WW II aircraft fatigue life

[FLYBOYJ]

Corrosion is the big problem with most WWII aircraft, often triggered by galvanic action of dissimilar metals, i.e. steel bolt in aluminum fittings. Cables will corrode internally although they look good visually, usually failing around pulleys where stresses build up. Some places are near impossible to inspect or lubricate.
Rubber has a limited life, especially when exposed to liquids of all types which may interact. Gas tank self sealing bladders and de-icing boots are a special issue.
Remember a lot of wood was used and weathers badly ... and glues vary in longevity. I know of two accidents caused when a good looking wooden instrument panel suddenly fell apart due to engine vibration alone, and a BT-13 crashed when the wooden pilot seat collapsed in a moderate G manuver.
Don't trust any fabric more than 5 years old.
Remember, these craft were planned for a service life of max 5 years, and were expected to be obsolete by then.

I helped an owner/ operator maintain a PBY for a few years and it was a corrosion nightmare even though the last operator seemed have maintained well (it was operated in Spain as a fire bomber). Although manufactured way later, some of the east block aircraft I worked on (MiG-15s, L29s, L39s) had little or no corrosion issues on the airframes, the hardware seemed to be more susceptible to corrosion.

Agree with your assessment on fabric and wood. I saw a Pitts basically shrink itself apart when it was brought to SoCal from Washington state.

 

[fannum]

I helped an owner/ operator maintain a PBY for a few years and it was a corrosion nightmare even though the last operator seemed have maintained well (it was operated in Spain as a fire bomber).

PBYs and WWII seaplanes almost deserve a separate discussion as they not only were subjected to salt air, but through leakage and condensation, had it pervade into every internal nook and cranny. Anodizing was largely developed to a fine art by Consolidated to protect their seaplanes, but they still needed constant inspection and treatment.
The Japanese had a remarkable brilliant green lacquer they sprayed on the interior of Naval aircraft, so effective that wrecks show far less corrosion even after decades in jungles. However, it was not as effective on seaplanes, and the last remaining Emily had holes through the skin from salt exposure before being transferred from Norfolk back to Japan ... I believe in the '70s.
Another factor was wartime metallurgy. Effective blockading of Germany and Japan denied the Axis of critical elements like cobalt, chromium, etc. to alloy with their steels and aluminums. NASM's Kyūshū J7W Shinden has only been partially restored as the wing spar has become unstable in the internal structure due to alloying chemistry, and will need an entirely new spar of stable alloys to complete. German jet engines were failing within 25 hours of running due to low strength steels deprived of critical elements.

 

[FLYBOYJ]

PBYs and WWII seaplanes almost deserve a separate discussion as they not only were subjected to salt air, but through leakage and condensation, had it pervade into every internal nook and cranny. Anodizing was largely developed to a fine art by Consolidated to protect their seaplanes, but they still needed constant inspection and treatment.

The one I worked on had, in some areas the same corrosion preventative compound used by Boeing. During the time I was working on this PBY, my fulltime job was at a Repair Station where we were doing C checks and avionic mods on 737s. I think the previous owner's intent was to do the whole aircraft.

 

[Big Jake]

Aghast! You mean the Confederate Air Force lied about this?!?!?

Like somebody asked me once: "What, the Confederacy used these aircraft during the Civil War"?

 

[Big Jake]

No you do not want 'over engineered'.
You want as many planes as possible in the shortest time for the lowest cost.
Nope, the crews were expendable too - that's war.

The USAAF wasn't drooling over the 'over engineering' of the B-17 in 1944, they were giving it the bums rush in favour of the quicker and cheaper to build B-24.
Yes, the B-24 was a fairly fragile plane, but who cared, they had them pouring off the lines so fast, they couldn't train crews fast enough to man them.
And when VJ Day came, its job done, the B-24's were ushered off fast to the boneyards

The B-17 was the preferred bomber because it was much easier to fly and could sustain much more damage than the B-24.

