Newsgroups: rec.aviation.military
From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer)
Subject: Re: Project Aurora and the utility of secrecy
Date: Mon, 8 Jan 1996 22:16:43 GMT

On 4 Jan 1996 14:41:12 GMT, mbohlman@ux4.cso.uiuc.edu (Mike Bohlmann) said:

MB> thomsona@netcom.com (Allen Thomson) writes:

>   The F-22 is a different matter: it does look a lot more like a
>conventional airplane, and it would be very interesting to understand
>why.

MB> I would guess that a big reason is because it is supposed to be a
MB> super-sonic cruiser.  What good, or rather, how much good, is
MB> radar stealth going to do when you are making sonic booms?

Just because you go supersonic doesn't mean the boom is going to reach
the ground and be sufficiently loud and recognizable to provide any
sort of warning.

Every now and then we fly the SR-71 over Dryden at Mach 3 and 85,000
feet.  I've been in the control room where I could see the ground
track and it's gone right overhead, but there was either no audible
boom or just a brief rumble.  Sensitive pressure sensors have recorded
the rather tatty remnants of the N-wave, but it's not really much of
an event to the ear.

If the N-wave from a big Mach 3 plane dissipates, you can bet that the
boom from a slower smaller plane will do the same.

--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA 
shafer@ferhino.dfrc.nasa.gov                               DoD #362 KotFR   
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html

Newsgroups: sci.aeronautics.airliners,misc.transport.air-industry
Date: 24 Nov 97 03:27:49
From: kls@ohare.Chicago.COM (Karl Swartz)
Subject: Re: Concorde's other customers

>Now imagine the Concorde takes off from JFK, goes up to is cruising
>level (60000ft?), and then crosses the sound barrier right above my
>head. How much noise will I perceive?

I was at Edwards AFB for their recent airshow, which included an
SR-71B doing a Mach 3 flyover at about 75,000 ft.  The boom sounded
like a couple of gunshots from a few hundred yards.  I don't know if
lower speed would reduce the intensity (I have a feeling it wouldn't)
but lower altitude and a larger aircraft would probably cancel out any
advantage of lower speed.

>If it is a heck of a lot, then you are right. If it is not, then the
>ban imposed by the US on supersonic flights over its own land was a
>political knee jerk to assure the Concorde was a failure.

While not tremendous, I can see how the noise could be startling and
thus worse than a conventional jet flying over at a few thousand feet,
especially if it happened a number of times per day, every day.

There was also the matter of engine noise on takeoff.  Having heard
a Concorde departure when the aircraft was about fifteen miles out
from Heathrow, I can easily understand why nobody wanted the thing
around.  The racket must be horrific up close.

--
Karl Swartz	|Home	kls@chicago.com
		|Work	kls@netapp.com
		|WWW	http://www.chicago.com/~kls/
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills

From: Mary Shafer <shafer@reseng.dfrc.nasa.gov>
Newsgroups: rec.aviation.military
Subject: Re: Blue Angels supersonic at airshows
Date: 13 Feb 1998 11:20:31 -0800

johnnynosspam@bright.net (John S.) writes:

> During the show, one of the solo planes flew right over the crowd
> (from our back to show center) about 200 feet above and I heard two
> distinctive "booms" as he passed over. It was like "POP,POP" then the
> sound of the engine thrust.
>
> I think he hit supersonic and we heard the sonic booms from the
> leading edge of his wing (fuselage strakes included)
> and the leading edge of the horizontal stab.

I think it's highly unlikely that the plane was supersonic.  I work in
a building under the medium-altitude supersonic corridor here at EDW
and when a plane goes over supersonic the boom is strong enough that
it makes the building flex so much that my Sparc monitor shakes.

No one who has been boomed that closely would describe the noise as a
"pop".  They're called "booms" because they're loud.  At that
distance, you would have felt it as much as heard it and you would
have spent the next 15 minutes or so saying "Huh?  What did you say?"

You may have heard a small shock that had formed on some portion of
the aircraft.  As has been mentioned in the discussion on hypersonic
flight, shocks do form well before the entire flow is supersonic and
it's possible that one might have been strong enough to reach you at a
Mach number well below Mach 1.

I remember being told that the F-104 would produce a _crackle_ at
about Mach 0.85 or so which was caused by a shock setting up on either
the wing or horizontal or, perhaps, both.  I didn't hear it, but I was
inside the plane at the time and the pilot was telling me that the
folks in the EDW control tower might have heard it as we did our
high-speed tower flyby.  I know the controllers were so pleased by it
all that they thanked the pilot for doing it, which is pretty
uncommon.

