Whistling Bombs And Dive Bombers

[gabriel pagliarani]

......Many times, in movies, there is a loud whistling sound as bombs fall. Were the bombs made to whistle intentionally or is this just a special effect produced for the movie itself?...Z

During WW2 simply nobody cured aerodynamics of such devices in a "tunnel of the wind", and no supersonic shape was developed.

British very large bombs(20,000lbs Grand Slam and 10,000lbs Tallboy) had been designed specifially for supersonic speed, by Dr. Barnes Wallis.

~The Witch King of Angmar

Designed, not tested, like many other weapons But this is not the real point. The top celing for a Lancaster carrying a "Grand Slam" not exceeded 6000 mt. or less.
By kinetiks:
6000= 0.5*9.81*t*t ; t= sq root(12000/9.81) ; T=35 secs
6000= v*35 ; V= 171 m/sec or 617 km/h.
Galilei showed that 2 graves dropped from the same height must touchdown all together without any drag of air.
Even if 1 of them is only a feather. Consequently in vacuum a 500kg bomb touch down with the same speed of a "Grand Slam": in air they can only be dragged back reaching a lower speed than 617 Km/h.
Galileo Galilei vs. Barnes Wallis scored 1-0

[Scott Smith]

Armor-piercing bombs are supersonic but not because they are heavier, of course. The Herreswaffenamt and Luftwaffe at Peenemünde used supersonic wind tunnels to test aerodynamics for the A4 rocket, armor-piercing bombs and artillery shells. Bombs and rocket airframes were also dropped from aircraft at high altitude for such testing. I don't know if the standard gravity bombs of WWII reached supersonic speeds or not, but the ones today do and those on the ground can hear the sonic booms crack overhead.

[lisset]

Udet I think had a thing about dive bombers......the JU-88 was a real maid of all work and was a very effective dive bomber , large dive brake under each wing.
Ville is correct , the cardboard tudes were attached to the fins of the bomb , between the sirens and the whistle of the bomb.... psychological warfare against those on the ground.
Barnes Wallis tall boy dstroyed Tirpitz...one offcier who in a post war interview on escaping from the sinking ship was amazed to see her turn turtle....he later found out that bombs which had exploded close to the ship had blown away so much of the seabed that it allowed the ship to turn over completely.
The shpe and fins on the bomb slightly off set impared a spin to the falling bomb which improved accuracy and penetration.
The He-III , Ju-88 were both used as torpedo bombers , Ju-87 was it seemed only really safe from fighter attack when in its dive !!

[gabriel pagliarani]

Armor-piercing bombs are supersonic but not because they are heavier, of course. The Herreswaffenamt and Luftwaffe at Peenemünde used supersonic wind tunnels to test aerodynamics for the A4 rocket, armor-piercing bombs and artillery shells. Bombs and rocket airframes were also dropped from aircraft at high altitude for such testing. I don't know if the standard gravity bombs of WWII reached supersonic speeds or not, but the ones today do and those on the ground can hear the sonic booms crack overhead.

Easy to compute it.
Mach 1= 330 to 360 m/sec (varying with temp.and density) let we choose the worst figure (hot and dense air) V=360m/s
g= 9.81 m/ sec*sec
H= height in meters
V= 360m/s
H=V*t and also
H=0.5*9.81*t*t
V*t=0.5*9.81*t*t from which...t=73.4 secs
By substitution:
H= V*t = 360*73.4 = 26276meters.. no way of such a steady bombing!
But effectively there are (..now, not in WW2) supersonic dropping motorless bombs. How they works?
By adding the speed due to gravity to the speed of the air carrier: if a bomb released by a B-52H cruising over Hanoi during Linebaker 2 could save 80% of kinetik energy while launched, we can add the 80% of the B-52's speed to the speed due to height.
B-52's speed is about 1000 km/h or Mach 0.9 at 10000 metrs..800 km/h can be added to "only gravity" speed.
If you are a communist hiding in a fox-hole, you never heard anything before exploding in thousands pieces, just because the bomb killing you is supersonic...

[Scott Smith]

Thanks, Gabriel. So, if the bomb were dropped from a stationary helicopter it would have to be at a theoretical altitute of 26 kilometers or over 80,000 feet before it would reach supersonic speed, assuming constant air density?

