I’ll be super excited to have low-to-null-boom supersonic transcontinental flights! But if this becomes a passenger plane, what kind of fuel efficiency would that have? Are supersonic aircraft more or less efficient (oranges and apples I presume).
Surprisingly enough, supersonic planes have good fuel economy while supercruising - thanks to thin air at the high altitude, and speeds around Mach 2 ... 3 being good for turbojet engines.
Expect worse taxiing, take-off and climb fuel economy, due to dense air and also suboptimal (high) angle of attack. This means supersonic planes are best suited for longer routes.
Even the grandpa Concorde had good fuel economy in cruise, however it was overshadowed by atrocious fuel economy at low speeds, and the use of afterburners in transsonic region[1]. The designed but never built Concorde "B" would have notably better economy thanks to more advanced engines doing away with the afterburners.
Yes, because of the second point, it makes sense to build new runways just to accommodate SSTs outside of normal landing procedures to let SST land while gliding down from their cruising altitude.
Concordes were wasting double digit of their fuel reserve while flying in the holding pattern if runways were not available for some reason.
> Concordes were wasting double digit of their fuel reserve while flying in the holding pattern if runways were not available for some reason.
Though note this was uncommon; they were typically cleared for a direct approach all the way from cruise to touchdown. Part of the reason why they rarely got put in the holding pattern was the fact that it would quickly turn into a low fuel emergency, and part was giving the SST preferential treatment.
APU, normally. A smaller turbine generator, just enough to run electrical and hydraulic things, usually, and maybe to start the main engines. I think they shut off APUs after the mains come up. They use almost nothing compared to, say, an Olympus engine on the Concorde at idle.
An apu doesn't generate nearly enough power to taxi the aircraft. Since a large APU is essentially another turbine, you're back to using a turbine to propel the aircraft. If this really were a place to save money then the simplest solution would just have the tug pull it all the way to the runway. That way the aircraft doesn't need to take on additional weight for motors/apus which will sap fuel economy during flight.
The overall thermal efficiency of the engine in supersonic cruising flight (supercruise) was about 43%, which at the time was the highest figure recorded for any normal thermodynamic machine.
> Expect worse taxiing, take-off and climb fuel economy, due to dense air and also suboptimal (high) angle of attack.
This reminds me, in the book "Skunk Works", SR-71 Blackbird pilots mentioned their schedule of mid-air refueling 20-30min after takeoff. After that they could make it 3-5hrs at high altitude before refueling again.
This is because the Blackbird took off with only partially filled tanks, to lower the weight and therefore the takeoff speed. It was not designed to take off or land with full tanks.
You can compensate by cramming in seats closer or trying exotic designs. And there's some efficiency buy-back by operating at higher altitudes where the engine can expand to lower pressures (and thus increase the pressure ratio), but overall, roughly half as efficient is a decent guesstimate.
Then again, conventional aircraft are about double the efficiency they used to be, so supersonic aircraft today could conceivably be approximately the same efficiency as transonic aircraft of yesteryear.
I think exotic designs could enable decent range low supersonic electric flight (i.e. Mach 1.5 or something). Going to need good batteries, though, and extremely high aspect ratio wings.
A lot of the fuel efficiency of modern aircraft comes from having giant turbofans instead of turbojets. By attaching a giant fan the front of your compressor and redirecting most of the air around the engine you can get great efficiency at subsonic speeds. However, the nature of the fan has fundamental limitations when approaching the speed of sound and turbo/ram jets are basically just pouring gas in a tube of precompressed air.
Apart from the Aerion as2 i dont think there are many other credible supersonic aircraft in development other than the Nasa one. Concorde, other than the booms, had engines so loud, and i mean insanely loud they would not be popular these days. I remember covering my ears as it flew overhead.
I do find Elon Musks frequent mentions of a vtol ss aircraft quite interesting.
Electric engines would not have the same issues at high altitude as conventional ones. Battery density is starting to get in the right area to make this feasible.
He is frequently distainful of flying cars but one logical conclusion of this is indeed potentially flying cars (Tesla secret projects anyone?). When you think about how much of the world is inaccessible, one of these would make a great thunderbirds style exploration vehicle ( provided it had a large expandible solar array stowed somehow) . Fancy a trip to the Kamchatka ground zero? No problem! I wonder whether aerodynamically they would not need to be so concorde like and maybe just bullet shaped. Perhaps on Mars you could have supersonic blimps
You would use the hydrogen in gaseous form to reduce the net weight of the aircraft to be lighter than the surrounding atmosphere (hydrogen gas has an extremely low density). This enables the craft to float without having to burn fuel just to stay aloft.
