The plan is to stress the B-1B fuselage to a “certified service life” of 27,000 hours, while its wing is being stressed to 28,000 hours.
After a seven-year process and the amassing of almost 73 years of simulated flying time, the US Air Force (USAF) expects to conclude its structural fatigue test of a B-1B bomber in 2021, Air Force Magazine reports.
Underway since 2012, the fatigue test, that was expected to conclude this year, is being carried out on the carcass and wing of a retired B-1B harvested from the boneyard at Davis-Monthan Air Force Base (AFB), Ariz. According to an Air Force Materiel Command (AFMC) spokesman, the plan is to stress the fuselage to a “certified service life” of 27,000 hours, while the wing is being stressed to 28,000 hours. The Lancer, which was delivered between 1985 and 1988, was originally specified for a service life of about 8,000 hours, and has undergone service life extension programs since. At least one B-1B has racked up about 12,500 hours.
The test is being performed by Boeing, which inherited the program from the original prime. It was initially expected to take five years, but has been interrupted several times to repair structural failures.
As told by Air Force Magazine, structural fatigue tests employ calibrated weights, pulleys, pressure bars, and other physical means to simulate the stress of repeated takeoffs, landings, and typical mission G-loads on an aircraft. The tests continue around-the-clock, so that many years of stress can be applied for each year of testing. When the aircraft breaks under pressure, the test is stopped, the fault analyzed, and a fix applied as if the aircraft was an operational example, and the test resumes.
The AFMC spokesman explained that the USAF is “evaluating fatigue points in the wing (mid-spar, leading and trailing edge tabs, upper wing splice bolts, and fuel drain holes) and various issues on the fuselage (cracks in longerons, forward/intermediate fuselage skins, Xf38 rib, shear angles, and tension clips).”
He said that the findings of the test are “driving a fleet safety analysis, which includes analyzing data and conducting research. Results are then applied to the fleet to determine which aircraft are at risk and when inspection and repairs should begin.”
The B-1B was broken by operating it in a way it wasn’t designed to fly, and as a result has seen significant structural damage that may make it too expensive to fix many of the Lancers still serving, the USAF said.
The US eliminated the nuclear mission for the B-1 in 1994. Even though the Air Force expended no further funding to maintain nuclear capabilities, the B-1 was still considered a heavy bomber equipped for nuclear armament until 2007. The conversion to conventional only began in November 2007 under the original START treaty and was completed in March 2011 under the New START treaty.
Today, thanks to its capability to carry the largest conventional payload of both guided and unguided weapons in the Air Force inventory, the multi-mission B-1 is the backbone of America’s long-range bomber force. It can rapidly deliver massive quantities of precision and non-precision weapons against any adversary, anywhere in the world, at any time.
The USAF plans to retire the B-1B around 2032, handing off its mission to the stealthy and largely secret B-21 Raider bomber. However, Gen. Timothy M. Ray, head of Air Force Global Strike Command, said in September 2019 that if the B-1s can be made to last, they would make an excellent carrier for standoff weapons, such as the new hypersonic AGM-183 ARRW, and add capacity to USAF’s bomber fleet.
Photo credit: Boeing