 

[Big Jake]

M4 Sherman Production. The US made an assumption about the amount of tanks needed in 1943 that proved an over estimate.
8,017 in 1942
21,245 in 1943
13,179 in 1944
6,793 in 1945

Heavy Bomber Production
1940, 53 B-17, 7 B-24
1941, 144 B-17, 169 B-24
1942, 1,412 B-17, 1,164 B-24
1943, 4,179 B-17, 5,214 B-24
1944, 5,352 B-17, 9,519 B-24
1945, 1,552 B-17, 2,117 B-24
Total, 12,692 B-17, 18,190 B-24

Heavy bomber, cost of airframe ONLY, which represents around 50 to 60% of total cost.
28-Feb-43 B-17 $111,443 Costs based on weighted average of uncompleted contracts
28-Feb-43 B-24 $115,338 Costs based on weighted average of uncompleted contracts
31-Jul-44 B-17 $157,484 Costs are weighted average of all Army contracts from 1939 to date
31-Jul-44 B-24 $169,452 Costs are weighted average of all Army contracts from 1939 to date
31-Aug-44 B-17 $129,150 Costs based on uncompleted contracts
31-Aug-44 B-24 $138,585 Costs based on uncompleted contracts
30-Nov-44 B-17 $125,464 Costs based on uncompleted contracts
30-Nov-44 B-24 $114,951 Costs based on uncompleted contracts

USAAF Statistical Digest table 82, total cost.
Year B-17 B-24
1939/41 $301,221 $379,162
1942 $258,949 $304,391
1944 $204,370 $215,516
1945 $187,742 na

8th Air Force combat sortie loss rates, 1944

Type	MIA	Cat E	credit sorties	MIA*100/credit	Lost*100/credit
B-17	1957​	502​	121882​	1.61​	2.02​
B-24	858​	346​	66154​	1.30​	1.82​

As noted before a higher percentage of 8th Air Force B-24 combat losses made it back to allied lines, how much of that is due to the B-17 being more crash worthy is unclear. B-17 were 68.8% of all sorties, 70.2% of effective sorties, 62% of mechanical aborts, 58.7% of weather aborts. Also as noted before B-24 production was cancelled before B-17.

Source Book of World War II Basic Data, Airframe Industry, Volume 1, man hours per aircraft

Type	B-17	B-17	B-17	B-24	B-24	B-24
Factory	Seattle	Long Beach	Burbank	San Diego	Willow Run	Fort Worth
Jan-42​	51,520​
Feb-42​	44,800​
Mar-42​	37,632​	na	na	44,872​
Apr-42​	25,536​	na	na	43,400​
May-42​	65,455​	na	na	36,707​
Jun-42​	45,695​	na	na	33,402​
Jul-42​	41,990​	na	na	31,057​
Aug-42​	40,261​	na	na	28,405​
Sep-42​	39,026​	na	na	26,094​	493,000​
Oct-42​	37,050​	151,082​	na	24,082​	187,920​
Nov-42​	35,815​	103,240​	na	24,001​	245,920​
Dec-42​	32,851​	90,233​	na	24,303​	222,024​
Jan-43​	31,369​	64,179​	55,425​	23,442​	73,721​
Feb-43​	29,393​	58,209​	50,554​	24,429​	44,824​
Mar-43​	27,417​	45,522​	55,242​	23,051​	41,776​	59,341​
Apr-43​	26,676​	40,746​	49,812​	21,111​	31,412​	59,341​
May-43​	25,688​	38,657​	49,281​	20,357​	25,294​	51,648​
Jun-43​	24,917​	36,119​	40,284​	19,419​	27,619​	40,000​
Jul-43​	24,453​	32,985​	32,216​	19,432​	25,714​	37,209​
Aug-43​	23,712​	31,269​	28,243​	15,816​	20,361​	32,346​
Sep-43​	22,724​	29,627​	25,027​	15,569​	20,135​	28,519​
Oct-43​	22,230​	28,507​	23,470​	15,135​	17,123​	33,500​
Nov-43​	21,212​	27,761​	21,413​	15,004​	16,377​	26,410​
Dec-43​	20,254​	26,866​	19,386​	14,676​	13,881​	26,410​
Jan-44​	18,679​	25,909​	18,880​	13,738​	13,077​	26,039​
Feb-44​	18,400​	22,823​	18,465​	12,673​	12,308​	23,243​
Mar-44​	17,463​	22,049​	16,820​	12,124​	11,406​	18,581​
Apr-44​	17,358​	20,492​	16,195​	11,797​	10,313​	15,026​
May-44​	16,418​	16,833​	15,424​	11,692​	9,844​	14,667​
Jun-44​	16,119​	16,833​	14,483​	10,938​	9,219​	13,600​
Jul-44​	16,119​	16,833​	13,793​	11,515​	9,048​	14,400​
Aug-44​	15,672​	17,424​	13,448​	15,286​	8,730​	14,000​
Sep-44​	15,672​	17,424​	13,103​	14,861​	7,333​	13,733​
Oct-44​	16,716​	17,424​	13,158​	14,028​	7,500​	12,800​
Nov-44​	17,313​	15,371​	13,982​	14,583​	7,813​	13,133​
Dec-44​	17,015​	14,603​	13,036​	13,944​	8,750​	14,000​
Jan-45​	17,761​	14,276​	13,036​	14,444​	8,125​
Feb-45​	17,910​	14,793​	13,091​	14,085​	8,281​
Mar-45​	17,910​	14,569​	12,909​	13,333​	8,125​
Apr-45​	20,896​	14,172​	12,727​	13,235​	8,047​
May-45​	na	13,871​	12,727​	13,235​	5,938​
Jun-45​	na	13,776​	12,545​	12,206​	3,750​
Jul-45​	na	13,431​	12,545​