What are the issues at high altitude? Current turbine engines can already operate efficiently at 50,000 feet or more. There's not much to gain in drag reduction at altitudes higher than that. And there are safety concerns in terms of time to descend in case of loss of cabin pressure.
Haha I personally would love it, but I cannot imagine car alarms going off would be tolerated on a daily basis! Great video if thats yours. On the flip side, I think about how we have tornado siren tests every week at 3p, and my office tower is immediately adjacent to a fire station with the siren on the rooftop blasting at my window for 2 minutes a week, we have to mute conference calls and whatnot during the test... its just a part of life.. I mean, surely they could test those things every month during tornado season and be just fine.
> Electric engines would not have the same issues at high altitude as conventional ones
Some of them they still do. Their air is still less dense, so if you force the same volume out per second, you generate less thrust anyways cause there is less mass per volume (and thus less thrust for you)
Fun fact/rumor: in the early 2000s, Lockheed SW was rumored to have a mature design for a QSP bizjet that they were shopping around to hedge funds for funding into production, since Wall Street were avid customers of the Concorde. Cessna was also working on something that has probably been abandoned.
Perhaps I'm in the minority, but I'm concerned that commercial-supersonic will be a net-negative in my life.
I'm assuming that, as with the Concords, most of the benefit for supersonic travel would be to very wealthy individuals and corporations. But everybody living/working beneath the flight path would have to endure the added noise pollution.
The entire point of this concept is removing that noise pollution. Additionally, a more modern, efficient aircraft than the Concorde might conceivably someday make sense for more widespread, and hence more affordable use.
> The entire point of this concept is removing that noise pollution.
My understanding was that the noise-reduction was specifically for sonic booms. If I understand correctly, commercializing this would mean a transition from no sonic booms to quieter-than-before sonic booms. From my own, personal perspective that's a net-negative.
Speaking as someone who used to live pretty close to an airport, I'd point out that normal airliners are not without noise pollution, and I'd rather it be gone sooner rather than later.
The faster a plane crosses the horizon, the less of your time will have noise pollution. Then the question becomes how much quieter these sonic booms are, and how they compare to more traditional airliners' noise pollution.
I live 10-15 miles from a small regional airport, but apparently near one of the approach paths. I agree with the potential tradeoffs you listed. I'd also add that my concerns are ultimately pyscho-acoustic, which complicates the analysis.
The planes you are noticing are all below the 10,000 ft level (i.e., on approach or takeoff) and are required to fly no faster than 250 knots. No supersonic aircraft will be flying supersonic on approach or at low altitude. If their engines are noisy they will be louder for the same amount of time as others.
Almost all new consumer-accessible technologies benefit the wealthy first, simply due to the initially-high costs. Just imagine if people like you had decision making power. We'd not have microwaves, televisions, cell phones, etc...
I'm not sure there's a "dead" status quo around technical feasibility so much as there's a great deal of skepticism about economically viable commercial supersonic passenger air travel. (At least, possibly, beyond a niche for the very wealthy.)
See, building aircraft is not so really that expensive. First supersonic aircrafts were built with manufacturing equipment which will not sell even on a liquidation sale today.
Military jet bombers, while expensive by all measures, did cost less in the mid-20th century than equivalently sized airliners today.
A lot of cost increase since eighties in the industry was due to increasing regulatory lockdown and decrease in efficiency due to decrease in competition.
The $100 per piece "aerospace grade" nuts and bolts is exactly what I am talking about.
I'm not really into aircraft engineering. I had a dip in it when I was really into drones in my high school years, and then tried myself at motogliders.
For as long as engineering goes, I'm more into electronics and process.
This is a very good observation, though I'd make one nitpick... The tooling used for the airframes then isn't much different than the tooling used to build them now. The industry has only just started to embrace robotic composite construction, otherwise it's the same rivet guns and squeezers that they've always used more or less. If you know of any liquidation sales giving away 100s of clecos or dies for nothing, let me know...
It's almost certainly a render of the plane landing at Armstrong Flight Research Center (longstanding home to the NASA X planes), which does in fact bear a striking resemblance to Tattoine.
