* In the 1950s and into the 1960s, a large number of prototype "vertical take-off & landing (VTOL)" aircraft were developed, most of which amounted to little. However, they did eventually lead the way to operational VTOL aircraft -- a significant example in the 21st century being the Bell-Boeing "V-22" Osprey, which is now in operational service. This document provides a history and description of the V-22, and the Bell "XV-15" demonstrator that preceded it -- as well as the more recent Leonardo "AW609" and Bell "V-280 Valor" VTOL machines, both along the same lines as the V-22. A list of illustration credits is provided at the end of this document.
* From World War II, there were studies for and experiments with vertical take-off & landing aircraft that used props or wings that rotated to the vertical for take-off and landing, and to the horizontal for normal flight. Such "tiltrotor" and "tiltwing" machines as were built had varying degrees of flight success, but none entered production.
In the mid-1950s, the Bell Helicopter Company developed a primitive experimental tilt-rotor, the "XV-3", performing trials with it into the mid-1960s. Following up on the work with the XV-3, Bell proposed moving on to an operational tiltrotor, the "Model 266", for a US Army requirement for a light tactical transport. It would be powered by twin General Electric (GE) T64 turboshafts and be able to carry 30 passengers.
The XV-3 had been something of an experimental "kluge", nothing like a practical aircraft, and the Army felt that more research was needed before committing to development of an operational machine. The US National Aeronautics & Space Administration (NASA) had been conducting ongoing research on VTOL aircraft, the NASA Ames Research Center in California having initiated design studies for a tilt-rotor demonstrator aircraft in 1971. Following up on that work, in 1973 the US Army Air Mobility Laboratory and NASA Ames awarded Bell a contract to built two "Model 301 Research Tiltrotor" aircraft, to be given the military designation of "XV-15". The first prototype performed its initial free flight on 3 May 1977, with the second prototype following on 23 April 1979.
The XV-15 was still a purely experimental machine, with no real operational capability, but it was far more refined than the XV-3, indeed being trim and futuristic in appearance. It was built primarily of aircraft aluminum alloy; it had a high wing with a 6.5-degree forward sweep -- it seems to ensure proper center of gravity in vertical flight -- and a 2-degree dihedral, plus a twin-fin tail with swept tailfins. Flight surfaces were conventional, including flaps, flaperons, elevators, and rudders; all under manual control with hydraulic boost.
The XV-15 had a rotating engine pod at each wingtip; the engines could pivot under electro-hydraulic actuation from horizontal to five degrees beyond the vertical. Each pod featured an Avco Lycoming LTC1K-4K turboshaft, driving a three-bladed stainless-steel rotor with a diameter of 7.62 meters (25 feet). The LTC1K-4K was a T53-L-13B turboshaft, providing 1,155 kW (1,550 SHP), modified to operate vertically.
The two engines were linked by a driveshaft, allowing the aircraft to stay in the air if one engine failed; if both engines failed, the rotors would auto-rotate at the same RPM, to prevent the aircraft from rolling over as it fell to ground. There were twin bladder fuel tanks in each wing, total fuel capacity being 830 liters (219 US gallons), Each engine could draw fuel from both tanks. An auxiliary fuselage tank was later added to increase fuel load by 64%.
The XV-15 featured a climate-conditioned cockpit for two crew, with dual controls and side-by-side seats for pilot and copilot, both sitting on Rockwell-Columbus LW-3B ejection seats -- originally designed for the Rockwell OV-10A Bronco battlefield spotter aircraft. Cockpit layout was analog, flight control was by stick and rudder. The controls worked conventionally in airplane mode, the stick operating as a helicopter-style collective control for up and down movement, the rudders operating as cyclic controls, for directional movement. Each pilot had two switches to control rotor tilt -- one giving continuous tilt across the entire tilt range, the other giving tilts at presets including 0, 60, 75, and 90 degrees relative to the horizontal. There was an emergency control, used in case of electrical system failure, that flipped the nacelles up into helicopter mode.
There was a cargo compartment behind the cockpit, for accommodating test kit, additional crew, or baggage and such for flights to remote test locations. The entry door was on the left side of the cargo compartment. The XV-15 also featured retractable tricycle landing gear, all gear with dual wheels -- the nose gear retracting back, the main gear retracting forward into sponsons. The landing gear was obtained from the Canadair CL-84, an earlier twin-turboprop tiltwing research aircraft. A switch on a main gear strut prevented the retraction of the landing and tilt of the rotors more than 30 degrees off vertical when the aircraft was in contact with the ground. Incidentally, for ground taxiing, the pilot would simply tilt the rotors one degree forward; and brake by tilting them one degree back.
