In January 1978, the same day the AMST program ended, the C-X (cargo experimental) program began. The CX program was needed because formulation of the Pentagon’s RDF (Rapid Deployment Force) in the late 1970s. CX would serve as RDF’s airborne transport. In short CX combined the roles of strategic and tactical airlifters. Specifically, CX requirements, among others were a max takeoff weight of 580,000 lbs, max speed of Mach0.825, a range of 2400nm, a landing run requirement of 2,700ft, and all of this with a 3 person crew (2 pilots and a loadmaster)
Out of the CX program came the McDonnell Douglas (Boeing after the 1996 merger) C-17 Globemaster 3. The C-17 first flight was on 15 September 1991. The C-17 was able to combine the tactical and strategic airlift roles because of its STOL characteristics. On the outside, the YC-15 and C-17 have a very similar appearance because both use EBF to achieve STOL.
The YC-15 made quite a few contributions to the C-17 program. Many of the Mc Donnell Douglas personnel that worked on the YC-15 worked on the C-17 program. During it’s development the C-17 ran into many of the same problems that the YC-15 had. There were excessive thermal, air and acoustic loads on the portions of the flaps that were directly in the jet exhaust.
This table highlights further differences between the 2 aircraft.
Incorrect predictions of airframe drag again resulted in slightly reduced range at given takeoff weights. Range\payload went from 2,400 nm at 172,000lb to 167,000lb. A few years after the C-17 entered service it gained a reputation as a somewhat “short legged” aircraft when transiting the Pacific. However by the year 2000 this was resolved by adding a fuel tank in the overhead wing\fuselage body joint.
There were also quite a few “lessons learned” that were incorporated into the C-17. Windows for a downward view were moved slightly forward in the cockpit. The YC-15’s GWS was replaced, in the C-17 by an indexed switch attached to a mission computer that calculated optimal takeoff flap settings at a given gross weight. Loading ramp “toes” were added to the C-17. The thrust reversers were limited to idle when deployed in-flight. Flaps were not moved during the takeoff roll and improvements were made in the DLC. The VAM in the YC-15 became a HUD (Heads-Up Display) displaying far more information on approach to the pilot.
In 1998 the YC-15 was at AMARC and that year Mc Donnell Douglas contracted with AMARC to make the YC-15 again flyable. The YC-15 was to be used as a test-bed for testing defensive countermeasures and techniques for lowering the infared signature of the C-17. The process to make 875 again flyable began in April 1996. 875 was remarkably well preserved aside from many birds’ nests in the nooks and crannies of the aircraft. The JT9D engines had to be reinstalled and 875 was given the FAA registration “N15YC.”
On 11 April 1997 YC-15 875 again took the air from Davis-Monthan AFB for a shakedown flight. The jet flew for 2 hours 1 minute and taken to 250kt at 25,000ft. 875 was flown three more times before a planned flight to Long Beach for further modification and test work, including the addition of a new paint job.
Again 875 was flown again on 11 July 1998 to the Edwards AFB test ranges and some approach work at Palmdale. It was during this work that the number one engine third stage LP turbine came apart. While able to land at Palmdale without incident the YC-15 languished on the ramp until money could be made to make repairs. This was to never be.
After the Boeing/McDonnell Douglas merger, the cost of repairing 875 couldn’t be justified. As of 2002, the aircraft remained at Palmdale.
There was talk of using the YC-15 as an airborne avionics test platform to support the x-32 but Boeing opted for a 737 instead. There was thought of bringing 875 back to test some concepts for the NOTAIL ATT and to test a STOL “tilt wing” concept but none of these came to fruition.
At the time of writing YC-15 72-0876 is on display of sorts at AMARC in a semi scrapped state with the engines removed. YC-15 72-0875 was moved from Palmdale to Edwards in 2008 and is on display at the west gate of Edwards AFB, just off the Century Circle.