This is an experiment rather than a finished product:
The X-59 will never carry passengers, but it will likely kick off a new generation of quiet supersonic commercial planes that can fly over land and dramatically reduce the time it takes to get you across the U.S. and to other countries.
I’ll be super excited to have low-to-null-boom supersonic transcontinental flights! But if this becomes a passenger plane, what kind of fuel efficiency would that have? Are supersonic aircraft more or less efficient (oranges and apples I presume).
>Are supersonic aircraft more or less efficient
Surprisingly enough, supersonic planes have good fuel economy while supercruising - thanks to thin air at the high altitude, and speeds around Mach 2 ... 3 being good for turbojet engines.
Expect worse taxiing, take-off and climb fuel economy, due to dense air and also suboptimal (high) angle of attack. This means supersonic planes are best suited for longer routes.
Even the grandpa Concorde had good fuel economy in cruise, however it was overshadowed by atrocious fuel economy at low speeds, and the use of afterburners in transsonic region[1]. The designed but never built Concorde "B" would have notably better economy thanks to more advanced engines doing away with the afterburners.
[1] https://www.quora.com/How-fuel-efficient-was-the-Concorde-co...
Is it accurate to say that high speed efficiency matters much more for any flight a supersonic jet would reasonably take
Yes, because of the second point, it makes sense to build new runways just to accommodate SSTs outside of normal landing procedures to let SST land while gliding down from their cruising altitude.
Concordes were wasting double digit of their fuel reserve while flying in the holding pattern if runways were not available for some reason.
> Concordes were wasting double digit of their fuel reserve while flying in the holding pattern if runways were not available for some reason.
Though note this was uncommon; they were typically cleared for a direct approach all the way from cruise to touchdown. Part of the reason why they rarely got put in the holding pattern was the fact that it would quickly turn into a low fuel emergency, and part was giving the SST preferential treatment.
The taxi phase, at least, can be mitigated with an electric tug motor built into nose gear. Engines can be off or idle until needed.
https://en.wikipedia.org/wiki/WheelTug
Great point. Or motors in the rear wheels could probably get it up to 100MPH on the runway before the jets had to take over.
I'm not sure if those fuel savings would be worth getting rid of the integrated pre-takeoff engine thrust test, though.
Yea what is generating the power for those motors?
APU, normally. A smaller turbine generator, just enough to run electrical and hydraulic things, usually, and maybe to start the main engines. I think they shut off APUs after the mains come up. They use almost nothing compared to, say, an Olympus engine on the Concorde at idle.
An apu doesn't generate nearly enough power to taxi the aircraft. Since a large APU is essentially another turbine, you're back to using a turbine to propel the aircraft. If this really were a place to save money then the simplest solution would just have the tug pull it all the way to the runway. That way the aircraft doesn't need to take on additional weight for motors/apus which will sap fuel economy during flight.
To give some perspective, the hourly fuel consumption for Concorde is almost identical at Mach 2 than at max subsonic speed...
And Concorde powerplant had at some point the highest overall thermal efficiency at max speed:
https://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593
The overall thermal efficiency of the engine in supersonic cruising flight (supercruise) was about 43%, which at the time was the highest figure recorded for any normal thermodynamic machine.
> Expect worse taxiing, take-off and climb fuel economy, due to dense air and also suboptimal (high) angle of attack.
This reminds me, in the book "Skunk Works", SR-71 Blackbird pilots mentioned their schedule of mid-air refueling 20-30min after takeoff. After that they could make it 3-5hrs at high altitude before refueling again.
The SR-71 did take off with much less than full fuel load; IIRC to keep the mass low enough for safe T/O abort or maybe for a safe go-around.
As for books, I wholeheartedly recommend the excellent https://www.barnesandnoble.com/w/sled-driver-brian-shul/1123... written by one of the pilots.
Yea the SR-71 has very poor lift at slow speeds because of its lack of wing hence why it needs the chines on the forward section of the fuselage.
This is because the Blackbird took off with only partially filled tanks, to lower the weight and therefore the takeoff speed. It was not designed to take off or land with full tanks.
Also the tanks leaked untill thermal expansion at supersonic speed sealed them.
Wow, shouldn’t that be a safety concern? Fuel leaking all over the airbase prior to takeoff?
The fuel was so resistant to ignition that it required an external source (TEB in this case) to even get alight.
Fundamentally, about half as efficient.
You can compensate by cramming in seats closer or trying exotic designs. And there's some efficiency buy-back by operating at higher altitudes where the engine can expand to lower pressures (and thus increase the pressure ratio), but overall, roughly half as efficient is a decent guesstimate.
