Earlier in June 2018, anyone driving on the highways near the city of Wichita, Kansas might have caught a glimpse of what seemed
on the back of a large flatbed truck. What they were actually looking at is part of the work being done to answer the very important question of just how long an F-35 Joint Strike Fighter is supposed to last before it's no longer airworthy. So far, the U.S. Air Force's
and U.S. Navy's
look to be as durable as expected, but tests on an example of the U.S. Marine Corps's
have exposed more serious issues.
On June 6, 2018, the F-35A aircraft arrived at Wichita State University’s National Institute for Aviation Research,
, as part of the Joint Strike Fighter program's durability testing regimen. Manufacturer Lockheed Martin had sent the jet from its Fort Worth plant to the research facility so that specialists could tear it down and inspect its internal structure to determine whether it had adequately withstood earlier tests. At present, all versions of the F-35 are supposed to have a lifespan of 8,000 flight hours.
“As part of the F-35 program, durability ground test aircraft undergo exhaustive testing to validate the structural integrity of the airframe to withstand a variety of maneuvers it will experience throughout its lifetime,” NIAR said in a statement to the
. The latter organization also released
about the plane on the back of the truck to allay any possible public concerns.
This isn’t the first time NIAR has helped analyze the results of structural and durability tests on F-35 aircraft. In August 2017, the facility
model for inspection. The institute also performed a wide array of other aviation testing services for the U.S. government and private companies and hosts
that it operates in cooperation with the Federal Aviation Administration and the U.S. Air Force.
Lockheed Martin has built a total of
, two of each of the three F-35 variants, to support these experiments and has been actively stress and fatigue testing the airframes since 2009. The company and its subcontractors have used a host of different test stands and other equipment to drop and otherwise simulate typical operations and maneuvers that the aircraft will experience during its expected life cycle.
The U.S. military’s central Joint Program Office (JPO) for the Joint Strike Fighter has mandated that testing put each type of jet through testing that simulates the equivalent of
three full life cycles, or 24,000 flight hours.
This doesn’t mean that each one of the test F-35s will go through that full amount of abuse or that contractors can’t perform normal, expected repairs and preventive maintenance during the experiments. The objective is to simulate typical use, not simply shake the airframes apart. Lockheed Martin only set aside one of each type specifically for ground fatigue testing, as well. The other three aircraft have gotten subjected to different kinds of stress tests, including
to see how the airframe might hold up in combat.
The F-35A that arrived at NIAR in June 2018 had just finished the third cycle of tests for that variant. The F-35C was slated to finish its final round of testing in December 2017, but it is unclear if that has occurred and when analysis of the results might begin.
“For all variants, this testing led to discoveries requiring repairs and modifications to production designs and retrofits to fielded aircraft,” the Pentagon’s Office of the Director of Operational Test and Evaluation, or DOT&E, reported in its
of the program, covering the 2017 fiscal year, which ended on September 30, 2017. This is, of course, exactly why the U.S. military conducts these tests in the first place.
But while the F-35A and C variants look set to meet the stated durability goals, the Marine Corps’ F-35B has had
. The F-35 JPO suspended durability testing on that variant in February 2017 after one of the two test articles finished the second simulated life cycle, according to DOT&E.
“Due to the significant amount of modifications and repairs to bulkheads and other structures, the program declared the F-35B ground test article was no longer representative of the production aircraft, so the JPO deemed it inadequate for further testing,” the Pentagon testing office’s report noted. “The program canceled the testing of the third lifetime with [the F-35B known as] BH-1 and made plans to procure another ground test article, but has not yet done so.”
It is very likely that the F-35Bs structural woes are, in no small part, due to a massive effort early in the Joint Strike Fighter's development to cut the weight of that variant in particular. Beginning in 2004, a group of engineers at Lockheed Martin called the STOVL (Short Take Off/Vertical Landing) Weight Attack Team, or SWAT, found ways to shave
off the Marine Corps' version. They trimmed 1,300 pounds from the A and C types, too.
This weight reduction project was critical to advancing the program at the time, but persistent reports of
and
,
, raise questions about what got sacrificed to meet those targets.
Now, there is a very real concern that the B variant may not meet the 8,000 flight hour target. These jets may have a shorter service life than the other types “even with extensive modifications to strengthen the aircraft,” DOT&E warned.
On top of that, these versions are having serious problems with the durability of their wheels specifically. Unlike the F-35As and Cs, the B models have the ability to take off and land vertically, which requires tires that are at the same time durable enough for a conventional landing and soft enough to cushion the jet when it comes straight down.
As it stands now, ground crews have to change the tires, on average, after fewer than 10 full-stop conventional landings, which is less than half the target number. Lockheed Martin has reportedly sourced a possible replacement tire, but will only begin testing it sometime in late 2018, according to a report on the F-35 program that
(GAO), a congressional watchdog, released earlier in June 2018.
Ensuring that the jet’s airframe, as well as other ancillary components, last as long as they’re supposed to, is extremely important for both safety and sustainment reasons. Without an accurate understanding of when the planes will literally fall apart, the U.S. Air Force, Navy, and Marines Corps, as well as foreign operators, could risk putting pilots in the cockpit of aircraft that simply aren’t airworthy.
It is also an essential component for long-term planning with regards to
since these tests will provide additional data on what components are most likely to fail and when. This, in turn, can help give an early sense of what portions of the airframe might need an overhaul or outright replacement, and how much that might cost, during any service life extension program down the road.
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