WIX Archives
Re: What about the current active B-52s?
Posted by bdk on Fri Apr 19, 2002 01:22:03 PM
In reply top What about the current active B-52s? posted by Mike Henniger on Fri Apr 19, 2002 07:13:54 AM
The specific airframe hotspots that are prone to fatigue are well known on the B-52 fleet and are monitored through repetetive inspections. When the cracks in a specific area reach a predetermined length, they are repaired, often with bonded boron/epoxy patches which redistribute the load and reduce the stress levels in that area to preclude further cracking.
Some aircraft, like the C-5A, have had the entire fleet rewinged to the C-5B configuration due to wing fatigue cracking as part of a life extension program. Note that these fatigue cracks almost never cause catastrophic failures, but tend to grow over time at predictable rates based on the stress levels and the number of cycles. Parts are repaired or replaced long before the aircraft is at risk of structural failure.
Newer aircraft such as the C-17 were designed from the outset using the lessons learned by the USAF and are designed for significantly longer fatigue lives. The C-17 was designed for a 30 year/30,000 flight hour service life, and has been durability tested with a full size airframe to the equivalent of three lifetimes of service for fatigue.
I'm sure none of the original designers had any idea that a B-52 would be flying 20 years later, let alone 40, 50 or 80 years later! The USAF has spent significant amounts of money on R&D testing and structural analysis to keep the B-52 fleet in the air for a long time to come.
: The currently active B-52H's in the USAF came off the prod
: uction line in 1962 (or around then). They are expected t
: o be in service until 2040. How could this be possible?
: As I understand it they are kept servicable by the many co
: mponents of airframes obtained from the AMARC boneyards of
: B-52 airframes already retired. I remember reading some
: place that whole sections have been removed from a retired
: airframe, refurbished, then used as a replacement part on
: an active airframe. Makes you wonder, how much of the cu
: rrent fleet will be "original" by the time they are retire
: d in 2040.
:
: Just thinking out loud.
:
: Mike