Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
sean1234
Topic Author
Posts: 401
Joined: Fri Aug 18, 2000 2:52 pm

Sound Barrier

Mon Oct 03, 2005 9:21 am

I was at the Salinas, CA air show today. An F-18 super-hornet was going through his display and flew past very fast one time in level flight with the spherical condensation cloud effect around the aircraft, after this I heard a loud pop. I'm just wondering if this guy broke the speed of sound? I wasn't tremendously loud at least compared to the engines, but it was certainly noticeable.
 
EMBQA
Posts: 7858
Joined: Sat Oct 25, 2003 3:52 am

RE: Sound Barrier

Mon Oct 03, 2005 9:51 am

If he had broken the sound barrier you would have know it. It would sound like a very loud clap of thunder then you would have also felt. It sound like he was close to it though. The condensation is formed if the humidity is just right, and the noise you heard was just the shock wave of the engine noise moving past you.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Sound Barrier

Tue Oct 04, 2005 1:09 am

Worth mentioning that the mach range from 0.75 to 1.2 is called "trans sonic" meaning that as slow as .75 there might be locally supersonic airflow over some parts of the aircraft (called MCRIT) and at speeds as high as M 1.2 there may still be subsonic airflow over some parts. (Not counting the always-subsonic air intakes.) When we are talking about supersonic flight we are talking about free-stream mach number, in other words the whole airplane moving through the air faster than the local speed of sound.

Advanced designs such as the F-18 slip through this region much more easily than earlier designs such as the F-100, disturbing the air far less and therefore producing fewer pressure waves like that. Hard to say what produced the pressure wave you experienced. I get that kind of effect every time "Rare Bear" flies past my house, I assume from his prop tips. I agree though, if his meter was fully above 1.0 you'd have experienced more than a pop.

edit: There is a terrific picture of an F-4 going super at (I believe) El Toro. The shockwave is dramatically visible beneath the plane. (Bob Hoover is also sitting in the background.) Anyone have a link to that picture?

[Edited 2005-10-03 18:11:25]

[Edited 2005-10-03 18:14:05]
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
TedTAce
Posts: 9098
Joined: Sun Mar 27, 2005 12:31 am

RE: Sound Barrier

Tue Oct 04, 2005 3:59 am

Quoting SlamClick (Reply 2):
Anyone have a link to that picture?

You mean the one you get when you type "f-4 supersonic" @ Google?
http://www.tom-chris.com/galleries/aviation/Navy/images/F-4,%20supersonic.jpg
This space intentionally left blank
 
Wilsonjcobb
Posts: 30
Joined: Tue Oct 21, 2003 10:54 pm

RE: Sound Barrier

Tue Oct 04, 2005 12:56 pm

I too saw an F/A-18F doing a TAC demo this past weekend in Millington, Tn and the narrarator said he will come in just under Mach 1 taking extreme care not to excede that and sure enough just as he passed the crowd the vapor cloud started to form. It was a pretty cool sight. But I would say he didn't break the barrier.

Joe
 
Lurch
Posts: 721
Joined: Mon Jul 21, 2008 11:54 am

RE: Sound Barrier

Tue Oct 04, 2005 8:03 pm

If you watch this video right click and save it.

http://concorde002.free.fr/tesgo_dvpal.rm

You will se and hear what a Sonic Boom is like.

It will show you what the SONIC BOOM is like although this machine is miles above the people on the Fishing Boat!
 
sean1234
Topic Author
Posts: 401
Joined: Fri Aug 18, 2000 2:52 pm

RE: Sound Barrier

Wed Oct 05, 2005 1:41 am

Ya, that's the sound it made. The F-18 was only a few hundred feet off the ground and maybe half a mile away. So perhaps as mentioned above parts of it went supersonic. I assume that if the whole plane did break the sound barrier I would have felt a shock wave because of my close proximity, though I didn't.

[Edited 2005-10-04 18:58:27]
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Sound Barrier

Wed Oct 05, 2005 10:51 pm

Quoting TedTAce (Reply 3):

That is the one. Thanks for doing that! (Never chase your own hat, someone else will be glad to do it for you.)

