The de Havilland Comet entered service in 1952 as the world’s first jet airliner, changing how people imagined long distance travel. Its jet engines let it fly higher, faster, and more smoothly than propeller airliners of the same era. The Comet was a major engineering achievement, but it also became one of aviation’s most important safety case studies.
Its story matters because modern aircraft design learned directly from both its success and its failures.
Early Comets suffered catastrophic accidents caused by metal fatigue in the pressurized fuselage, especially near square window corners and other stress concentration points. Each flight cycle repeatedly pressurized and depressurized the cabin, creating small cracks that could grow until the structure failed. Investigators used full scale water tank testing and wreckage analysis to identify the mechanism, leading to redesigned windows, stronger structures, and better inspection methods.
The lessons helped shape today’s safer jet airliners, including rounded windows, fatigue testing, and damage tolerant design.
Key Facts
- The de Havilland Comet 1 entered airline service in 1952 with BOAC.
- Jet thrust is produced by accelerating exhaust backward, described by F = dp/dt.
- Cabin pressure difference creates stress in the fuselage, with hoop stress approximately σ = pr/t for a thin cylinder.
- A stress concentration makes local stress higher than average, often written σmax = Ktσnominal.
- Metal fatigue occurs when repeated loading cycles grow cracks over time, even if each load is below the static failure strength.
- Rounded windows reduce stress concentration compared with sharp square corners.
Vocabulary
- Jet airliner
- A passenger aircraft powered by jet engines rather than propellers.
- Pressurized fuselage
- The sealed body of an aircraft that holds cabin air at a pressure suitable for passengers at high altitude.
- Metal fatigue
- Progressive weakening and cracking of a metal caused by repeated loading and unloading.
- Stress concentration
- A location where stress becomes much higher than the average because of shape features such as corners, holes, or notches.
- Flight cycle
- One complete operating sequence of takeoff, climb, cruise, descent, and landing, including one cabin pressurization cycle.
Common Mistakes to Avoid
- Blaming the Comet accidents only on jet engines is wrong because the main failure mechanism was fuselage metal fatigue from repeated cabin pressurization.
- Thinking square windows failed because glass was weak is wrong because the dangerous issue was high stress in the surrounding metal at sharp corners.
- Assuming a structure is safe if one test load does not break it is wrong because fatigue damage can accumulate over many repeated cycles.
- Ignoring pressure difference when analyzing high altitude flight is wrong because cabin pressurization creates significant forces on the fuselage skin.
Practice Questions
- 1 A simplified Comet fuselage has radius 1.5 m, skin thickness 0.0015 m, and cabin pressure difference 55,000 Pa. Estimate the hoop stress using σ = pr/t.
- 2 If a stress concentration factor is Kt = 3.0 and the nominal stress near a window is 40 MPa, what is the maximum local stress?
- 3 Explain why modern airliners use rounded window corners and extensive fatigue testing, using the Comet accidents as evidence.