
Lee-Gardner Amendment would reduce supersonic fuel burn - Osiris30
https://blog.boomsupersonic.com/lee-gardner-amendment-would-reduce-supersonic-fuel-burn-by-20-percent-or-more-34a189465af4
======
jessaustin
[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...](https://www.commerce.senate.gov/public/_cache/files/0238c447-3e61-475b-bbb1-27eeb54c3831/A8CDC5A8788C7557D876E4B78421F805.s.-1405-lee-3.pdf)

~~~
idlewords
You're ignoring section 2, which says the sonic boom can be as loud as other
things the public tolerates (like jackhammers).

~~~
jessaustin
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?

~~~
idlewords
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.

~~~
jessaustin
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...](https://military.id.me/aircraft/can-a-sonic-boom-break-glass/)

~~~
idlewords
Sonic boom strength scales with aircraft size, and you know this. Your
footnote is in bad faith.

------
idlewords
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...](https://www.commerce.senate.gov/public/_cache/files/0238c447-3e61-475b-bbb1-27eeb54c3831/A8CDC5A8788C7557D876E4B78421F805.s.-1405-lee-3.pdf))

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".

------
c517402
"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-...](https://www.google.com/amp/jalopnik.com/the-
sr-71-blackbird-retired-by-flying-coast-to-coast-in-1689846454/amp)

~~~
vilhelm_s
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...](https://aviation.stackexchange.com/questions/17661/can-a-sonic-boom-
produced-at-60-000-be-heard-on-the-ground)

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.

~~~
c517402
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

~~~
vilhelm_s
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...](http://adl.stanford.edu/aa210b/Lecture_Notes_files/AIAA-1989-1105-891.pdf)),
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.)

~~~
c517402
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...](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640014910.pdf)

PS - If you are getting three digits of accuracy eyeballing Fig. 10, you must
have gotten a much cleaner copy than I did. ;)

~~~
vilhelm_s
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.

------
Alupis
> 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.

~~~
dragonwriter
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_.

~~~
Alupis
> 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).

~~~
dragonwriter
> 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.

~~~
Alupis
> 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.

~~~
dragonwriter
> 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.

------
NegativeLatency
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?

~~~
johnm1019
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."

~~~
barronlroth
Can somebody explain this please?

~~~
Avshalom
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.

~~~
sbierwagen
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.

~~~
mvid
This seems like exactly the political environment to let the rich do whatever
they want

------
LightskinKanye
"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

~~~
pdelbarba
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...](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Specific-
impulse-kk-20090105.png/700px-Specific-impulse-kk-20090105.png)

~~~
toomuchtodo
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.

~~~
idlewords
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.

~~~
pdelbarba
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.

~~~
Avshalom
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)

------
venning
> _[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?

~~~
idlewords
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.

~~~
Avshalom
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.

------
pricechild
> 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.

~~~
dsfyu404ed
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.

------
zkms
Good. Now the tiny minority ([https://www.washingtonpost.com/news/dr-
gridlock/wp/2016/03/0...](https://www.washingtonpost.com/news/dr-
gridlock/wp/2016/03/07/are-you-the-person-who-filed-6500-noise-complaints-
against-national-airport/)) of insufferable NIMBYs who spend all day lodging
airport noise complaints have something real to complain about.

