Warbird Information Exchange

Some WW2 bombs had straight fins, and others had a circular ring around the fins. Does the rign have effects on aerodynamic stability or drag?

Thank you;


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Bombs came/come in all shapes and sizes, depending on the country and the aircraft used to carry them.

The two you've shown appear to be German, but no matter who made the bomb the primary reason for the fins was to keep the bomb from tumbling when dropped.

These are dumb bombs and it didn't matter what the shape of the fins were, because they were going to hit the ground once they were released.

Dik, I'm sorry but I gotta ask.

ed

Does that mean that there are smart bombs somewhere that never hit the ground after release ?

Hi

Agree with DIK and would add that once sufficent speed / velocity has been acieved the fins provide stability and accuracy in much the same way as the tail on a dart does - the ring is to provide strength and additional directional stability.

Some fins such as those on the British Tallboy and Grand Slam also provide stability through inducing a spin on the bomb which from the height they are dropped is considerable rpm by the time of contact and assists greatly in penetration of the bomb

Here is everything you ever wanted to know about bombs
Bombs for Beginners
Aircraft bombs are released over enemy targets to reduce and neutralize the enemy's war potential. This is done by destructive explosion and fire. Aircraft bomb ammunition is used strategically to destroy installations, armament, and personnel; and tactically in direct support of land, sea, and air forces engaged in offensive or defensive operations. Bombs are designed to be carried either in the bomb bay of aircraft or externally under the wings or fuselage.

At the outset of the Vietnam War, tactical aviation pilots were achieving a 750-foot circular error probable (CEP)--the radius from the aim point that half of the bombs dropped will fall within. This number is sufficient for the impact of a tactical nuclear weapon but is far from adequate for conventional weaponry. It took several years for the CEP to be lowered to a manageable 365 feet. [SOURCE] The advantage of guided bombs was revealed when compared with the F-105’ s work in Vietnam. The F-105s achieved a circular error probable (CEP) of 447 feet and 5.5 percent direct hits during the end of Rolling Thunder, compared with guided bombs’ CEP of 23 feet and 48 percent direct hits during the period of February 1972 through February 1973. [SOURCE]

Robust Munitions are munitions having a ratio of the explosive weight to the empty case weight less than 1.00 and a nominal wall thickness of 0.4 inches. Examples of robust ammunition include MK 80 series bombs, Ml07 projectiles, Tomahawk and Harpoon penetration warheads and 20,25, and 30 mm cartridges. Examples of non-robust ammunition include CBUs, torpedo warheads, underwater mines and TOW, HELLFIRE, Sparrow, and Sidewinder Missiles. Unless otherwise noted, all air-to-air missile warheads are defined as non-robust.

A bomb is an explosive filler enclosed in a casing. Bombs are generally classified according to the ratio of explosive material to total weight. The principal classes are general-purpose (GP), fragmentation, penetration and cluster bombs.

Approximately 50-percent of the General Purpose [GP] bomb's weight is explosive materials. These bombs usually weigh between 500 and 2,000 pounds and produce a combination of blast and fragmentation effects. The approximately one-half-inch-thick casing creates a fragmentation effect at the moment of detonation, and the 5O-percent explosive filer causes considerable damage from blast effect. The most common GP bombs are the MK-80 series weapons.

General-purpose bombs were the type of ordnance most frequently employed in the Gulf War. According to Iraqi prisoners of war, formations of B-52s dropping general-purpose bombs were one of the most feared aircraft-weapon combinations of the war. GP bombs served as the basic building blocks for many of the other munitions used during the Gulf War.

Only ten to twenty percent of a fragmentation bomb's weight is explosive material; the remainder include specially scored cases that break into predictably sized pieces. The fragments, which travel at high velocities, are the primary cause of damage.

Penetration bombs have between twenty-five and thirty percent explosive filler. The casings are designed to penetrate hardened targets such as bunkers before the explosives detonate. Penetration is achieved by either kinetic energy of the entire projectile or the effects of a shaped-charge.

Cluster bombs are primarily fragmentation weapons. Cluster bombs, like GP bombs, can feature mix and match components (submunitions, fuzes, etc.) to produce the desired effect.







