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View Full Version : Heard a double sonic boom yesterday



Captain Kidd
2004-Nov-17, 01:28 PM
Walking to my car yesterday and I heard a couple F22s go by in super cruise (they can fly supersonic without using afterburners). Weíve been hearing them fairly regularly; Lockheed is building them nearby and as itís too far to the Gulf of Mexico to do their testing, theyíve received permission to do it along the Tennessee valley area. What surprised me was that until now Iíve been inside and the building muffles the shock wave enough that itís more felt than heard; yesterday, however, I was outside with no buffering and I noticed that it was a double boom.

It was pretty cool, I stopped and listened to the echoes bouncing around the buildings trying to figure out if I had indeed heard a double boom when the second plane went by and sure enough it was a double. I didnít know the nose and tail were far enough apart to create a noticeable time lag between the shock waves.

I had given up hope of hearing one as Iíll probably never get around to being in the right place and time to watch a shuttle landing before theyíre retired.

Nicolas
2004-Nov-17, 01:34 PM
Isn't it so that a supersonic plane is constantly doing BOOM BOOM BOOM BOOM but due to the speed you only hear one or two booms that were close to you, rather than due to the plane's length? I remember hearing double booms often as a kid (from starfighters) these flew in pairs often however, so I'm not sure if I heard them ever coming from one plane.
Any info?

Wally
2004-Nov-17, 01:38 PM
Isn't it so that a supersonic plane is constantly doing BOOM BOOM BOOM BOOM but due to the speed you only hear one or two booms that were close to you, rather than due to the plane's length? I remember hearing double booms often as a kid (from starfighters) these flew in pairs often however, so I'm not sure if I heard them ever coming from one plane.
Any info?

It's not so much as doing a "BOOM BOOM BOOM". Rather, it's a single BOOM (or shock wave) spreading out from the nose (and wing tips and tail fins) like a bow wave on a boat. You hear the BOOM as the wave travels over you.

editted to add: I too thought the F22 was too small to be able to detect separate waves from the nose/tail. . . Hmmmm!

BlueAnodizeAl
2004-Nov-17, 02:24 PM
The F-22 is quite large! I've seen one of the ealry ones on the ground at the National Air Force Museum in Dayton Ohio, Wright Patterson Air Force Base. Absolutely beautiful airplane!

Wally
2004-Nov-17, 02:33 PM
The F-22 is quite large! I've seen one of the ealry ones on the ground at the National Air Force Museum in Dayton Ohio, Wright Patterson Air Force Base. Absolutely beautiful airplane!

it's all relative, I guess. Looks like it's comparative in size to an F-14 (my overall favorite, by the way. Just love the looks of the thing!).

Hey, while googling for the stats on the planes, I came across this awesome image of an F-18 hornet just breaking the sound barrier.

http://www.chinfo.navy.mil/navpalib/ships/carriers/constellation/con-sndbar.jpg

Supposedly, the conditions were perfect as far as moisture content of the air, ect. Pretty darn cool. . .

Nicolas
2004-Nov-17, 04:20 PM
Belgian airshows often take place in quite bad weather, but the moisture is excellent to see some cone forming as they close in to mach 1 (but don't cross it of course).

So the plane does booooooooooooooooooooooooooooooooooom and you hear a "boom" as the shock wave passes you. So in order to hear "boom boom" you'd need 2 shocks. If one would be from the tail and one from the nose, and both would have the same shock angle, there would be very little time between the booms (15 meters @ 1000 km/u is about 0.05 sec). So what can happen:

1) It were 2 planes (obvious possibillity).
2) One plane made 2 shocks eg nose cone and tails, or nose cone and rear end of canopy. These shocks have a different bow angle, and considering the plane's flight height, this gives quite some distance difference when the shocks reach the ground.

I believe that with option 2, you'd hear the rear shock first, as the first shock is the hardest and therefore has the sharpest angle. That is if I remember my colleges correctly.

I remember the sound of a double boom as "booboom" and sometimes just getting to "boom boom"(so you have an idea of the interval) but what I heard were often 2 planes. maybe the boobooms were 1 starfighter, the boombooms 2.

Captain Kidd
2004-Nov-17, 04:37 PM
I'm also going with option 2 unless there were 4 planes buzzing around yesterday in a tight formation.

I almost did the interval in the OP, probably should have. It was indeed extremely close between the shock wave arrivals, far less than a second. A "bo-boom", I'd almost hazard "b-boom" if spoken aloud.

crateris
2004-Nov-17, 04:43 PM
What and AWESOME pic of an F-18 emerging from its cloaking fog!

:lol:

C.

tlbs101
2004-Nov-17, 07:42 PM
I thought all sonic booms were doublets; one from the nose and one from the tail.