Fort Worth excludes knock downs. Ford invested a lot more in tooling and it shows, but the constant production changes made it very hard to recover the tooling costs.

The reason it took more man-hours (worker-hour as many of the workers were females...) to build a a B-17 in Long Beach was because more rivets were used in the construction of a Douglas built B-17 than a Seattle built one. I was told this piece of information by an old "Rosie the Riveter" who used to work in Douglas's B-17 production line. She came to see "Sentimental Journey" (which was built by Douglas) and immediately recognized that it was a Douglas built B-17. Asked how she knew she replied "by the abundance of rivets". She even showed me the rivets she herself drove. The imbalance in man-hours lasted until the end of 1944 when I guess many experienced Boeing workers were diverted to build B-29s, leaving the B-17 to inexperienced workers.

It is interesting to see that Vega caught up very quickly with Boeing, surpassing everyone with lower man-power per ship than everyone else.

 

[FLYBOYJ]

many experienced Boeing workers were diverted to build B-29s, leaving the B-17 to inexperienced workers.

Fast forward 45 years later. In 1990 I worked on the B-2 program. Boeing made the outer wing sections as a contractor and supplied Northrop with manpower to assemble the first several units. At the same time Boeing was opening the 767 line. What I discovered is Boeing had an apprentice program where they sent folks from Seattle down to Palmdale to assist on the B-2 final assembly. When these folks got some experience under their belt they went back the Seattle to work on the 767 line. I seen a lot of "hacks" that hung around, some were eventually terminated.

 

[thunderbird]

Its not Fatigue that is the biggest risk for our irreplaceable warplanes. Its stupid people that don't know that they don't know.

 

[BiffF15]

Its not Fatigue that is the biggest risk for our irreplaceable warplanes. Its stupid people that don't know that they don't know.

Thunderbird,

I have been watching this story and numerous news streams (including my own in house union) regarding causes and or factors. It is a terrible tragedy. However let the investigators do their work and unravel this event before coming to a conclusion. It very well may be exactly what it looks like (loss of situationAl awarenes) SA, but what contributed to it will need to be assessed (and may lay additional blame outside the P63 driver).

And we see people everyday in traffic who absolutely don't know what they don't know (I have a 16 y/o son who is getting close to obtaining his DL) and we have that conversation every single time he is in the car.

He also has to obtain enough situational awareness as well as physical skill before his fighter pilot father will consider him ready to go solo (get his DL).

Cheers,
Biff

 

[ww2restorer]

Thunderbird,

I have been watching this story and numerous news streams (including my own in house union) regarding causes and or factors. It is a terrible tragedy. However let the investigators do their work and unravel this event before coming to a conclusion. It very well may be exactly what it looks like (loss of situationAl awarenes) SA, but what contributed to it will need to be assessed (and may lay additional blame outside the P63 driver).