Also, I suspect that the plane did not fly right over the crowd.  The
Blues, like the T-Birds, haven't flown over the crowd for decades.
When they had that accident in Europe, with the Frecce Tricolare (I
can't spell in Italian at all, obviously) midair over the crowd, both
US teams, plus the Canadians, British, and everyone else, made very
righteous announcements about how _they_ never flew over the crowd
ever and hadn't since the year dot.

--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA
shafer@reseng.dfrc.nasa.gov                               DoD #362 KotFR
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html
For personal messages, please use shafer@ursa-major.spdcc.com

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Sonic booms from spacecraft?
Date: Sun, 7 Jun 1998 04:31:14 GMT

In article <357724BC.1E6A@ozemail.com.au>, IanD  <iand@ozemail.com.au> wrote:
>Does anyone know if "old-style" (non-shuttle) spacecraft make sonic
>booms?

They do, although the fact that most such US spacecraft launched and
reentered over water and slowed to subsonic speed well before recovery
meant that few people heard them.

>Does max-q during launch generate a sonic boom, and if so, was it
>audible from the ground.

There is a real bone-shaker of a sonic boom in a crescent-shaped region
50km or so downrange from KSC, where the combination of over-water launch
and safety regulations mean there's generally nobody to hear it.  Rockets
typically go supersonic while still climbing nearly vertically, but they
do of course tip over toward the horizontal fairly quickly.  Near the
launch site, any boom is from the vertical flight; far away, any boom is
from the horizontal phase.  In between, there is a small region which gets
the combined booms from a substantial length of the curved transition
trajectory, compressed and focussed into a single almighty slam.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

From: Mary Shafer <shafer@orville.dfrc.nasa.gov>
Newsgroups: sci.space.shuttle
Subject: Re: Double sonic-boom
Date: 23 Feb 2000 15:20:06 -0800

nyrangerfan@prodigy.notcombutnet (John) writes:

> I think I saw this a few months ago here on the NG, but...

> Aren't there actually three booms?  (But two being so close they
> sound like one?)

Not usually.  What happens is that all the little booms coalesce into
one double-peaked N wave and we hear the two peaks.  There are
conditions where you can hear more than one set of shocks, as when an
airplane is supersonic on the deck and there's not enough time for the
entire collection to merge together into the single N wave, but there
are not many aircraft that can fly that fast any more, so the
experience is uncommon.

--
Mary Shafer    http://www.dfrc.nasa.gov/People/Shafer/mary.html
shafer@orville.dfrc.nasa.gov Of course I don't speak for NASA
Senior Handling Qualities Research Engineer
NASA Dryden Flight Research Center, Edwards, CA
For non-aerospace mail, use shafer@spdcc.com please

From: Mary Shafer <shafer@orville.dfrc.nasa.gov>
Newsgroups: sci.space.shuttle
Subject: Re: Double sonic-boom
Date: 23 Feb 2000 15:17:04 -0800

"Julian" <julian@NOSPAMunhalfbricking.com> writes:

> I've heard this mentioned several times now, and it seems pretty much taken
> for granted, but could someone please explain why the shuttle has 2 of them?
> I understand how a sonic boom occurs but can't see why a second one may
> happen..... Mary??

The shock field reaches the ground in the form of an N and what you
hear are the two peaks.  The first peak is the compression shock at
the front of the airplane and the second is the expansion shock at the
back.  The reason there are two is that the compression shock is
formed at the front because the air can't move fast enough to get out
of the way of the airplane when it's supersonic and the expansion
shock is formed at the back because the air has to slow down and
uncompress to go back to being like the undisturbed rest of the air.

Actually, each sticky-outy bit has its own shocks, each one an N wave,
but the further you get from the airplane, the fewer there are,
because they all coalesce until there just the one big N wave that
comes down to the ground.  (Great tee shirt caption: Our SR-71 went
Mach 3.23 and all I got was one lousy N wave).

Have a look at the papers by Ed Haering at http://www.dfrc.nasa.gov/
and you can even see a photo of the whole set of close-up shocks taken
in flight.  If you want to hear the inside story of how we did the
sonic-boom measurements for the SR-71, invite me to visit (send money)
and I'll give my AIAA Distinguished Lecturer dinner speech.

On shorter aircraft flying at the same speed at the same altitude, the
sonic boom can sound like only one boom because the two step on each
other.  Other things that affect how the boom sounds on the ground are
speed, weight, altitude, the atmosphere, bank angle, distance from the
ground track, topography, the atmospheric boundary layer, and so on.
Sonic booms are sort of like thunder--if the boom is rumbly and dull,
the airplane is probably high or slow or farther away, but if the boom
is sharp, the airplane is probably low or fast or close by.  That's
because the high-frequency stuff gets lost first.