[Witch-King of Angmar]

But effectively there are (..now, not in WW2) supersonic dropping motorless bombs. How they works?
By adding the speed due to gravity to the speed of the air carrier: if a bomb released by a B-52H cruising over Hanoi during Linebaker 2 could save 80% of kinetik energy while launched, we can add the 80% of the B-52's speed to the speed due to height.
B-52's speed is about 1000 km/h or Mach 0.9 at 10000 metrs..800 km/h can be added to "only gravity" speed.

How is the airplane's speed added to the bomb speed since the plane is releasing the bomb in a level flight, and not in a dive?

~The Witch King of Angmar

[lidrob]

Only Operatives, if you want to know about prototypes and experimental let me know about it.

Dive bombers:
-Ju 87 (except the model G)
-Hs 123A-1
-Ju 88 A(not the C,G & S versions), the Ju 88A-12 was specificaly constructed as dive bomber

Torpedo carrier
-Focke Wulf Fw 190 A-9, only a few with III/KG 200
-Arado Ar 95 A-1
-Dornier Do 217 E-1; E-2; E-3; E-4 & K-1 with the field conversion R4
-Heinkel He 59 B-2
-Heinkel He 111 H-6
-Heinkel He 115 A-1; B-1 & C-1
-Heinkel He 177 A-3/R7 operative with KG 26
-Heinkel He 177 A-5 operative with KG 40
-Junkers 88 A-17
-Junkers 188 A-3
-Junkers 188 E-3

Regards
lidrob

[gabriel pagliarani]

Physics of free-falling bombs.

Total energy (U)= kinetic (E) + potential (P) Joules
m= bomb weight kg (f.e 250 kg)
h= cruise ceiling mt (f.e 10000 m)
g = gravity acceleration = 9.81 m/(sec*sec)
v = cruise speed of B52H = 1000Km/h or Mach 0.98 at 10000 mt std. ISO air or 280 m/sec
U = E + P
E = 0.5*m*v*v joules
P = m*g*h joules
U = (0.5*m*v*v) + (m*g*h) = m*(0.5*(v*v)+(g*h)) = 250 *(39200 + 98100) = 34325000 joules or 34.325 MJ
The front-dragging force lowering the speed of the bomb is due to air viscosity F= -Cx * v newtons: the front-drag coefficient Cx is related to air density which is increasing down-falling and to the shape of the bomb.
I cannot know exactly the Cx coefficient of such a bomb; but using simple energy evaluations I can easily determine the range of speeds tue to a high Cx (high drag) or to a low Cx (low drag).
High drag force (HDF) causes high loss of energy or at least 20%. Higher values than this are impossible or non-sense: the bomb is clearly chuted down, not free-falling!
Medium drag force (MDF) causes a medium loss of energy or (f.e.)10% of total
Low drag force (LDF) causes low loss of energy or 5% (f.e.). Values lower than this require long expensive wind-tunnel studies: the same required for the bomber. Possible but economically unbelievable.

HDF causes an impact energy U-20% = 27.46000 MJ
MDF causes " " U-10% = 30.89250 MJ
LDF causes " " U- 5% = 32.60875 MJ
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Now you can imagine an equivalent bombing:

A 250Kg bomb is released from upstairs: it was simply locked to a ballon quiet and steadily firm in the sky. The bomb has no speed when released from its own ceiling. It will arrive at ground with "c" speed. But we want that the impact energy had to be the same if released from a B-52 cruising at 10000 mt. This is the trick..

These are the hypothetical counts of impact-equivalent energy. less than 10% increase of speed reducing drag losses from 20% to 5%...

U-20% = 27460000 J = 0.5 * m * c*c ; c*c = 27460000/125 ; c = 468.7 m/s
U-10% = 30892500 J = 0.5 * m * c*c ; c*c = 30892500/125 ; c = 497.1 m/s
U- 5% = 32608750 J = 0.5 * m * c*c ; c*c = 32608750/125 ; c = 510.7 m/s

BOOM!..but 510,7 m/s = 468,7+9% only...

....less than 9% increase of speed by reducing "drag losses" due to Cx from 20% to 5%...a lot of money wasted in a "wind tunnel" for having a so weak result....

