知識社｜冷知識 02｜為什麼飛機窗戶都是圓角？ Why Do Airplane Windows Have Rounded Corners?
搭飛機時，你是否留意過所有機窗都是圓角，而不是一般建築常見的方形？這個設計並非為了美觀，而是與飛行安全息息相關，更曾改變整個航空工業。
Airplane windows all seem to share one feature—rounded corners. While many people assume it’s simply a design choice, the shape actually plays a critical role in aircraft safety and has influenced modern aviation engineering for decades.
中文版本
每次乘搭飛機，大部分乘客都會透過窗戶欣賞雲海、日落或城市夜景，但很少人會思考，為什麼飛機上的窗戶全部都是圓角，而不是容易製造的方形。答案其實與高空飛行時承受的巨大壓力有關。當飛機升上約三萬至四萬呎高空，機艙內需要保持適合人體呼吸的氣壓，而機艙外的空氣卻十分稀薄，因此飛機機身每天都要承受內外巨大的壓力差。每一次起飛、巡航及降落，都等於讓機身經歷一次加壓與減壓循環，金屬結構長期受到反覆拉伸與壓縮，容易產生金屬疲勞。如果窗戶設計成直角方形，四個角落便會形成應力集中點，壓力會集中於尖角位置，隨著飛行次數增加，細小裂縫便可能由角落開始擴大，最終影響機身安全。航空史上曾發生過著名事件。1950年代初，全球第一款商業噴射客機「德哈維蘭彗星號（De Havilland Comet）」因採用了接近方形的窗戶設計，在多次飛行後出現金屬疲勞裂縫，導致數宗空中解體事故。經過深入調查，工程師發現問題並非單一材料，而是窗角令壓力過度集中，加速裂縫擴展。這次事故徹底改變了飛機設計理念，航空工程師開始全面採用圓角甚至接近橢圓形窗戶，讓壓力能平均分散到整個窗框，避免集中於某一點，大幅提升機身耐用性與安全性。除了外形之外，現代機窗其實由多層特殊材料組成，一般包括外層承受壓力、中間保護層及內層透明面板，不但能承受高空低溫及巨大氣壓差，亦可防止玻璃碎裂造成危險。乘客常見到底部的小圓孔，稱為「呼吸孔」或「排氣孔」，作用是平衡內外玻璃之間的壓力，同時減少起霧情況。今天所有大型民航客機，包括波音及空中巴士系列，都沿用圓角窗戶設計。這個看似普通的小改變，背後卻是航空工業用無數測試、事故經驗及工程技術換來的重要成果，也提醒我們，許多日常生活中的設計，其實都隱藏著科學與安全考量。
English Version
Most passengers spend their flight looking through the window at clouds, mountains, or city lights, but few ever ask why airplane windows are rounded instead of square. The answer lies in one of the most important principles of aircraft engineering: managing stress. At cruising altitude, commercial aircraft fly where the outside air is extremely thin, while the cabin is pressurized to keep passengers comfortable. This creates a significant pressure difference between the inside and outside of the aircraft. Every flight subjects the fuselage to a complete cycle of pressurization and depressurization, causing the metal structure to expand and contract repeatedly. Engineers know that sharp corners concentrate mechanical stress. If aircraft windows had square corners, those corners would become weak points where tiny cracks could develop and gradually grow after thousands of flight cycles. This lesson was learned the hard way during the early jet age. In the 1950s, the de Havilland Comet, the world’s first commercial jet airliner, suffered several catastrophic accidents. Investigations revealed that cracks had formed around the aircraft’s nearly square windows because stress accumulated at the corners. These discoveries transformed aircraft design forever. Modern airplanes now use rounded or oval-shaped windows because curved edges distribute pressure much more evenly across the surrounding structure, greatly reducing the likelihood of fatigue cracks. Today’s airplane windows are also far more sophisticated than they appear. They are made from multiple layers of specially engineered materials, with each layer serving a different purpose. The outer pane bears most of the pressure, additional layers provide structural support, and the inner pane protects passengers. You may also notice a tiny hole near the bottom of the inner window. Known as a bleed hole, it helps regulate air pressure between the window panes while preventing condensation from forming. Nearly every commercial aircraft in service today, whether built by Boeing or Airbus, follows these engineering principles. The rounded airplane window is therefore much more than a stylish feature—it is a direct result of lessons learned from history, advances in engineering, and a relentless commitment to passenger safety. Sometimes the smallest design details carry the greatest responsibility.
總評
飛機窗戶的圓角設計，不只是外觀上的選擇，而是經歷航空事故後累積出的工程智慧，充分展現安全設計往往藏在最不起眼的細節之中。
Summary
Rounded airplane windows are not decorative—they are a lifesaving engineering solution developed through experience, research, and innovation. Their simple shape reflects decades of progress in aviation safety.
