Still only in its third year, the Irish Business and General Aviation Association’s annual conference has already become an industry highlight. It relies on sponsorship, none more so than from principal sponsor Gulfstream, which this year also provided its Chief Developmental Test Pilot, Eric Holmberg, as keynote speaker.
A former operational US Navy F/A-18 Hornet pilot, Holmberg also flew developmental test flights during the Super Hornet program, before leading production acceptance and test flying on the AV-8B, F-15, F/A-18, and T-45 at Boeing. He rounded out his military career in 2013, after a stint testing the EA-18G, and went straight to Gulfstream.
Describing the Gulfstream G700 test program, Holmberg spoke with the understated confidence of one who has been to the cutting edge and knows what happens when you fall off.
He described a close-knit community of Gulfstream flight testers, working from a dedicated hangar at the OEM’s Savannah headquarters. “We have mechanics, flight test engineers, instrumentation folks and a group of highly experienced test pilots, all of them from the military.
“We equip the test airplanes with workstations for flight test engineers where they record data and video, we put thermocouples and strain gauges all over the airframes, add systems that leak what looks like fuel, and resistors to make sure the generators can handle huge electrical loads.”
Various levels of simulation play a huge part before and during test campaigns. This developmental G700 simulator includes the Gulfstream Symmetry Flight Deck. Image: Gulfstream Aerospace
Through high-altitude trials to water ingestion tests and stalling, Gulfstream operates its test programs with an abundance of caution should the most unlikely event happen.
Holmberg added: “We also install a rope along the cabin ceiling. We could pull ourselves along to the back of the cabin where there’s a kick-out door, should we need to bail out during some of the necessary higher-risk events.”
During water ingestions trials aircraft run through water troughs at high speed, ensuring all systems and especially engines operate normally, even on the wettest runways. Image: Gulfstream Aerospace
Holmberg noted that Gulfstream certified the G700 up to FL510, or 51,000ft, and 0.935 Mach, although customers seldom exceed 0.9 Mach. “We test beyond that envelope and for the G700 and G800 that’s out to 0.999 Mach, or essentially Mach 1.
“We need to ensure the airplane is safe beyond its normal envelope because we can never know if a customer is going to meet a situation where they exceed the certified speed.”
Stall and low-speed characteristics are also essential areas of investigation. “In modern fly-by-wire airplanes we don’t let pilots stall. For flight test, we modify the flight control system to turn off the stall protection, then go out and aerodynamically stall the airplane,” he explained.
“We work out where the aircraft stalls in multiple configurations, then we put shapes on the airframe to simulate ice accretion in the event of a deicing system failure and go stall it again. We have a stall ’chute mounted, our bail-out door, and we wear parachutes, just in case it doesn’t recover as we expect. All that data goes into our control laws and prevents pilots getting to more than 95% of the stall speed.”
The ’stall ’chute’ is a parachute-like recovery system mounted at the aircraft’s tail and deployed to slow its descent should it spin out of a high-altitude stall.
High-altitude trials test an aircraft’s take-off and landing performance from runways thousands of feet above sea level. Image: Gulfstream Aerospace
In an era where test pilots primarily expect to verify predicted aircraft behaviors, Holmberg noted that sometimes things don’t quite go to plan, then showed an inflight video to prove the point. “We’d already worked out the control laws, then we went out, got the airplane really slow and performed an abusive maneuver. We rolled 45 degrees and pulled the stick hard back,” he said.
The aircraft stalled, rolling inverted, nose well below the horizon before the crew calmly recovered. Holmberg concluded: “That’s why we do developmental test flying. We went back, worked on those flight control laws and fixed the issue.”
Eric Holmberg, Chief Developmental Test Pilot at Gulfstream. Image: Gulfstream Aerospace
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Featured image credited to Gulfstream Aerospace
