The reason modern jets have rounded windows

[GON]

Came across this intersting article on why modern jets have rounded windows- design changes from a tragedy.

It was meant to restore trust in the jet age. But on 8 April 1954, South African Airways Flight 201 vanished over the Mediterranean, taking 21 lives and dealing another blow to the de Havilland Comet.

The aircraft had left Rome bound for Cairo, following the same route as BOAC Flight 781 just months earlier. Both jets suffered the same fate — sudden mid-air breakups caused by undetected structural failure. The Comet’s pressurised cabin, once seen as a technological leap, had turned into its greatest weakness.

Investigators traced the cause to metal fatigue. Stress concentrated around the corners of the aircraft’s square windows and rivet holes. With each flight cycle, microscopic cracks grew — until, without warning, the fuselage tore apart.

The crash marked the second catastrophic loss of a Comet in less than three months. Confidence in jet travel collapsed.



But from the wreckage came revolution. Engineers tore the aircraft apart, studied fatigue, and redefined how planes were built. Design standards changed. Window shapes rounded. Testing became more rigorous.

Flight 201’s loss was a tragedy. But it forced a young industry to confront its blind spots — and made every jet that followed stronger.

https://www.theheritageportal.co.za/article/1954-saa-comet-disaster

https://en.wikipedia.org/wiki/South_African_Airways_Flight_201

 

[Reggaemon]

Well they did look nice.

 

[97prizm]

Came across this intersting article on why modern jets have rounded windows- design changes from a tragedy.

It was meant to restore trust in the jet age. But on 8 April 1954, South African Airways Flight 201 vanished over the Mediterranean, taking 21 lives and dealing another blow to the de Havilland Comet.

The aircraft had left Rome bound for Cairo, following the same route as BOAC Flight 781 just months earlier. Both jets suffered the same fate — sudden mid-air breakups caused by undetected structural failure. The Comet’s pressurised cabin, once seen as a technological leap, had turned into its greatest weakness.

Investigators traced the cause to metal fatigue. Stress concentrated around the corners of the aircraft’s square windows and rivet holes. With each flight cycle, microscopic cracks grew — until, without warning, the fuselage tore apart.

The crash marked the second catastrophic loss of a Comet in less than three months. Confidence in jet travel collapsed.



But from the wreckage came revolution. Engineers tore the aircraft apart, studied fatigue, and redefined how planes were built. Design standards changed. Window shapes rounded. Testing became more rigorous.

Flight 201’s loss was a tragedy. But it forced a young industry to confront its blind spots — and made every jet that followed stronger.

https://www.theheritageportal.co.za/article/1954-saa-comet-disaster

https://en.wikipedia.org/wiki/South_African_Airways_Flight_201
View attachment 279996

Engineers put a Comet fuselage in a water tank test to replicate what happened. They were able to see first hand in real time the failure.
BOAC Comet failure

It's Air Crash Investigation season 3

 

[Just a civilian pilot]

https://www.faa.gov/lessons_learned/transport_airplane/accidents/G-ALYV

 

[ka9mnx]

I thought the square window theory was debunked years ago.

 

[Just a civilian pilot]

One broke apart simply because it flew into severe thunderstorms after take off.

Imagine flying around thunderstorms with no weather radar back then ( with square windows ).

https://en.wikipedia.org/wiki/BOAC_Flight_783

 

[97prizm]

I thought the square window theory was debunked years ago.

When the Comets fuselage was put in a water pressure tank they could accelerate the wear and were able to find cracks propagating from the square windows.

 

[KrisZ]

The Comet tragedy is when the stress due to fatigue was discovered or at the very least started to be a design consideration, if I remember correctly.

 

[Just a civilian pilot]

Even properly designed aircraft can break apart if they fly into extreme turbulence.

Not to scare people, it would have to be extreme but read about the B707 over Japan.