Bomb Construction
For safety reasons, some bomb ammunition is shipped and stowed without the fuzes or arming assemblies and associated components installed. This ammunition must be assembled before use. Other types, such as cluster bomb units (CBUs), are shipped and stowed as complete assemblies, with fuzes or arming assemblies and associated components installed.

Most bombs don’t come straight from the factory, ready to drop on the enemy. On the contrary, munitions mechanics must install fuses, attach fins, install mounts for different aircraft configurations and laser guidance systems for “smart bombs.” Ammo airmen — technically called munitions systems specialists and classified under the specialty code 2W0X0 — belong to a relatively small career field, only 6,200 or so strong. Their mission: handling, maintaining, building, delivering and accounting for conventional munitions used on aircraft. “Ammo” troops are not to be confused with weapons loaders, known as “load toads” in ammo circles, or with nuclear weapons technicians, maligned as “mushroom mechanics.” Of course, these other two vocations have their pet name for ammo — BB stackers. The ammo troops motto is the catchy “IYAAYAS,” which means “If you ain’t ammo, you ain’t spit” (more or less).

Free-fall bombs have three sections. The bomb body is the casing containing the explosive material. The fuze section can be located in the nose and/or the rear of the bomb and determines the timing of the explosion. The tail section, or fins, determines how the bomb flies through the air. Desired weapons effects are achieved by selecting a particular combination of bomb body, fuzing, and tail section.

The bomb body is shipped with a plastic plug installed in the nose and tail fuze well to prevent damage to the internal threads and to keep out moisture. The aft end of the bomb body has a metal shipping cap installed. Plastic lug caps are installed in the suspension lug wells, and a plastic plug is installed in the fuze-charging receptacle well. Some bombs contain a hoisting lug packaged in the tail fuze well. Bombs are shipped on metal pallets. The number of bombs loaded on each pallet depends on the bomb size. For example, six Mk 82 bombs can be shipped on a pallet, three Mk 83 bombs can be shipped on a pallet, and two Mk 84 bombs can be shipped on a pallet.

Many things go into preparing bombs for flight. First, the parts must be ordered from the depot and received. All operations begin with safety briefings and must comply with strict explosive safety rules. Then, each bomb, fuse, fin, nose support cup and other parts must be inspected for serviceability. The preparation of these parts takes almost as long as actual assembly. The bombs are removed from their pallets and placed on modified 40-foot flatbed trailers where they are assembled. The crew chiefs then verify the fuse's settings and assign "lot" numbers for accounting purposes. The bombs are then positioned on holding pads until needed.


Bomb Bodies
Bomb bodies vary in size, weight, and thickness of casing. GP bombs have a thinner case and more explosive filler than penetrating bombs, whereas cluster bombs generally come in dispensers that open to release bomblets at predetermined altitudes. The bomb body casing (except for cluster munitions) houses the explosive filler. Upon detonation, the high-explosive filler creates an explosive train to achieve the desired weapons effect; detonation is triggered by fusing.

Fuzes
A fuze initiates bomb detonation at a predetermined time and under the desired circumstances. Fuzes are located in the nose or tail of the munition, or both. They are armed by one, or a combination, of the following methods:

The arming vane, a small propeller, is rotated by airflow after weapon release. A specified number of rotations arms the fuse.
The arming pin is ejected or withdrawn by a spring action releasing the arming mechanism and allowing the fuze to arm.
The inertia fuze is armed by abrupt changes in the velocity of the bomb caused by the deployment of fins or ballutes.
The electric fuse is armed by a time-delay circuit powered by a thermal battery activated by extraction of the arming lanyard upon bomb release.


Different effects are obtained by mating different bombs to different fuzes. A fuze functions in one of the following ways. An impact fuze is designed to function on or after impact. Detonation upon impact is selected for targets such as supply dumps when the main destructive energy desired is blast. For a building, a delayed detonation might be selected so the bomb can penetrate several floors before exploding. A proximity fuze contains a miniature doppler radar set that senses height above the ground. When the explosion occurs above the ground, most of the destructive effect is caused by the bomb casing fragments.