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BELL XV-15:
___________________________________________________________________
span, rotors turning:
17.42 meters (57 feet 2 inches)
wing area:
15.7 sq_meters (168.9 sq_feet)
length:
12.83 meters (42 feet 1 inch)
height:
3.86 meters (12 feet 8 inches)
empty weight:
4,574 kilograms (10,083 pounds)
MTO weight:
6,000 kilograms (13,000 pounds)
max speed:
555 KPH (345 MPH / 300 KT)
service ceiling:
8,840 meters (29,500 feet)
range:
825 kilometers (515 MI / 445 NMI)
___________________________________________________________________
The XV-15 was sized to permit it to fit into the wind tunnel at Ames, which had a cross-section of 12 x 24 meters (39.4 x 78.7 feet). The two XV-15 prototypes were put through a wide-ranging set of trials by NASA and the Army, and had long subsequent lives as test and trials aircraft. They often flew demonstrations at airshows to successfully "wow the crowd". The XV-15s were flown by hundreds of pilots, in order to get as much feedback as possible; they were generally found to be straightforward to fly.
The XV-15s were updated in service, being fitted with a Rockwell-Collins "glass cockpit". The first XV-15 prototype was lost in a crash on 20 August 1992; a bolt gave way, with one rotor going to full pitch, and the aircraft flipping over to impact on the ground. Both aircrew survived with little injury, the cockpit being salvaged for use as a flight simulator. The second prototype continued in tests to 2003, when it was donated to the Smithsonian National Air & Space Museum, to be put on display at the Steven F. Udvar-Hazy Center at Dulles International Airport in Virginia.
BACK_TO_TOP* XV-15 trials going well, in 1982 the Pentagon initiated the "Joint Services Advanced Vertical Lift Aircraft (JVX)" program, to develop a production machine for use by America's armed services. The US armed services had not been particularly enthusiastic about VTOL transport aircraft up to 1980, having had no interest in the Ling-Temco-Vought XC-142 four-engine tiltwing transport of the 1960s. Conventional rotorcraft were perceived as being able to do the job.
However, the need for a next-generation vertical lift machine had been underscored by the disastrous failure of Operation EAGLE CLAW, an attempt to rescue American hostages being held in Tehran, Iran, on 24 April 1980. The mission was badly planned and ended in disaster, with a Sikorsky CH-53 helicopter colliding with a Lockheed C-130 transport at a desert rendezvous point; both machines were destroyed and eight servicemen killed.
The failure of EAGLE CLAW suggested that, along with better planning, similar missions in the future would benefit from a vertical-lift capability with much greater range and speed. The JVX effort was originally run by the Army, being transferred to US Navy control early in 1983, with a contract issued in April 1983 for a 24-month preliminary design study.
The aircraft that emerged from the study in January 1985 was the "V-22 Osprey". A seven-year full-scale development (FSD) contract was awarded to a Bell-Boeing team in May 1986, which gave the type the company designation of "Model 901". The FSD contract specified delivery of six prototypes:
The first prototype performed its initial flight on 19 March 1989. It was followed by prototypes 2 through 5 -- the sixth being a ground-test airframe. Osprey prototype development was paralleled by experiments and trials performed with the XV-15, including tests of operations off the amphibious assault ship (helicopter carrier) USS WASP. The Osprey flight test program was completed, with all the surviving prototypes retired, the last flight of a prototype being on 27 March 1997. Two prototypes had been destroyed in accidents to that time:
In the interim, political support for the Osprey wavered, doubts growing about the wisdom of actually producing it, the 1992 crash having been a particular discouragement. The services were generally insistent, however, and a contract for four pre-production prototypes was accordingly issued in 1997.
The four pre-production Ospreys were significantly different from the initial prototypes, featuring a modified and lighter airframe structure, an improved engine / drive system, a redesigned rotor system, and pyrotechnic escape hatches. The US Marines were first in line to receive Ospreys, the USMC variant being designated "MV-22B", intended for the tactical transport role. Low rate initial production was begun in parallel with manufacture of the pre-production prototypes, and the first LRIP MV-22B for the Marines Corps flew on 30 April 1999. The aircraft was handed over to the Marines in May, and was joined by three more MV-22Bs for operational evaluation.
The operational evaluation included trials on the aircraft carrier USS ESSEX. One was loaned to the Air Force 58th Special Operations Wing, the USAF intending to acquire the type for the Air Force Special Operations Command (AFSOC) as the "CV-22B", with two pre-production Ospreys converted in 1999 as prototypes.
However, the Osprey's troubles were by no means over. On 8 April 2000 when the fourth LRIP MV-22B crashed at an airport in Arizona during a test exercise, with all 19 on board killed. After an investigation, the problem was attributed to pilot error, and the MV-22B was cleared for flight operations once more.
