Which is faster?

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CmdrKeen
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Which is faster?

Postby CmdrKeen » Fri Mar 01, 2013 5:04 pm

An F4U Corsair can carry two wing-mounted 1,000 pound bombs and one 2,000 pound belly mounted bomb, a 4,000 pound bomb load.

Which one will be falling faster by the time it hits a ship's deck?
1. A 1,000 or 2,000 pound bomb dropped from a level flight at a height of 9,000 feet by something such as a B-17.
2. A dive bomber attack in which an F4U Corsair dives on the target from 9,000 feet and releases its two 1,000 pound and one 2,000 pound bombs at the last possible moment before pulling out of the dive.

1. An F4U will be helped in its power dive by the weight of the bomb load, but has a limited top speed; that is, it cannot dive faster than a particular speed.
2. A free-fall set of the same bombs dropped from a B-17 will be unimpeded by the top speed limit of an F4U, but will not have the added initial impetus of the F4U's engine making a power dive.

I'm not asking which one will hit 'first'; I'm asking which one will result in the bombs hit going faster (which is to say, the bombs will hit harder).

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Re: Which is faster?

Postby tommy303 » Fri Mar 01, 2013 7:57 pm

The free fall bombs from 9000-ft will hit hardest as they are accelerating due to the effects of gravity from the moment of drop; those carried on a dive bomber or in the case of your example, an F4U, will be limited by the top speed in the plane's dive since the pilot must maintain control, have enough room to pull out, and not exceed the structural limits of his aircraft. This will generally be far below the acceleration speed due to gravity operating on a free fall bomb. To achieve a hard enough hit to penetrate a hardened target, a dive bomber will have to release its bomb from a fairly high altitude, not at the last possible moment.

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CmdrKeen
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Re: Which will hit harder?

Postby CmdrKeen » Fri Mar 01, 2013 8:32 pm

Thank you, that's exactly what I thought, though not in such excellent detail.
I apologize for my confusing post title, which should have asked the same as my post.

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Re: Which is faster?

Postby RNfanDan » Sat Mar 02, 2013 12:59 pm

Although the dive-bomber has a GREAT advantage in PUTTING THE BOMBS ON TARGET. No matter how fast or hard a bomb hits, WHAT it hits is far more important. Look no further than the Tirpitz for examples....
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CmdrKeen
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Re: Which is faster?

Postby CmdrKeen » Mon Mar 11, 2013 8:40 pm

Thank you very much. What would be the bomb load for an F4U dive bombing a ship? Sources seem to say as much as one 1,000 pound bomb under each wing, and one 2,000 pound bomb under the belly; total of 4,000 pounds for a dive bombing attack?

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Re: Which is faster?

Postby paul.mercer » Mon Mar 11, 2013 9:27 pm

tommy303 wrote:The free fall bombs from 9000-ft will hit hardest as they are accelerating due to the effects of gravity from the moment of drop; those carried on a dive bomber or in the case of your example, an F4U, will be limited by the top speed in the plane's dive since the pilot must maintain control, have enough room to pull out, and not exceed the structural limits of his aircraft. This will generally be far below the acceleration speed due to gravity operating on a free fall bomb. To achieve a hard enough hit to penetrate a hardened target, a dive bomber will have to release its bomb from a fairly high altitude, not at the last possible moment.

Gentlemen,
This is something that I am still struggling to understand.
If for instance a free fall bomb from around 9000 feet will hit hardest when dropped from that hight, why would a shell of equivelent weight and dropping from a similar hight almost vertically (when it has reached the end of its tragectory) not apparently penetrate so far or cause so much damage? Actually, this poses another question, what sort of hight would a shell normally achieve when fired from say, 18-20000 yards?

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Re: Which is faster?

Postby ElBanditoVerde » Mon Mar 11, 2013 11:00 pm

Paul,
While I can't speak to penetration, all things being equal damage from the bomb is probably greater due to the larger amount of explosive it carries. Based on what I can recall a modern 2,000lb bomb carries ~950lb warhead while a 2,000lb 16"/50 shell carried a bursting charge ~150lb. I would assume the amount of explosive that could be have crammed into a bomb hasn't changed all that much over the years but even if it has I wouldn't imagine the gap during WWII to be any less significant.

