[EDIT] Many here are acting as if TFA were about the noise of sonic booms, and it is not. From the actual amendment:
(3) specifies a noise standard for landing and take-off of civil supersonic aircraft that is no more stringent than large subsonic aircraft in use for transporting passengers in the United States on January 1, 2017. [0]
That is, Boom are claiming that their engines could be narrower, if they were allowed to make as much noise taking off and landing as large passenger jets make taking off and landing. Perhaps TFA could have been clearer on this, but the reading comprehension is not strong on HN this morning.
On the very first page of the PDF you linked: paragraph a, "Not later than one year after the date of the enactment of this Act, the Secretary shall publish in the Federal Register a notice of proposed rulemaking that permits the development, testing, manufacturing and operation of civil supersonic aircraft in the United States."
I mean, it's right there. S. 1405 is about operating supersonic aircraft in the US, aircraft that by definition make sonic booms.
It's fine to be suspicious, but one should at least read carefully while in that state. TFA is about "amendment -> more noise on takeoff -> narrower engine -> fuel savings -> lower costs". Literally one paragraph mentions the sonic boom restriction, while the rest is about fuel savings. Lots of comments here are skipping that entirely, which indicates some confusion. Perhaps Boom will publish something else with more detail about flying jackhammers?
To address that issue, ISTM we trust FAA to get many things right, but previously the thoughtful regulation of supersonic civil aviation was not one of those things. If this amendment passes, it will become one of those things. Is there a particular reason not to trust FAA thoughtfully to regulate this sort of flight?
Boom is writing about narrower issues of engine noise and fuel economy because they don't want to discuss the intractable problem they're named after. That doesn't mean we can't discuss it.
I think the status quo (no shattered windows in Chicago) is desirable and worth preserving. The FAA may regulate it sanely, but then again, given the current political climate, they may not.
It has been several months since I visited Chicago, but that was not my impression of the status quo? This is a very hypothetical concern, however. It's quite unlikely that any passenger flights will pass the sound barrier at an altitude of 200 ft. [0]
Then again, if Vladimir Putin wants to break some American glass in a really roundabout way, who are we to oppose him? Perhaps he needs to brush up on his Bastiat?
I don't know what that quip about Chicago was meant to accomplish, but I don't think you can complain about other people's "reading comprehension" while misapprehending that comment so thoroughly. Obviously, the point being made is that sonic booms break windows (some people near airports that saw supersonic traffic used to buy special windows), and Chicago is a major air transport hub.
This is somewhat misleading. What they are asking for is to be able to certify their plane under stage 3 noise regulations. Currently, it's legal to fly a stage 3 plane, but any design for a new plane submitted to the FAA after 2006 has to meet stage 4 regulations. Any design submitted as of the end of this year needs to be stage 5.
Effectively this is like a car manufacturer asking to only be required to meet fuel economy/emissions/safety standards from 10-20 years ago for a new vehicle. IMO this is reasonable. Stage 3 planes are fairly quiet, at least compared to what was flying around in the 70s and 80s. If regressing a bit on airport noise is the price we pay to go twice as fast, that's OK with me. I'd love it if we talked about this honestly, and shamed the people who whine about every tiny negative impact of human progress.
Boom and other proponents of lifting the supersonic aviation ban are trying to cause confusion between engine noise restrictions (relevant at takeoff) and the inescapable noise from a passing shock wave that is the byproduct of supersonic flight.
"Pilot Lt Col Ed Yielding and Reconnaissance Systems Officer Lt Col Joseph Vida took off at Palmdale, California and landed at Washington-Dulles a scant hour, four minutes, and 20 seconds later."[1]
I don't remember any sonic boom complaints when this or other record setting SR-71 flights over the US occurred. If you are flying in thin atmosphere the magnitude of the sonic boom at the surface should be much reduced. So, maybe it would be ok to fly supersonic at 70,000+ feet. Of course, it might be disconcerting if you were flying subsonic at 38,000 feet.
They also point out that the space shuttle flew even higher and still made booms.
I think the lack of complaints for the SR-71 may be more due to the fact that it didn't fly very often, and that people had more understanding for the need for military aviation to be supersonic.
Thank you for the link to the stackexchange discussion. I read it and the Wikipedia and NASA pages it links to. Based on the Wikipedia link the calculated second table by the stackexchange author is incorrect. The Wikipedia article points out that the path of the N-wave will generally be curved upwards due to the temperature gradient from altitude to the ground making the distance longer. The path of the N-wave is not going to be the cone normally depicted. But, there are two things not discussed in the Wikipedia article that I think will also play a role in the magnitude of the sonic boom. 1) As altitude increases, air density decreases; meaning that for a given speed a smaller number of air molecules will be displaced thus reducing the magnitude of the sonic boom at the ground. 2) The sharp N-wave close to the supersonic source is not a soliton and will undergo dispersion reducing the over pressure. That is, as altitude increases and the distance to the ground increases, the N-wave is going to spread out into more of a layed-over-S wave reducing the magnitude of the sonic boom.