Then again, conventional aircraft are about double the efficiency they used to be, so supersonic aircraft today could conceivably be approximately the same efficiency as transonic aircraft of yesteryear.
I think exotic designs could enable decent range low supersonic electric flight (i.e. Mach 1.5 or something). Going to need good batteries, though, and extremely high aspect ratio wings.
A lot of the fuel efficiency of modern aircraft comes from having giant turbofans instead of turbojets. By attaching a giant fan the front of your compressor and redirecting most of the air around the engine you can get great efficiency at subsonic speeds. However, the nature of the fan has fundamental limitations when approaching the speed of sound and turbo/ram jets are basically just pouring gas in a tube of precompressed air.
The attached image of the assembly has a nice easter egg:
https://imgur.com/a/df6XnAs
Apart from the Aerion as2 i dont think there are many other credible supersonic aircraft in development other than the Nasa one. Concorde, other than the booms, had engines so loud, and i mean insanely loud they would not be popular these days. I remember covering my ears as it flew overhead.
I do find Elon Musks frequent mentions of a vtol ss aircraft quite interesting. Electric engines would not have the same issues at high altitude as conventional ones. Battery density is starting to get in the right area to make this feasible.
He is frequently distainful of flying cars but one logical conclusion of this is indeed potentially flying cars (Tesla secret projects anyone?). When you think about how much of the world is inaccessible, one of these would make a great thunderbirds style exploration vehicle ( provided it had a large expandible solar array stowed somehow) . Fancy a trip to the Kamchatka ground zero? No problem! I wonder whether aerodynamically they would not need to be so concorde like and maybe just bullet shaped. Perhaps on Mars you could have supersonic blimps
Buoyant forces in the Martian atmosphere would be teeny tiny no? I don’t think blimps would work very well.
You could maybe get some sort of inflatable lifting body to work at high speeds though.
An advantage you have is that you can fill them with hydrogen and be fine, since there's no oxygen to allow them to suddenly combust
Which you would then do what with, as there's no free supply of oxygen to burn it with in the engine?
You would use the hydrogen in gaseous form to reduce the net weight of the aircraft to be lighter than the surrounding atmosphere (hydrogen gas has an extremely low density). This enables the craft to float without having to burn fuel just to stay aloft.
https://en.wikipedia.org/wiki/Airship
Boom's XB-1 demonstrator fabrication is well underway: https://www.linkedin.com/posts/boom-technology-inc%2E_avgeek.... They're very legit, hiring tons of people from Scaled, SpaceX, Lockheed etc.
Yeah, Boom is quite credible.
What are the issues at high altitude? Current turbine engines can already operate efficiently at 50,000 feet or more. There's not much to gain in drag reduction at altitudes higher than that. And there are safety concerns in terms of time to descend in case of loss of cabin pressure.
> ... had engines so loud, and i mean insanely loud they would not be popular these days. I remember covering my ears as it flew overhead.
I lived near Heathrow and Concorde was such a thing of beauty that the noise, if anything, just added to the spectacle!
Trust me, this never got old:
https://m.youtube.com/watch?v=i1ShTUVIzCI
Haha I personally would love it, but I cannot imagine car alarms going off would be tolerated on a daily basis! Great video if thats yours. On the flip side, I think about how we have tornado siren tests every week at 3p, and my office tower is immediately adjacent to a fire station with the siren on the rooftop blasting at my window for 2 minutes a week, we have to mute conference calls and whatnot during the test... its just a part of life.. I mean, surely they could test those things every month during tornado season and be just fine.
> Electric engines would not have the same issues at high altitude as conventional ones
Some of them they still do. Their air is still less dense, so if you force the same volume out per second, you generate less thrust anyways cause there is less mass per volume (and thus less thrust for you)
Is anyone else around the world working on quiet supersonic passenger jets?
Boom is one company working on supersonic passenger jets. Various others also pop up from time to time.
Boom is for real: https://www.linkedin.com/posts/boom-technology-inc%2E_avgeek...
Fun fact/rumor: in the early 2000s, Lockheed SW was rumored to have a mature design for a QSP bizjet that they were shopping around to hedge funds for funding into production, since Wall Street were avid customers of the Concorde. Cessna was also working on something that has probably been abandoned.
Perhaps I'm in the minority, but I'm concerned that commercial-supersonic will be a net-negative in my life.