CmdrKeen
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Re: Which is faster?

Postby CmdrKeen » Mon Mar 11, 2013 11:49 pm

CmdrKeen wrote:Thank you very much. What would be the bomb load for an F4U dive bombing a ship? Sources seem to say as much as one 1,000 pound bomb under each wing, and one 2,000 pound bomb under the belly; total of 4,000 pounds for a dive bombing attack?

I was actually asking, is that the normal bomb load for an F4U doing a dive bomb attack; one 1,000 pound bomb under each wing, and one 2,000 pound bomb under the belly; total of 4,000 pounds? It seems like an awful lot of weight.

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Re: Which is faster?

Postby tommy303 » Tue Mar 12, 2013 7:26 pm

If for instance a free fall bomb from around 9000 feet will hit hardest when dropped from that hight, why would a shell of equivelent weight and dropping from a similar hight almost vertically (when it has reached the end of its tragectory) not apparently penetrate so far or cause so much damage?


Even at maximum range a shell's impact angle will be less than that of a bomb dropped from sufficient height to stabilize in a nose down attitude. The fins on a bomb will move the center of pressure aft of the center of gravity causing it to drop the nose and impact will usually be very close to 'normal', that is at nearly a right angle to a horizontal surface. If a gun were fired in a perfect vacuum, the shell would have a parabolic trajectory and at the extreme ballistic range of the gun, the shell's angle of descent would be close to its angle of ascent. However, guns are not fired in vacuums and so drag comes into play and the usual trajectory is elliptical rather than parabolic. The angle of descent does not correspond with the angle of elevation. According to the natural law of sines, a projectile achieves its maximum range at 45* of elevation; for some really powerful guns, such as on battleships or long range land guns, maximum range actually occurs at around 48* since the height of the shell at the top of its trajectory takes it into very thin air where friction and drag caused by the air becomes much less.

Essentially, a shell from a high velocity naval gun will never have an impact angle as close to normal as that for a falling bomb, and will always strike a horizontal surface at considerably less than the optimum angle for penetration. Most battleships had gun mountings which allowed between 30 and 40 degrees of elevation by the start of WW2 and this was considered sufficient to achieve adequate range; this meant that angle of impact for a gun fired from say 30* might have a fall angle of 42* which would give it an oblique angle of impact with a horizontal surface compared to a near normal impact for a free fall bomb, and this accounts for why a shell will usually have less potential for penetrating horizontal surfaces.

note: when talking about armour penetration from guns or bombs, I am speaking strictly of AP bombs and usually APC shells.

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tommy303
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Re: Which is faster?

Postby tommy303 » Tue Mar 12, 2013 8:56 pm

While I can't speak to penetration, all things being equal damage from the bomb is probably greater due to the larger amount of explosive it carries. Based on what I can recall a modern 2,000lb bomb carries ~950lb warhead while a 2,000lb 16"/50 shell carried a bursting charge ~150lb.


The quoted weight for the filling of a 16-inch shell would be for a HC high-explosive shell, not an armour piercing one. An APC for the 16-in had a filler of about 41-lbs for a Mk8. AP or more commonly SAP bombs normally had greater weights of explosives because the bomb was not stressed to the same degree as a shell. For one, the impact speed was less and the impact angle was quite close to normal. A shell on the other hand would have at least far greater speed at impact and a more oblique impact angle (which would stress the sides of the shell as it yawed during penetration). To survive both the high impact forces and the shearing effect as it yawed in an attempt to pass through the plate at a right angle, the sides of the shell and the nose had to be massively constructed. An AP or SAP bomb on the other hand did not have to be quite so strongly made as both impact force and stress on the sides were generally less, and so the explosive cavity could be made larger and more explosives packed into it than was possible with a similar sized AP shell. Thus, a similar sized German PC 1400 Fritz anti-armour bomb (an SAP design), had a bursting charge of over 600-lbs. A true AP bomb, such as the USN AN-Mk1 had an overall weight of 1500-lbs and a burster of 200-lbs.

