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The paper I posted on the change in deployment is dated August 9, 1945, which is ironic as the second atomic bomb was dropped on Nagasaki that day rendering the decision moot. The comparison paper is dated August 11, 1945, so I presume it was the basis for the decision.Good catch. I knew that the deployment was planned, did not know the final reason they were stood down. Do you have the date for this?
On the B-17 vs B-24 thing the B-17 may have been overbuilt as they weren't sure how large aircraft structures behaved. One of the YB-17s had been slated for destructive testing to see how well the structure would standup but when one of the early ones survived being flipped upside down in a thunderstorm they canceled the tests and completed the airframe as a regular flying aircraft.
I believe the B-17 main spar was also steel. This was supposed to give a bit more time before the spar failed in wing fuel tank fires but that would be rather hard to prove. The B-24 did have the reputation of wing failure due to fire/combat damage. Basically any advantage was going to mean a few more crewmen might have the opportunity to bail out. A very hard thing to prove as with hundreds if not thousands of planes shot down you are going to find examples of both types surviving extreme damages and examples of both types failing in a matter of seconds from unknown damage. An awful lot of variables.
You would be surprised (or maybe not) what some people will argue over. I was on a committee to select a new ladder truck for the Fire Dept and some members insisted we should get a steel ladder instead of aluminum ladder because it would last longer if exposed to heat/fire. We were looking at a 100ft bucket truck that could hold 3-4 men in the bucket. My view was that if the ladder structure was exposed to enough heat/fire for it to fail with either material I wasn't going to worry about it because I was going to be 10-30ft above the heat/flames and even with Nomex and an air tank I was going to be dead before the ladder collapsed.
Maybe not moot, maybe already preparing for the post war situation?The paper I posted on the change in deployment is dated August 9, 1945, which is ironic as the second atomic bomb was dropped on Nagasaki that day rendering the decision moot. The comparison paper is dated August 11, 1945, so I presume it was the basis for the decision.
The properties of nearly any steel are so dramatically superior to Aluminium at high temperatures, that I dont think any "proof" would be needed of the contention that a steel spar would last dramatically longer in exposure to fire than an aluminium one. There is of course a "slight" element in favour of the Aluminium in that the conductivity is very high, but I do not think that anywhere near balances out the difference.On the B-17 vs B-24 thing the B-17 may have been overbuilt as they weren't sure how large aircraft structures behaved. One of the YB-17s had been slated for destructive testing to see how well the structure would standup but when one of the early ones survived being flipped upside down in a thunderstorm they canceled the tests and completed the airframe as a regular flying aircraft.
I believe the B-17 main spar was also steel. This was supposed to give a bit more time before the spar failed in wing fuel tank fires but that would be rather hard to prove. The B-24 did have the reputation of wing failure due to fire/combat damage. Basically any advantage was going to mean a few more crewmen might have the opportunity to bail out. A very hard thing to prove as with hundreds if not thousands of planes shot down you are going to find examples of both types surviving extreme damages and examples of both types failing in a matter of seconds from unknown damage. An awful lot of variables.
You would be surprised (or maybe not) what some people will argue over. I was on a committee to select a new ladder truck for the Fire Dept and some members insisted we should get a steel ladder instead of aluminum ladder because it would last longer if exposed to heat/fire. We were looking at a 100ft bucket truck that could hold 3-4 men in the bucket. My view was that if the ladder structure was exposed to enough heat/fire for it to fail with either material I wasn't going to worry about it because I was going to be 10-30ft above the heat/flames and even with Nomex and an air tank I was going to be dead before the ladder collapsed.
As noted above, if the aluminium is in an environment hot enough to make it fail, the people on it will be in no shape to care. Steel does have better fatigue properties, but this may not count with a lightweight structure.The properties of nearly any steel are so dramatically superior to Aluminium at high temperatures, that I dont think any "proof" would be needed of the contention that a steel spar would last dramatically longer in exposure to fire than an aluminium one. There is of course a "slight" element in favour of the Aluminium in that the conductivity is very high, but I do not think that anywhere near balances out the difference.
As noted above, if the aluminium is in an environment hot enough to make it fail, the people on it will be in no shape to care. Steel does have better fatigue properties, but this may not count with a lightweight structure.
The B-17 wing looks a lot sturdier than the B-24's wing.
The reason was the 8th greatly preferred the B-17 and the Germany first doctrine meant they got their way.The really important advantage of the B-24 over the B-17 was it's range while still carrying a useful load which only expanded as the war went on.
For example, RAF Coastal Command B-17 could fill the bomb bay with fuel but could then only carry 4 depth charges externally. The B-24 with extra fuel filling the forward bomb bay could still carry 8 depth charges or 4 plus a Mk24 homing torpedo internally and still fly further.