I'm assuming that, as with the Concords, most of the benefit for supersonic travel would be to very wealthy individuals and corporations. But everybody living/working beneath the flight path would have to endure the added noise pollution.
The entire point of this concept is removing that noise pollution. Additionally, a more modern, efficient aircraft than the Concorde might conceivably someday make sense for more widespread, and hence more affordable use.
> The entire point of this concept is removing that noise pollution.
My understanding was that the noise-reduction was specifically for sonic booms. If I understand correctly, commercializing this would mean a transition from no sonic booms to quieter-than-before sonic booms. From my own, personal perspective that's a net-negative.
Speaking as someone who used to live pretty close to an airport, I'd point out that normal airliners are not without noise pollution, and I'd rather it be gone sooner rather than later.
The faster a plane crosses the horizon, the less of your time will have noise pollution. Then the question becomes how much quieter these sonic booms are, and how they compare to more traditional airliners' noise pollution.
I live 10-15 miles from a small regional airport, but apparently near one of the approach paths. I agree with the potential tradeoffs you listed. I'd also add that my concerns are ultimately pyscho-acoustic, which complicates the analysis.
The planes you are noticing are all below the 10,000 ft level (i.e., on approach or takeoff) and are required to fly no faster than 250 knots. No supersonic aircraft will be flying supersonic on approach or at low altitude. If their engines are noisy they will be louder for the same amount of time as others.
Almost all new consumer-accessible technologies benefit the wealthy first, simply due to the initially-high costs. Just imagine if people like you had decision making power. We'd not have microwaves, televisions, cell phones, etc...
That's what the 'Quiet' part of the name is trying to solve.
From another source:
The X-59 has been designed to achieve a PLdB of 75, similar to what might be heard when standing next to a heavily trafficked road.
I'm very impressed that they managed to keep it going for so long.
It will be good to dispel the ideological status quo in aeronautics community that "SST is dead and buried"
I'm not sure there's a "dead" status quo around technical feasibility so much as there's a great deal of skepticism about economically viable commercial supersonic passenger air travel. (At least, possibly, beyond a niche for the very wealthy.)
See, building aircraft is not so really that expensive. First supersonic aircrafts were built with manufacturing equipment which will not sell even on a liquidation sale today.
Military jet bombers, while expensive by all measures, did cost less in the mid-20th century than equivalently sized airliners today.
A lot of cost increase since eighties in the industry was due to increasing regulatory lockdown and decrease in efficiency due to decrease in competition.
The $100 per piece "aerospace grade" nuts and bolts is exactly what I am talking about.
You seem to know a lot of things. Do you have like a newsletter I could subscribe to?
I'm not really into aircraft engineering. I had a dip in it when I was really into drones in my high school years, and then tried myself at motogliders.
For as long as engineering goes, I'm more into electronics and process.
This is a very good observation, though I'd make one nitpick... The tooling used for the airframes then isn't much different than the tooling used to build them now. The industry has only just started to embrace robotic composite construction, otherwise it's the same rivet guns and squeezers that they've always used more or less. If you know of any liquidation sales giving away 100s of clecos or dies for nothing, let me know...
+1 for the googly eyes and mustache on the forward bulkhead...
(dunno if that's what it's called, it was the name that sort of felt most right)
Are you referring to the skunk on the nose cone just forward of the canard? I assume that's an indicator of a skunkworks project.
A bulkhead is a wall inside a ship. The main structure of an aircraft is called the fuselage and the outer surface is the skin.
Looks like its landing on Tattoine, which is appropriate for that thing.
It says 'illustration' in the caption that's probably not a real image especially not given the article title.
It's almost certainly a render of the plane landing at Armstrong Flight Research Center (longstanding home to the NASA X planes), which does in fact bear a striking resemblance to Tattoine.
Tunisia looks a lot like Tatooine too!
How many seats?
This is an experiment rather than a finished product:
The X-59 will never carry passengers, but it will likely kick off a new generation of quiet supersonic commercial planes that can fly over land and dramatically reduce the time it takes to get you across the U.S. and to other countries.
https://www.nasa.gov/nasa-x59-quesst-takes-shape
The Quesst is an experiment to see if the annoyingness of the boom can be mitigated by converting the boom into a "thump" (i.e. quieter boom).
Src: I work there
As for the boom, why don't they just wait to be in very high altitude or to be at a place where there's almost no human in the surroundings?