Offshore support will be a key market for the Bell Boeing 609 nine-passenger civil tilt-rotor
Graham Warwick/ORLANDO
WHENBELL BOEING unveiled the Model 609 civil tilt-rotor in Washington DC on 18 November, it was repaying US politicians for their support of its V-22 military tilt-rotor by fulfilling a long-standing promise to transfer the technology to the civil sector.
After a shaky beginning, the V-22 is now approved for production - deliveries to the US Marine Corps will begin in 1999 - and Bell Boeing has decided that the time is right to launch a civil tilt-rotor. Bell chairman Webb Joiner decribes the decision as "...an aviation milestone" rivalling the introduction of the jet engine and supersonic travel.
Joiner says that Bell Boeing "-conducted an enormous amount of research to determine what markets could use a speedy, long-distance aircraft that didn't need a runway". The result is the decision to launch a six- to nine-passenger aircraft aimed principally at the utility, offshore, corporate and search-and-rescue markets. The company foresees demand for 1,000 aircraft over 20 years, mainly as replacements for existing medium-sized twin-turbine helicopters.
At $8-10 million, the Bell Boeing will be more expensive than competing helicopters, principally the Sikorsky S-76, but its greater speed and range will result in seat-kilometre costs which are "...more than competitive with similar-sized twin helicopters", Joiner says. While other sizes of civil tilt-rotor have been studied, a nine-passenger aircraft "-is the right place to start", he believes.
LEAP OF FAITH
Launching a civil tilt-rotor is a bold move. For Bell, the aircraft will replace its popular Model 412 medium twin. For Boeing, it is a new veture into commercial rotorcraft. Both believe that a nine-passenger aircraft can be successful without any of the ground and airspace infrastructure that would be needed to operate a larger civil tilt-rotor. The 1,000-aircraft market size is based on operating the Bell Boeing 609 within the infrastructure now used for helicopters.
Boeing Helicopters general manager Jim Morris says that the decision to launch the 609 was based on three primary criteria: market need, technology maturity and immediate value. He says that the market is there, the technology is proven and the aircraft will provide operators "-with an quantative increase in productivity using the existing infrastructure. As new tilt-rotor infrastructure becomes available, the productivity will increase further."
The tilt-rotor is a well-proven concept. The Bell XV-3 experimental tilt-rotor was first flown 1957 and some 100 conversions between helicopter and aeroplane modes were completed during flight testing of two aircraft. The Bell XV-15 technology-demonstrator was first flown in 1977, and flight testing of two aircraft set the benchmark for tilt-rotor performance, including a maximum level speed of 300kt (550kt/h).
The XV-15 paved the way for the V-22 programme, which was begun in 1982 when the team of Bell Helicopter Textron and Boeing Helicopters received a contract to build six full-scale-development aircraft. The contract was terminated after four aircraft had been flown, but not before the operational utility of the V-22 had been demonstrated. Bell Boeing was subsequently awarded a new engineering- and-manufacturing-development contract to build four "production-representative" V-22s, the first of which will be flown later this month.
Between them, the XV-15 and V-22 have demonstrated convincingly the viability of the tilt-rotor concept. Fundamentally, the aircraft combines the capabilities of a twin-rotor helicopter and twin-turbine aeroplane in a single airframe. A tilt-rotor can be taken off and landed vertically and flown to 100kt forward speed in helicopter mode, or converted to aeroplane mode and flown at speeds approaching 300kt and altitudes up to 25,000ft (7,600m).
TILTING AT MARKETS
Designed to rival helicopters such as the S-76 and turboprops such as the Raytheon Beech King Air 200, the Bell Boeing 609 has a maximum gross-weight of 7,265kg, cruise speed of 275kt, maximum range of 1,400km (750nm) and operational ceiling of 25,000ft. Two 1,380kW (1,850shp) Pratt & Whitney Canada PT6C-67A turboshafts will provide Category A single-engine fly-away performance from elevated structures such as rooftop helipads.
