WW II aircraft fatigue life

[Barrett]

Loss of Texas Raiders has spurred the inevitable calls for grounding warbirds "because they're too old."

Batguano.

PBA's DC-3s and C-47s were still flying at 80k hours, and the senior delegate retired at 91,500.

Inevitably warbird losses have nothing to do with age--it's nearly always pilot error and/or poor maintenance (the Collings Foundation '17 a few years ago, check NTSB.)

The reason that 1940s airframes can last so long is that, unlike jets, the oldies are not pressurized. Some will recall the "convertible" 737 that landed in Hawaii late 80s minus the upper portion of the fuselage. The airline flew numerous short-haul legs within the islands, increasing the number of cycles beyond limits. That meant metal fatigue.

What's of more concern for Keeping 'Em Flying is parts. Engines less than props, wheels, and maybe tires. Also, it's possible that compatible fuel may be a problem downstream.

The foregoing is separate from the philosophical question as to when rare birds should be grounded. I think the P-63 in Dallas was the last remaining F model. For decades there's been discussion, if not agreement, as to when the last of the mohicans should be preserved on the ground. When one remains? Two? Three?

And who's to make that decision? Many warbirds go for something north of $1 million. Is the US Govt going to tell the owners, "Sorry (well, not really) but you're going to sacrifice for Generations Unborn."

Just FWIW.

 

[Barrett]

Loss of Texas Raiders has prompted calls for grounding warbirds "because they're so old."

As I noted on a related thread, that's absurd. There were/are DC-3s and C-47s with 80,000 airframe hours.

So...
Wonder what Boeing computed the 17's fatigue life to be--assuming the company did so. Certainly few expected Fortresses to be flying in numbers 80 years downstream. (Last figure I recall was 30 or more.).

Also interested in fatigue life estimates for any other warbirds. (IIRC the average Lancaster lasted 14-15 sorties.)

 

[wlewisiii]

Well, I tend to think that we should consider grounding them but more because:



We're running out of a lot of very historical planes and can't afford to lose all of a type.

Just my opinion, yada yada yada.

 

[gumbyk]

We're running out of a lot of very historical planes and can't afford to lose all of a type.

If it weren't for the flying community, most of these planes would have rotted away a long time ago.

 

[thunderbird]

It isn't fatigue that destroys our old warbirds.

The Collins B-17 crashed because essential maintenance was deferred. Was it deferred because the organization couldn't afford to do the maintenance? One wonders.

The fact is, our warplanes are essentially irreplaceable.

I did material substitution investigations for a venerable, but still flying aircraft. I got thrust into the job because the last guy doing the job didn't want to move when the company said move. I was looking for a replacement for …, mostly because the vendor was long out of business. The material supposedly had some special qualities needed for its original mission, but was not an aircraft type material, and nor was it bought to or qualified by a specification of any sort. I asked the designer what the requirements were for the old material and its replacement. He cursed me and said "how the *&#@ am i supposed to know?". He'd only been in the job for ten or twenty years, long after the I asked my lead where were the requiments documented. And his response was that i was supposed to know them, that's why they hired me. It wasn't. I can't imagine what its like trying to find replacement parts or materials for our old warplanes.

The crash in Dallas looks to be human error. Or perhaps a chain of human errors. Not metal fatigue. Two more irreplaceable aircraft gone. and six irreplaceable humans with them.

.

 

[gumbyk]

The crash in Dallas looks to be human error. Or perhaps a chain of human errors.

They're almost all a chain of human errors.

 

[pbehn]

Also interested in fatigue life estimates for any other warbirds. (IIRC the average Lancaster lasted 14-15 sorties.)

I don't think a Lancasters average live depended on fatigue, more like flak, fighters and accidents of all types. With the Lancaster they werent supposed to leave them standing with a Tall Boy of Grand Slam loaded because it stressed the spar. Also the BBMF Lancaster has had a new spar fitted, to prolong its life, this is the only Lancaster known to have been re sparred, in the war it would have been cannibalised.

 

[Barrett]

I don't think a Lancasters average live depended on fatigue, more like flak, fighters and accidents of all types. With the Lancaster they werent supposed to leave them standing with a Tall Boy of Grand Slam loaded because it stressed the spar. Also the BBMF Lancaster has had a new spar fitted, to prolong its life, this is the only Lancaster known to have been re sparred, in the war it would have been cannibalised.