They encountered the extreme turbulence at max speed ( 370 indicated airspeed ) which didn’t help.

https://en.wikipedia.org/wiki/BOAC_Flight_911

 

[Owen Lucas]

The Otto Aviation Phantom 3500 will have no passenger windows. There will be view screens along the walls though.

Apparently the plane will be up to 50% more fuel efficient than comparable planes.

https://newatlas.com/aircraft/phantom-3500-windowless-transonic-flight/

 

[BusyLittleShop]

De Havilland design number 106 named the Comet was the worlds first
jet airliner capable of flying 36 passengers nearly 500 mph and
shrinking the globe by 40% rendering the piston power competition
obsolete... but the giant leap forward in Jet travel would soon be
associated with failure and disaster...

Uncovering the real clue the engineers submerged a Comet in a 112 foot
long tank filled with water to under go a fatigue test... The pressure
changes had pulled rivets through the skin and caused cracks in the
fuselage frame and floor beams...

After the equivalent of 3,057 flights a larger split suddenly appeared
at the forward escape hatch... Exterior and interior views of the
escape hatch where the cabin first split show that the window stayed
in place but the metal popped out... There were no square corners in
either the hatch nor window for the investigators to focus on...

 

[y_p_w]

I'm kind of confused since they actually use flat pane windows.

 

[MolaKule]

I thought the square window theory was debunked years ago.

No it is true.

Here is how you analyze stresses around aircraft windows:

https://www.egr.msu.edu/classes/me424/averillr/Marc.FuselageWindow.pdf

 

[Exhaustgases]

Really just now learning this one? I think I first heard about this in grade school.

But then school was more advanced in those days.

 

[andrew_j]

My degree is in structural engineering. I remember actually doing this analysis of round hole vs square.

 

[slo town]

A question for your pilot types. @Just a civilian pilot, @Astro14.

Is an aircraft fuselage 100% leak free, or does it need to be "recharged" while in flight, however slightly?

Scott

 

[Astro14]

A question for your pilot types. @Just a civilian pilot, @Astro14.

Is an aircraft fuselage 100% leak free, or does it need to be "recharged" while in flight, however slightly?

Scott

The fuselage itself does not leak.

However, the airplane is pressurized by air from the engines (compressors in the case of a 787), and the air is exchanged, and excess air is dumped overboard via a “outflow“ valve.

The rate at which the air is allowed to leave the airplane controls the cabin altitude inside the airplane.

The outgoing air is offset by the continuous flow of fresh air from the engines or compressors.

 

[y_p_w]

A question for your pilot types. @Just a civilian pilot, @Astro14.

Is an aircraft fuselage 100% leak free, or does it need to be "recharged" while in flight, however slightly?

Scott

Not an expert on this, but I do have an engineering background.

No - an aircraft fuselage isn't hermetically sealed. There's leaking going on all the time. It's just not possible to perfectly seal a fuselage. There are all those windows and rivets.

They just have pretty good environmental controls that regulate the pressure inside despite all the leaks.

 

[slo town]

The fuselage itself does not leak.

No - an aircraft fuselage isn't hermetically sealed. There's leaking going on all the time.

I'm not trying to pit you guys against each other or anything, but let me ask my question a different way.

Suppose the fuselage was parked at sea level. Suppose I pressurized the interior to greater than sea level. Would the fuselage hold that additional pressure or would it slowly leak itself back to sea level pressure?

Scott

 

[Astro14]

I'm not trying to pit you guys against each other or anything, but let me ask my question a different way.

Suppose the fuselage was parked at sea level. Suppose I pressurized the interior to greater than sea level. Would the fuselage hold that additional pressure or would it slowly leak itself back to sea level pressure?

Scott

Is the outflow valve closed, or open?

The outflow valve on a widebody is BIG.

It will leak slowly - very, very slowly - if the valve is closed.

So slowly in fact, that you can blow up the airplane by adding interior pressure. It's not "gushing" out through door seals, windows, or anything (and no, I don't think rivets leak).

https://theaviationgeekclub.com/time-kc-135-stratotanker-aircraft-exploded-failed-pressure-test/