Love that picture. I'd forgotten that it was the VX-4 Playboy F-4 that did it. Figures! That shockwave underneath would probably knock you fifty feet down the runway.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
aeroguy
Posts: 66
Joined: Wed Aug 15, 2001 1:33 am

RE: Sound Barrier

Thu Oct 06, 2005 12:01 pm

If you have not seen this site yet, it has an excellent description of what is happening here (i.e. just because you see some vapor, that doesn't mean the plane is supersonic):
http://www.fluidmech.net/tutorials/sonic/prandtl-glauert-clouds.htm

I just came across this site recently and I was pretty relieved that there was actually a nice (and correct!) explanation out there among all the misinformation on this topic.

And there are links to a number of pictures:
http://www.galleryoffluidmechanics.com/conden/pg_sing.htm

[Edited 2005-10-06 05:09:11]
 
TedTAce
Posts: 9098
Joined: Sun Mar 27, 2005 12:31 am

RE: Sound Barrier

Thu Oct 06, 2005 12:31 pm

Quoting Aeroguy (Reply 8):

Great Links  Smile  thumbsup 
This space intentionally left blank
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Sound Barrier

Thu Oct 06, 2005 11:22 pm

So here's a question; if you were in that speed range, and at those atmospheric conditions to produce the Prandtl-Glauert singularity could you make yourself IMC on an otherwise-clear day?

The F-16 picture on the second site appears to depict a canopy wreathed in visible vapor.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
waterpolodan
Posts: 1621
Joined: Sun Feb 13, 2005 3:46 pm

RE: Sound Barrier

Thu Oct 06, 2005 11:49 pm

If you want an even cooler video of what a sonic boom sounds like (actually, I don't know, the other video didn't play for me), watch this F14 fly past a carrier, no more than 80 feet off the water... he is deffinately supersonic, the plane is well past the camera before you hear any noise at all, and then WHAM, a deafening boom... sooooo cool! Also, just before he passes it looks like he is dropping flares into the water...

http://www.alexisparkinn.com/photoga...deos/Supersonic%20F14%20flyby.mpeg

[Edited 2005-10-06 16:51:21]
 
TedTAce
Posts: 9098
Joined: Sun Mar 27, 2005 12:31 am

RE: Sound Barrier

Fri Oct 07, 2005 1:16 am

Quoting Waterpolodan (Reply 11):
just before he passes it looks like he is dropping flares into the water...

Either that or the engines are falling apart in a very orderly fashion  stirthepot 
This space intentionally left blank
 
SATL382G
Posts: 2679
Joined: Sat Aug 14, 2004 12:02 am

RE: Sound Barrier

Fri Oct 07, 2005 1:43 am

Quoting TedTAce (Reply 12):
Either that or the engines are falling apart in a very orderly fashion

No, that's another hi-speed F-14 passes by the ship video.  Smile Ends with a dual ejection. I have never seen that video on the web though, I think it's copyrighted by Discovery Channel.

[Edited 2005-10-06 18:45:57]
"There’s nothing quite as exhilarating as being shot at and missed" --Winston Churchill
 
waterpolodan
Posts: 1621
Joined: Sun Feb 13, 2005 3:46 pm

RE: Sound Barrier

Fri Oct 07, 2005 2:09 am

The accelerative forces involved in ejecting at supersonic speeds and low altitude must be really intense... I don't envy those guys in the video you're talking about
 
SATL382G
Posts: 2679
Joined: Sat Aug 14, 2004 12:02 am

RE: Sound Barrier

Fri Oct 07, 2005 2:43 am

Quoting Waterpolodan (Reply 14):
The accelerative forces involved in ejecting at supersonic speeds and low altitude must be really intense... I don't envy those guys in the video you're talking about

In this particular video, they do a hi-speed pass by the ship and then the engines comes unglued. They do a zoom climb to get some altitude and assess situation, meanwhile they are losing hydraulic fluid. Controls lock up. By the time they punch out they've slowed considerably and have gained (I'm guessing) 1500 or 2000 ft.

Video also shows SAR helo picking them up, discharging them on the deck, and a interview with the crew.

It's on one of Discoverys aircraft carrier documentaries.
"There’s nothing quite as exhilarating as being shot at and missed" --Winston Churchill
 
User avatar
RayChuang
Posts: 8138
Joined: Sat Jun 24, 2000 7:43 am

RE: Sound Barrier

Fri Oct 07, 2005 5:55 am

If I remember correctly, you can do an analogy of supersonic flight like this:

1. In subsonic flight, it would be like rowing a boat in calm water.

2. In transonic flight, it would be like rowing a boat in choppy water.

3. In supersonic flight, it would be like riding a boat with a higher power onboard motor.

That's why the de Havilland DH. 108 Swallow crashed--the plane lost aerodynamic control because it couldn't stay aerodynamically stable from the shockwaves of transonic flight. Those transonic shockwaves nearly foiled the Bell X-1's attempt at supersonic flight until engineer Jack Ridley figured out how to keep the plane stable with that "flying" horizontal tail surface to mitigate the transonic shockwaves.
 
