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  #1  
Old 02-24-2010, 10:02 AM
Baal Houtham Baal Houtham is offline
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Whistling Bombs

There's a sound associated with falling bombs, a long steady whistle that gradually decreases in pitch. What's the origin of this association?

Did most WWII bombs make this sound? Do modern bombs? If there was such a sound, could a person on the ground hear the bombs approaching?

Last edited by Baal Houtham; 02-24-2010 at 10:03 AM..
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  #2  
Old 02-24-2010, 10:05 AM
Whack-a-Mole Whack-a-Mole is offline
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IIRC bombs that did that were made to do so to scare people.

Most bombs I do not think make a sound (or rather not intentionally).
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  #3  
Old 02-24-2010, 10:08 AM
tdn tdn is offline
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Weren't Luftwaffe planes designed the same way?
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Old 02-24-2010, 10:11 AM
Whack-a-Mole Whack-a-Mole is offline
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Originally Posted by tdn View Post
Weren't Luftwaffe planes designed the same way?
Yes.

The Stuka dive bomber (do not know about any others) had a siren affixed to it to make a noise when it dove on a target to scare the people below.
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  #5  
Old 02-24-2010, 10:17 AM
Rocketeer Rocketeer is offline
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The Ju-87 Stuka dive-bomber was equipped with a siren which was used during the dive to frighten the attackees. As if the bombs wouldn't be enough.
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  #6  
Old 02-24-2010, 10:17 AM
Chessic Sense Chessic Sense is offline
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Modern mortars do, indeed, whistle. And yes, it's scary - for about a second.
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Old 02-24-2010, 11:16 AM
Dog80 Dog80 is offline
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Originally Posted by Chessic Sense View Post
Modern mortars do, indeed, whistle. And yes, it's scary - for about a second.
Artillery rounds like those fired from a M110 are supersonic so they make a sonic boom like sound. That also means that you'll hear the sound some seconds after the round has already dropped on you

Are mortar rounds supersonic?
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  #8  
Old 02-24-2010, 11:22 AM
Saltire Saltire is offline
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I'm not an artillery expert, but I don't think a mortar could possibly be supersonic. They are made to drop onto the target using gravity alone, so they should hit with some subsonic terminal velocity.

Is it even possible for freefall terminal velocity to be supersonic?
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  #9  
Old 02-24-2010, 11:26 AM
Lightnin' Lightnin' is offline
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One thing I always giggle at in movies is when a falling bomb makes the descending whistle noise. It's completely backwards, if you think about it- the sound should doppler shift the opposite way.

A bomb dropped from a plane would only make that descending (high-to-low pitch) sound from the point of view of someone on the plane. Someone on the ground would hear the bomb whistle low-to-high.
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Old 02-24-2010, 11:38 AM
LiveOnAPlane LiveOnAPlane is offline
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Originally Posted by Saltire View Post
...

Is it even possible for freefall terminal velocity to be supersonic?
I have heard of some very heavy, deep-penetrator bombs that supposedly have a supersonic terminal velocity, but I couldn't find anything that I would consider conclusive. (some forums, a few pics with opinions/statements, nothing official or authoritative)

<<Edited to add: I am assuming we're all talking about the earth here, and not some other planet with a thinner atmosphere or plasma jets in an astronomical event, etc.>>

Last edited by LiveOnAPlane; 02-24-2010 at 11:41 AM..
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  #11  
Old 02-24-2010, 11:58 AM
Zsofia Zsofia is offline
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I think a lot of what we think bombs sound like come from Bugs Bunny, so take that with a grain of salt.

V-1 rockets did make a really loud noise, though. It often stopped before it hit, because (I might remember this incorrectly) early in their development the engine often ran out before it was supposed to, but later on they'd figured them out so they hit under power.
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Old 02-24-2010, 12:09 PM
engineer_comp_geek engineer_comp_geek is online now
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The V-1's had a small propeller in its nose which was turned by the air that the V-1 was moving through. This propeller turned a counting device, which was how the V-1 measured how far it had gone. When it had reached its target distance according to this counter, the V-1's control system would throw it into a steep dive. This steep dive tended to make the fuel stop flowing to the engine, so the engine would cut out at that point.

Later V-1's fixed this problem and dove under full power.
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  #13  
Old 02-24-2010, 12:11 PM
Washoe Washoe is offline
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Originally Posted by Saltire View Post
Is it even possible for freefall terminal velocity to be supersonic?
Yes—it’s even been achieved by a skydiver.
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  #14  
Old 02-24-2010, 12:44 PM
Chessic Sense Chessic Sense is offline
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Originally Posted by Lightnin' View Post
One thing I always giggle at in movies is when a falling bomb makes the descending whistle noise. It's completely backwards, if you think about it- the sound should doppler shift the opposite way.

