiet Supersonic Technology

#5 2018-12-13 20:17:06

Re: Quiet Supersonic Technology

#6 2018-12-14 10:59:23

Re: Quiet Supersonic Technology

#7 2018-12-14 17:48:25

Re: Quiet Supersonic Technology

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