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少将
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发表于 2013-5-21 17:33
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本帖最后由 剑桥的老铁匠 于 2013-5-27 16:56 编辑
流言之一:
衣阿华舷侧9炮齐发,全舰位移十数米。
辟谣如下:
16寸炮开火时的总机械能
Given:
Projectile Weight (弹重): Wp = 2,700 lbs.
Charge Weight(药包重): Wc = 650 lbs.
Muzzle Velocity(炮口初速): Vo = 2,500 fps.
Weight of Recoiling Parts(后座部件重): Wr = 250,000 lbs.
g (重力加速度)= 32.174 fps^2
Projectile Kinetic Energy (弹丸动能)= 0.5*((Wp/g)/2)*Vo^2 = 2.622*10^8 ft-lb.
To compute the kinetic energy of the propellant gases we must know the average velocity of the gases as they escape the muzzle. Experiments have shown that this velocity varies between 1,200 and 1,400 mps. depending on the muzzle velocity of the weapon. For purposes of these calculations we will use 1,200 mps or 3,937 fps.
计算发射药燃气动能
Average outflow velocity of propellant gases(平均燃气喷射速度): w = 3,937 fps
Gas Kinetic Energy(燃气动能) = 0.5*((Wc/g)/2)*w^2 = 78.29*10^6 ft-lb
To compute the Kinetic energy of the recoiling parts, we must determine the velocity that they would achieve if allowed to recoil with no retarding force. This is commonly referred to as the free recoil velocity. To account for the difference between the velocity of the projectile and that of the propellant gases, we will use the aftereffect coefficient B which is defined by the relationship:
计算后座部件动能
w = B*Vo, therefore B = 1.5748
Free Recoil Velocity(自由后座速度): Vre = (((Wp/g)+B*(Wc/g))/(Wr/g))*Vo = 37.236 fps
Recoil Energy (后座能量)= ((Wr/g)/2)*Vre^2 = 5.387*10^6 ft-lb
The rotational energy of the projectile is small by comparison and can be neglected.
弹丸的旋转能量极小可以忽视。
The overall mechanical energy is only a part (40 to 50%) of the chemical energy of the propellant, since a considerable portion of the energy is carried off as heat by the propellant gases, or transmitted to the gun barrel.
总机械能只是发射药化学能的40%-50%,其余部分作为热能被燃气带走,或传递给炮管。
Ref. Rheinmetall Handbook on Weaponry, 1982, chapter 9.
Now, with these factors in mind, here are some additional calculations.
The momentum of a single projectile can be calculated as follows:
单一弹丸的动量
Projectile momentum (弹丸动量)= (Weight of projectile/g) * Muzzle velocity of projectile (弹丸重量/重力)×炮口初速
= (2,700 / 32.174) * 2,500
= 209.80 x 10^3
Momentum of the propellant gasses can be calculated from Leo's numbers as follows:
Propellant gas momentum (燃气动量)= (Wc/g) * w
= (650 / 32.174) * 3,937
= 79.54 x 10^3
Summing these:
两者的和:
Projectile momentum + Propellant gas momentum = 209.80 x 10^3 + 79.54 x 10^3
= 289.34 x 10^3
The Free Recoil momentum calculation can be used as a check, as it should be about equal to the sum of the momentums of the projectile and propellant gasses.
后座动量应该和弹丸加燃气的动量大致相等。
Free Recoil momentum = (Wr/g) * Vre
= (250,000 / 32.174) * 37.236
= 289.33 x 10^3
The Broadside Momentum for 9 projectiles can now be calculated as follows:
9发齐射的动量:
Broadside Momentum = 9 * (momentum of projectile + momentum of propellant gasses)
= 9 * (209.80 x 10^3 + 79.54 x 10^3)
= 2.60 x 10^6
Using Greg's formula, the velocity of an Iowa firing a 9-gun broadside can be recalculated as follows:
计算IOWA在齐射后的速度:
Mass of broadside * Velocity of broadside = Mass of ship * Velocity of ship
齐射质量×速度=船质量×船速度
As the Mass of broadside * Velocity of broadside term is equivalent to Broadside Momentum, this formula can be restated as follows:
因为齐射质量×速度等于之前计算的齐射动量,推得:
Broadside Momentum = Mass of ship * Velocity of ship
齐射动量=船质量×船速度(横移速度)
Solving for the velocity of the ship and using the above calculated momentum figures:
计算:
Velocity of ship (船横移速度)= Broadside Momentum / [Mass of ship] (齐射动量/船质量)
= 2.60 x 10^6 / [58,000 * (2,240 / 32.174)]
= 0.64 fps
So, the ship's velocity ON ICE with the guns firing at zero degrees elevation would be about 7.7 inches per second rather than the 6 inches per second calculated above. When one considers that any sideways motion of the ship through water is actually resisted by the wall created by the hull of the ship, whose wetted surface is about 860 feet long and 38 feet deep, then it can be easily understood that Dick Landgraff's comment above, "theoretically, a fraction of a millimeter," is closer to the truth.
结论:IOWA在冰面上以0角度齐射造成到船体横移速度为每秒7.7英寸。考虑到横移会被船体在水中部分阻挡,而船体的水线长度为860英尺,吃水38英尺,具体横移距离应该不到一毫米。
(原文链接:http://www.navweaps.com/index_tech/tech-022.htm)
流言之二
大和主炮口径是457mm
辟谣如下。
出处为美军战后调查报告
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