The Pentagon had instituted time limits on the number of seconds the F-35B short-takeoff-and-landing variant and the F-35C carrier variant could spend at supersonic speeds.
Those limits were imposed after two separate tests in 2011 where the “B” model incurred “bubbling [and] blistering” of its stealth coating and the “C” model suffered “thermal damage” to the tailboom and horizontal tail, according to documents exclusively obtained by Defense News.
According to the defense news article in which Billie Flynn, the Lockheed Martin test pilot who flew both of those missions during F-35 developmental testing at Naval Air Station Patuxent River in Maryland share details about the incident.
According to him, both incidents took place during flutter tests where the B and C models were flying at speeds of 1.3 Mach and 1.4 Mach. However, that damage didn’t occur in a vacuum, Flynn said. It materialized after F-35B and F-35C test articles flew repeated supersonic runs that pushed to the plane’s maximum of 1.6 Mach, making it the result of cumulative pressures on the aircraft.
“I was flying out at 700 knots in the C model up and down the East Coast of the state of Maryland and Delaware — that’s where we fly at Pax River — and then out over the ocean, firing missiles at almost 1.6 Mach as we cleared out the weapons for the airplane. That’s extreme speed, and that’s repeated flights in those environments,” said Flynn, who has flown more than 800 hours in all three F-35 variants.
“Make a run at 700 knots, make another run at 700 knots, go to an aerial refueling tanker, get fuel for myself … and then race out again and again and again. Repeat this cycle for four- and five-hour missions,” he added.
Similarly, the flights for the B model involved aggressive maneuvering at the edge of the aircraft’s flight envelope for hours at a time.
“Nobody is going to do [that] tactically,” he said. “There’s not a combat scenario where that is going to happen.”
Although Flynn, like all fighter pilots, ended missions by walking around the aircraft and inspecting the jet for damage, he doesn’t remember seeing the blistered stealth coating or thermal damage noted in the Pentagon’s deficiency report.
Instead, Flynn offered the possibility that the degradation was only visible to engineers monitoring the internal impacts to the F-35B and F-35C test planes, which are specially equipped to measure imperceptible damage to the jet’s structure and give insight into how forces such as gravity and heat will affect it over time.
“I don’t know if I really ever saw much after a flight. I just knew that our engineers had told us about [the problem],” he said. “So an engineer whose specialty is structures would see that it would be hotter than they predicted, which would lead them to tell us: ‘If this airplane is going to last 40 years long, then we have to manage this exposure.’ ”