From RotorHub:AUSA: Bell’s Ewing Ties Quad Tiltrotor JHL Response To Realistic Appraisal Of Challenges.
|Washington DC:- Bell’s Alan Ewing - in charge of the company’s quad tiltrotor development effort - says here that any flying prototype to emerge from current design studies will be limited to the power range of the current V-22 engines. |
But scaling up beyond that will require a new engine initiative. Engines with the requisite power are out there, he says, but they will have to be modified and qualified to operate through the rotational angles required in a tiltrotor design.
Ewing shows that Bell (which is working with Boeing, but not yet on any type of formal business basis) is moving steadily ahead on the design challenges inherent in developing a vehicle capable of meeting presumed JHL (Joint Heavy Lift) targets.
A defined design requirement is awaited, but is still considered some way off while requirements issues are under study by various DoD and service agencies.
The Army, however, issued a statement at ‘AHS63' (The most recent AHS forum, held this past May in Virginia beach, Va.,) committing to tilt engine technology as the preferred approach of choice.
In the meantime, more detailed work that will lead to a preliminary design review next year is underway on what Bell is currently calling a ‘B2A-26-6' quad tiltrotor concept design - B2A for the second iteration of design, 26 for its payload (in tons) and 6 because it will be able to fly a 250nm radius at that weight at a density altitude of 6,000 ft.
But, Ewing stresses, the design group is ready to get working on whatever mission design emerges from the current joint requirements process. He anticipates the ‘quad’ could get larger as a result.
The design work facing the two manufacturers is enormous. Currently only about 30 engineers are engaged on the project, but Ewing says it will ramp up shortly and could reach 250-300 not far down the road.
Ewing admits aspects of the blade and hub design are still in early analysis to determine the types of loads and moments any design will incur.
Current thinking is targeting a four-blade layout 38 ft in diameter, but he admits that could change and go larger, again depending on requirements.
More precise information on the hub moments and other factors likely ‘seen’ by the design will emerge from NASA Langley wind tunnel testing set to begin later this year.
An associated problem is actuation of blades. ‘We have actuators now, so I don’t think scaling them will be a problem in terms of weight and drag,’ he told a meeting here.
Bell is studying two alternative ways to handle blade mounting - either as ‘gimbaled’ blades in case there’s a blade-fold requirement from the maritime community, or a design based on direct attachment elastomerics, along the lines of a hingeless blade configuration for a conventional helicopter.
Ewing updated the audience on how much detailed design - down to a frame-by-frame fuselage schematic - had been done in the last year. The baseline ‘B’ version was frozen this past March is awaiting an internal report.
He said Bell and Boeing are still some way away from defining work-share on the project and for now both are using ‘best practices’ as they work together on concept definition.
Bell management is scheduled to look at required ongoing investment to proceed to next steps next week, Ewing said. This stage will include a flight test of a 70 percent scale prototype perhaps within two or three years.
The US Army, meanwhile, is currently working to get kick-off funding for JHL prototype development into its key Program Objective Memorandum (POM) funding plans for 2010 onwards.
Although the Army will (notionally) become the main sponsor for JHL, Ewing confirms USAF has been requesting regular updates on the aircraft - which could end up operating routinely at 30,000 ft. ‘Although I have to say we haven’t been over there (to USAF) lately,’ he said.
In summary, Bell/Boeing’s work is an undeniably exciting project to anyone interested in the future of rotorcraft technology - a genuine push into a future replete with challenges in almost all the aerodynamic domains of the future.
The team has taken a long-term - visionary - view and as a result is clearly ahead of potential competitors in coming to terms with some of these issues.
It is a case study, perhaps, in how to ‘do’ aerospace R&D in the current environment - a commitment to company funded IRAD started early, and as realistically tied as Ewing and his team can calculate to breakthrough, future requirements.
‘We certainly are keeping going,’ he says, and we realise no models are perfect but some are useful,’ he commented wryly at he beginning of his presentation, drawing from a well known quotation.
Equally clearly this is no mere ‘scale-up’ of a V-22 either. It’s a whole new aerospace ‘big project’ in the making which Ewing admits will make heavy demands on the Bell and Boeing resource base.
- David S. Harvey
Sorry, I don't have access to any image hosting websites from work or I'd dig up a few pics from google or something.