Unfortunately, on 11 December 2000 a second MV-22 crashed near New River, North Carolina, killing all four on board. The accident was traced to a hydraulic system problem, an issue that had plagued Osprey development. The accident dealt a serious blow to the program. The AFSOC seriously considered withdrawing from the program, which would in turn affect the already high unit cost of Marine MV-22s. The incoming Bush Administration was very uneasy about the program, given its long and expensive development history, and its future was very much in doubt.
The military proceeded carefully, however, resuming testing in 2002 and putting the aircraft through a year of exhausting trials. The test results were impressive enough to convince senior Pentagon acquisition official E.C. "Pete" Aldridge, who had been one of the skeptics, to recommend that the Osprey be taken off life support and put into full-rate production. Robert Wall of AVIATION WEEK reported the event in an article aptly titled: "More Phoenix Than Osprey". The test and evaluation program was finally completed in the summer of 2005, with the machine stamped "ready for production", though a few minor fixes in kit, none of them show-stoppers, were directed.
By that time, about 25 Ospreys had been built, all prototypes or test and evaluation machines. Approval for full-rate production was granted in the fall of 2005, with the first MV-22Bs fielded in 2007, to be quickly deployed to Iraq. That was 21 years after the issue of the original developmental contract. The CV-22B went into service with AFSOC in 2009. Fortunately, there were no more fatal accidents or losses of airframes to the end of that decade -- though some machines were badly damaged in incidents, and there were groundings.
BACK_TO_TOP* The US Army is the only one of the four US military branches to not obtain the Osprey, having pulled out of the program in 1989. The Marines, as noted above, were the first to obtain the type, in the form of the MV-22B variant. The MV-22B was intended to replace the Marines' Boeing CH-46 Sea Knight helicopter, though the original plan to buy 552 Ospreys was scaled down to a projected buy of 360.
The MV-22B, as it emerged, clearly showed its roots in the XV-15 -- featuring a very similar configuration, if substantially scaled up. The MV-22B was built with an aluminum frame and composite skins; by weight, it was about three-fifths graphite-epoxy composite, a fifth metal, a tenth fiberglass, and a tenth "other". The MV-22B had retractable tricycle landing gear, with two wheels on each unit. The nose gear retracted backwards, the main gear tucked into sponsons on each side of the fuselage.
The wing had a slight forward sweep. The tailplane was straight, while the tailfins were swept back. Flight control surface arrangement was straightforward, including rudders, elevators, and twin "elevons" in each wing; of course, there were no flaps. There were de-icing boots in the leading edges of the wings and tailfins. Like the XV-15, there was an engine in each wingtip nacelle, which rotated to the vertical for vertical flight operations. Transition from hover to forward flight took about 12 seconds.
The powerplants were Rolls-Royce T406-AD-400 (501-M80C) turboshafts, each with a take-off rating of 4,585 kW (6,150 SHP), and a continuous rating of 4,395 kW (5,890 SHP). They had full-authority digital engine controls (FADEC), with analog backup, and an automatic fire extinguisher system. The engines were mounted on the wingtips -- like the XV-15, each driving a shaft running through the wing that connected the two engines, with a coupling scheme that allowed the two engines to operate independently under normal circumstances, while allowing one engine to get the aircraft home if the other failed. The exhaust system for each nacelle incorporated a thermal emission suppression system to make the aircraft less vulnerable to heat-seeking missiles.
___________________________________________________________________
BELL BOEING MV-22B OSPREY:
___________________________________________________________________
rotor diameter:
11.58 meters (38 feet)
wingspan:
15.52 meters (50 feet 11 inches)
width across rotors:
25.40 meters (83 feet 4 inches)
stowed width:
5.61 meters (18 feet 5 inches)
length:
17.47 meters (57 feet 4 inches)
stowed length:
19.08 meters (62 feet 7 inches)
height over tailfins:
5.38 meters (17 feet 7 inches)
height, nacelles up:
6.63 meters (21 feet 9 inches)
stowed height:
5.51 meters (18 feet 1 inch)
empty weight:
15,030 kilograms (33,140 pounds)
max loaded weight:
23,980 kilograms (52,870 pounds)
maximum speed:
509 KPH (316 MPH / 275 KT)
service ceiling:
7,925 meters (26,000 feet)
range:
1,760 kilometers (1,090 MI / 950 NMI)
___________________________________________________________________
Each engine drove a three-blade propeller of composite construction -- the composite rotors were trialed on the XV-15 -- with the engines rotating in opposite directions. The propellers had a powered folding mechanism, and the entire wing could swivel 90 degrees, with the engines turned horizontal, to permit compact stowage. The stowage sequence took about a minute and a half; when done, the Osprey had about the same footprint as the Sikorsky CH-53E. When sitting on the runway with the engine nacelles flat, the props were locked with one blade directly upright, to ensure they cleared the ground.