With regard to the SR-71 making record setting flights and flying at the limits of its flight envelope to do so(100,000+ feet or "the edge of space"), I think the sonic boom at that altitude may not be noticeable to human hearing.
I know the that the SR-71 and the Space Shuttle have produced very noticeable sonic booms, but what isn't answered is at what altitude did the sonic booms become noticeable or annoying. It seems to me that with all the things that reduce the the magnitude of a sonic boom that it may be possible to fly supersonic without being annoying and slow down to subsonic to takeoff and land. It might also be possible to design the aircraft body to promote dispersion of the N-wave.
Yeah, there's lots of potential issues, I don't know. It's true that the air is much thinner higher up, but I'm not sure how much that will help--I think a large part of the sonic boom comes from air displaced by the plane to create lift, and of course the momentum imparted by the plane to the air is constant (= the weight of the plane).
Also, I'm not sure the fact that the rays that forms the sonic boom are curved makes the sound itself weaker, it just takes longer to propagate down the the ground. But the fact that the sound spreads out towards the sides of the plane should help, the circumference of the shock cone at the point where it touches ground is proportional to the height of the airplane, so I'd expect things to scale down because of that?
First, it notes that the shape of the wave does change while it propagates, but it turns out that the effect is in the opposite direction from what you suggested. That is, close to the aircraft the pressure forms a smooth S (the "mid-field" shape), but then as it moves further away, nonlinear effects causes the wave to bunch up to create the discontinuous N-shape. (See fig 1 and 2 on page 30.) So it seems, in this respect flying higher is actually worse---most research about reducing sonic booms tries to shape the aircraft to be long and thin, in order to make the waveform smoother, so we'd want there to less time for the wave to bunch up again.
Second, the document actually has a diagram of how the over-pressure depends on altitude! In fig 10 on page 34 it plots the calculated overpressure from a hypothetical Mach 2.7 supersonic transport. As I eyeball it, the over-pressure goes from 212 pounds/ft^2 at 40,000 feet (airliner level) to 129 pounds/ft^2 at 80,000 feet (SR-71 level), so it went down by a factor of 0.6. (In a cute coincidence, that 60% is almost exactly what's predicted by the scaling law eq. 25 on page 16, even though that equation is only intended for hypersonic aircraft.)
For an Advanced SST the quote near the end is, "Advances in aircraft technology suggest that sonic boom amplitudes for this type of aircraft, also referred to as a High Speed Civil Transport (HSCTJ or the "Orient Express". could be made substantially lower than first generation SSTs. potentially to the point that overland flight could be acceptable."
I'm not sure what to make of Fig. 10. I'm sure they are accurately plotting their equations, but the impulse for the SST is a minimum at 50,000 feet and increases for higher altitudes altitudes. The impulse for the HST generally increases with altitude. OTOH they discuss the N-wave forming in the far field and maintaining its shape, but also broadening which seems like it would reduce the impulse just like the overpressure.
I'm not sure, but the way I read it was that the impulse is the slope of the first "vertical" bar of the N, rather than the slope of the diagonal line. So as the pulse travels, the vertical part gets compressed and steeper (I increases), and the height of the N gets smaller (Δp decreases), and the the distance between the bars gets longer (broadening).
But yeah, figure 17 on page 26 of the document you linked seems to be exactly what we are looking for, great find! One can see exactly how the waveform changes with altitude. Moving from 42,100 feet to 70,700 feet reduced Δp from 1.82 to 1.13, a factor of 0.71.
> The Lee-Gardner Amendment would help us reduce drag by allowing us to make our engines narrower
What am I missing?
They're comparing things to current-day high-bypass turbofan jet engines, which are very wide by design and on-purpose (not because of some regulation).
Sure, part of the high-bypass allows for quieter noise levels, but it's also about efficiency at cruise altitude and speeds.
Turbojet engines designed for supersonic speed are already much narrower, well at least the nacelle is, or lack-thereof (again, by design -- optimized for fast speeds, not because of some regulation).
As far as I'm aware, the reason there aren't supersonic civil aircraft is because of the enormous cost involved in operating them, and the restrictions of supersonic flight over mainland due to shock wave damages, etc... not the size of the engine as appears to be asserted in this article.
So, any new legislation only needs to target lifting the over mainland restrictions (and somehow change physics to not have shock waves...), but you can't legislate-away the enormous costs involved in building and operating supersonic aircraft.
