Greatest aviation myth this site “de-bunked”.

[Shortround6]

it took about 2 years in the US to go from a bare plot of ground to a factory making just under 1000 engines a month. That is for a licensed engine they are given the plans for.
So the buildings would have had to have been built and equipped in 1937 with workers hired in 1938 to come close to putting out hundreds of engines in the fall of 1939.
ANd what wonder engine should they have tooled up for?

 

[SaparotRob]

Here's an extract from a Luftwaffe report from 20 November 1942, which was the first time the Germans reported the P-38 in North Africa.

View attachment 588348

Cheers,
Andrew A.

Thanks for that. I went with winner instead of informative. It was a toss up.

 

[Koopernic]

Here's an extract from a Luftwaffe report from 20 November 1942, which was the first time the Germans reported the P-38 in North Africa.

View attachment 588348

Cheers,
Andrew A.

Most German pilots would have had at least a little English. Being reasonable at one language and having a little of a 2nd would be normal for a German of the time.

 

[fastmongrel]

like why did some Liberty ships break in two?

The Liberty was based on a British WWI design for a cheap easily built cargo vessel. The original design was for a rivetted vessel altering it to a welded construction introduced the problems. The hulls were too rigid, rivetted hulls could flex. The Royal Navy preferred to use rivetted ships on Arctic convoys because a crack in a cold rivetted vessel would only grow as far as a rivet hole and stop. A crack in a cold weld can grow at a very fast speed.

 

[pbehn]

The Liberty was based on a British WWI design for a cheap easily built cargo vessel. The original design was for a rivetted vessel altering it to a welded construction introduced the problems. The hulls were too rigid, rivetted hulls could flex. The Royal Navy preferred to use rivetted ships on Arctic convoys because a crack in a cold rivetted vessel would only grow as far as a rivet hole and stop. A crack in a cold weld can grow at a very fast speed.

For myths to survive they must deliberately ignore all known facts, which was what I was doing (deliberately). The SAW welding process was only patented in 1935 which meant they learned all the drawbacks during the war. As a welding process it was revolutionary but there is no "free lunch" in engineering. Much of my working life was in testing of SAW welds and almost all of the tests and testing regimes grew out of WW2 experience. It created not only a new welding process but also a whole new area of metallurgy and production engineering and new types of destructive and non destructive testing. One of the peculiarities of the problem is that a perfectly sound weld doesn't crack but does induce cracking in the parent material. There are various types of cracking and crack propagation, when it changes from growing due to cyclical stress to the "letting go" with a catastrophic failure the crack propagates at the speed of sound in steel which is circa 5,900m/s. I only witnessed it once and it is like an explosion.

 

[Simon Thomas]

My materials lecturer told us that the problem with the Liberty ship welding was due to the welders being paid by the rod, so "they" used to put a pile of welding rods in the joint and then put a capping weld over the top.
How widespread "they" used to do that - and even if it is true I have never established.

 

[Acheron]

Here's an extract from a Luftwaffe report from 20 November 1942, which was the first time the Germans reported the P-38 in North Africa.

View attachment 588348

Cheers,
Andrew A.

You wouldn't happen to have the Luftwaffe's reports on first encountering the long-range escorts (P-51s) over Europe? I would kinda imagine this being a major shock for the Luftwaffe, with some immediate emergency meetings to figure out how to deal with this?

 

[pbehn]

My materials lecturer told us that the problem with the Liberty ship welding was due to the welders being paid by the rod, so "they" used to put a pile of welding rods in the joint and then put a capping weld over the top.
How widespread "they" used to do that - and even if it is true I have never established.

Your lecturer was wrong, or at least couldn't prove that he was right legends about welders welding over rods exist all over the world. I have seen welders "blocking in" welds which increases the risk of cracking but the issue is that a perfectly sound weld by a coded welder can crack. Here is a report on a failed pipeline that I was sort of involved in. The manufacturer had fraudulently stated incorrect Carbon Equivalent Values on the material certificates. That alone was enough to cause cracking, starting at the weld root and propagating through the weld/parent material. It was discovered by fishermen noticing gas bubbling up in the Irish Sea. BHP BILLITON PETROLEUM LTD & ORS v DALMINE SPA (2003) I knew one of the men responsible, he ended up in jail. The other issue is that cracks can form a long time after the weld is completed which leads to everyone involved in testing being accused of not doing their job.

 

[fastmongrel]

I thought the filling gaps with rods and welding over was a German tank thing done by slave labour.

 

[pbehn]

I thought the filling gaps with rods and welding over was a German tank thing done by slave labour.

Welders live just a few millimetres up the scale from slave labour in the eyes of many, and are easily blamed, when corners were really cut short on quality for the sake of production management was always involved, it had to be to organise the fiddles needed.

 

[Reluctant Poster]

It wasn't just liberty ships that broke in two. Esso Manhattan was a T2 tanker
Esso Manhattan - (1942-1959)
She was built by Sun Shipbuilding, a very reputable yard. She was repaired and had a long career, finally scrapped in 1974.

 

[Reluctant Poster]

Welders live just a few millimetres up the scale from slave labour in the eyes of many, and are easily blamed, when corners were really cut short on quality for the sake of production management was always involved, it had to be to organise the fiddles needed.

The full paper is attached

 

[Reluctant Poster]

The Liberty was based on a British WWI design for a cheap easily built cargo vessel. The original design was for a rivetted vessel altering it to a welded construction introduced the problems. The hulls were too rigid, rivetted hulls could flex. The Royal Navy preferred to use rivetted ships on Arctic convoys because a crack in a cold rivetted vessel would only grow as far as a rivet hole and stop. A crack in a cold weld can grow at a very fast speed.

