Hmmm. tell me again about the corrosive environment at sea and aircraft having to be designed to withstand it......
Ares:
Rust and Stealth - GAO on F-22 vs F-35
Costly corrosion problems on the F-22 caused by stealth materials and coatings have been addressed on the F-35, but risks remain, concludes a
report by the U.S. Government Accountability Office.
The GAO's presentation to Congress on its review of the DoD's corrosion evaluation report on the F-22 and F-35, completed at the end of September, says:
"Corrosion of the aluminum skin panels on the F-22 was first observed in spring 2005, less than 6 months after the Air Force first introduced the aircraft to a severe environment. By October 2007, a total of 534 instances of corrosion were documented, and corrosion in the substructure was becoming prevalent. For corrosion damage identified to date, the government is paying $228 million to make F-22 corrosion-related repairs and retrofits through 2016."
Lessons learned have been applied, the GAO saying:
"The F-35 program is mitigating corrosion risk associated with conductive gap filler and paint by using a gap filler that is less galvanically dissimilar from aluminum, an alternative to the conductive paint, a design with fewer seams that require gap filler, and more representative verification and qualification testing. Many of the F-22’s corrosion problems were linked to problems with gap filler materials and paint. The F-35 drainage design is significantly improved with more, adequately sized drain holes. Drain holes in the F-22 were found to be too small to enable good water drainage."
But remaining risks identified include:
"Environmental and occupational health concerns drove the initial use of a nonchromated primer on the F-22 that did not provide corrosion protection, and the program later switched to a chromated primer. The F-35 has also chosen to use a nonchromated primer that has never been tested on an aircraft in a corrosive operating environment.
- No operational-level test for corrosion was conducted on the F-22 prior to initial operating capability, and none are currently planned for the F-35.
- The length of the F-22 full-scale climatic test was cut in half, and the program office for the F-35 is currently considering reducing its full-scale climatic test."
And the GAO cautions:
"The corrosion study concluded that, if the F-22 program had accomplished testing earlier in the program, many of the corrosion problems could have been addressed at greatly reduced cost and the associated readiness issues avoided. If the F-35 conducts tests that are planned and conducted properly and in full, these tests could reveal many corrosion-susceptible areas on the aircraft."
On the issue of why corrosion was allowed to become a problem, the Congressional watchdog says:
"...neither aircraft had a corrosion prevention user requirement that would drive CPC [corrosion prevention and control] as a design requirement. Further, the program offices for both aircraft only required “corrosion resistance” within the system specifications, a poorly defined and nonspecific term that is difficult to ensure incorporation into aircraft components and to verify.
And on why the F-35 should be different, it says:
"While not necessarily due to lessons learned from the F-22 program, the study identifies several important differences between the programs. For example, the F-35 program:
- has several technical performance metrics, such as sortie generation rate, that are indirectly driving actions to improve supportability, while the F-22 program did not;
- has a more robust corrosion design largely due to inclusion of more stringent Navy corrosion qualification tests;
- has a longer service life requirement (30 years vs. 20 years fo rthe F-22); and
- has a Corrosion Prevention Advisory Board where corrosion issues are discussed in detail and both the contractor and the government display a willingnessto address these issues."