Proximity-fuzed bombs are used against targets such as troops in trenches, radars, trucks, and other vehicles. In a timed fuze, the delay is normally initiated at bomb release rather than on impact. The timing element is a mechanical or electrical device. A hydrostatic fuze is employed in depth bombs used for underwater demolition work. The MK-36/40 Destructor is a special fuze with a sensor that can be mated to a bomb. It senses the presence of metallic objects such as trucks or ships, making it, in effect, a mine. These weapons can be used against either land or water targets. In Southwest Asia, the MK-36 (500-pound) detonators were used to mine the waters in the vicinity of Umn Qasr naval facility.


Stabilizing Devices
Bombs are stabilized in flight by either fin or parachute assemblies. These assemblies attach to the rear section of the bomb and keep the bomb nose-down during its descent. These assemblies can separate from the bomb after the bomb hits the ground. Two common types of fin assemblies used by foreign countries are the conical- and box-fin assemblies. The retarding-fin assembly is used by the US for most of its general-purpose bombs.

Fin assemblies, used with the Mk 80 (series) LDGP bombs, provide stability to the bomb. They cause the bomb to fall in a smooth, definite curve to the target, instead of tumbling through the air.

The conical fin was the tail section type most often installed on GP bombs dropped in Southwest Asia. The conical fin assembly helped stabilize the bomb in flight, allowing the bomb to exhibit the best effects of low drag and stabilization after release. A conical fin mated with a GP bomb results in a low-drag general-purpose bomb. The conical fin may be used with all Mk 80 (series) bombs. The basic difference between the types of conical fins is their physical size, the larger the bomb, and the larger the fin.

The typical BSU-33 conical fin assembly is steel, conical in shape, and has four fins to provide stability. Access covers, attached by quick-release screws, are located on the sides of the fin body, providing access for dearming and inspections. There is a drilled or punched hole at the top and bottom of the forward end of the fin body. This hole is used to install an arming wire when the bomb is being configured for electric tail fuzing. The fin is attached to the aft end of the bomb, and is secured in place by tightening the fin setscrews into the V-groove of the bomb.

Two types of high-drag retarders were used in Desert Storm. The first was the air-inflatable retarder tail assembly containing a ballute (combination balloon and parachute) device that deployed shortly after bomb release.

There were two types of ballutes used in Desert Storm, the BSU-49 mated to a 500-pound MK-82 bomb, and the BSU-50 mated to a 2,000-pound MK-84 bomb. The second type of retarding fin was the Snakeye, which had four metal vanes that opened into the windstream to slow the bomb after release. The BSU-85/B Air Inflatable Retarder bomb fin attaches to the Mk 83 general-purpose bomb. It is an air-inflatable retarder designed for very low altitudes. It can be dropped in either high-drag (retarded) or low-drag (unretarded) mode. The BSU-85/B fin

Snakeye fin assemblies are used with the Mk 82 LDGP bombs. They are capable of delivering bombs at high speed and low altitude without the danger of damaging the aircraft from ricocheting bombs or fragments. Snakeye fins were used used in Desert Storm by Navy aircraft to deliver mines into the waters around Iraqi naval bases. These high-drag retarder tail assemblies were used to slow the bomb quickly after a high-speed, low-level release, thereby reducing the chance of an aircraft being damaged by its own bomb fragments.

The Mk 15 bomb fin assembly is a retarding fin. It is used with the 500-pound LDGP, Mk 82 bombs. The fin assembly presents a low-drag configuration when dropped in the unretarded position and a high-drag configuration when in the retarded position. The fin support tube is the main structure of the fin. It provides a means of attaching the fin assembly to the bomb. Eight setscrews attach the fin. The crushing of a convoluted steel tube absorbs the shock. The fin support tube has a fuze-mounting ring for attaching the tail drive of a mechanical tail fuze. The fins are spring-loaded and secured in the closed position by a spring-loaded release band. The release band lever is prevented from opening by a cotter pin, which stays installed until an arming wire is installed. The fin assemblies have drilled holes at the top and bottom of the forward end for installation of arming wires when the weapon is being configured for electric tail fuzing.