The 10m wingspan, 7.9m prop-rotor diameter and 13.3m fuselage length will enable the 609 to be operated from spaces similar to those required for the S-76. The pressurised cabin, which is 1.5m wide and 1.4m high, has a cross-section which is larger than those of the S-76 and King Air and similar to that of the Learjet 45 business jet. There is a 914mm-wide entry door and a 1.55m3 (55ft3) baggage compartment.
While an S-76 is able to carry a 1,660kg useful load 650km at 155kt, and a King Air can carry some 1,800kg for 3,700km at 290kt, the 609 is designed to carry a 2,500kg useful load 1,400km at 250kt. Bell Boeing calculates that the aircraft will be able to perform a 650km office-to-office mission in under 2h, compared with a typical 2.5h for a turboprop flight when the drives to and from airports are included.
While a tilt-rotor is a less-efficient hovering machine than a helicopter, once wingborne it can fly faster, higher and further. Bell Boeing believes that a helicopter is better for hops of less than 90km, and a business jet for flights of over 925km, but calculates that a tilt-rotor will save time over a turboprop aircraft on missions of 90-925km.
In the emergency-medical-service mission, the 609 will provide hospital-to-hospital capability at higher speeds than a helicopter, carrying two litters and three passengers. In the search-and-rescue mission, the tilt-rotor will enable operators to replace both fixed-wing search and rotary-wing rescue aircraft with a single airframe, Bell Boeing believes.
Bell Boeing studied both six- and 14-passenger civil tilt-rotors before deciding on a nine-seat aircraft. The direct operating-costs of the six-seat aircraft "did not work out", and offshore operators persuaded the team away from the larger aircraft by arguing that their emerging requirement was to carry smaller crews to platforms further from shore. The 609 is therefore designed to carry nine passengers nonstop to rigs 480-500km offshore.
Designed for single-pilot instrument-flight-rules operation, the 609 will have a two-crew, flat-panel "glass cockpit" and be approved for flight into known icing conditions - refinements more usual on with fixed-wing aircraft.
TAKING THE PLUNGE
The Bell Boeing 609 uses technology from the V-22, including an all-composite airframe and triplex digital flight-control system, but is similar in size to the XV-15. The gross weight is just 450kg more than that of the XV-15 and the prop-rotor diameter just 305mm more. One XV-15, now painted to resemble a corporate aircraft, is still used by Bell Boeing to demonstrate the tilt-rotor's potential.
Bell has 51% of the 609 programme and Boeing 49% and, as on the V-22, Boeing will build the fuselage while Bell produces the wing and nacelles. The aircraft will be assembled at Bell's Fort Worth, Texas, plant. Plans call for four flight-test aircraft, with a first flight in mid-1999 and certification and first deliveries early in 2001. The 609 will be certificated under a new category being drawn up by the US Federal Aviation Administration using the appropriate elements of the Part 29 rotary-wing and Part 25 fixed-wing rules for certification of transport-category aircraft. A new type rating will also be established for tilt-rotor pilots.
Boeing's Morris says that a key criterion of the 609 programme is to make the aircraft affordable. He says that the two companies will be tied together by an advanced digital design and pre-assembly system already used on the V-22 and Boeing 777 programmes. The fuselage, for example, will be composite, with aluminium internal structure, and produced using automated fibre-placement technology developed for the V-22. Bell will build the composite wing using automated tape-laying techology developed for the V-22.
Bell Boeing sees the 609 as the start of a family of civil tilt-rotors which will include a commuter aircraft. By first targeting those markets accustomed to flying helicopters, rather than waiting indefinitely for infrastructure improvements, the two companies have embarked on a bold venture that could, as Joiner passionately espouses, "change the way we fly". o
Bell Boeing has frozen the external design of the Model 609 after windtunnel testing
The Model 609 is sized to fit into spaces now used by the Sikorsky S-76
Source: Flight International