The MV-22B featured flexible self-sealing fuel tanks from ILC Dover, with a 1,809-liter (478 US gallon) fuel tank in the front of each sponson; a long-range fuel tank with a capacity of 1,196 liters (316 US gallons) in the rear of the right sponson; and a 333-liter (88 US gallon) fuel tank outboard in each wing, for a total fuel load of 5,480 liters (1,448 US gallons). Up to three 1,628-liter (430 US gallon) ferry tanks could be installed in the cargo bay. There were refueling points on each wing and in the front of the right sponson. There was a retractable inflight refueling probe in the right side of the nose; apparently it could be removed, but rarely was.
The Osprey had two independent hydraulic systems and a backup system. A Hamilton Standard Turbomach T-62T-46-2 auxiliary power unit (APU) turbine, in the rear of the wing center section, drove two electrical generators and an air compressor; the APU also had an automatic fire extinguisher system. The aircraft had an onboard oxygen generator system (OBOGS) to eliminate the need to stock crew oxygen bottles, and a similar nitrogen generation system for fuel tank pressurization. The MV-22B was not pressurized.
The MV-22B was crewed by a pilot, in the right seat, and a copilot and crew chief, all on crashworthy armored seats. Cockpit flight controls, all of "hands on throttle and stick (HOTAS)" configuration, were conventional for an aircraft, including stick, rudder pedals, and throttle, which operated as cyclic, yaw pedals, and collective in helicopter mode. The flight control system adroitly handled the transition between horizontal and vertical flight, without the flight crew worrying overmuch about the details.
The main cabin was big enough to carry 24 troops in full combat gear, sitting on inward-facing crashworthy folding seats, plus a gunner. In the medevac role, it could carry 12 litters, in four stations of three litters, and medical attendants. In the cargo transport role, the Osprey could haul 9,070 kilograms (20,000 pounds) of cargo; it included a cargo winch and pulley system with a load capacity of 900 kilograms (2,000 pounds). A removeable cargo roller system could also be installed. There were dual cargo hooks on the belly for external sling loads; one hook by itself could handle up to 4,535 kilograms (10,000 pounds), the two together could handle 6,800 kilograms (15,000 pounds). Flight with the nacelles turned horizontal is ruled out when hauling sling loads.
There was a rear loading ramp; there was also a large cargo door at the front on the right side, with the top half opening up and inward and the lower half -- featuring built-in steps -- opening out and downward. There were emergency exit windows on the left side, and an escape hatch on top of the fuselage in back of the wing. There were provisions for a rescue hoist for use through the rear door; it was originally fitted to the side door. Three fast rope / rope ladders could be deployed through the rear door.
The Osprey had a triple-redundant digital fly-by-wire (FBW) flight control system, and dual MILSTD-1553B databuses. It had an autopilot and a "glass cockpit" with four multifunction displays -- two each for pilot and copilot -- plus a central status and alarm display, along with a small monochrome status display. Early aircraft had CRT displays, but they soon gave way to color LCD flat panels.
The pilot and copilot also had helmet-mounted displays (HMD), like those often used in modern military multirole helicopters; they have been misleadingly described as head-up displays -- HUDs -- not HMDs, in some sources. It appears that the HMDs were originally monochrome, but were updated to color. The cockpit was night vision goggle (NVG) compatible. A range of military radios, including satcom links, was fitted, along with an identification friend or foe (IFF) system. Other standard kit included:
The Osprey was fitted with a defensive countermeasures suite, including:
The initial MV-22B "Block A" configuration was in a baseline configuration, lacking full kit, with "Block B" and "Block C" bringing the Osprey up to spec. Initial production plans envisioned the Osprey as being armed with a cannon in a nose turret, but it was deleted due to budget concerns. However, the idea didn't go away, and in 2000 an MV-22 was tested with a 12.7-millimeter (0.50-caliber) gun in a nose turret. The gun is a variant of the General Dynamics GAU-19/A three-barrel Gatling gun, with a cyclic rate of fire of 1,200 rounds per minute.
The turret wasn't fielded. In practice, Marine Ospreys used a machine gun on a flexible mount, firing out the tail door -- originally the 7.62-millimeter (0.30-caliber) M240 MAG, but this giving way to the classic, more potent Browning M2 12.7-millimeter (0.50-caliber) machine gun. The idea of a turret didn't go away, with the "Interim Defensive Weapon System (IDWS)" turret from BAE Systems introduced late in the decade, being fitted with a 7.62-millimeter GAU-17 three-barrel Gatling gun. It was fielded by the Marines but didn't prove satisfactory, it appears because it was too heavy, and was sometimes removed in the field.