Duce50Boom
Posts: 723
Joined: Tue May 29, 2001 8:03 am

RE: Sound Barrier

Wed Oct 12, 2005 5:28 am

The Tomcat carrier flyby/crash investigation found the accident to be the fault of the pilot, LtCdr Jonathon Bates. IIRC, the engine compressor stalled and he screwed up the recovery.

A year or two later, the same pilot was involved in another class A. This time whilst doing an unrestricted climb out of Nashville, the engine compressor stalled and he fu--ed up again. Killed two or three civilians sitting at home as well as himself and his RIO
 
Silver1SWA
Posts: 4666
Joined: Wed Mar 10, 2004 6:11 pm

RE: Sound Barrier

Wed Oct 19, 2005 2:16 pm

Quoting Sean1234 (Reply 6):
Ya, that's the sound it made. The F-18 was only a few hundred feet off the ground and maybe half a mile away.

You serious? It made the same sound as the one in the video? Hmm...

Usually the high speed passes are just under the sound barrier. As the aicraft passes, different vapor formations form and a very deep rumble is heard/felt right before you hear him pass by. I could also hear this from a distance of a couple miles this weekend while the Blues practiced at Miramar. I heard this rumble that I seemed to also feel. It wasn't that loud...but you could sense the power of the air disturbance.

Here is what the high speed pass looked like at Oceana. I got lucky and captured this. Sorry about the quality. He was flying out of frame. lol

It pretty much looked the same at Miramar this past weekend.

Check this out. I found these a while back.




The Blues used to use their high speed pass as a sneak pass while you are supposed to be watching the other 4 do something overhead. It used to come from behind you scaring the sh*t out of everyone. Now they do it along the runway from left to right. Makes it easier to keep an eye on him for a picture. hehe
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
bhill
Posts: 1789
Joined: Thu Sep 13, 2001 8:28 am

RE: Sound Barrier

Mon Oct 24, 2005 11:19 am

Curious..in all of those videos..there is a "double boom". Why is that? Are different sections of the aircraft causing more than a single boom? If so, why only two?

Thanks
Carpe Pices
 
Duce50Boom
Posts: 723
Joined: Tue May 29, 2001 8:03 am

RE: Sound Barrier

Fri Oct 28, 2005 9:49 am

Quoting Bhill (Reply 19):
Curious..in all of those videos..there is a "double boom". Why is that? Are different sections of the aircraft causing more than a single boom? If so, why only two?

You are correct, sir. The first boom is caused by the nose going supersonic, the second by the tail. I'm no aeronautical engineer, but there are quite a few websites, courtesy of google, that explain the why's.
 
khenleydia
Posts: 383
Joined: Tue Feb 15, 2005 2:18 am

RE: Sound Barrier

Fri Oct 28, 2005 5:49 pm

A long time ago, I was on a fishing boat around San Clemente island (out past Catalina). A couple of A-7s did a low level, high speed pass and had our attention completely. Everyone on the boat was watching them. They went over us and then starting climbing out. The next thing I remember is that while everyone is staring at that, we get the double boom and then the LOUD afterburner sound as an F-14 screamed by. It was followed by another pair of F-14s too. They were on the edge of the sound barrier. Oh, it was the coolest thing!!!! Throughout the day of fishing, they would do some fly byes, but nothing like that first pass. Wow!

KhenleyDIA
Why sit at home and do nothing when you can travel the world.
 
vikkyvik
Posts: 12574
Joined: Thu Jul 31, 2003 1:58 pm

RE: Sound Barrier

Sun Oct 30, 2005 11:51 am

I was up at the Edwards air show last Sunday, and a few different planes did high speed passes (around 700 mph according to the announcer). None of them made a sound like a sonic boom (or at least what I would expect a sonic boom to sound like). Just the usual deafening sound of afterburners. Nor was there any vapor cloud (then again, this is in the desert).

I heard, however, that during the Saturday show an F-16 intentionally broke the sound barrier. Unfortunately they didn't do that on Sunday, unless they did it at the beginning of the show.