And we see people everyday in traffic who absolutely don't know what they don't know (I have a 16 y/o son who is getting close to obta his DL) and we have that conversation every single time he is in the car.

He also has to obtain enough situational awareness as well as physical skill before his fighter pilot father will consider him ready to go solo (get his DL).

Cheers,
Biff

Totally agree Biff. When I was active flying, we were constantly told "never turn on the inside of an aircraft" the wing always blocks the aircraft you are turning inside of.
Personally, I think that something happened with the p-63 and the pilot got distracted, hence he was flying faster and inside aircraft that should have been on his inside. It will be interesting to see the final report.

 

[gumbyk]

Totally agree Biff. When I was active flying, we were constantly told "never turn on the inside of an aircraft" the wing always blocks the aircraft you are turning inside of.
Personally, I think that something happened with the p-63 and the pilot got distracted, hence he was flying faster and inside aircraft that should have been on his inside. It will be interesting to see the final report.

As I understand it he was also #3 in a formation - he was looking to his lead. If the lead was slightly out of position, then he could easily have inadvertently put the P-63 in harms way.
Note - "COULD" there are many possibilities.

 

[ww2restorer]

The aircraft are seen in the video's, he was in flight of 3, p51, p63 and b17. the videos show clearly, he was travelling faster than the p51 and b17, also turning inside the path of the b17, his line-of-sight would have been compromised by his right wing. This will all come out in the official investigation.

 

[pinehilljoe]

As an aeronautical structures engineer and Warbirds maintainer, here are my comments: (Warbirds are warbirds that are being operated today)

a. Non of the so-called warbirds (including the C-47/DC-3) were designed with fatigue life in mind. The concept was known but applicability wasn't. It took many years until the concept was understood and adopted. (As I recall, the first US fighter to have a fatigue program developed for it was the F-16).
b. The warbirds were designed to fulfill certain missions. Non of the Warbirds which are flying today operate in conditions that come even close to the flight operations to which the particular aircraft were designed. (FiFi rarely flies above 10,000 and carries no payload except for a few people and fuel as do the B-17s, and just about every other type.)
c. The Warbirds that fly today are maintained by dedicated, experienced maintainers using modern practices and materials. That was not the case when these Warbirds were warbirds, maintained by teenagers off the farms and flown by people who knew that if they break the airplane then the Government will give them another one. At those times, carrying out a mission was number one priority - now it's safety (and compliance with regulations).
d. Anybody operating a Warbird is aware of the historical significant of the equipment he or she is operating. They take the best care they can though sometimes this is not enough.
e. What will eventually ground a Warbird will be shortage of funds, shortage of specific parts, availability of gasoline, insurance companies or lawyers. It will have nothing to do with technical issues.

Didn't fatigue become an issue when planes were being pressurized ( like the Comet) and the structures optimized (like Gen 4 fighters, F-16, F-15). Prior to these, structures were designed for infinite life and for the predicted life of the aircraft fatigue didn't come into play? It may have been assumed the earlier planes would be retired or shot down before fatigue was an issue, let alone the engineering of fatigue analysis was in its infancy. Asking this as a question, not pretending to be an expert.

Wings/Airpower had an article about the B-47 and it's fatigue failures. When tactics changed from high altitude bombing to low level penetration and a pop up for bomb delivery, the primary structure suffered fatigue. The pins holding the wing spars together suffered from fatigue and the wings literally fell of the aircraft. The USAF did not regret retiring the B-47.

 

[Macandy]

Didn't fatigue become an issue when planes were being pressurized ( like the Comet) and the structures optimized (like Gen 4 fighters, F-16, F-15). Prior to these, structures were designed for infinite life and for the predicted life of the aircraft fatigue didn't come into play? It may have been assumed the earlier planes would be retired or shot down before fatigue was an issue, let alone the engineering of fatigue analysis was in its infancy. Asking this as a question, not pretending to be an expert.

Wings/Airpower had an article about the B-47 and it's fatigue failures. When tactics changed from high altitude bombing to low level penetration and a pop up for bomb delivery, the primary structure suffered fatigue. The pins holding the wing spars together suffered from fatigue and the wings literally fell of the aircraft. The USAF did not regret retiring the B-47.

Pitting corrosion causing cracking was identified as an issue in the 30's.