The MAU-91A/B fin assembly is a retarded tail fin used with the 1,000-pound LDGP bomb Mk 83 and Mods. This fin assembly can be dropped in either the retarded or unretarded position. The MAU-91 fin consists of four folding drag plates with links, a support flange, and a support tube. An energy absorber, made of aluminum honeycomb tubing, is located on the support tube between the stationary collar and the sliding collar. The sliding collar is driven against the energy absorber, causing it to compress and deform. A channel located on the top drag plate holds the fin release wire until it is pulled out at bomb release. The drag plates are held in the closed position by a release band that is secured by a fin release wire pin located in the latch of the release band. The band tabs fit into slots located near the end of each drag plate. The band is securely attached to the bottom drag plate by a stainless steel clamp, which prevents damage from the band striking the aircraft after release.

Fin adapter ADU-320/B attaches the MAU-91 fins to the Mk 83 bomb. The adapter is secured to the aft end of the bomb by eight setscrews. The fin support flange has eight teeth that mate to ears on the fin adapter. A garter spring is forced into the gap between the flange teeth and the adapter, making sure that the teeth fit tightly against the ears. Two locking pins, which fit through matching holes in the flange and adapter, prevent rotation of the fin.

The BSU-86/B bomb fin is used with general-purpose bombs, Mk 82 Mods, or the practice bomb BDU-45/B. The fin provides a retarded (high-drag) or unretarded (low-drag) bomb delivery capability for the aircraft. The BSU-86/B fin is attached to the Mk 82 or BDU-45/B bomb by eight setscrews. A 25-degree wedge is located at the tips of each fin to impart spin. The air stream drives the fin open rapidly, when the MAU-199/B spring arming wire (SAW) is activated. The spring load under each fin blade initiates fin opening.

There are three modes of delivery available for the Snakeye fin assembly. They are retarded, unretarded, and in-flight selection (pilot option) of either mode.

In the retarded mode of delivery, the fins open to retard or slowdown the weapon. Since the aircraft and the weapon are traveling at the same speed when the weapon is released, the weapon and the aircraft arrive at the target at the same time. During low-level bombing, the aircraft could be damaged; therefore, the retarded mode of delivery is used during low-level bombing. The fin assembly is positively armed in the retarded configuration. In this configuration, the fin release arming wire is looped over a permanent structure on the bomb rack. As the weapon is released from the aircraft, the arming wire is pulled from the fin release band, and the spring-loaded fins pop open. The fins are forced to the full-open position by the air stream, which causes the weapon to rapidly decelerate and allows the releasing aircraft sufficient time to safely clear the target area.

In the unretarded mode of delivery, the weapon is released from the aircraft, and the fins remain in the closed position. The weapon free falls to the target. In the unretarded mode of delivery (without pilot option), the cotter/safety pin installed in the fin release band is not removed or replaced with an arming wire. However, the safety tag that reads REMOVE BEFORE FLIGHT is removed.

The most frequently used mode for delivery is the in-flight selection (pilot option) mode. The pilot can drop the weapon in the retarded or unretarded mode. This is possible by connecting the swivel loop of the fin release arming wire to the tail arming solenoid of the bomb rack. If the pilot energizes the arming solenoid upon weapon release, the arming wire remains connected to the arming solenoid and is pulled from the fin release band at weapon release, which allows the fins to pop open and results in a retarded delivery. If the pilot does not energize the arming solenoid upon weapon release, the arming wire is pulled free of the arming solenoid. This allows it to remain in the fin release band, preventing the fins from opening, which results in an unretarded delivery.








WEAPONS HIT CRITERIA


EVENT
F-15E
F-16
OA-10

CCIP/MAN

LOFT EVENT

LOFT
105M/345FT
229M/750FT
NA

LEVEL EVENTS

VLB
40M/130FT
40M/130FT
38M/76M

SLD
60M/195FT
60M195FT


DIVE & TOSS EVENTS

LAHD
25M/80FT
23M/75FT
23M/32M

LALD
30M/100FT
31M/100FT
31M/53M

DB
26M/85FT
26M/85FT
26M/44M

HADB
40M/130FT
38M/125FT
38M/76M

HARB
78M/255FT
136M/510FT
78M/136M

LAT
53M/175FT
53M/175FT
53M

MAT
91M


Safe escape data is generally limited to release airspeeds between 450 KTAS [Knots True Airspeed] and 600 KTAS. For the A-10, safe escape is generally limited to release airspeeds between 300 KTAS and 400 KTAS. For the B-1, safe escape is limited to release airspeeds between 340 KTAS and 560 KTAS. For the B-52, safe escape is limited to release airspeeds between 350 KIAS [Knots Indicated Airspeed]and 390 KIAS. [Airspeed may also be expressed as KCAS - Knots Calibrated Airspeed, or KGSP Knots Groundspeed].