The article asserts that the problem fixed by the legislation is noise regulations that end up requiring wider supersonic engines to meet, which increase drag and cost of operation.
> So, any new legislation only needs to target lifting the over mainland restrictions
Which the legislation does...
> but you can't legislate-away the enormous costs involved in building and operating supersonic aircraft.
To the extent the costs result from legislative mandates, and are not inherent in building supersonic aircraft, you obviously can.
> The article asserts that the problem fixed by the legislation is noise regulations that end up requiring wider supersonic engines to meet, which increase drag and cost of operation.
> To the extent the costs result from legislative mandates, and are not inherent in building supersonic aircraft, you obviously can
The problems with cost are real, but it's more from flight restrictions than drag (subsonic flight over mainland to final destination using a supersonic-optimized engine is going to be very inefficient).
We can just look at the Concord as a prime example. Barred from supersonic flight over mainland, it became economically infeasible to continue to operate only trans-oceanic flights (I believe all 3 operators ran it as a loss-leader, of sorts, due to the novelty). Even then, when approaching the destination, the Concord had to revert to subsonic speeds, and ditch the shock wave while still out at sea. Unless there's some magical way to generate only minute shock waves from large passenger aircraft (I'm highly skeptical here), you're going to break people's windows etc, or you're going to burn up a bunch of fuel and wind up with the same issues all over again.
The other lesson learned from the Concord is, there's very few cases where people need to be somewhere that quickly, and are willing to pay the high ticket prices to do so. One can almost always book an earlier flight, for a substantial savings (I'm also highly skeptical there's any fuel cost savings with supersonic flight as the article seems to claim).
> The problems with cost are real, but it's more from flight restrictions than drag
No one is arguing that that isn't the case; as the article points out, the legislation addresses both the flight restrictions and the noise rule that the article claims functionally requires engine designs which increase drag.
> the legislation addresses both the flight restrictions and the noise rule
Noise rules are there for good reason (nobody likes broken windows)... and I'm sure there's military applications for quieter supersonic engines, but we don't have any (either because we haven't tried, or, more likely, because it can't be).
I suppose I'm just highly skeptical they can do both, or either, in reality. Sort of, having their cake and eating it too.
I'd love to be proved wrong here though, so I guess we'll have to wait and see.
> Noise rules are there for good reason (nobody likes broken windows)...
The engine noise rule at issue has nothing to do with broken windows, and the change is to use the same engine noise level restrictions as subsonic aircraft, rather than stricter rules for supersonic aircraft.
I didn't see any mention of how this would impact overall noise levels. Is there some regulatory process being added to handle supersonic passenger aircraft?
That's probably because changing fuel consumption goals has absolutely nothing to do with the magnitude or propagation characteristics of an atmospheric shockwave.
Unless the shockwave's shape (distorting coarseness of the wave front to soften the impact of sound waves; think: tweaking the volume knob to fade-in/fade-out a noise floor with gradual easing, rather than slamming a door as hard as you can) or size (how much air gets pushed around, overall) is altered by how a moving body breaks the sound barrier, a sonic boom will still be loud, and reach just as far.
When you crack a whip, the sound is just as loud, no matter how much energy your arm expends making the motion.
FTA
"Additionally, the Lee-Gardner Amendment would require the FAA to eliminate the Mach 1 speed limit over the United States and replace it with a well tailored sonic boom standard."
At super sonic speeds the noise is awful so to make it simple the FAA just says "no super sonic flight".
This changes that to force the FAA to do the complicated thing and be like "okay in these locations at this altitude and this size plane" and "at these locations at these altitudes and that size plane" and maybe "never at this location" or maybe "only during local business hours " and we end up with a book of "well tailored" regulations. Which while complicated might at least allow for Boom to operate inside the US, which opens up a lot business.
This is perhaps a bad political environment to propose a bill that would let billionaires operate supersonic pleasure craft over the US, at considerable annoyance to 99.99% of the population.
For example, an SF - NY flight could be allowed to boom over northern Nevada, much of which is completely uninhabited. Right now it's completely forbidden over US territory.
> The Lee-Gardner Amendment would help us reduce drag by allowing us to make our engines narrower. Current engine noise rules for new supersonic aircraft are more stringent than those for the existing subsonic fleet. By setting our engine noise to the same levels as existing subsonic airplanes, we could make our engines produce so much less drag that we would save 20–40 percent on fuel, depending on whether you use this year’s or next year’s rules as a baseline.
They're narrowing the engine to get less drag and setting the noise to the same levels as conventional planes.
Skeptical. I know what narrower means but noise is a result rather than a parameter.
