by Martin Maisel (photos as credited)
The U.S. Army, the Air Force and the Marines, seeking a replacement for the venerable, but aging CH-46 helicopter, conducted a study in 1982 to identify the VTOL vehicle that would be best suited for current and future vertical lift missions. Scientists, engineers and military personnel from each military service and from NASA participated in the four-month study that examined conventional helicopters, compound helicopters (with auxiliary propulsion), fan-in-wing aircraft and tilt rotor aircraft. Parameters such as operational effectiveness, cost effectiveness, life-cycle costs, combat survivability and maintainability were evaluated for a number of diverse military missions. The study concluded that the tilt rotor aircraft best met the requirements and Congress subsequently authorized funding to initiate the design and development of the JVX (Joint Vertical Experimental) program. Release of the funding to the contractor, however, was withheld for about a year by the Secretary of Defense who had preferred the funding be used for other procurements. The logjam was broken when the Secretary of Defense was threatened with contempt of Congress charges and work on the JVX (later designated the V-22) was initiated.
Since only Bell had experience in designing, building and flying a tilt rotor aircraft, the issue of “sole-sourcing” such a potentially large Government contract was a possible show-stopper. In what might be considered to be a “stroke of genius”, the probable challenge to the sole-source contract was eliminated when the only likely contender, Boeing, was asked to join Bell in a joint venture, thereby creating the Bell-Boeing V-22 team. Full-scale development was authorized in December 1986. Bell, with its XV-15 experience, was responsible for the design of the wing, nacelles, rotors, drive system and tail surfaces.
The Boeing Military Aircraft Mobility Division (formerly Boeing Helicopters), having significant experience in composite materials, designed the fuselage and was also responsible for the V-22’s cockpit, avionics and flight controls.
It should be noted that the intended multiservice application of the V-22 imposed significant, and often conflicting requirements that influenced the design of the aircraft. One example is the Navy and Marines need to operate off of amphibious assault ships (such as light “Wasp-class carriers”). For shipboard compatibility, the rotor blades fold and the wing rotates over the fuselage to minimize the aircraft’s footprint for storage, impacting the
aircraft’s weight and complexity. Furthermore, the requirement to operate on the carrier deck adjacent to the island, while maintaining a safe distance from the deck edge restricted the wing span and rotor diameter. The 38.1 ft diameter of the Osprey’s rotors requires more power and produces higher downwash velocities than a larger rotor would. Also, a smaller diameter rotor produces a higher downwash that affects ground personnel and increases “brown-out” (i.e. loss of visual reference) problems when operating in a dusty environment.
The design of critical dynamic elements of the V-22 drew heavily from Bell’s experience with the XV-15 Tilt Rotor Research Aircraft. Key features of the XV-15, such as the three-bladed rotor, engines mounted in tilting nacelles, a forward swept thick wing, a cross-shaft connecting the nacelle gear-boxes, and an “H” vertical tail, were incorporated in the Osprey.
The V-22 had its share of problems. Among the configuration changes influenced by the Marine management early in the program was the use of a throttle-type control like the one used in the VTOL Harrier, instead of a helicopter collective lever. During one developmental test at Boeing the pilots found they could not control roll properly after they lifted to a hover. After erratically dancing around for several seconds the aircraft was finally planted on the ground. The pilot, with lots of helicopter experience, intended to reduce the power – but pushed the throttle forward (the helicopter collective lever would be pushed down to reduce power). The aircraft again jumped into the air and again began to gyrate wildly in roll until a nacelle and rotor contacted the ground, leading to the loss of the aircraft, but fortunately without injury to the two-man crew.
(A video of the final moments of this unfortunate event can be seen at: https://www.youtube.com/watch?v=JCUmJbsrL7g)
It was later discovered that the loss of roll control was due to the incorrect installation of roll sensors, which produced a roll opposite to the input
command. The use of the throttle contributed to the crash because of the poor “human engineering” of that control. The throttle was subsequently modified to improve the input/response relationship.
Further accidents plagued the early years of the Osprey program. After completing environmental testing in Florida, a V-22 in transit back to the Boeing test facility in Maryland, converted from the airplane mode to the helicopter mode over the Potomac River in preparation for landing at the Quantico Marine Base. Flammable fluids that had collected in the nacelle during the flight suddenly ignited. The flash fire severed a composite rotor shaft resulting in a crash into the Potomac killing all seven people onboard. The rotor shaft was subsequently changed to a metal component to tolerate high temperature conditions and other design changes resolved the fluid leaks.
Tragedy struck again on April 9, 2000, during a night training exercise at Marana Regional Airport, AZ. One aircraft in a flight of two V-22s descended rapidly to avoid overflying the intended landing spot. The aircraft crashed causing the loss of 19 Marines. An investigation determined that the pilot had exceeded the allowable descent rate that resulted in the loss of rotor lift. This was due to a condition called the “vortex ring” state in which the induced flow below the descending rotor is sucked back into the rotor, creating a nolift “donut” vortex instead of the thrust-producing downwash. This phenomenon exists for all rotorlift aircraft. To avoid further occurrences, automatic warnings were provided to alert the crew if they are approaching airspeed and descent conditions where the vortex ring state could develop and improvements in flight training were instituted.
Another fatal accident occurred on December 11, 2000 near Jacksonville, NC after a hydraulic line failed. The complex automatic flight control system was not properly programmed to handle that failure and the subsequent loss of control resulted in the aircraft descending into terrain, killing all four onboard. After another long standdown the flight control code was modified and the V-22 returned to flight status.
While none of the accidents were specifically attributable to the tilt rotor concept (but were charged to design, maintenance or pilot error causes) they nevertheless provided ammunition to industry and Government advocates of other aircraft systems that were competing for DoD funding. The Marines, however, pressed Congress to continue the development of the Osprey that they were depending on for enhancing their future warfighting capabilities. The Marine Corps request proved to be persuasive and V-22 production funding was approved.
In September 2007 the first ten V-22s were deployed to a combat zone. In the sandy environment of Iraq, engine life and other maintenance problems had resulted in a lower-than-target mission-capable-availability rate (not unexpected for the first use of a new aircraft system), but the aircraft had received high grades for its effectiveness from flight crews and commanding officers.
In November 2009 MV-22s were deployed to Afghanistan where they played key roles in the conflict with the Taliban. By February 2011, Marine Commandant General James Amos stated that the Ospreys in Afghanistan had surpassed 100,000 flight hours and were “the safest airplane, or close to the safest airplane” in the Marine Corps inventory. By early 2017 the Osprey fleet was approaching 400,000 flight hours.
In addition to ongoing military operations of the V-22, several MV-22 Ospreys have also been configured to support the Marine One presidential transport squadron.
Current plans call for a fleet of 360 Marine MV-22s, 48 Navy MV-22s and 52 Air Force Special Operations CV-22s. By early 2017, the Bell plant in Amarillo, Texas had delivered 287 MV-22Bs and all 52 CV-22s. The Navy has announced that their Ospreys, now designated as the CMV-22B, will replace the aging Northrup Grumman C-2 Greyhound for Carrier Onboard Delivery (COD) duties.
International sales of the Osprey are also evolving. Japan is the first foreign country slated to receive up to 17 MV-22 aircraft for their Self Defense Force with the first five to be delivered in 2018. Other nations that have expressed an interest in acquiring the Osprey include India, Israel, South Korea, and the United Arab Emirates
The V-22 Osprey was the first tilt rotor aircraft to go into production – but it probably would not be the last.