BACK_TO_TOP* The US Air Force's CV-22B was intended for the long-range special missions role with the AFSOC, replacing the Sikorsky MH-53J Super Jolly helicopter in that organization. The Air Force originally planned to buy 80 Ospreys, but the order was eventually trimmed down to 50. The two CV-22B prototypes were rebuilt from Osprey production prototypes.
The CV-22B's airframe was the same as that of the MV-22B, with the cockpit arrangement, navigation gear, and IFF being much alike. There were a number of significant differences, however, including:
Early deliveries of the CV-22B were in the "baseline" Block 0 configuration with a subset of operational avionics, but they were then updated through "Block 10" and "Block 20" to full planned avionics.
* Early on, the US Navy had intended to obtain 48 "HV-22B" Ospreys, for combat search and rescue (CSAR), special operations, and fleet logistics support. The deal fizzled out -- but in 2009, the Osprey was put forward in response to a requirement for replacement of the Navy's Grumman C-2 Greyhound carrier onboard delivery (COD) aircraft, for delivering material and personnel to carrier groups at sea.
As part of the evaluation, in 2012 an MV-22B landed and refueled on board the carrier USS NIMITZ, with cargo-handling trials conducted on board the USS HARRY S. TRUMAN the next year. In early 2015, the Navy and Marines signed a memorandum of understanding to obtain the Osprey for the COD mission, with an order formally confirmed later that year. The Osprey seemed well-suited to the role, having a carrying capacity like that of the Greyhound, but also capable of operating off other large ships with helipads, and carrying sling loads.
The Navy variant will be designated "CMV-22B". The CMV-22B will feature more fuel tankage to extend range from 1,590 kilometers (990 miles / 860 NMI) to 2,125 kilometers (1,320 miles / 1,150 NMI); it will also feature a beyond-line-of-sight communications system to stay in touch with a carrier group, and a public address system to stay in touch with passengers. The Navy has experimented with "rolling take-offs and landings" with an MV-22B; straight vertical take-offs and landings are not efficient for a heavily laden cargo transport. Initial flight of the CMV-22B was on 20 January 2020, with deliveries following. 48 CMV-22Bs will be obtained.
Bell-Boeing has promoted the Osprey as a platform for various Navy missions, such as communications relay, aerial refueling, search and rescue, antisubmarine warfare, and electronic warfare (EW). The US Army originally had a requirement for 231 V-22 transports, similar to the Marine MV-22. The Army withdrew the requirement, but remains interested in the type for medevac, special operations, and combat assault missions.
* The Osprey has distinguished itself in Iraq, Afghanistan, and other front lines in the "war on Islamic terror". Although there have been operational losses of Ospreys, concerns over reliability and vulnerability have been, admittedly after strenuous efforts, put to rest. The Osprey had several times the operational radius of the CH-46 that it replaced in Marine service, and could get a force onto the ground in about half the time. In the medevac role, the Osprey could get casualties to a field hospital much more rapidly than a helicopter. Major General Thomas Trask, an AFSOC commander, commented about the Osprey:
BEGIN QUOTE:
Pilots love this aircraft. It's comfortable, and very easy to get accustomed to. It has the flexibility you can't get with most helicopters. Bottom line, it's a joy to fly.
END QUOTE
Senior officers are inclined to put a positive spin on everything, but flight engineer TSGT Nathan McKinney praised the aircraft as highly:
BEGIN QUOTE:
We can take this aircraft into almost any landing zone. We can operate in difficult conditions in terms of weather and terrain, and insert and extract special operations teams far more effectively than any previous aircraft.
END QUOTE
From 2013, the Marine helicopter squadron HMX-1, which provides lift services for the US president and other senior government VIPs, obtained the first of what was supposed to be a total of a dozen or so MV-22Bs for the presidential flight. These MV-22Bs -- no VIP designation -- were only for support roles, and not tasked with carrying the president.
The only foreign country to obtain the Osprey was Japan, which ordered 17 in 2014, the first two being delivered in 2020. There has been interest from other nations -- Britain has considered the Osprey for service on the Royal Navy's two new aircraft carriers -- but so far no other purchases.
* The Osprey continues to be enhanced in service. Software updates have been ongoing, as well as hardware modifications to deal with problems. A "Common Configuration -- Readiness And Modernization (CC-RAM)" was begun in 2017 to ensure that Marine MV-22Bs are brought up to a common specification by 2026. The upgrade features a weather radar, improved environmental controls, an enhanced electronic warfare suite, upgraded cockpit displays, and display systems in the main cabin of the aircraft for use of the rear crew members. Initial redelivery of a CC-RAM MV-22 was in late 2019.
