NASA Armstrong’s F-15B aeronautics research test bed, a workhorse at the center since 1993, has received an engine upgrade that will keep the airplane flying well into the foreseeable future.
Prior to this work Armstrong officials were considering retiring the F-15B, which carries NASA tail number 836, and replacing it with a newer F-15D model. An advanced data acquisition system gives the F-15B a capability that makes it one of the most versatile research aircraft NASA flies, but transferring the extensive research instrumentation to the newer aircraft would be very costly and time-consuming, and result in delays to projects needing the F-15s’ capabilities.
NASA’s F-15B is the oldest F-15 still flying and maintenance support for the airplane’s engines was becoming increasingly difficult. However, NASA Armstrong’s recent acquisition of six new engines with digital controls will greatly extend the F-15B’s service life.
The U.S. Air Force has retired all early model F-15A and F-15B aircraft, all of which, including NASA 836, were powered by Pratt & Whitney F100-PW-100 engines. Following phase-out of the F-15A/B, those engines were no longer supported by the Air Force supply chain. In the hope of keeping NASA 836 flying and eventually replacing it with a newer model, Armstrong acquired three F-15D aircraft from Tyndall Air Force Base, Florida that were surplus to Air Force needs. One of these was put on flight status while the other two were primarily used to provide spare engines.
Around the same time, according to F-15 crew chief Walter Kondracki, two F-100-PW-229 engines were removed from NASA’s highly modified NF-15B No. 837, which had been retired from service. Both powerplants required full teardown and rebuild following long years of service. In the meantime maintenance crews struggled to keep NASA 836 flying for the next few years.
“By the summer of 2012 we had removed and replaced six engines in 836,“ Kondracki said. “It decimated our spare engine supply and replacement parts were $300K, plus labor, with little or no funding available for repairs.“
Then, through a fortuitous set of circumstances, Armstrong acquired some F100-PW-220 engines, which are equipped with more advanced technology than in the -100 including digital electronic controls, as well as improved durability and reliability. Tom Grindle, Armstrong’s chief of maintenance, learned that the Air Force needed a set of -229 engines for an F-15E and arranged to swap the two rebuilt powerplants from NASA 837 for six -220 engines.
Adapting the F-15B to accept the new engines required modifying the airplane’s electrical wiring system. Ron Rohe, lead F-15B avionics technician, learned that engine wiring harnesses for the -220 were no longer available from the Air Force so he developed a plan to modify the airplane’s electrical system. After comparing the original -100 wiring configuration against that of the -220 he developed a hybrid solution using the existing wiring and incorporating changes that allowed the -220 engines to function properly.
The F-15B project team then contracted Boeing to review the proposed wiring modifications and, with only minor changes, the plan was approved in March 2014. Rohe and L-3 avionics technician Chris Brookes completed the modifications in less than three weeks.
Kondracki’s F-15 maintenance crew then installed the new engines and NASA research pilot Nils Larson conducted a ground run to ensure the engines were fully functional from idle power to full afterburner. Research pilot Jim Less and flight-test engineer Tom Jones performed a functional check flight on June 4 and found that the engines and their associated electronics performed flawlessly.
Project officials expect this engine upgrade to extend the F-15B’s service life for several more years and allow for continued supersonic research. High Speed Project support manager Brett Pauer said the new engines will increase reliability, and decrease maintenance downtime between flights.