Conclusions:
A strong reduction in Cx doesn't mean a really strong increase in impact speed: I think that the poor Viet-cong waiting to be killed in his fox-hole just out Haiphong Harbour during Linebaker II bombings in 1972, didn't care if the bomb killing him was faster than others or not... much better it was For USAF to reduce Cy and Cz coefficients in order to have a more precise than faster bomb, reaching the target previously aimed at. (Haiphong Harbour fulfilled of soviet cargos, obviously)

[Lustmolch]

One aircraft that doesn't appear to have been mentioned is the Heinkel He177 (the Luftwaffenfeurzeug as the crew sardonically referred to it).

This aircraft was to have been capable of dive bombing (as were most of the bombers designed in the late 1930s - apparently Udet had a bit of a dive bomber fetish or something). In order to minimise drag, the four DB 601 engines were coupled in pairs in two nacelles, driving the propellor through reduction gear. Problems with regulating the cooling of these powerplants (called DB 606) resulted in a number of fires, both in flight and on the ground. This delayed the introduction of the He177 until halfway through the war and consequently, it did not see the widespread service that it was intended to.

By contrast, the Junkers Ju88 did everything that was asked of it and more. Designed as a fast horizontal/dive bomber, it also served as a heavy fighter in diurnal and nocturnal roles, torpedo bomber, reconnaisance aircraft, anti tank on the Eastern Front (with a modified Pak 40) bomber destroyer with twin 3.7 guns and unguided missile (Mistel-Programm).

The Junkers Ju87 got a new lease of life when it was modified to carry two 3.7cm anti tank guns under the wings. These saw widespread action on the Eastern Front, the most famous exponent of the machine being Hans-Ulrich Rudel, who destroyed 519 Soviet vehicles.

[gabriel pagliarani]

...The Junkers Ju87 got a new lease of life when it was modified to carry two 3.7cm anti tank guns under the wings. These saw widespread action on the Eastern Front, the most famous exponent of the machine being Hans-Ulrich Rudel, who destroyed 519 Soviet vehicles.

Dive bombing was not a fetish: it worked really. The real advantage was not in increasing the speed of the bomb as over showed but in dropping bomb exactly where you were aiming at. But you are right if reffering at Stukas' best hits while diving. The best shots from divers were done by USNavy and Japs in PTO: dive bombers destroyed Jap carriers at Midway. Before A-bomb no other weapon was as much effective as divers during WW2.
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Sorry Scott,
I omitted to reply to your own quest: I beg your pardon. Galilei's kinetiks motion rules work only without air drag as astronauts showed on Moon. The drag force opposed to free falling motion is R= -Cx * V newtons. This drag force acts against the gravity forge G= 9.81 * m newtons.
The resistance increases till equilibrium: any paratrooper or skydiver knows that a human body cross opened and facing ground could not exceed the speed of 200 km/h (56 m/s) So the Cx of a human reactive body 80 kg. cross-opened and facing target is easily evaluated.
R+G=0 or R=-G ; -Cx * v = - m * 9.81 ; Cx = (m * 9.81)/v ; Cx = 314 (no unit : it is a pure number). If you can determine the max. speed (or threshold limit speed) of the body falling down, I can adjust your statement. But remember that Galilei's 1st law of motion (..a body not subject to any force keeps indefinitely its own "motion quantity" = m*v).
The body falling down from any height is due to gravity acceleration till equilibrium with air resistance: after that point the body falls down with a steady average speed. Obviously the threshold limit of a bomb falling down at Mach 1.7 must be over that limit point. F.e. Mach 3. The bomb reaches equilibrium with air drag force only over 3000 Km/h. This problem was very actual for V2: the warhead could reach easily Mach 5. For this reason the shape of V2 really needed a supersonic "wind-tunnel". And I am sure it was not enough fast... the right shape was obtained step by step in experimental mode, not designed before.

[Scott Smith]

Thank you, Gabriel. Always interesting stuff.

[gabriel pagliarani]

Thank you, Gabriel. Always interesting stuff.

It's a pleasure and physics are my own job: ask me more!

F.e. the Cx of the bomb dropped on Haiphong is easily determined. If we are sure that the speed limit before equilibrium of such a bomb is Mach 3 (at ground level ISO air) or 1000 m/sec consequently

Cx=(250*9.81)/1000= 2,14

..if you think that the best cars perform a Cx from 8 to 10, you have the right scale of the frontal air penetration coefficient worldwide known as Cx!