The Air Force is now moving towards replacement of the CV-22B's AN/APQ-186 radar with the Raytheon "AN/APQ-187 Silent Knight Radar" -- which will be a "low probability of intercept" radar, hard for the Black Hats to pick up. It will provide the all-weather, day-night, low-level terrain-following flight capability essential for special operations missions. The upgrade will be completed in 2021. The USAF is also obtaining armor for the CV-22B, in the form of the "Advanced Ballistic Stopping System (ABSS)", which will be a relatively lightweight set of armor elements to protect crew and critical aircraft systems.
In 2014, Bell-Boeing conducted armed trials of the Osprey on their own funding, the aircraft being fitted with a targeting turret and a stores pylon on the right side of the nose. Weapons fired included 70-millimeter unguided rockets, laser-guided APKWS 70-millimeter rockets, and Griffin small laser-guided missiles.
In 2017, the Navy and Air Force moved forward on an effort to evaluate a "Degraded Visual Environment (DVE)" system, developed by Elbit of Israel, on the Osprey. The DVE is to be used in reduced-visibility environments, most notably the clouds of dust churned up by an Osprey in hover, providing "synthetic vision" to the pilot through the HMD when nothing can be seen with the eyeball. There has also been talk of an engine replacement.
In 2016, Bell-Boeing awarded a contract to Cobham Mission Systems of the UK to develop a palletized aerial refueling system that will allow the Osprey to act as an inflight refueling tanker. The "V-22 Aerial Refueling System (VARS)" will use a modified version of Cobham's existing FR300 Hose Drum Unit (HDU). The contract followed investigatory work going back to 2013, with operational capability expected in late 2019. The FR300 HDU is a well-established system; the first version of the FR300 was designed in the 1960s, with the Lockheed Martin C-130 Hercules being the best-known platform that uses the FR300. Proof-of-concept tanker trials with the Osprey were performed with an existing FR300 haywired into the Osprey.
The production Osprey VARS will be a "roll-on / roll-off" system, easily installed and removed as needs require. It will require some modifications to the MV-22B for use -- including changes to allow the refueling hose to be deployed regardless of rear door position, and electrical system changes to allow the VARS to be used in both rotary- and fixed-wing flight modes. The changes are not seen as extensive or, by aerospace standards, expensive.
Along similar lines, the Marines have qualified the "AN/ALQ-231(V)4 Intrepid Tiger II (IT II)" electronic warfare system on the MV-22B -- the IT II also being a roll-on / roll-off system, mounted in a rack and controlled by a laptop computer. It will be introduced to service in 2024.
A less visible improvement was development of new engine nacelles, the original nacelles having been a problem in terms of reliability and maintainability. A contract was issued to Bell-Boeing in 2020 for updated nacelles, with the entire Osprey fleet to be upgraded by 2025.
BACK_TO_TOP* In 1996, Bell and Boeing came to an agreement to work on civil tiltrotor, as a complement to the development of the V-22, with plans for a first flight in 1999. That didn't happen. In 1998, Boeing withdrew from the partnership; Bell then hooked up with Augusta Aerospace of Italy to continue the effort, coming up with a design for a "Bell-Augusta 609 (BA609) civil tiltrotor aircraft, with a general configuration similar to that of the Osprey but in the size range and style of a business aircraft.
Augusta merged with Westland of the UK in 2000 to become "AugustaWestland"; the partnership with Bell on the BA609 continued. Initial flight of the first BA609 prototype was in March 2003, with the first full vertical take-off / forward flight test on 22 July 2005. A second prototype followed a year later.
The program was well lagging the original estimate of a first flight in 1999, and was to encounter further delays. Bell had been cooling on the exercise, partly because of distractions with getting the Osprey into proper service, and frictions with AgustaWestland grew. AgustaWestland negotiated with Bell to obtain complete control over the program in 2011, with the tiltrotor redesignated "AW609". Bell retained a minority involvement in the program as a subcontractor, with the deal stipulating that AgustaWestland not sell an armed military version of the machine. AgustaWestland moved forward on the construction of two more prototypes, with the third flying in 2015, and the fourth flying in 2017 -- the fourth being near to production standard.
The program suffered a major setback in 2015, when the second prototype broke up in mid-air, killing the two test pilots, Herb Moran and Pietro Venanzi. However, the program continued, though certification kept slipping out -- one big obstacle being that the AW609 had to meet specs for both fixed-wing aircraft and rotorcraft. Certification was in 2022, with the first production machine flying in that same year. There were buyers in the wings, though specifics have not been released.