Engine noise is understood well enough that you can choose the level you want and develop an engine that is as good as possible that reaches that level.
Sonic booms are very loud and disruptive. NASA has done some research into mitigation by using blunt-nosed aircraft, but none of that applies to Boom's more conventional design.
TL;DR This is legislation Boom wants enacted to allow for more relaxed noise emission levels.
"Current engine noise rules for new supersonic aircraft are more stringent than those for the existing subsonic fleet. By setting our engine noise to the same levels as existing subsonic airplanes, we could make our engines produce so much less drag that we would save 20–40 percent on fuel, depending on whether you use this year’s or next year’s rules as a baseline."
Curious if they've hit a wall in their aerodynamic design and need this to move forward.
They want the regulations banning overland supersonic flight removed, and are trying to frame it as a fuel efficiency issue rather than the "we will make people's lives miserable with noise" issue that led to the ban.
It can be done sanely, but they don't have anything flying yet (was supposed to be May 2017 but that came and went).
Also, don't be fooled. The smaller test aircraft, if it ever flies, will have a much lower sonic boom than the larger airliner. Sonic boom is largely proportional to aircraft weight.
Reading between the lines it would appear that they are so far from having anything that flies that they're still willing to redesign their engine and presumably plane as a result.
(And yet they have the hubris to talk about how much a ticket will cost)
> They want the regulations banning overland supersonic flight removed
True, but
> and are trying to frame it as a fuel efficiency issue
No, they are trying to frame the changes they want to engine noise regs as a fuel efficiency issue; that's a separate rule change from (in the same legislation as) the one removing the overland supersonic flight ban.
> What I don't understand is the engine size rule.
It's not a size rule, it's an engine noise rule which ends up (per the article, I don't know enough about the relevant fields to confirm this) requiring wider engines which end up producing more drag.
You can think of it this way: at subsonic speeds, air ahead of the aircraft "knows" that the plane is coming, and can flow around it. At supersonic speeds, this information doesn't propagate forwards, and the plane smashes into the air ahead of it, creating a shock wave.
I'm anthropomorphizing and oversimplifying (airflow over a wing can be locally supersonic even in subsonic flight) but I don't care because I enjoy thinking of this in terms of information flow.
I am delighted by the idea of a little anthropomorphic chunk of air shouting "Move, there's a plane coming!" and then face palming upon realizing too late that it is using sound to warn other bits of air about something moving at supersonic speeds.
The speed of sound through air is effectively the speed of shockwaves through air. The way that the air responds to being pushed around at speeds faster than its shockwaves can respond results in something that behaves more like a liquid than a gas.
Not an engineer, but from my understanding air is a fluid that can be compressed. At extreme rates of speed in general atmospheric conditions, that results in a compression that the object is punching through. Often I learn about this stuff from high speed auto experiments (Bugatti, Toyota Land Speed Cruiser).
> One of the best ways to get fares down is to burn less fuel.
Edit: Removed the previous comment text here as I misread/misunderstood. This isn't just about the cost of the fuel, it's also about what you can do with the same amount if you burn it slower.
[EDIT] Many here are acting as if TFA were about the noise of sonic booms, and it is not. From the actual amendment:
(3) specifies a noise standard for landing and take-off of civil supersonic aircraft that is no more stringent than large subsonic aircraft in use for transporting passengers in the United States on January 1, 2017. [0]
That is, Boom are claiming that their engines could be narrower, if they were allowed to make as much noise taking off and landing as large passenger jets make taking off and landing. Perhaps TFA could have been clearer on this, but the reading comprehension is not strong on HN this morning.
[0] https://www.commerce.senate.gov/public/_cache/files/0238c447...
?
On the very first page of the PDF you linked: paragraph a, "Not later than one year after the date of the enactment of this Act, the Secretary shall publish in the Federal Register a notice of proposed rulemaking that permits the development, testing, manufacturing and operation of civil supersonic aircraft in the United States."
I mean, it's right there. S. 1405 is about operating supersonic aircraft in the US, aircraft that by definition make sonic booms.
You're ignoring section 2, which says the sonic boom can be as loud as other things the public tolerates (like jackhammers).
It's fine to be suspicious, but one should at least read carefully while in that state. TFA is about "amendment -> more noise on takeoff -> narrower engine -> fuel savings -> lower costs". Literally one paragraph mentions the sonic boom restriction, while the rest is about fuel savings. Lots of comments here are skipping that entirely, which indicates some confusion. Perhaps Boom will publish something else with more detail about flying jackhammers?
To address that issue, ISTM we trust FAA to get many things right, but previously the thoughtful regulation of supersonic civil aviation was not one of those things. If this amendment passes, it will become one of those things. Is there a particular reason not to trust FAA thoughtfully to regulate this sort of flight?
