FROM THE BONEYARD TO THE TEST PAD: A SUPER HORNET TEST ARTICLE FINDS NEW LIFE AFTER 20 YEARS OF RETIREMENT
By: Charles Frankenberger and Dennis Williams
The F/A-18E model test article identified for the Super Hornet Live Fire Test (LFT) program has had a long and colorful life, extending all the way from its use in the F/A-18 E/F developmental testing beginning in the mid-1990s to its current use in the F/A-18 Block III upgrade in 2019 (see Figure 1). Through it all, the fighter jet has stood the test of time—as well as its share of abuse—and is ready for more.
FROM DT50 TO ST56
As with most aircraft test programs, the use of test articles is critical in shaping various aspects of the program. For both ground and flight testing, the number of available aircraft often dictates the volume and pace of test activities, and each article often must fill several roles. The Super Hornet test article discussed herein, which was the third production F/A-18E engineering and manufacturing development (EMD) aircraft, was no different. Designated as a ground test article, the fighter jet was initially configured for and used as the Full-Scale Aircraft Drop Test article, with the designation DT50. Then, after a series of extensive and successful drop tests, McDonnell Douglas (now Boeing) personnel reconfigured the aircraft to fulfill its second role, as the Barricade Engagement Test article, with the designation ST56.
In September 1997, during one of the barricade engagement events, ST56 ended up on its back in the woods (see Figure 2). Naval Air Warfare Center Weapons Division (NAWCWD) and Boeing LFT personnel were sent to assess the damage and determine if the remaining structure would still be a viable LFT test article. They found that the starboard side of the aircraft was in generally poor shape. The aft control surfaces were lost, and the fuselage was tweaked as a result of tumbling into the woods. The team concluded, however, that the aircraft could still be used for LFT if certain repairs were made to the aircraft and if some of the planned testing was relocated from the starboard side to the port side of the aircraft.
Accordingly, the F/A-18E was shipped back to the Boeing facility in St. Louis, was repaired, and was configured to meet numerous primary LFT requirements. In particular:
- All flight controls surfaces were provided and installed, except the right-hand horizontal stabilator and the right-hand vertical stabilizer.
- All structural and nonstructural doors and fairings were installed.
- Fuel and hydraulic plumbing integral to the wing were installed.
- Wing integral fuel tank ullage explosion suppression foam was installed.
- The windshield, canopy, and radome were installed.
- The inlet duct fuel tank Damage Control System (with foam and leak-attenuating materials) was installed between fuel tanks 3 and 4 and the inlet duct walls.
- All fuel cells and related components were installed.
- The fire suppression system was installed in the applicable dry bays.
- An operating F414 engine was installed (for some tests).
THE ABUSE CONTINUES
With new life—as well as a new designation of SV52—given to the test article, the aircraft was delivered to NAWCWD in China Lake, CA, in May 1998 for full-scale LFT (see Figure 3). And, in compliance with the LFT law, thus began yet another phase of “use and abuse” in the F/A-18E’s history. In fact, of the more than 200 ballistic shots conducted for the LFT program, nearly 30 ballistic tests were conducted on SV52, with threats ranging from missile warhead fragments to armor-piercing (AP) and high-explosive (HE) incendiaries.
Figure 4 illustrates the different test types and locations conducted on SV52, and Figure 5 shows where LFT and damage control didn’t always go quite as planned.
As a testament to the F/A-18E/F’s robust and survivable design, hydrodynamic ram testing on the test article’s wing and torque box demonstrated the aircraft’s ability to maintain high structural loads after threat impact. Likewise, tests on the active dry bay fire suppression system in the aircraft’s center fuselage section demonstrated the system’s capability against a wide range of threats.
When the F/A-18E/F LFT program was completed in October 1999, the program summary stated that the aircraft design was more likely to survive combat damage than that of any of its predecessors. In addition, it was concluded that the LFT program—which at the time represented the largest single sequence of ballistic tests accomplished by the Department of Defense—met all the specification requirements and fulfilled the requirements of the Test and Evaluation Master Plan for the aircraft.
And with that, SV52 was given a well-deserved rest, taking up residence in the boneyard of NAWCWD’s Weapons Survivability Laboratory (WSL). At least for a while.
RESURRECTED FROM RETIREMENT
For the current Block III Development/Upgrade program for the F/A-18 Super Hornet, numerous performance enhancements are being incorporated, including Conformal Fuel Tanks (CFT) to improve the range of the fighter. The CFTs are aerodynamically shaped fuel tanks, mounted on the top of the aircraft on either side of the centerline dorsal, that provide approximately 3,500 lb (515 gal) of fuel in a low-drag configuration.
To represent and test the external and internal configuration of the CFTs, fabrication of a full-scale CFT simulator—called the Iron Bird—is planned. The series of tests using this simulator will gather data to allow detailed design of the production CFTs. In particular, pressure data will be gathered to determine bay overpressure during a ballistic event, with the requirement that the explosion suppression configuration not produce local pressure spikes exceeding the capability of the CFT structure. The testing will also help determine if there are opportunities to optimize the foam weight.
However, as Block III program planners began to define the testing needed to assess the CFTs, they discovered that the availability of aircraft assets was limited. Possible options to address this limitation included coordinating the use of a recently retired aircraft between Government and industry sites, as well as fabricating individual test articles to support both CFT ullage and fuel leakage migration testing.
And then someone remembered SV52. Now, more than 20 years since its “retirement,” the test article is being resurrected, repaired, and reconfigured to support the Block III program. As seen in Figure 6, many parts of SV52 were damaged during the LFT program, and many other parts were removed (delicately or otherwise) for use in various other studies over the last two decades. But substantial program risk is being minimized by renewed use of the aircraft.
Two series of testing are planned to be conducted on SV52. In the first series, the CFT simulator will be installed on the Super Hornet (as shown in Figure 7), and the aircraft will be placed behind WSL’s Super High-Velocity Airflow System (SHIVAS) to conduct CFT fuel leakage safety testing.
As shown in Figure 8, SV52 will be positioned on jack stands with the CFT at the centerline of SHIVAS airflow, and testing will be conducted at airflow velocities of up to 500 knots. Engineers will assess possible leak migration paths that could result in catastrophic loss of the aircraft. If leak paths are determined to be critical, then several leak mitigation concepts will be tested.
The second test series will consist of ballistic testing to evaluate the vulnerabilities of the CFT and induced vulnerabilities to the aircraft in the CFT configuration. This testing will assess ullage overpressure, dry bay fire, fuel ingestion, and unknown interactions with the aircraft.
READY FOR MORE
No matter its designation, the F/A-18 test article discussed herein has proven to be a sturdy, robust aircraft that has held up to extensive inflicted damage over many years of testing. And there appears to be no immediate end in sight for the potential use of the old warbird. If proposed Block Upgrade Programs occur, or if other future design changes are incorporated that could potentially impact the Super Hornet’s vulnerability, the test article will likely be ready and waiting for whatever new abuse awaits.
ABOUT THE AUTHORS
Mr. Charles Frankenberger heads the Vulnerability Branch of the Weapons Survivability Laboratory at the Naval Air Warfare Center Weapons Division. He has been in the Vulnerability Branch for the past 25 years, supporting V-22, F/A-18, and F-35 LFT&E programs. Mr. Frankenberger holds a B.S in aerospace engineering from the University of Arizona.
Mr. Dennis Williams is a Technical Fellow with the Boeing Company’s Phantom Works Division. He has more than 38 years of experience in the area of survivability/vulnerability engineering and testing. Mr. Williams holds a B.S. in mathematics from Voorhees College and an M.S. in mathematics from Southern Illinois University.