In 1945 the Liberator in SEAC was flying 24 hour missions out of Ceylon. Before the introduction of the B-29 it was the B-24 that were flying the longest ranged bombing missions of the war in 1942 and 1943. Check out the failed HALPRO mission to Ploesti in 1942 or the Shady Lady mission to Balikpapan in 1943.
There was a reason why the USAAF swapped B-17s for B-24s in the Pacific from early 1943. Range.
There is no doubt that the steel lasts longer and will stand up "better".
However when it comes down to crew survival we have to figure out what it means.
Hypothetical numbers, steel lasts 3 times longer than aluminum before failing.
Aluminum spar lasts 12 seconds under XXX Flame impingement.
Steel lasts 36 seconds.
You are a turret gunner getting out of a turret, grabbing parachute from rack on fuselage, attaching parachute to harness and getting out of escape hatch.
How long?
I have seen aluminum components reduced to puddles on the floor/ground. I have also seen iron water pipes (Sprinkler pipes 6in in diameter) and structural components that looked like cooked spaghetti draped over parts/rubble that were lower. Steel, if I remember correctly, becomes "plastic" at around 800 degrees. The steel pipe or beam will maintain it's "shape" like tube or I beam but can no longer support itself, and droops/sags down onto whatever will support it. It hasn't "melted" like aluminum but it isn't holding up a lot either.
Steel buildings are known as "non-combustible" buildings which basically means that the building structure (beams, siding, etc) will not contribute to the fire load over and above what the contents are doing. It does NOT mean the steel building is fire proof. Steel structure can be fire proofed with the application of layer/s of insulation or coatings to give a certain rating for flame impeachment, some times given as how many minutes before failure.
Now with a damaged aircraft how big is the fuel fire, how big is the airflow through the compartment/s where the fire is, how fast/volume is the airflow and what is the altitude (air density) of the air feeding the fire?
That is just stuff I can think of off the top of my head. I would guess that steel stands up better there is a lot of stuff that affects the result in each case.
A lot of this is "engineering". Steel is a remarkable series of alloys, with a huge range of properties. A steel "can" with a large diameter and low wall thickness will deform under its own weight at room temperature. Above a certain ratio of diameter and wall thickness you cannot measure ovality, you are measuring gravity, and if you roll the "can" as we called them a quarter turn the ovality has moved with the rotation. Steel used for pipelines is certainly affected above 137C because I have worked on projects where the steel was tested at room temperature and at the exit temperature of the product which was 137C on 1 project and 145C on another. The difference is only noticed statistically, after performing hundreds of tests on the same material at both temperatures there is a lower average result at the higher temperature, however they are not exactly the same size of test piece, or the same type of extensometer and strain regime.I am not familiar enough with aluminum and it's fail modes.
I do now that steel can fail as a loading bearing component well below it's melting temperature.
But that is low grade steel. How well alloys do could be very different.
No disrespect intended, it may be that you wanted to ask if the B-17 was more numerous.Sorry if I may not be right. I'm no native English speaker.
How come?
The accident rate for the B-26 got progressively lower as the war progressed. Improvements in training and the adoption of the longer wing contributing greatly. Both A-26 and A-20 had higher accident rates.
There is no doubt that the steel lasts longer and will stand up "better".
However when it comes down to crew survival we have to figure out what it means.
Hypothetical numbers, steel lasts 3 times longer than aluminum before failing.
Aluminum spar lasts 12 seconds under XXX Flame impingement.
Steel lasts 36 seconds.
You are a turret gunner getting out of a turret, grabbing parachute from rack on fuselage, attaching parachute to harness and getting out of escape hatch.
How long?
I have seen aluminum components reduced to puddles on the floor/ground. I have also seen iron water pipes (Sprinkler pipes 6in in diameter) and structural components that looked like cooked spaghetti draped over parts/rubble that were lower. Steel, if I remember correctly, becomes "plastic" at around 800 degrees. The steel pipe or beam will maintain it's "shape" like tube or I beam but can no longer support itself, and droops/sags down onto whatever will support it. It hasn't "melted" like aluminum but it isn't holding up a lot either.
Steel buildings are known as "non-combustible" buildings which basically means that the building structure (beams, siding, etc) will not contribute to the fire load over and above what the contents are doing. It does NOT mean the steel building is fire proof. Steel structure can be fire proofed with the application of layer/s of insulation or coatings to give a certain rating for flame impeachment, some times given as how many minutes before failure.
Now with a damaged aircraft how big is the fuel fire, how big is the airflow through the compartment/s where the fire is, how fast/volume is the airflow and what is the altitude (air density) of the air feeding the fire?
That is just stuff I can think of off the top of my head. I would guess that steel stands up better there is a lot of stuff that affects the result in each case.