Boom is writing about narrower issues of engine noise and fuel economy because they don't want to discuss the intractable problem they're named after. That doesn't mean we can't discuss it.
I think the status quo (no shattered windows in Chicago) is desirable and worth preserving. The FAA may regulate it sanely, but then again, given the current political climate, they may not.
It has been several months since I visited Chicago, but that was not my impression of the status quo? This is a very hypothetical concern, however. It's quite unlikely that any passenger flights will pass the sound barrier at an altitude of 200 ft. [0]
Then again, if Vladimir Putin wants to break some American glass in a really roundabout way, who are we to oppose him? Perhaps he needs to brush up on his Bastiat?
[0] https://military.id.me/aircraft/can-a-sonic-boom-break-glass...
Sonic boom strength scales with aircraft size, and you know this. Your footnote is in bad faith.
I don't know what that quip about Chicago was meant to accomplish, but I don't think you can complain about other people's "reading comprehension" while misapprehending that comment so thoroughly. Obviously, the point being made is that sonic booms break windows (some people near airports that saw supersonic traffic used to buy special windows), and Chicago is a major air transport hub.
This is somewhat misleading. What they are asking for is to be able to certify their plane under stage 3 noise regulations. Currently, it's legal to fly a stage 3 plane, but any design for a new plane submitted to the FAA after 2006 has to meet stage 4 regulations. Any design submitted as of the end of this year needs to be stage 5.
Effectively this is like a car manufacturer asking to only be required to meet fuel economy/emissions/safety standards from 10-20 years ago for a new vehicle. IMO this is reasonable. Stage 3 planes are fairly quiet, at least compared to what was flying around in the 70s and 80s. If regressing a bit on airport noise is the price we pay to go twice as fast, that's OK with me. I'd love it if we talked about this honestly, and shamed the people who whine about every tiny negative impact of human progress.
Boom and other proponents of lifting the supersonic aviation ban are trying to cause confusion between engine noise restrictions (relevant at takeoff) and the inescapable noise from a passing shock wave that is the byproduct of supersonic flight.
From the amendment text (https://www.commerce.senate.gov/public/_cache/files/0238c447...)
Proposed rule:
2) specifies a noise standard for sonic boom over the United States that—
(a) is economically reasonable and technologically practicable;
(b) is informed by noise levels that are tolerated in the United States for non-aviation purposes; and
(c) will foster employment in aircraft and aircraft engine manufacturing in the United States.
In other words "fuck you, we can make it as loud as a jackhammer".
"Pilot Lt Col Ed Yielding and Reconnaissance Systems Officer Lt Col Joseph Vida took off at Palmdale, California and landed at Washington-Dulles a scant hour, four minutes, and 20 seconds later."[1]
I don't remember any sonic boom complaints when this or other record setting SR-71 flights over the US occurred. If you are flying in thin atmosphere the magnitude of the sonic boom at the surface should be much reduced. So, maybe it would be ok to fly supersonic at 70,000+ feet. Of course, it might be disconcerting if you were flying subsonic at 38,000 feet.
[1] https://www.google.com/amp/jalopnik.com/the-sr-71-blackbird-...
The SR-71 definitely did produce sonic booms, there is a Stackexchange thread about it here: https://aviation.stackexchange.com/questions/17661/can-a-son...
They also point out that the space shuttle flew even higher and still made booms.
I think the lack of complaints for the SR-71 may be more due to the fact that it didn't fly very often, and that people had more understanding for the need for military aviation to be supersonic.
Thank you for the link to the stackexchange discussion. I read it and the Wikipedia and NASA pages it links to. Based on the Wikipedia link the calculated second table by the stackexchange author is incorrect. The Wikipedia article points out that the path of the N-wave will generally be curved upwards due to the temperature gradient from altitude to the ground making the distance longer. The path of the N-wave is not going to be the cone normally depicted. But, there are two things not discussed in the Wikipedia article that I think will also play a role in the magnitude of the sonic boom. 1) As altitude increases, air density decreases; meaning that for a given speed a smaller number of air molecules will be displaced thus reducing the magnitude of the sonic boom at the ground. 2) The sharp N-wave close to the supersonic source is not a soliton and will undergo dispersion reducing the over pressure. That is, as altitude increases and the distance to the ground increases, the N-wave is going to spread out into more of a layed-over-S wave reducing the magnitude of the sonic boom.
With regard to the SR-71 making record setting flights and flying at the limits of its flight envelope to do so(100,000+ feet or "the edge of space"), I think the sonic boom at that altitude may not be noticeable to human hearing.
