It tells us why engines are placed slightly in front of wings, and why the fuselage of supersonic planes narrows along the wings,

它能讓我們了解為什麼發動機會被放置在機翼的前方、為什麼超音速飛機的機身會沿著機翼變窄，

and why redesigning the hump of the 747, to be longer, not only allowed it to carry more passengers but also increased its cruise speed and decreased drag.

以及為什麼將波音 747 的頂部重新設計並拉長，不僅使其能夠承載更多的乘客，更能提高巡航速度並減少阻力。

This simple rule is called the area rule, and it tells us the ideal distribution of cross sectional area along the length of a transonic or supersonic plane will look something like this.

這個單純的規則被稱為面積規則，而根據規則，一架穿音速或超音速飛機的理想截面積分布應該像是這樣。

That includes the wings, engines, everything.

這包括機翼、引擎等所有的東西。

Because a gradual change in cross-section results in a reduction in wave drag, which is the drag that arises from shockwaves forming over the plane as it approaches the speed of sound.

這是因為只要使截面積慢慢地逐漸變化，便能降低音波所造成的阻力，也就是飛機在接近音速時由於音波所產生的震波而造成的阻力。

In reality, planes never achieved this ideal distribution.

在現實中，從沒有飛機能達到如此裡想的分布。

The Concorde's distribution looked similar to this, and could have been closer to the ideal had they tapered the fuselage over the wing—but more on that later.

協和號的分布看起來像是這樣，而且如果他們在機翼連接部分縮減機身大小的話，還能更接近理想的分布－但我們之後再來詳談。

The rule was discovered as planes started to edge ever closer to the speed of sound,

此規則是在飛機開始越來越接近音速的時候被發現的，

and designers started to notice that adjusting the position and shape of features on the plane had significant effects on performance.

設計師們開始注意到，調整飛機外觀的位置和形狀對於性能表現有顯著影響。

Take this patent from the Junkers Company company, in 1944, showing obvious attempts to experiment with the distribution of cross-sectional area along the length of the plane.

以 1944 年容克斯公司的這項專利為例，上面顯示出對於跨越整台飛機的截面積分布進行實驗的明顯嘗試。

With the cross-sectional areas highlighted here.

下圖顯著標示出了截面積。

This ultimately lead to the bizarre-looking Ju 287.

而這最終催生了看起來相當奇怪的 Ju 287。

The effect was discovered again by Richard Whitcomb when testing models in a wind tunnel in the 1950s.

再 1950 年代，理查·惠特科姆在風洞中測試模型時，再次發現了這種效應。

His discovery was used to redesign the F-102 Delta Dagger, which was originally designed with a straight fuselage.

他的發現被運用於重新設計 F-102 三角劍戰鬥機，最初的設計本來有著筆直的機身。

The redesign tapered the fuselage over the wings and allowed the distribution of cross-sectional area to more closely resemble the ideal.

重新設計使機身在機翼連接的部份變得更細，使得機翼部分的截面積分布更接近於理想。

This small change, along with slightly more powerful engines, brought its max speed from 0.98 Mach to 1.22.

這一微小的變化，加上強大些許的引擎，使它的極速從 0.98 馬赫提升到了 1.22 馬赫。

Sometimes it's not possible or does not make economic sense, as was the case for the Concorde, to narrow the fuselage over the wing.

然而有時想縮小機身在機翼連接處的大小並不可能，或是在商業上並不合裡，就像是協和號那樣。

Instead, it makes more sense to make the fuselage before the wing larger to make the change in cross-section less dramatic.

相對的，把位於機翼連接處前方的雞慎做得更大，好讓截面積的變化不會如此顯著是個更加合理的選擇。

The 747 800 featured a longer hump for exactly this reason, which allowed its cruise speed, passenger capacity and fuel economy to rise.

747 800 較長的頂部正是出於這個原因，使得它的巡航速度、載客量和燃油效率得以提高。

This rule even affects the placement of engines.

這一規則甚至還影響到了引擎的位置。

Most large planes mount the engines slightly forward of the wing and not directly under, as that would compound the wings' addition to the cross-sectional area.

大多數大型飛機會將引擎安裝在機翼的稍前方，而不是直接安裝在機翼下方，因為直接裝在下方將增加機翼部分的截面積。

And in narrow-body planes, the engines are often mounted above and behind the wing for the same reason.

而在窄體飛機上基於同樣的原因，引擎通常會被安裝在機翼的上方和後方。

There are countless other examples of this rule that you can find in the real world and I challenge you to name some of them in the comment section below.

你可以在現實世界中找到無數個應用到這個規則的例子，而我挑戰各位在評論欄中說出幾個來。

I'll pick up my favorite one and send you a free Real Engineering t-shirt.

我將挑選我最喜歡的一個留言，並免費送你一件 Real Engineering T 恤。

This video was made possible by Hover: The easiest and best place to register a custom domain or email.

本影片由 Hover 贊助波出。Hover 是註冊自定義網域或電子郵件最簡單和最好的地方。

They have over 400 domain extensions, and the best customer service in the business.

他們有 400 多個網域後綴，並有業內最好的客戶服務。

Seriously, they've won awards.

真心不騙，他們還有贏過獎項。

I couldn't believe my luck when I saw that the real.engineering domain was available on Hover, and purchased it immediately, and it took less than 20 seconds to make it mine.

當我看到 Hover 上有 real.engineering 網域名時，我簡直不敢相信自己的運氣如此之好，並立即購買了它，只花了不到 20 秒就這個網域就變成我的了。

I now have a custom email address that couldn't suit my channel better.

我現在有一個與我的頻道再適合不過的訂製電子郵件地址。

If you are looking for a unique domain name, Hover is the best place to get one, and you can get 10% off your next purchase using the code realengineering.

如果你正在尋找一個獨特的網域，Hover 是購買的最佳地點，而且你還可以使用代碼 realengineering 在下次購買時獲得九折折扣。

You could get the real.surf domain to use for your surfing videos, or maybe you want the real.adult domain name and pretend that you are one.

你可以取得 real.surf 域名來用於你的衝浪影片，或者也許你想要 real.adult 域名來假裝你真的長大了。

Whatever domain you want, you'll probably be able to find one that suits your needs at Hover.

無論你想要什麼域名，你可能都能在 Hover 找到適合你的需求。

And once again, you can get 10% off your next purchase using the code realengineering.

再次提醒，你可以使用代碼 realengineering 來在下次購買時獲得九折折扣。

There's been a slight delay for my next video on ICBM defense, and I've committed to posting videos at least every second Friday.

我下一部有關洲際彈道飛彈防禦系統的影片進度有點延遲，而我希望至少每兩個星期五能上傳一部影片。

So please forgive how short this video is!

因此抱歉，這部影片比較簡短一些！

Thanks for watching, and thank you to my Patreon supporters for helping this channel exist.

感謝觀看，並感謝我的 Patreon 贊助者們幫助維持了這個頻道的經營。