Nicolas
2004-Nov-17, 07:47 PM
The amount of shocks coming from an object going supersonically depend on its shape (including surface condition). If you'd have a supersonic saw, you'd probably get a shock from every tooth. Planes can make shocks at the nose, tail fins, wing edges, canopy rear or other negative curved parts and others. There are different types of shocks too.

If you heard a b-boom it probably was one plane flying not too high.
Here at TU Delft we are loking for designs that minimize the boom loudness.

Captain Kidd
2004-Nov-17, 07:53 PM
I thought all sonic booms were doublets; one from the nose and one from the tail.It's my understanding that most supersonic fighters are short enough that the booms arrive nearly simultaneous so that it appears to be only one.

Mars
2004-Nov-17, 07:57 PM
I got to hear it the last time Endeavor landed, actually it was the last shuttle to land.

Nicolas
2004-Nov-17, 08:29 PM
It's my understanding that most supersonic fighters are short enough that the booms arrive nearly simultaneous so that it appears to be only one.

But what when the bow and trailing edge shock have severly different angles? Then they can arrive at considerable distances when they reach the ground, can't they? Not like an hour difference, but just the boo(m)boom" effect instead of a b-boom. (I love the technical terms concerning sonic booms we're using here 8) )

Captain Kidd
2004-Nov-17, 10:39 PM
Big ba-da-boom :D

I'm now outside my knowledge area, I only studied the simple stuff and never when into the details. Heck maybe it's just an UL that you can only discern 1 sonic boom on fighters.

But I could have sworn that I've heard somewhere that a double boom was a signature of the shuttles due to their size.

Nicolas
2004-Nov-17, 11:10 PM
Well, the sources of booms at the shuttle are quite far apart: the nose cone/windshield on the one hand, and the trailing edge/tail on the other hand. But still I think the shock angle has got a lot to do with it, plus in this respect the flying height of the shuttle at the beginning of the return phase. Plenty of time for the shocks do move away due to their different angles. I guess.

man on the moon
2004-Nov-18, 01:05 AM
Weíve been hearing them fairly regularly; Lockheed is building them nearby and as itís too far to the Gulf of Mexico to do their testing, theyíve received permission to do it along the Tennessee valley area.

you must be pretty close to me here (Chattanooga). i have enjoyed watching them from time to time myslef over the past year or so. usually they just sound like distant thunder though.

I had given up hope of hearing one as Iíll probably never get around to being in the right place and time to watch a shuttle landing before theyíre retired.[/quote]

that WOULD be cool!

Captain Kidd
2004-Nov-18, 12:03 PM
Weíve been hearing them fairly regularly; Lockheed is building them nearby and as itís too far to the Gulf of Mexico to do their testing, theyíve received permission to do it along the Tennessee valley area.

you must be pretty close to me here (Chattanooga). i have enjoyed watching them from time to time myslef over the past year or so. usually they just sound like distant thunder though
Does Ooltewah ring a bell? :D (And I work downtown.)
Haven't seen them fly by yet.

Wally
2004-Nov-18, 12:32 PM
Well, the sources of booms at the shuttle are quite far apart: the nose cone/windshield on the one hand, and the trailing edge/tail on the other hand. But still I think the shock angle has got a lot to do with it, plus in this respect the flying height of the shuttle at the beginning of the return phase. Plenty of time for the shocks do move away due to their different angles. I guess.

This is definitely out of my realm of expertise (if I even had one. . .), but I guess I'm a bit confused on your whole "angle" thing. In my mind, the multiple shock waves produced by a single aircraft will all be "in parallel" for the most part, dictated by the direction of travel. Not sure why you feel the tail wave (for example) would travel outward at a different angle than, say the nose wave. . .

Nicolas
2004-Nov-18, 01:11 PM
OK I get the confusion now.

First: planes can make shocks in different parts like the nose, wing edges, canopy rare, and tail. The most severe shocks are from teh nose and the tail. It is these two shocks who create the double boom. The length and speed of the plane will determine the time between the shocks. That's why planes can be heard as b-boom or in some cases bo-boom.

The shuttle's size, large tail and flying speed give rise to two quite independent booms. Still not boom..............coffee anyone?.....boom, but a nice boomboom.

Second: what I was talking about is the shock pattern in the immediate vicinity of the object. This can be a separated shock, an attached shock, sharp, curved, with different angles etc. But the propagation of all shocks at bigger distance from the object is more or less identical. Here only the airspeed is of importance. Of course, shock/shock interaction can change this, but this too normally only takes places close to the object, e.g. in ducts.

So when you hear boom, b-boom or bo-boom it is one plane. When you hear boomboom it is the shuttle. Separate booms are multiple planes. Not that it's so simple to hear these differences in reality. The booms tend to sound like rolling thunders, often with no clearly audible beginning or end.[/quote]