I know the that the SR-71 and the Space Shuttle have produced very noticeable sonic booms, but what isn't answered is at what altitude did the sonic booms become noticeable or annoying. It seems to me that with all the things that reduce the the magnitude of a sonic boom that it may be possible to fly supersonic without being annoying and slow down to subsonic to takeoff and land. It might also be possible to design the aircraft body to promote dispersion of the N-wave.
Typo edit
Yeah, there's lots of potential issues, I don't know. It's true that the air is much thinner higher up, but I'm not sure how much that will help--I think a large part of the sonic boom comes from air displaced by the plane to create lift, and of course the momentum imparted by the plane to the air is constant (= the weight of the plane).
Also, I'm not sure the fact that the rays that forms the sonic boom are curved makes the sound itself weaker, it just takes longer to propagate down the the ground. But the fact that the sound spreads out towards the sides of the plane should help, the circumference of the shock cone at the point where it touches ground is proportional to the height of the airplane, so I'd expect things to scale down because of that?
I found and skimmed this document, "Review of Sonic Boom Theory" by K.J. Plotking (http://adl.stanford.edu/aa210b/Lecture_Notes_files/AIAA-1989...), which has some helpful information.
First, it notes that the shape of the wave does change while it propagates, but it turns out that the effect is in the opposite direction from what you suggested. That is, close to the aircraft the pressure forms a smooth S (the "mid-field" shape), but then as it moves further away, nonlinear effects causes the wave to bunch up to create the discontinuous N-shape. (See fig 1 and 2 on page 30.) So it seems, in this respect flying higher is actually worse---most research about reducing sonic booms tries to shape the aircraft to be long and thin, in order to make the waveform smoother, so we'd want there to less time for the wave to bunch up again.
Second, the document actually has a diagram of how the over-pressure depends on altitude! In fig 10 on page 34 it plots the calculated overpressure from a hypothetical Mach 2.7 supersonic transport. As I eyeball it, the over-pressure goes from 212 pounds/ft^2 at 40,000 feet (airliner level) to 129 pounds/ft^2 at 80,000 feet (SR-71 level), so it went down by a factor of 0.6. (In a cute coincidence, that 60% is almost exactly what's predicted by the scaling law eq. 25 on page 16, even though that equation is only intended for hypersonic aircraft.)
For an Advanced SST the quote near the end is, "Advances in aircraft technology suggest that sonic boom amplitudes for this type of aircraft, also referred to as a High Speed Civil Transport (HSCTJ or the "Orient Express". could be made substantially lower than first generation SSTs. potentially to the point that overland flight could be acceptable."
I'm not sure what to make of Fig. 10. I'm sure they are accurately plotting their equations, but the impulse for the SST is a minimum at 50,000 feet and increases for higher altitudes altitudes. The impulse for the HST generally increases with altitude. OTOH they discuss the N-wave forming in the far field and maintaining its shape, but also broadening which seems like it would reduce the impulse just like the overpressure.
The references 31-33 have alot of data. Here is a link to the first one: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196400...
PS - If you are getting three digits of accuracy eyeballing Fig. 10, you must have gotten a much cleaner copy than I did. ;)
I'm not sure, but the way I read it was that the impulse is the slope of the first "vertical" bar of the N, rather than the slope of the diagonal line. So as the pulse travels, the vertical part gets compressed and steeper (I increases), and the height of the N gets smaller (Δp decreases), and the the distance between the bars gets longer (broadening).
But yeah, figure 17 on page 26 of the document you linked seems to be exactly what we are looking for, great find! One can see exactly how the waveform changes with altitude. Moving from 42,100 feet to 70,700 feet reduced Δp from 1.82 to 1.13, a factor of 0.71.
> The Lee-Gardner Amendment would help us reduce drag by allowing us to make our engines narrower
What am I missing?
They're comparing things to current-day high-bypass turbofan jet engines, which are very wide by design and on-purpose (not because of some regulation).
Sure, part of the high-bypass allows for quieter noise levels, but it's also about efficiency at cruise altitude and speeds.
Turbojet engines designed for supersonic speed are already much narrower, well at least the nacelle is, or lack-thereof (again, by design -- optimized for fast speeds, not because of some regulation).
As far as I'm aware, the reason there aren't supersonic civil aircraft is because of the enormous cost involved in operating them, and the restrictions of supersonic flight over mainland due to shock wave damages, etc... not the size of the engine as appears to be asserted in this article.
So, any new legislation only needs to target lifting the over mainland restrictions (and somehow change physics to not have shock waves...), but you can't legislate-away the enormous costs involved in building and operating supersonic aircraft.
The article asserts that the problem fixed by the legislation is noise regulations that end up requiring wider supersonic engines to meet, which increase drag and cost of operation.