--
Mary Shafer    http://www.dfrc.nasa.gov/People/Shafer/mary.html
shafer@orville.dfrc.nasa.gov Of course I don't speak for NASA
Senior Handling Qualities Research Engineer
NASA Dryden Flight Research Center, Edwards, CA
For non-aerospace mail, use shafer@spdcc.com please

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: launcher shocks (was Re: Loan Guarantees for Launch Vehicles)
Date: Thu, 6 Apr 2000 03:41:19 GMT

In article <8cfu60$b33$1@nnrp1.deja.com>,
Len (Cormier) for MMI  <len@tour2space.com> wrote:
>IIRC, one of the FAQ answers on Shuttle says there is
>no boom on ascent, since the flight path angle is so
>steep that the shock fronts never reach the ground
>(or water?).  Perhaps the shocks are out to sea -- and
>therefore the writer of the FAQ answer ignores such shocks...

I think that would have to be it... or else the writer simply doesn't know
the full story.  See the "Shuttle Sonic Boom" paper, p. 397 in vol. 38 of
Progress in A&A, 1973.  Saturn V focused booms were heard and measured,
offshore; shuttle booms were predicted to be generally similar.  The
Saturn V ones were strong enough (overpressure peak around 420Pa) to break
windows.

The flight path angle is *initially* too steep for the boom to reach the
surface, but it doesn't stay that way long enough, and the transition is
what produces the focus, which hits the ground around 30nmi downrange for
the Saturn V.  Closer in, you do get some noise, because the focus passes
overhead, dissipating energy as it goes.  Farther out, you get a double
boom whose intensity trails off very rapidly.

There may be tricks you could pull to reduce this.  Note that the boom
comes mostly from the exhaust plume, because it's so much bigger
(especially at high altitude) than the vehicle itself.
--
"Be careful not to step                 |  Henry Spencer   henry@spsystems.net
in the Microsoft."  -- John Denker      |      (aka henry@zoo.toronto.edu)

From: Mary Shafer <mary.shafer@dfrc.nasa.gov>
Newsgroups: sci.space.shuttle
Subject: Re: Double sonic-boom
Date: Thu, 11 May 2000 09:54:36 -0700

Francisco Lameira wrote:
>
> On Tue, 22 Feb 2000 23:07:05 -0500, Tom <t2jr@bellsouth.net> wrote:
>
> As I've read, every plane (supersonic) produce both sonic booms. BUT
> only the shuttle has the dimensions to make the second
> distinguishable.

I sit right under the medium-altitude supersonic corridor at Edwards
and can tell you that numerous aircraft, few bigger than the F-15 or
F-22, make double booms that can be heard as being double.

In fact, I've also been overflown by an SR-71 at Mach 3.23 at about
83,000 ft (higher and faster than the Orbiter's boom right at the
landing site) and it too is _usually_ capable of producing booms that
are distinctly double, but it does sometimes produce one longish boom.
It does the same at Mach 1.5 or so and 28,000 ft.

The usual causes of a single-sounding boom are distance from the
centerline of the ground path of the boom and atmospheric conditions,
particularly the state of the boundary layer at about 7500 ft AGL.
The boundary layer is a very good filter and can turn a nice, if faint,
boom into an indistinct rumble, particularly if aided by an inversion
layer.

As for the effect of distance, right at the surface of the vehicle, say
a couple of hundred feet below it, there are two booms for every sticky-
outy piece of the vehicle--nose, cockpit front (and back, depending on
fairing), inlet, wing leading and trailing edges, vertical tail leading
and trailing edges, and horizontal tail leading and trailing edges.  Of
course, physical proximity can cause some of these to coalesce almost
immediately.  However, we've measured as many as six or eight pressure
peaks (booms) up close.  As the shock cone moves away from the vehicle,
the shocks continue to coalesce, usually into the double-boom N-wave.  I
believe that recordings of the Orbiter boom on the ground have shown that
it has two large peaks, but still has smaller peaks between the two big
ones.  People don't hear them because the pressures aren't that large,
compared to the large peaks, though.

If you'd like to see a photo of an F-18 with multiple sets of shocks in
the near field, go to the technical reports archive or the Public Affairs
press releases at http://www.dfrc.nasa.gov/ and look for the name "Haering".
There's a great Schlieren photo of an F-18 with about six shocks at the
surface, and the coalescing into fewer shocks is also visible in this
photo.  Also, AvWeek printed a similar photo of the Langley T-38, which
may be available on the Langley site, http://www.larc.nasa.gov/ or in the
AvWeek web-site archives.