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CmdrKeen
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Re: Which is faster?

Postby CmdrKeen » Tue Mar 12, 2013 9:01 pm

I see now where my confusion over bomb loads arises. There were different versions of the Corsair which had different bomb capacities.

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Re: Which is faster?

Postby paul.mercer » Tue Mar 12, 2013 9:49 pm

tommy303 wrote:
If for instance a free fall bomb from around 9000 feet will hit hardest when dropped from that hight, why would a shell of equivelent weight and dropping from a similar hight almost vertically (when it has reached the end of its tragectory) not apparently penetrate so far or cause so much damage?


Even at maximum range a shell's impact angle will be less than that of a bomb dropped from sufficient height to stabilize in a nose down attitude. The fins on a bomb will move the center of pressure aft of the center of gravity causing it to drop the nose and impact will usually be very close to 'normal', that is at nearly a right angle to a horizontal surface. If a gun were fired in a perfect vacuum, the shell would have a parabolic trajectory and at the extreme ballistic range of the gun, the shell's angle of descent would be close to its angle of ascent. However, guns are not fired in vacuums and so drag comes into play and the usual trajectory is elliptical rather than parabolic. The angle of descent does not correspond with the angle of elevation. According to the natural law of sines, a projectile achieves its maximum range at 45* of elevation; for some really powerful guns, such as on battleships or long range land guns, maximum range actually occurs at around 48* since the height of the shell at the top of its trajectory takes it into very thin air where friction and drag caused by the air becomes much less.

Essentially, a shell from a high velocity naval gun will never have an impact angle as close to normal as that for a falling bomb, and will always strike a horizontal surface at considerably less than the optimum angle for penetration. Most battleships had gun mountings which allowed between 30 and 40 degrees of elevation by the start of WW2 and this was considered sufficient to achieve adequate range; this meant that angle of impact for a gun fired from say 30* might have a fall angle of 42* which would give it an oblique angle of impact with a horizontal surface compared to a near normal impact for a free fall bomb, and this accounts for why a shell will usually have less potential for penetrating horizontal surfaces.

note: when talking about armour penetration from guns or bombs, I am speaking strictly of AP bombs and usually APC shells.


Thanks Tommy,
Out of interest, what sort of hight would a shell from a powerful gun attain if fired from an angle of 48 degrees

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tommy303
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Re: Which is faster?

Postby tommy303 » Tue Mar 12, 2013 11:23 pm

That is a difficult question due to the fact that there are many factors in exterior ballistics which would combine to affect the trajectory--drag, ballistic coefficient of the shell, velocity, etc. On the average, a large gun such as one would find on a battleship, would easily send a shell to 20,000+ft at the height of its trajectory when fired from a mounting permitting optimum elevation in order to achieve absolute ballistic range. An extreme example is the Paris Guns of WW1. These fired an shell at a velocity of almost a mile a second and had a range of 70 miles. At the top of the trajectory, the shells were 21--25 miles above the earth.

As a point of interest, most battleship shells, when fired with full charges, never drop below the speed of sound at any point, whereas most WW2 AP or SAP bombs do not reach the speed of sound at all (there being some exceptions such as the Tallboy bombs used against the Tirpitz).

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Re: Which is faster?

Postby alecsandros » Wed Mar 13, 2013 6:42 am

... Gun mounts inside of turrets would limit maximum elevation and thus maximum height.

For most WW2 battleships, maximum theoretical height at highest point in the trajectory was around 6km.

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Re: Which is faster?

Postby tommy303 » Wed Mar 13, 2013 5:57 pm

... Gun mounts inside of turrets would limit maximum elevation and thus maximum height.

For most WW2 battleships, maximum theoretical height at highest point in the trajectory was around 6km.


Correct. The design complications of providing a shipboard mount allowing main battery guns to elevate enough to achieve maximum ballistic range was not considered worth the trouble in most battleship designs. If I remember correctly, the 16-in HC shell, when fired at 40 deg elevation reached a maximum height of around 9200m.

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