> So, any new legislation only needs to target lifting the over mainland restrictions
Which the legislation does...
> but you can't legislate-away the enormous costs involved in building and operating supersonic aircraft.
To the extent the costs result from legislative mandates, and are not inherent in building supersonic aircraft, you obviously can.
> The article asserts that the problem fixed by the legislation is noise regulations that end up requiring wider supersonic engines to meet, which increase drag and cost of operation.
> To the extent the costs result from legislative mandates, and are not inherent in building supersonic aircraft, you obviously can
The problems with cost are real, but it's more from flight restrictions than drag (subsonic flight over mainland to final destination using a supersonic-optimized engine is going to be very inefficient).
We can just look at the Concord as a prime example. Barred from supersonic flight over mainland, it became economically infeasible to continue to operate only trans-oceanic flights (I believe all 3 operators ran it as a loss-leader, of sorts, due to the novelty). Even then, when approaching the destination, the Concord had to revert to subsonic speeds, and ditch the shock wave while still out at sea. Unless there's some magical way to generate only minute shock waves from large passenger aircraft (I'm highly skeptical here), you're going to break people's windows etc, or you're going to burn up a bunch of fuel and wind up with the same issues all over again.
The other lesson learned from the Concord is, there's very few cases where people need to be somewhere that quickly, and are willing to pay the high ticket prices to do so. One can almost always book an earlier flight, for a substantial savings (I'm also highly skeptical there's any fuel cost savings with supersonic flight as the article seems to claim).
> The problems with cost are real, but it's more from flight restrictions than drag
No one is arguing that that isn't the case; as the article points out, the legislation addresses both the flight restrictions and the noise rule that the article claims functionally requires engine designs which increase drag.
> the legislation addresses both the flight restrictions and the noise rule
Noise rules are there for good reason (nobody likes broken windows)... and I'm sure there's military applications for quieter supersonic engines, but we don't have any (either because we haven't tried, or, more likely, because it can't be).
I suppose I'm just highly skeptical they can do both, or either, in reality. Sort of, having their cake and eating it too.
I'd love to be proved wrong here though, so I guess we'll have to wait and see.
> Noise rules are there for good reason (nobody likes broken windows)...
The engine noise rule at issue has nothing to do with broken windows, and the change is to use the same engine noise level restrictions as subsonic aircraft, rather than stricter rules for supersonic aircraft.
I didn't see any mention of how this would impact overall noise levels. Is there some regulatory process being added to handle supersonic passenger aircraft?
That's probably because changing fuel consumption goals has absolutely nothing to do with the magnitude or propagation characteristics of an atmospheric shockwave.
Unless the shockwave's shape (distorting coarseness of the wave front to soften the impact of sound waves; think: tweaking the volume knob to fade-in/fade-out a noise floor with gradual easing, rather than slamming a door as hard as you can) or size (how much air gets pushed around, overall) is altered by how a moving body breaks the sound barrier, a sonic boom will still be loud, and reach just as far.
When you crack a whip, the sound is just as loud, no matter how much energy your arm expends making the motion.
FTA "Additionally, the Lee-Gardner Amendment would require the FAA to eliminate the Mach 1 speed limit over the United States and replace it with a well tailored sonic boom standard."
Can somebody explain this please?
At super sonic speeds the noise is awful so to make it simple the FAA just says "no super sonic flight".
This changes that to force the FAA to do the complicated thing and be like "okay in these locations at this altitude and this size plane" and "at these locations at these altitudes and that size plane" and maybe "never at this location" or maybe "only during local business hours " and we end up with a book of "well tailored" regulations. Which while complicated might at least allow for Boom to operate inside the US, which opens up a lot business.
This is perhaps a bad political environment to propose a bill that would let billionaires operate supersonic pleasure craft over the US, at considerable annoyance to 99.99% of the population.
This seems like exactly the political environment to let the rich do whatever they want
For example, an SF - NY flight could be allowed to boom over northern Nevada, much of which is completely uninhabited. Right now it's completely forbidden over US territory.
Within the existing framework that forbids sonic booms, we suggest to adopt a flexible posture, pivot and disrupt air travel.
tldr: Screw the peasants on the ground, Silcon Valley tycoons should be allowed their pet jets.
> The Lee-Gardner Amendment would help us reduce drag by allowing us to make our engines narrower. Current engine noise rules for new supersonic aircraft are more stringent than those for the existing subsonic fleet. By setting our engine noise to the same levels as existing subsonic airplanes, we could make our engines produce so much less drag that we would save 20–40 percent on fuel, depending on whether you use this year’s or next year’s rules as a baseline.
They're narrowing the engine to get less drag and setting the noise to the same levels as conventional planes.