* Leonardo Helicopters -- which superseded AgustaWestland in 2016 -- saw the AW609 as a high-priority project, seeing it as giving a decade step ahead of competitors, nobody else having been willing to endure the level of pain the company had endured to come up with a machine with such capabilities. Leonardo officials had no expectation of overnight success, since the new technology will have to carve out a market for itself. However, the fact that the AW609 could use existing heliports is a plus.
As introduced, the general configuration of the aircraft had changed little since the first mock-ups made their trade show debuts in the early 2000s. The AW609 was made primarily of composites, with a circular-section pressurized fuselage, along with a high-set wing featuring a slight forward sweep. It had a tee tail but no rudder, yaw control being performed by differential thrust from the props. Production machines featured aerodynamic refinements that cut drag by 10%.
The AW609 was powered by twin Pratt & Whitney Canada PT6C-67A turboshaft engines with 1,450 kW (1,940 HP) each and FADEC. The engines were mounted on the wingtips, each driving three-bladed rotors with a diameter of 7.9 meters (26 feet). The engine modules could tilt from horizontal to 95 degrees upright, just beyond vertical; as with the Osprey, the engines were cross-coupled, allowing one engine to keep the aircraft aloft if the other failed.
The AW609 had a sophisticated FBW flight control system designed by BAE Systems. The prototypes were fitted with Rockwell Collins Pro Line 21 avionics suites, but production aircraft had the Pro Line Fusion system -- featuring 36-centimeter (14-inch) touchscreen displays, plus an integrated flight management system with satellite-based navigation, synthetic and enhanced vision, as well as head-up display interfaces. Weather radar was optional.
The AW609 was designed to be flown by a single pilot; the control layout was like that of a helicopter, with cyclic and collective sticks. The controls worked effectively the same in both vertical and horizontal flight. The engine module tilt was controlled by a thumbwheel on the collective; they rotated at 3 degrees per second normally, 8 degrees per second in an emergency.
___________________________________________________________________ LEONARDO HELICOPTERS AW609: ___________________________________________________________________ rotor diameter 7.9 meters (25 feet 11 inches) wingspan 10 meters (32 feet 10 inches) width across rotors 18.3 meters (60 feet) length 13.4 meters (44 feet) height over tailfin 4.6 meters (15 feet 1 inch) empty weight 4,765 kilograms (10,505 pounds) max take-off weight 7,620 kilograms (16,800 pounds) maximum speed 509 KPH (316 MPH / 275 KT) service ceiling 7,620 meters (25,000 feet) range 1,390 kilometers (865 MI / 750 NMI) ___________________________________________________________________
The AW609 could be fitted with from 6 to 9 passenger seats, though combi-cargo, medevac, and SAR configurations were possible as well. Leonardo has investigated a large double door that could be opened in flight, with a hoist for SAR missions. Potential markets include business aviation services, search and rescue organizations, emergency medical evacuation services, and offshore oil drillers.
Although the AW609 was more expensive than a helicopter of comparable size and capacity, it was much faster and had much greater range, while still being able to operate off of existing helipads -- it was sized to do so. In response to customer input, an auxiliary wing fuel tank system is in the works, which would extend maximum range to 2,000 kilometers (1,240 miles / 1,100 NMI), or fly six passengers over a range of 1,480 kilometers (920 miles / 800 NMI) in a little over three hours.
As a follow-up to the AW609, Leonardo Helicopters has considered a "next-generation civil tiltrotor (NGCTR)" -- along the lines of a scaled-up AW609, with 20 seats. The NGCTR remains in the concept phase, the company having been preoccupied with getting the AW609 on the market.
BACK_TO_TOP* Bell has worked on other tiltrotor designs, such as the "Eagle Eye" drone, flying a subscale demonstrator in 1993. Although the US Coast Guard awarded Bell a contract for the Eagle Eye in 1998, it was canceled, and the Eagle Eye disappeared.
Bell has developed another crewed tiltrotor, smaller than the Osprey. In 2013, the company released drawings of a "V-280 Valor" machine being considered by the US Army's "Future Vertical Lift (FVL)" competition, with a full-scale mockup unveiled later in the year, and a demonstrator performing its initial flight on 18 December 2017. Lockheed Martin signed on to the V-280 program to provide systems expertise.
The V-280 demonstrator featured a composite airframe, a vee tail, retractable taildragger landing gear, and twin engines -- though the engines didn't tilt, they drove the rotors through a pivoting transmission system. The demonstrator was powered by GE T64 turboshafts, coupled via a driveshaft as with the Osprey. Production machines will be powered by Rolls-Royce AE 1107F turboshafts, these being a derivative of the T406 used on the Osprey.