WEAPON/FUSE -34 LIMITS:


FMU-54 / MK-82 AIR
MIN 330 KCAS

FMU-54 / MK-82 SE
MIN 350 KCAS

FMU-54 / MK-84 AIR
MIN 550 KCAS

FMU-54 / M117R
MIN 175 KCAS

FMU-139 / MK-82 AIR
MIN 280 KCAS

FMU-139 / MK-82 SE
MIN 310 KCAS

FMU-139 / MK-84 AIR
MIN 450 KCAS

FMU-139 / M117R
MIN 280 KCAS

MK-82 SE
450 to 500 KCAS

_________________
Air Vice Marshall
Sunshine State Air Farce

Thats gotta be the longest freaking post Ive seen!

_________________
The conquest of space is worth the risk of life. - Gus Grissom

Oh Reallly

Theres more much more ..................LOL!!!!
JP

_________________
Air Vice Marshall
Sunshine State Air Farce

Uh--ohhh!!

_________________
He bowls overhand...He is the most interesting man in the world.
"In Peace Japan Breeds War", Eckstein, Harper and Bros., 3rd ed. 1943(1927, 1928,1942)
"Leave it to ol' Slim. I got ideas...and they're all vile, baby." South Dakota Slim
"Ahh..."The Deuce", 28,000 pounds of motherly love." quote from some Mojave Grunt
DBF

Hi Dik,
Not an unreasonable 'off the cuff remark', but if I may comment further?


'Smart' and 'dumb' are really modern concepts, which came to practical fruition during W.W.II, with the German sinking of the defecting Italian ships with guided glide bombs (The Fritz X' http://en.wikipedia.org/wiki/Fritz_X ) although not with those over-simplistic terms. It's indicative that most people misinterpret the implications of these terms.

As for the second part of the statement - Not so. The fins give the bombs, once released, a predictable path, and thus will be able to hit a aiming point chosen by a bomb-aimer using a sight in the aircraft. Three W.W.II era contrasts that immediately come to mind are:
1. The RAF's 'Cookie' - basically an unfinned untapered blast bomb. Accuracy wasn't possible and wasn't necessary.

http://en.wikipedia.org/wiki/Blockbuster_bomb

2. The Luftwaffe's use of mines over land dropped with parachutes. Again, no fins, and with the parachutes only a very general aim was possible, but they intended to take a bomb-disposal officer with them, who would come to the mine after it's landing to defuse it, so again accuracy wasn't important.

3. The RAF's 'Grand Slam' bombs had fins (no rings) which were angled off, so the airflow would spin the bombs, as Setter's said above, so that they would remain tracking on the chosen trajectory, not diverging. However, there was a difference between the 'Tallboy' and the 'Grand Slam' which came later, was heavier and fell faster - the fins helping it through the sound barrier.
See: http://en.wikipedia.org/wiki/Grand_Slam_bomb



Not so dumb. A bit of research of the work of the Royal Navy's mine and bomb disposal teams in W.W.II would also illuminate the degree with which what they had to tackle wasn't 'dumb' either. Truly terrifying, and IMHO some of the bravest men who ever worked in cold blood in a war. See the entries for the award winners on this page: http://www.stephen-stratford.co.uk/gc_and_gm.htm

_________________
Raven

Interesting post. If I am remembering correctly during the Manhattan project they were filming 500 and 1000 pounders and discovered that the tail fins were collapsing during the drop resulting in less than accurate high altitude bombing. However, because it was part of a super secret program the info was not released

Along the same lines there is quite a bit of interesting info from "Project Alberta" and "W-47" on the building and ballistic testing of the "Fat Man" and "Little Boy" bomb casings.

Tom P.