On an unrelated note, seeing an F-22, a B-52, a B-2, and an F-117 all do demos was the highlight of my air show life.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
bhill
Posts: 1789
Joined: Thu Sep 13, 2001 8:28 am

RE: Sound Barrier

Sun Oct 30, 2005 4:52 pm

Vik, as I understand Dr. Mach's equations, and Slamclicks discussions on this subject, Mach functions are primarily a function of atmospheric density and ambient temperature. You can make a boom at a lower velocity at a higher altitude where the mmHg are lower. For the vapour effect, all of the pictures that I have seen were at or near sea level, I'm pretty sure this is a function of temperature as I do not remember seeing a shock wave form aircraft breaking the barrier in the desert; the higher the temp, the less the atmosphere can hold water to get in the way to be condensed...no?

Cheers
Carpe Pices
 
vikkyvik
Posts: 12574
Joined: Thu Jul 31, 2003 1:58 pm

RE: Sound Barrier

Mon Oct 31, 2005 9:04 am

BHill,

The vapor effect would depend on the local relative humidity. In a desert situation, with a humidity of say 10%, the air can cool down much more and still hold the same amount of water vapor (the saturation vapor pressure decreases with temperature). If the humidity were, say, 80%, then the air might only be able to cool a couple degrees before the vapor starts condensing. I forgot to mention, however, that I did see lift-induced condensation when the F-16s were doing high-G maneuvers.

The speed of sound in a particular substance fluctuates with temperature. The higher you go in the troposphere, the lower the temperature (in general), and hence, the lower the speed of sound.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
jwenting
Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

RE: Sound Barrier

Mon Oct 31, 2005 8:06 pm

A double boom could also be caused by reflection of the sound from buildings (like hangars).

If you can hear the direction of the booms you can tell. If the second one comes from somewhere else it's reflection.
I wish I were flying
 
beefstew25
Posts: 596
Joined: Fri Sep 30, 2005 11:40 am

RE: Sound Barrier

Tue Nov 01, 2005 1:55 am

Quoting SlamClick (Reply 2):
(Not counting the always-subsonic air intakes.)

Why do the air intakes stay subsonic, and how is that even possible?
MLB
 
jwenting
Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

RE: Sound Barrier

Tue Nov 01, 2005 2:14 am

The air intakes go supersonic, but are designed to slow the air inside them in order to ensure a subsonic airflow into the combustion chamber.
I wish I were flying
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Sound Barrier

Tue Nov 01, 2005 4:12 am

One example:

The F-4 had these movable inlet ramps as part of the system.

View Large View Medium
Click here for bigger photo!

Photo © Günter Grondstein


(Isn't that a great photo? Looks like an oil painting.

The F/A-18 has perforations in the intake, like an air hockey table. I'm sure they play some role in slowing the intake air.

Someone more familiar with these planes than I am will have to explain just how these systems work.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
User avatar
vzlet
Posts: 820
Joined: Thu Mar 11, 2004 10:34 am

RE: Sound Barrier

Wed Nov 02, 2005 1:24 am

Quoting Beefstew25 (Reply 26):
Why do the air intakes stay subsonic, and how is that even possible?

Intakes on supersonic planes have some means of generating a shockwave or series of waves which decelerate the airflow entering the intake. Typical devices are a sharply edged splitter plate:

View Large View Medium
Click here for bigger photo!

Photo © Charles Falk
View Large View Medium
Click here for bigger photo!

Photo © Italian Spotter


View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle
View Large View Medium
Click here for bigger photo!

Photo © Steven Hadlow


or cones or partial cones:

View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle
View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle



I don't know if it's the same on sharp-edged but continuously curving inlets. Perhaps someone can elaborate on how these work:

View Large View Medium
Click here for bigger photo!

Photo © Michael Baldock
View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle



Quoting SlamClick (Reply 28):
The F/A-18 has perforations in the intake, like an air hockey table.

Perforations on inlet ramps are used to draw off air to help prevent formation of a stagnant boundary layer:

View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle
View Large View Medium
Click here for bigger photo!

Photo © Bart Hoekstra

"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
 
beefstew25
Posts: 596
Joined: Fri Sep 30, 2005 11:40 am

RE: Sound Barrier

Wed Nov 02, 2005 4:33 am

Quoting Vzlet (Reply 29):

Man you guys are smart.