A bomb dropped from a plane would only make that descending (high-to-low pitch) sound from the point of view of someone on the plane. Someone on the ground would hear the bomb whistle low-to-high.
I don't think the high-to-low is because it's approaching you. It's because it's going from "toward you" to "over your head" or "parallel to you". If you intend to catch it on the fly (thus putting the artillery gunner "out" ), then you'd hear a low-to high. But if you're alive to tell the tale, it's still high-to-low, just like a speeding 18-wheeler.
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  #15  
Old 02-24-2010, 01:22 PM
Zsofia Zsofia is offline
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Originally Posted by engineer_comp_geek View Post
The V-1's had a small propeller in its nose which was turned by the air that the V-1 was moving through. This propeller turned a counting device, which was how the V-1 measured how far it had gone. When it had reached its target distance according to this counter, the V-1's control system would throw it into a steep dive. This steep dive tended to make the fuel stop flowing to the engine, so the engine would cut out at that point.

Later V-1's fixed this problem and dove under full power.
Good to know I was in the neighborhood. At any rate, I've read the sound was very distinctive - it seems YouTube comes through.
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  #16  
Old 02-24-2010, 04:10 PM
md2000 md2000 is offline
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There was a bomb developed for the Gulf War (I or II?) which was designed to take the deeply buried bunkers used by the Iraqi high command. It had to go through 50 feet of dirt or gravel then a few feet of reinforced concrete. According to Time Magazine, some wag at the munitions plant even painted the name on it, "The Saddamizer". It had a time delay fuse, a nose cone that was 25 feet of solid steel and was dropped from 50,000 feet. I wonder if that hit supersonic speeds?

The V1 was a pulse-jet, which apparently are VERY noisy; also called a buzz-bomb. They were subsonic, and the time to panic from what I read was when the noise stopped. What I read was that they ran out of fuel. George Orwell describes setting up lawn chairs on the hill at Hampstead Heath in north London to watch them coming in over London;I thought he said the sound stopped before they dived. You could see them flying in, the noise stopped, then they dived and where they hit a big explosion happened.

The V2's OTOH, were parabolic flight rockets much faster than sound. When they first began to hit with no warning, the authorities blamed random explosions on gas mains. Some wags started calling the V2's "flying gas mains".
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  #17  
Old 02-24-2010, 07:54 PM
njtt njtt is offline
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Originally Posted by Washoe View Post
Yes—it’s even been achieved by a skydiver.
On the contrary, your link explicitly states that the peak speed attained in those jumps was "614 miles an hour, nine-tenths the speed of sound at my altitude."
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  #18  
Old 02-24-2010, 08:11 PM
UncleFred UncleFred is offline
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Originally Posted by engineer_comp_geek View Post
The V-1's had a small propeller in its nose which was turned by the air that the V-1 was moving through. This propeller turned a counting device, which was how the V-1 measured how far it had gone. When it had reached its target distance according to this counter, the V-1's control system would throw it into a steep dive. This steep dive tended to make the fuel stop flowing to the engine, so the engine would cut out at that point.
Fuzzy memory - but weren't there some 'dropped' bombs that employed a propeller like that? Or maybe it was one of the atomic bombs, that they wanted to detonate before it hit the ground?
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  #19  
Old 02-24-2010, 08:41 PM
Harry1945 Harry1945 is offline
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Some types of bomb fuses had/have (sorry, it's been many years since I was current) a vane that can be confused as a propeller. It's purpose is counting revolutions before it's armed, to let the bomb fall a safe distance from the aircraft.
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  #20  
Old 02-24-2010, 08:54 PM
engineer_comp_geek engineer_comp_geek is online now
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Quote:
Originally Posted by UncleFred View Post
Fuzzy memory - but weren't there some 'dropped' bombs that employed a propeller like that? Or maybe it was one of the atomic bombs, that they wanted to detonate before it hit the ground?
Many dropped bombs had similar sorts of things. They were usually used to arm the bomb, not detonate it. The mechanism would prevent the firing pin from striking the bomb's detonator until the propeller had rotated a certain number of times. This prevented the bomb from accidentally blowing up too close to the plane that dropped it.

Here's a good diagram of one:
http://www.fototime.com/BAF4773FDF98642/standard.jpg

Note the small propeller marked as "ARMING VANE".

I don't know how much these mechanisms contributed to the whistling sound when the bomb was dropped.

Fat man and little boy used radar altimeters to trigger their detonation.

ETA: Technically, as Harry1945 pointed out, it's a vane, not a propeller.