Certainly correct regarding causes of Land losses. I mentioned the average combat life to demonstrate that wartime aircraft were not concerned with longevity in mind. Sergei Sikorsky tells the story of the Klimov engineer called to Stalin's office (!) to discuss service life of the Sturmovik. The engineer had sent a memo explaining how to add about 500 hours engine life, and the presumed cost savings. Comrade Stalin, who was more detail oriented than some might expect, ordered the company to get on to other things: few Sturmoviks would survive to exceed the present design specs...

 

[pbehn]

Certainly correct regarding causes of Land losses. I mentioned the average combat life to demonstrate that wartime aircraft were not concerned with longevity in mind. Sergei Sikorsky tells the story of the Klimov engineer called to Stalin's office (!) to discuss service life of the Sturmovik. The engineer had sent a memo explaining how to add about 500 hours engine life, and the presumed cost savings. Comrade Stalin, who was more detail oriented than some might expect, ordered the company to get on to other things: few Sturmoviks would survive to exceed the present design specs...

With front line fighters in WW2, the engine may need an overhaul after 250 hours. The airframe of a Spitfire could show signs of fatigue after 150 hours (rivets in wheel wells had small cracks). If you did a lot of high G turns the skin and structure starts to creep, but in any case types were upgraded like the various marques of Spitfire or replaced by others like Typhoons Tempests Mustangs P-51s etc. Pretty much they were disposable items, very quickly going from brand new to out of date or more trouble to keep going than the effort was worth.

 

[FLYBOYJ]

Fatigue is only going to be an issue on restored warbirds if they are flown hard and excessive Gs put on the airframe.

 

[pbehn]

Fatigue is only going to be an issue on restored warbirds if they are flown hard and excessive Gs put on the airframe.

I dont think peacetime warbirds are cleared to carry what they did in combat, bombs guns and ammunition are obvious but I think the maximum tankage on stuff like the P-51 was only allowed for "the duration".

 

[gumbyk]

I dont think peacetime warbirds are cleared to carry what they did in combat, bombs guns and ammunition are obvious but I think the maximum tankage on stuff like the P-51 was only allowed for "the duration".

There's no difference - what's in the flight manual is what it was when the manual was written (certainly here in New Zealand).

But, most of these aircraft don't have armour, guns, etc fitted so are lighter. Often we have to put ballast into them to get C of G into the limits.

 

[pbehn]

There's no difference - what's in the flight manual is what it was when the manual was written (certainly here in New Zealand).

But, most of these aircraft don't have armour, guns, etc fitted so are lighter. Often we have to put ballast into them to get C of G into the limits.

I thought that the maximum tanks like 2 x 108 gals on a P-51 were only for combat operations.

 

[FLYBOYJ]

I dont think peacetime warbirds are cleared to carry what they did in combat, bombs guns and ammunition are obvious but I think the maximum tankage on stuff like the P-51 was only allowed for "the duration".

Actually they can be and sometimes those items are installed and are non-operating. In other situations you have to place ballast in gun bays so the aircraft meets weight and balance requirements. It isn't a matter of what they are carrying in areas designed to carry a load, but G forces placed on the airframe during maneuvers.

 

[Shortround6]

I thought that the maximum tanks like 2 x 108 gals on a P-51 were only for combat operations.

Depends on how the manual was written.

If you take out 400lbs worth of guns, 550lbs worth of ammo, the armor and replace the 320lbs self sealing wing tanks (I don't know the weight of the rear tank) with modern metal or flexible fuel cells you pick up a crap load of weight allowance to use for fuel.

If you could carry a 1000lb bomb under each wing a tank with around 660 lbs of fuel should not be a big problem.
This assumes the local structure holding the tank rack/mount is up to it.
Mustangs were cleared to use larger tanks for Ferry use. 569 US gallons total fuel capacity in some charts.

 

[pinehilljoe]

Question, does anyone know if FiFi, the B-29 flys pressurized?

 

[Admiral Beez]

We're running out of a lot of very historical planes and can't afford to lose all of a type.

Just fly them with care and follow SOPs and the historic warbirds can fly on for many decades still. We're only losing aircraft when their operators undertake CFIT, mid-air collisions or exceed the known capabilities, such as the Mosquito in Australia with its engine cutting out during a low altitude negative g - a maneuver every Merlin operator from over eighty years ago to now would know to avoid.

 

[Simon Thomas]

Question, does anyone know if FiFi, the B-29 flys pressurized?

I read an article recently (which I cannot locate) which said that it doesn't fly pressurized. (Could have been Doc - I can't recall.)
(edit for grammar)

 

[cvairwerks]

Fifi rarely flies above 10,000 feet, so no need for it.

 

[Snautzer01]

Fifi rarely flies above 10,000 feet, so no need for it.

Only when the AAA is heavy around Dallas.