There was a forward-hinged door on each side of the cockpit, as well as a back-sliding door on each side of the cabin. The Osprey had a tail ramp for troop access; the side doors on the V-280 were the primary reason the V-280 uses tilting rotors instead of engines, since tilting engines would have obstructed the troops on exiting the aircraft. In addition, the downward exhaust could start fires or scorch people below, and complicated hovering. Bell also claimed the tilting rotor system was simpler and more reliable than tilting engines.
The V-280 won the FVL competition in late 2022. Somewhat unusually, the follow-development phase was to develop a "virtual prototype" for evaluation, before moving on to building a flight prototype.
The production V-280 will have an NVG-compatible glass cockpit and a triple-redundant FBW system; it will be capable of autonomous flight. It will be able to carry a crew of 4 and 14 troops, and can mount a machine gun in a window on each side. Presumably a hoist will be available as well. It seems likely that a countermeasures system and imaging turret will be optional, or possibly standard kit. The V-280 will be able to haul a 155-millimeter howitzer as a sling load. It will be capable of inflight refueling. Preliminary performance specs for the V-280 include:
Projected maximum take-off weight is around 13,600 kilograms (30,000 pounds). Bell is considering an attack derivative down the road, concepts having been presented with an undernose cannon turret, and missile racks under or alongside the fuselage.
* Along with the V-280, Bell Helicopter also promoted a naval tiltrotor drone, the "V-247 Vigilant", in reply to a US Marine Corps requirement for a ship / shore-based armed drone. The V-247 would carry sophisticated sensor, electronic warfare, or communications-control systems -- not to mention munitions -- to perform a range of missions. The V-247 would have an "open architecture" to permit mission customization, with three internal bays that could carry sensors, fuel, sonar buoys, radar, a homing torpedo, or Hellfire / JAGM anti-armor missiles.
The Marines finally decided to acquire the shore-based General Atomics MQ-9 Reaper drone instead – but the Navy didn't give up on the V-247, scaling it down -- from 15.9 to 12.7 tonnes (35,000 to 28,000 pounds) -- with a folding rotor system to allow it to operate off of Aegis-class destroyers. Concepts showed the Navy V-247 carrying a pod to dispense sonobuoys and torpedoes for anti-submarine warfare, as well as sensors for maritime patrol. The Navy V-247 would be a complement to a navalized V-280 Valor in replacing the current US Navy rotorcraft fleet.
At the upper end of the size scale, Bell-Boeing proposed a next-generation four-propeller tiltrotor, simply called the "Quad Tiltrotor", that would be comparable to a Lockheed C-130 Hercules. It would be able to carry loads of up to 13.6 to 18.2 tonnes (30,000 to 40,000 pounds) over a range of 3,200 kilometers (2,000 miles) at a cruise speed of 520 KPH (320 MPH / 280 knots). In 2005 Bell Helicopter Textron was awarded an investigation contract for the Quad Tiltrotor as part of the US military's "Joint Heavy Lift (JHL)" program. It didn't go anywhere, with some Air Force officials saying the machine would not be able to operate in frontline combat conditions or behind enemy lines, and would have a tremendous propwash. The propwash of a V-22 is bad enough, but the Quad Tiltrotor would raise a hurricane of dust and debris when landing on an unprepared surface.
In 2021, Bell released concepts for a family of "High-Speed Vertical Take-Off & Landing (HSVTOL)" aircraft, capable of forward speeds of over 740 KPH (460 MPH / 400 KT). Three configurations were envisioned:
The three concepts all had retractable tricycle landing gear, twin tailfins, and a mid-mounted wing with tiltrotors at the tips. Unlike the Osprey, the tiltrotor blades folded in forward flight, with propulsion generated by jet-engine exhaust. Bell long ago demonstrated that it was practical to fold up rotor blades in the transition to forward flight. The current concepts envision separate engines for rotors and forward propulsion, though the longer-term thinking is to use some combined engine scheme. The HSVTOL concepts are not focused on any existing requirement, instead being proposals to guide future developments.
BACK_TO_TOP* I finally got to see Ospreys in service at an airshow at Miramar Marine Corps Air Station -- near San Diego, California -- in 2012. They were definitely sci-fi in appearance, giving me a sense that I was indeed living in the 21st century. Of course, the irony is that the Osprey has been flying since the 1980s, but didn't get into service until after the turn of the century.
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* Revision history:
v1.0.0 / 01 jul 17 v1.0.1 / 01 jun 19 / Review, update, & polish. v1.0.2 / 01 apr 21 / Review, update, & polish. v1.1.0 / 01 mar 23 / Review, update, & polish.BACK_TO_TOP