One of the Liberty ship myths is that they were an old design whereas in fact they were very new. In order to obtain new orders in the great depression British shipyards developed "economy" designs that minimized operating costs, in particular fuel, while being easy to build. The Dorington Court built by J L Thompson was one such design. Its hull form was further improved by extensive hydro dynamic testing to provide the optimum design combining ease of construction with maximum propulsion efficiency. The hull maximized the straight length and minimized the number of compound curves. The first ship built to this design was the Empire Liberty built by Thompson which became the prototype for the ships built in both British and American yards.
The other Liberty ship myth is that American know how made them easier to build. In fact it took more man hours to build in an American yard than a British one. The American system was designed to maximize the number of ships produced by minimizing the time a slipway was tied up, hence the emphasis on prefabrication.

 

[swampyankee]

Welds tend to degrade material qualities near them, in the heat affected zone. Poor weld quality can also build in tensile stresses around the weld and inclusions that act as crack initiation sites.

The other issue is that many steels have a temperature, called the nil ductility temperature, below which the steel behaves almost like glass. Above the NDT, the steel will plasticly yield at the tip of the crack, slowing and possibly stopping its propagation. Riveted joints will stop the crack, but welded joints won't.

 

[Reluctant Poster]

One of the interesting things to note is that the Liberty ship fractures often occurred at the square corners of the hatches. The design was modified to alleviate this problem. This reminds me of the sad story of the square windows on the de Havilland Comet.

 

[pbehn]

View attachment 588497

View attachment 588498
View attachment 588499

The full paper is attached

That is so bad AND typical it is laughable. As I said, for these fiddles to work management must be involved from the very top downwards. "Automatic welding adjacent to critical welds was prohibited after February 1943" so they decided what was "bad workmanship" after the event. Allowing "ringers" to sit tests is as old as testing itself, it is only allowed when people want it to happen. What part did the "great and good" who were experts in the field play, was everyone involved in ship building advised of the problems associated with SAW welding? Certainly not, because the great and the good were just learning themselves. The experts who wrote this piece don't seem to have the imagination to see any other scenario than the one presented by their retrospectoscope. If you have a new super duper welding machine it is perfectly reasonable to complete as much of all weld joints with it. If the operator doesn't know that you need run on and run off plates to do the weld properly whose fault is that? Try telling a welder in 1940 that welding out the last few inches of a weld with manual electrodes will cause the ship to split in two, until it happens and becomes common knowledge, with pictures and explanations it is as stupid an idea as soldiers marching across a bridge causing it to collapse through resonance (which also happened). A shipyard, welding or fabrication shop is a different world. Everyone who has worked in on has tales of apprentices being sent for "sky hooks", "tartan paint", "metric adjustables" or "long stands" because young people in a strange environment are very gullible. You may think it is perfectly obvious that laying down uncoated electrodes or "slugs" and welding over them is "cheating" but that is only because you know it is. In principle what is the difference between that and a backing strip or EB insert? Where did the slugs come from? In 1990 I was involved in a shipment of pipes from Bethlehem Steel to Europe, they were unable to provide a tally list of pipe number heat number and length for shipment which means they did not operate any sort of QA system in house, yet during the war some poor kid was held responsible for ships sinking. In 1992 I rejected half a dozen pipes that had had a "gash" repair to longitudinal SAW seams as bad as anything you read about on Liberty ships, but the welders were working to a procedure approved by the company, they dont see the client specification that states "blow throughs shall not be repaired". The managers even tried to say to me "I dont know why they tried to do that", well they tried to do THAT because you told them to do THAT. As late as 1995 I had a British quality assurance manager ask me "what is an arc strike, what is the problem with them"? When I explained the problem he said he would sack the operator that caused the arc strike, he never considered sacking himself, the ffing idiot.

 

[yulzari]

One of the interesting things to note is that the Liberty ship fractures often occurred at the square corners of the hatches. The design was modified to alleviate this problem. This reminds me of the sad story of the square windows on the de Havilland Comet.

The Comet windows were not square. De Havillands were well aware (as any engineer would) of the propensity of a square corner to initiate and propagate a crack. Thus the windows had rounded corners. What no engineer knew, at that time, was the effect of multiple pressurisation cycles on the aluminium used in the gauge used. After the discovery by sad accidents the next generation of airliners went overboard in window roundness but there are plenty of examples of round cornered airliner windows in modern service. A failure of knowledge not silly design. The square window Comet is a myth.

 

[Reluctant Poster]

The Comet windows were not square. De Havillands were well aware (as any engineer would) of the propensity of a square corner to initiate and propagate a crack. Thus the windows had rounded corners. What no engineer knew, at that time, was the effect of multiple pressurisation cycles on the aluminium used in the gauge used. After the discovery by sad accidents the next generation of airliners went overboard in window roundness but there are plenty of examples of round cornered airliner windows in modern service. A failure of knowledge not silly design. The square window Comet is a myth.

Did I say it was a silly design? Did I say It was a perfect square? Did I critsize the designers of the Comet in any way?

 

[yulzari]

Did I say it was a silly design? Did I say It was a perfect square? Did I criticise the designers of the Comet in any way?

Indeed not; but you did say 'square' and a 'reply' was the simplest way to refer to the popular myth. My apologies if I offended you.

 

[SaparotRob]

Another myth busted!