Re: [問題] 為啥麼弩射不遠??

[fw190a (las)]

前面有人提動能不受距離影響，
又有人提出十字弓與長弓誇張的磅數比。

我發現有人好像混用了弓拉到滿的最大磅數，以及十字弓儲存能量的"磅數"

基本上前者乘以"拉的長度"之後大致除以2才會變後者。

http://science.howstuffworks.com/crossbow.htm/printable

Two factors determine the amount of energy a bow can hold. Its draw weight is
the amount of force required to draw the bow. A bow's draw weight increases
the farther back you pull the string. Its draw length is the distance between
the bowstring's position at rest and its position when drawn. The total
amount of energy that a bow can hold is approximately equal to its draw
weight times its draw length, divided by two. In other words, a bow's overall
strength depends on how hard it is for you to pull the string and how far
back you are able to pull it. Bow manufacturers express this strength in
terms of:

The bow's energy, measured in foot-pounds or joules
The arrow's velocity, measured in feet or meters per second


另外補充一個連結
http://www.thebeckoning.com/medieval/crossbow/cross_l_v_c.html
W.F. Paterson (1990) published data from Stephen V. Grancsay about an
experiment comparing a longbow and a crossbow that was spanned with a
cranequin.

Type of Weapon @ Draw weight @ Bolt weight @ Speed of bolt @  Difference
Longbow            68 lbs.        2.5 oz      133.7 fps        Not much!!
Crossbow          740 lbs        1.25 oz.     138.7 fps        Not much!!


ps.下面都是簡短意譯

裡面也有做些比較，並說明除了拉的距離不夠長以外，弓臂彈回的速度無法達到該動能
所能允許的最大速度，因此造就了較低之速度，以及相對無效的系統。

Although it is impossible for any bow to be perfectly efficient, crossbows
are particularly inefficient when compared to longbows. The reason for this
is that the draw length and the lath (also called a prod) of crossbows are
much shorter than those of longbows. So even though a crossbow may have more
stored energy when spanned, the tips of the lathe do not have enough time to
reach the maximum velocity that the amount of stored energy would otherwise
allow. It is the lathe tip velocity that determines the speed of the bolt
that is loosed. (Crossbows are not "fired", which is a term related to
gunpowder.)

而現代十字弓則有辦法在較低之拉力下達到更高速度。
NOTE: through the use of modern engineering and advanced materials, modern
crossbows are now much more efficient. The Excalibur Exomag has a draw weight
of 185 pounds, and is able to send a bolt at 290 fps. The 165 pound draw
weight Excalibur Exocet looses bolts at 270 fps, and the 150 pound draw
weight Excalibur Vixen looses bolts at 250 fps. Special thanks to Excalibur
Crossbows for the use of crossbow specs.



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◆ From: 118.168.243.235
推 s955120     :推詳細
推 mackulkov   :這網頁我也有看 那句"距離短使加速時
推 mackulkov   :間不足" 令我頗難理解...
推 mackulkov   :還有"磅數"是力量 "呎磅"才是能量
→ djmez       :距離短使加速時間不足 道理就和為啥
推 mackulkov   :應是古代的弩材料共振頻率低無法產生
→ mackulkov   :足夠大的加速度  才會有此影響
→ djmez       :高初速的砲通常是長倍徑道理是相通的
→ mackulkov   :砲彈是一直受爆炸壓力前推在加速 弓
→ mackulkov   :弦在釋放過程中的力量則是越來弱喔
推 djmez       :但是力作用在箭上的時間不夠長 也就
→ djmez       :能量也就無法有效的轉移到劍的身上
→ djmez       :和假如你把高初速的砲切短 他初速也
→ djmez       :會變低是一樣的道理
→ mackulkov   :弓弦運動到未拉開前位置時應該已經低
→ mackulkov   :沒有加速度了 所有能量應該在之前已
→ mackulkov   :經傳遞完畢 跟砲彈在砲管中不同
→ mackulkov   :如果用簡諧運動的類比沒有錯誤的話..
→ djmez       :弦還沒到初始位置前箭就和弦分離了吧
→ mackulkov   :弦到達初始位置時速度是最大的
→ djmez       :那就是我有地方搞錯了
推 mackulkov   :看來需要流言終結者們的器材了XD
推 F23ko       :                            C4!
推 xgcj        :推                          C4!
→ s955120     :以這複雜程度大概真的要...   C4
推 josiah      :                            C4!
推 vixen       :現代復合弓剛射初速可破350fps,可怕!