Last edited by engineer_comp_geek; 02-24-2010 at 08:55 PM..
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  #21  
Old 02-25-2010, 12:58 AM
Washoe Washoe is offline
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Originally Posted by njtt View Post
On the contrary, your link explicitly states that the peak speed attained in those jumps was "614 miles an hour, nine-tenths the speed of sound at my altitude."
That’s weird. I coulda sworn that’s where I read it. I was just reading that wiki article recently, so I just posted the link without bothering to reread it. I must have read it somewhere else. But I distinctly remember reading somewhere that Kittenger is the only person ever to have broken the sound barrier without being in some sort of conveyance (rocket, plane, car, etc.).
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  #22  
Old 02-25-2010, 11:55 AM
smithsb smithsb is offline
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[quote=md2000;12157974]There was a bomb developed for the Gulf War (I or II?) which was designed to take the deeply buried bunkers used by the Iraqi high command. It had to go through 50 feet of dirt or gravel then a few feet of reinforced concrete. According to Time Magazine, some wag at the munitions plant even painted the name on it, "The Saddamizer". It had a time delay fuse, a nose cone that was 25 feet of solid steel and was dropped from 50,000 feet. I wonder if that hit supersonic speeds? quote]

Bomb used in Desert Storm described below. Made from surplus 8" artillery tubes, not 28 feet of steel (probably misplaced from the GBU-28 nomenclature.
Description

The Guided Bomb Unit-28 (GBU-28) is a special weapon developed for penetrating hardened Iraqi command centers located deep underground. The GBU-28 is a 5,000-pound laser-guided conventional munition that uses a 4,400-pound penetrating warhead. The bombs are modified Army artillery tubes, weigh 4,637 pounds, and contain 630 pounds of high explosives. They are fitted with GBU-27 LGB kits, 14.5 inches in diameter and almost 19 feet long. The operator illuminates a target with a laser designator and then the munition guides to a spot of laser energy reflected from the target.

The GBU-28 ""Bunker Buster"" was developed specifically to destroy Iraqi underground hardened command bunkers during the Gulf War. Scratch built from a section of surplus 8"" howitzer barrel filled with 600 pounds of explosives, the 5,000 pound GBU-28 is capable of penetrating more than 20 feet of reinforced concrete and deeper than 100 feet underground. Equipped with essentially the same guidance hardware as the GBU-10 Paveway II, the GBU-28 is capable of hitting discrete, hardened targets deep underground. The GBU-28 was successfully used twice during the Gulf War, with each of the weapons being released by FB-111F Aardvarks for use against buried command bunkers.
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  #23  
Old 02-25-2010, 12:49 PM
Maus Magill Maus Magill is online now
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Quote:
Originally Posted by Lightnin' View Post
One thing I always giggle at in movies is when a falling bomb makes the descending whistle noise. It's completely backwards, if you think about it- the sound should doppler shift the opposite way.

A bomb dropped from a plane would only make that descending (high-to-low pitch) sound from the point of view of someone on the plane. Someone on the ground would hear the bomb whistle low-to-high.
That would make sense only if the bomb were moving past you.

If you were on the ground, you wouldn't hear low-to-high or high-to-low. You would hear faint-to-loud.

Conversely, The bombardier would hear loud-to-faint, as the bomb wouldn't move past him either.
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  #24  
Old 02-25-2010, 01:44 PM
Raguleader Raguleader is offline
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IIRC, first and maybe second generation laser-guided smart bombs (such as the ones used in the Gulf War) made a "clicking" noise, because the guidance fins would snap back and forth (ie: all the way left, all the way right, all the way left, all the way right) like a group of cartoon firemen trying to catch a swerving-in-midair person with a safety net. The clicks came from the fins hitting the stops at either end of their range of movement.

Later generations of the smart bombs had fins that could make more subtle adjustments, so now you don't hear the clickclickclickclick sound anymore.

Also, IIRC, the dive flaps on the Douglas SBD Dauntless ("Slow But Deadly") dive bomber had holes cut in it as part of their design (I think it was to help slow the plane in a dive without stopping the airflow entirely). A side-effect of the design was that the SBD Dauntless had a banshee-like scream. That had to be a terribly un-nerving sound to hear from the deck of a ship at sea.
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  #25  
Old 02-25-2010, 09:46 PM
Kevbo Kevbo is offline
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Quote:
Originally Posted by Lightnin' View Post
One thing I always giggle at in movies is when a falling bomb makes the descending whistle noise. It's completely backwards, if you think about it- the sound should doppler shift the opposite way.

A bomb dropped from a plane would only make that descending (high-to-low pitch) sound from the point of view of someone on the plane. Someone on the ground would hear the bomb whistle low-to-high.
No. The bomb reaches terminal velocity fairly early, especially one with a high drag tail that would be likely to whistle much at all. To a person some distance from the impact point, it is approaching quickly when still at high altitude. As it nears the ground, the approach speed decreases to zero, thus decreasing Doppler shift.

Last edited by Kevbo; 02-25-2010 at 09:47 PM..
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