Skeptical. I know what narrower means but noise is a result rather than a parameter.
Engine noise is understood well enough that you can choose the level you want and develop an engine that is as good as possible that reaches that level.
It isn't the engine noise that is creating the sonic boom.
From my vague reminder about this the noise was widly exaggerated and booms design had a few things to make it slightly quieter.
Sonic booms are very loud and disruptive. NASA has done some research into mitigation by using blunt-nosed aircraft, but none of that applies to Boom's more conventional design.
Here's what the Concorde sounded like at altitude, from the ground: https://www.youtube.com/watch?v=cbPh2llw0-M
Being regularly subjected to anything even half as loud as that would be a complete non-starter for me.
"An engine this big generates a LOT of drag at Mach 2.2"
If this is the case write a Medium article about how BoomSuperonic is able to make turbofans go to Mach 2.2
Turbofans have no problem going mach 2.2 [1]. They're not super efficient at that speed but they're better than anything else we have.
What I don't understand is the engine size rule. I'm not aware of any regulation on the size of an engine air inlet....
[1] https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Sp...
TL;DR This is legislation Boom wants enacted to allow for more relaxed noise emission levels.
"Current engine noise rules for new supersonic aircraft are more stringent than those for the existing subsonic fleet. By setting our engine noise to the same levels as existing subsonic airplanes, we could make our engines produce so much less drag that we would save 20–40 percent on fuel, depending on whether you use this year’s or next year’s rules as a baseline."
Curious if they've hit a wall in their aerodynamic design and need this to move forward.
They want the regulations banning overland supersonic flight removed, and are trying to frame it as a fuel efficiency issue rather than the "we will make people's lives miserable with noise" issue that led to the ban.
It can be done sanely, but they don't have anything flying yet (was supposed to be May 2017 but that came and went).
Also, don't be fooled. The smaller test aircraft, if it ever flies, will have a much lower sonic boom than the larger airliner. Sonic boom is largely proportional to aircraft weight.
Reading between the lines it would appear that they are so far from having anything that flies that they're still willing to redesign their engine and presumably plane as a result.
(And yet they have the hubris to talk about how much a ticket will cost)
> They want the regulations banning overland supersonic flight removed
True, but
> and are trying to frame it as a fuel efficiency issue
No, they are trying to frame the changes they want to engine noise regs as a fuel efficiency issue; that's a separate rule change from (in the same legislation as) the one removing the overland supersonic flight ban.
> What I don't understand is the engine size rule.
It's not a size rule, it's an engine noise rule which ends up (per the article, I don't know enough about the relevant fields to confirm this) requiring wider engines which end up producing more drag.
> [When] at Mach 2.2, the air feels like Jello.
I know that's a metaphor, but it got me thinking. Can someone more learned help me out: does air behave in a non-Newtonian manner at supersonic speed?
You can think of it this way: at subsonic speeds, air ahead of the aircraft "knows" that the plane is coming, and can flow around it. At supersonic speeds, this information doesn't propagate forwards, and the plane smashes into the air ahead of it, creating a shock wave.
I'm anthropomorphizing and oversimplifying (airflow over a wing can be locally supersonic even in subsonic flight) but I don't care because I enjoy thinking of this in terms of information flow.
I am delighted by the idea of a little anthropomorphic chunk of air shouting "Move, there's a plane coming!" and then face palming upon realizing too late that it is using sound to warn other bits of air about something moving at supersonic speeds.
The speed of sound through air is effectively the speed of shockwaves through air. The way that the air responds to being pushed around at speeds faster than its shockwaves can respond results in something that behaves more like a liquid than a gas.
Not an engineer, but from my understanding air is a fluid that can be compressed. At extreme rates of speed in general atmospheric conditions, that results in a compression that the object is punching through. Often I learn about this stuff from high speed auto experiments (Bugatti, Toyota Land Speed Cruiser).
By non-Newtonian I think you mean relativistic. Boom is going Mach 2.2 or about 1500 mph. Light is going 186,000 mile per second.
Not even close.
https://en.wikipedia.org/wiki/Non-Newtonian_fluid
Thanks. They didn't cover viscosity in 7ABC at Cal. I just locked onto non Newtonian.
> One of the best ways to get fares down is to burn less fuel.
Edit: Removed the previous comment text here as I misread/misunderstood. This isn't just about the cost of the fuel, it's also about what you can do with the same amount if you burn it slower.
You burn a lot more fuel going fast in a low capacity aircraft.
Of course the fuel costs per person per mil of a bus are less than a van.
Good. Now the tiny minority (https://www.washingtonpost.com/news/dr-gridlock/wp/2016/03/0...) of insufferable NIMBYs who spend all day lodging airport noise complaints have something real to complain about.