Another question...I would imagine these inlets create a drag penalty...right?
MLB
 
aeroguy
Posts: 66
Joined: Wed Aug 15, 2001 1:33 am

RE: Sound Barrier

Thu Nov 03, 2005 12:30 pm

Vzlet, the inlets on the F-8 and the Saab you have there are normal shock type inlets. (In reality, the F-16 you show actually has a normal shock type inlet as well). Normal shock inlets have a normal shock that sits at the mouth of the inlet during supersonic flight. (It can also become detached but that's not important right now). So supersonic air enters the inlet and goes through the shock and decelerates to subsonic speed so it's ready to enter the engine compressor.

With that said, a big driver in inlet design is the pressure recovery. Pressure recovery is the ratio of total pressure delivered to the engine to that of the freestream. Simply stated, the higher your pressure recovery, the less loss you suffered because of your inlet. And pressure recovery is a fairly big deal because it directly affects engine thrust.

Pressure recovery across a shock is a function of the shock strength which is related to the change in speed across the shock. The stronger the shock, the less pressure recovery. So from a pressure recovery standpoint, you'd rather decelerate Mach 1.1 flow to subsonic than Mach 2 flow to subsonic across a normal shock.

Enter the ramp and cone type oblique shock inlets you mentioned on the F-22, MiG-21, and others. Oblique shock inlets are designed so that one or more oblique shocks form on the ramp or cone and extend back into the inlet. Inside the inlet, the oblique shock(s) are reflected off the walls in a zig-zag pattern. Supersonic air that enters the inlet passes through this series of oblique shocks. Oblique shocks take supersonic flow and slow it down to a lower but still supersonic speed. (Keep in mind, pressure recovery for oblique shocks isn't too shabby because they are not that strong).

So let's say we had Mach 2 air that we were able to take down to Mach 1.1 with a series of oblique shocks. We still need to get it down to subsonic before it enters the engine and the only way that's going to happen is with a normal shock. But thanks to the oblique shocks, the normal shock only has to take us down from Mach 1.1, not Mach 2. The pressure recovery is therefore better for this oblique shock inlet than a normal shock inlet.

Now there are some trade-offs in the design, namely the complexity of an oblique shock inlet (it's hard to do without some sort of variable geometry) and whether a fighter is really going to spend a lot of time flying supersonic, etc. The F-16 is a good example of just putting a simple and cheap normal shock inlet on what is intended to be a simple and cheap fighter.
 
User avatar
Loran
Posts: 690
Joined: Mon Jul 04, 2005 11:13 am

RE: Sound Barrier

Thu Nov 03, 2005 8:36 pm

Very good explanation, Aeroguy. In addition to that it is worth showing the complex system of the Concorde Olympus 593 Mrk610 turbojet inlets, which decellerate the airflow from over Mach 2 to a subsonic airflow.

Concorde Engine Subsonic:


Concorde Engine Supersonic:


You can see the series of oblique shocks which are directed by the ramps to a short series of vertical shocks, to decelerate to subsonic speeds. The major issue in the inlet ramp design is to identify the right number of oblique and vertical shock waves to obtain minimum losses (maximum efficiency), with keeping the ramp komplexity as low as possible. The high complexity of the concorde system is justified due to the major part of the flight envelope in supersonic speeds.

Check the webpage out, it has some further descriptions on this toppic:

http://www.concordesst.com/powerplant.html

Regards,
Loran
703 717 727 732-9 747 757 767 777 787 AB2/6 310 318-321 330 340 359 380 D8M D91/3/5 D1C M11 M81-90 L10 IL1/8/6/7/W/9/4 TU3/5/2 YK4/2
 
LMP737
Posts: 6027
Joined: Wed May 08, 2002 4:06 pm

RE: Sound Barrier

Sat Nov 05, 2005 8:18 am

The F-14 uses a system similar to the Concorde to decelerate the air flow and keep super sonic shock waves from hitting the compressor. On the F-14 it's called AICS (Air Inlet Control System), the bleed door is on top. It's a definite no-go item, fortunately it's a preety reliable system.
Never take financial advice from co-workers.
 
KDTWflyer
Posts: 825
Joined: Tue Jun 29, 2004 12:51 pm

RE: Sound Barrier

Sat Nov 12, 2005 6:39 am

Quoting Lurch (Reply 5):
If you watch this video right click and save it.

http://concorde002.free.fr/tesgo_dvpal.rm

You will se and hear what a Sonic Boom is like.

It will show you what the SONIC BOOM is like although this machine is miles above the people on the Fishing Boat!

Lurch... Amazing find! I've been looking on the net for a long time to find such a video.

Who is online

Users browsing this forum: No registered users and 14 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos