Airframe Life?
Tue May 09, 2006 7:00 am
I was wondering what were the airframe life expectancies for most of the popular warbirds flying today such as the P-51, P-47,P-38 and especailly the big ones like the B-17, B-24, and of course the B-29. Aren't most of these life expectancies exceeded already? What is done to extend the life of the airframes and make them safe to fly?
Shay
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Semper Fortis
Shay
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Semper Fortis
Tue May 09, 2006 6:38 pm
Shay,
I seem to recall something I read once that the "heavies" service life was estimated at around perhaps as many as 5 missions. The fighters maybe longer, but only moderately so. That's partly why the US Aviation industry became the behemoth it was back in the war years. The country as a whole, at the time, was one huge defense company with the vast majority of men of service age, being sent to the battlefront.
As to how do these aircraft survive in airworthy condition for as long as they have. A majority of why is directly related to the owners desire to maintain their respective investment. I know....that sounds too "financial", but it is mainly true to keep these RARE planes airworthy. Secondly, the primary restoration effort that took place to transform the aircraft back into an airworthy condition is a huge reason. Basically speaking it is a Major Overhaul. If done properly, given the relative small amount of flight hours the aircraft will likely see in any given year, the aircraft will likely not need too big of an extensive refurbishment in it's "new" life as a Warbird. Though, annual and if need be 100 hr maintenance still applies given the FAA regs. Third, the dedication of the volunteers or in some cases, guys who are paid to maintain these planes. Their skill and knowledge is slowly passing out of our time and if the planes are to be "here" with us in flyable condition, new blood must be brought in to learn the trade secrets, before it's too late.
If you are asking wether or not there is maintenance and engineering support out there. I am sure that there is, but approval is still required because for the most part, the Original MFG's no longer exist, and even if they do, they will not, for product liablility reasons sign THEIR company names to the aircraft. For instance, I was with an organization, that had several Grumman Warbirds, when it came to obtaining engineering approval for a major repair, we were told flatly....don't even think about talking to Grumman about it because even though they built it, they do not support it any longer. Additionally, the FAA also mandates certain things, AD notes for example, to mandate certain requirements to keep the plane in the air. One only has to look at the more recent "AD" notes pertaining to the T-6/Harvard aircraft, or for that matter, the Wing Spar AD note for the active flight worthy B-17's. Texas Raiders is still undergoing the maintenance cycle regarding that item.
Hopefully some of this helps answer your question.
Respectfully,
Paul
I seem to recall something I read once that the "heavies" service life was estimated at around perhaps as many as 5 missions. The fighters maybe longer, but only moderately so. That's partly why the US Aviation industry became the behemoth it was back in the war years. The country as a whole, at the time, was one huge defense company with the vast majority of men of service age, being sent to the battlefront.
As to how do these aircraft survive in airworthy condition for as long as they have. A majority of why is directly related to the owners desire to maintain their respective investment. I know....that sounds too "financial", but it is mainly true to keep these RARE planes airworthy. Secondly, the primary restoration effort that took place to transform the aircraft back into an airworthy condition is a huge reason. Basically speaking it is a Major Overhaul. If done properly, given the relative small amount of flight hours the aircraft will likely see in any given year, the aircraft will likely not need too big of an extensive refurbishment in it's "new" life as a Warbird. Though, annual and if need be 100 hr maintenance still applies given the FAA regs. Third, the dedication of the volunteers or in some cases, guys who are paid to maintain these planes. Their skill and knowledge is slowly passing out of our time and if the planes are to be "here" with us in flyable condition, new blood must be brought in to learn the trade secrets, before it's too late.
If you are asking wether or not there is maintenance and engineering support out there. I am sure that there is, but approval is still required because for the most part, the Original MFG's no longer exist, and even if they do, they will not, for product liablility reasons sign THEIR company names to the aircraft. For instance, I was with an organization, that had several Grumman Warbirds, when it came to obtaining engineering approval for a major repair, we were told flatly....don't even think about talking to Grumman about it because even though they built it, they do not support it any longer. Additionally, the FAA also mandates certain things, AD notes for example, to mandate certain requirements to keep the plane in the air. One only has to look at the more recent "AD" notes pertaining to the T-6/Harvard aircraft, or for that matter, the Wing Spar AD note for the active flight worthy B-17's. Texas Raiders is still undergoing the maintenance cycle regarding that item.
Hopefully some of this helps answer your question.
Respectfully,
Paul
Tue May 09, 2006 10:28 pm
Life expectancy of an aircraft is determined by how it was operated.
The alloys available during WW2 were not very fatigue resistant, but the aircraft didn't see a lot of flight time until they started doing things like fire bombing where you carry heavy loads in gusty conditions over a period of many years.
P-51s normally fly light- without a fuselage tank and drop tanks and are seldom operated at their G-limits day in and day out. A couple of rolls or loops at an airshow won't do much harm. Same for most of the other fighters.
The aircraft flying air combat manuever training see frequent high G-loads (and reportedly frequent over-G conditions) from pilots not well versed in aerobatics. High stress and repeated stress reversals (from tension to compression) eat up fatigue life.
With an old aircraft it is sometimes difficult to know what previous accident damage the airplane has been subjected to, what hidden corrosion exists, poor maintenance practices, structural overloads, etc. Any of these can lead to premature strucutral failure.
Plenty of our favorite warbirds have Airworthiness Directives against them now for these fatigue related conditions; B-17, T-34, T-6, A-26, C-47, etc.
I'm not an expert in this. In fact there is a whole field of aerospace engineers devoted to this kind of research. But those are some of the basics from an engineering perspective.
The alloys available during WW2 were not very fatigue resistant, but the aircraft didn't see a lot of flight time until they started doing things like fire bombing where you carry heavy loads in gusty conditions over a period of many years.
P-51s normally fly light- without a fuselage tank and drop tanks and are seldom operated at their G-limits day in and day out. A couple of rolls or loops at an airshow won't do much harm. Same for most of the other fighters.
The aircraft flying air combat manuever training see frequent high G-loads (and reportedly frequent over-G conditions) from pilots not well versed in aerobatics. High stress and repeated stress reversals (from tension to compression) eat up fatigue life.
With an old aircraft it is sometimes difficult to know what previous accident damage the airplane has been subjected to, what hidden corrosion exists, poor maintenance practices, structural overloads, etc. Any of these can lead to premature strucutral failure.
Plenty of our favorite warbirds have Airworthiness Directives against them now for these fatigue related conditions; B-17, T-34, T-6, A-26, C-47, etc.
I'm not an expert in this. In fact there is a whole field of aerospace engineers devoted to this kind of research. But those are some of the basics from an engineering perspective.
Fri May 12, 2006 1:45 am
In answer to the original question . . .
All combat aircraft from the World War Two period were considered expendable and didn't really have a listed life expectancy on the airframe.
Most fixed wing airframes today, regardless of when they were manufactured, are usually considered "conditional" items. That means that as long as their maintenance is kept up, i.e. annuals, corrosion control inspections, any ADs, Service Bulletins and the like, the airframe can keep on going, and going and going.
Helicopters, on the other hand, are a totally different story. Just about every component of a helicopter, including the airframe itself, has a time/life, in hours operated, applied to them. And that is one of the main, and biggest, reasons why it is so expensive to operate helicopters.
All combat aircraft from the World War Two period were considered expendable and didn't really have a listed life expectancy on the airframe.
Most fixed wing airframes today, regardless of when they were manufactured, are usually considered "conditional" items. That means that as long as their maintenance is kept up, i.e. annuals, corrosion control inspections, any ADs, Service Bulletins and the like, the airframe can keep on going, and going and going.
Helicopters, on the other hand, are a totally different story. Just about every component of a helicopter, including the airframe itself, has a time/life, in hours operated, applied to them. And that is one of the main, and biggest, reasons why it is so expensive to operate helicopters.
Fri May 12, 2006 2:40 am
Hi Shay!
I'm a nub, so take anything I say with a grain of salt, preferably of the single malt variety.
It looks like if all of the AD's are complied with, there isn't a top time, yet. It is different with jets and helicopters, like DS says. The only thing with them is, they actually have set times, but I think they have been and can be AD'd/ maintained out of it. Short story, be in compliance,and you can fly it.
The only time for prop warbirds I've heard of, (Be gentle all, I said I was a nub), is 35,000 hours for big engine T-28's. And that was arbitrarily assigned because the FAA dudes could see no upper limit to it. There is at least on T28 AD I know of, compliance with that and good maintenance, who knows how long they'll be flying. It's been 50+ years for the T28, and there really isn't any end in sight.
BTW, yes, the big engined T28 is the best airplane ever made.
I'm a nub, so take anything I say with a grain of salt, preferably of the single malt variety.
It looks like if all of the AD's are complied with, there isn't a top time, yet. It is different with jets and helicopters, like DS says. The only thing with them is, they actually have set times, but I think they have been and can be AD'd/ maintained out of it. Short story, be in compliance,and you can fly it.
The only time for prop warbirds I've heard of, (Be gentle all, I said I was a nub), is 35,000 hours for big engine T-28's. And that was arbitrarily assigned because the FAA dudes could see no upper limit to it. There is at least on T28 AD I know of, compliance with that and good maintenance, who knows how long they'll be flying. It's been 50+ years for the T28, and there really isn't any end in sight.
BTW, yes, the big engined T28 is the best airplane ever made.
Fri May 12, 2006 11:36 am
Look how long some DC-3/C-47 types have been flying.
Re: Airframe Life?
Fri May 12, 2006 4:48 pm
Shay wrote: especailly the big ones like the B-17, B-24, and of course the B-29. Aren't most of these life expectancies exceeded already? What is done to extend the life of the airframes and make them safe to fly?
Well some years ago, British Aerospace re-sparred the RAF Battle of Britain Memorial Flight Lancaster PA474, which gave it at least another 50 years of airframe life at current useage rates........
Airframe Life
Fri May 12, 2006 7:57 pm
G'Day Guys,
I have been following WIX for some time now but this is the first time I have registered and posted.
On the subject of airframe life, all aircraft are different, however I can relate to you my experiences with the P51, as I used to licensed on the airframe back in the days when one had to pass an exam on each aircraft type. I met a guy who used to work at the Aircraft Research Laboratory in Melbourne, Australia. One of his jobs was to conduct a fatigue life study on the P51 Mustang. Numerous sets of wings were used, some used and others brand new from production. He told me wings were removed from aircraft that were to be scrapped by cutting holes in the fuselage at the attach points to undo the bolts! Around four sets of these wings survive and I believe most or all are now flying in the US. The interesting thing he did tell me though was that with "normal" flying ie no aerobatics, they found the P51 had a virtually unlimited life. With aerobatics, +9 to -4G the life was reduced, I can't remember by how much, but for the sort of operations that are flown these days, you would run out of engines before the airframe broke! He did show me the main weak point was in the main spar area between the fuel tank bay cut out and the inboard gun shell ejector chute.
I have been following WIX for some time now but this is the first time I have registered and posted.
On the subject of airframe life, all aircraft are different, however I can relate to you my experiences with the P51, as I used to licensed on the airframe back in the days when one had to pass an exam on each aircraft type. I met a guy who used to work at the Aircraft Research Laboratory in Melbourne, Australia. One of his jobs was to conduct a fatigue life study on the P51 Mustang. Numerous sets of wings were used, some used and others brand new from production. He told me wings were removed from aircraft that were to be scrapped by cutting holes in the fuselage at the attach points to undo the bolts! Around four sets of these wings survive and I believe most or all are now flying in the US. The interesting thing he did tell me though was that with "normal" flying ie no aerobatics, they found the P51 had a virtually unlimited life. With aerobatics, +9 to -4G the life was reduced, I can't remember by how much, but for the sort of operations that are flown these days, you would run out of engines before the airframe broke! He did show me the main weak point was in the main spar area between the fuel tank bay cut out and the inboard gun shell ejector chute.