The Tiltrotor Test Rig gets installed in the calibration rig (2014). Photo courtesy of NASA
The end goal for NASA’s Revolutionary Vertical Lift Technology (RVLT) project is not to create the next NASA tiltrotor or heavy-lift aircraft. The end goal also is not to be the first to build the next best thing. Susan Gorton, NASA’s program manager for the vertical-lift project, said the end goal is to help other people create the next best vertical-lift aircraft.
“What we’re trying to do is put out there a database that many different people can use to design their own configuration,” Gorton told R&WI. “So we’re hoping that this database will support many different pieces of the industry.”
Called the TTR for short, NASA’s newest tool in gathering that data is the Tiltrotor Test Rig. Data it compiles would then be used to provide validation for design and analysis tools. The large apparatus resembles a tilting mechanism and can support rotors up to 26 ft in diameter. That’s the size planned for the rig’s first test run with blades. Testing is to take place from mid-February to mid-summer.
The following is NASA’s list of the test rig’s design capabilities:
- Wind speed: 300 kt axial, 180 kt edgewise (the exact limit is determined by dynamic pressure, hence atmospheric conditions)
- Rotational speed: from 126 to 630 rpm
- Rotor thrust: 20,000 lb steady; 30,000 lb peak
- In-plane force (resultant): 5,000 lb steady; 10,000 lb peak
- Moment (resultant): 30,000 ft-lb steady; 60,000 lb peak
- Shaft torque: 48,000 ft-lb steady; 72,000 lb peak
- Power: 6,000 hp max (presently qualified for 2 hrs at 5,000 hp)
The test rig and supporting equipment were designed and manufactured by Bell Helicopter and Triumph Aerospace Systems, procured through a competitive bidding process. The U.S. Army and U.S. Air Force provided funding with additional support under the American Recovery and Reinvestment Act. NASA’s overall budget is subject to the changing national budget. But as it stands, Gorton’s project, which falls under the Advanced Air Vehicles Program (AAVP) part of the Aeronautics Research Mission Directorate, has an annual budget of about $20 million.
About 65 full-time equivalent NASA civil servants work on the vertical-lift project in addition to contractors. That includes vertical-lift work done at three different facilities: NASA Langley Research Center in Hampton, Virginia; NASA Glenn Research Center in Cleveland; and NASA Ames Research Center in California’s Silicon Valley. First testing for the Tiltrotor Test Rig is set to take place at Ames in what NASA boasts as the largest wind tunnel in the world — the National Full-Scale Aerodynamics Complex (NFAC).
This is not the first time NASA has put resources into tiltrotors. Even in the 11 years Gorton has been with the vertical-lift project, it has undergone several name changes and some refocusing.
“NASA has had a long history in rotorcraft and helicopter research, and we’ve had various different programs and projects in that area,” Gorton said. “But we’re making a progression from just traditional helicopters … and now we're talking about vertical lift. [Vertical lift] is a broader scope encompassing both the traditional helicopter and tiltrotors, and then some of the other more nonconventional configurations that we're seeing start to take shape — the gleam in people's eyes.”
That “gleam” for future vertical-lift options dates way back. NASA documents show that the U.S. Army wanted tiltrotor capabilities as early as the 1940s and implemented the Convertiplane Program in 1950. The most successful designs submitted during the Convertiplane Program were McDonnell Aircraft Co.’s XV-1 compound helicopter and Bell Helicopter’s XV-3 tiltrotor (Sikorsky’s XV-2 stoppable rotor aircraft didn’t pass judging).
For about 45 years, government and the industry worked to develop that product into what ultimately became the XV-15 tiltrotor research aircraft (TRRA). Through the decades, technology advanced and more companies were contracted in to assist with the development. The XV-15 finally took its first flight May 3, 1977, with a Bell test pilot at a Bell facility.
The XV-15 flies at NASA Dryden Flight Research Center in October 1980.
An important part of preparation for the XV-15's first airborne experience was testing in the 40-by-80-ft wind tunnel at NASA Ames. The new Tiltrotor Test Rig has been designed for use in that tunnel, as well as the 80-by-120-ft NASA Ames wind tunnel. So when will the Tiltrotor Test Rig be ready to go into service?
“We are talking to different folks about that now. Especially with a piece of hardware that is [as big as the test rig] and as complex, we may find something during functional check-out that needs to be fixed or improved,” Gorton explained. “So we're anticipating that we'll have all that done by the end of the calendar year. Then we'll be negotiating with some other parties that have expressed interest. But, you know, nobody really wants to step up until we can show that [the Tiltrotor Test Rig] is working. That’s our main goal — Show that it's functional, it’s checked out, it’s ready for use.”
If no other parties step forward with interest, Gorton expects NASA will want to use it for research projects by the end of 2018.
But as Gorton mentioned before, the Revolutionary Vertical Lift Technology project is more than just the Tiltrotor Test Rig. The project has efforts in clean and efficient propulsion, which includes exploring alternative electric-type propulsion systems; something she calls safety, comfort and accessibility, which includes crashworthiness, and modeling, simulation and test, which involves gathering and validating data and tools.
“The Tiltrotor Test Rig is really just one piece of the project,” Gorton said. “Historically, NASA's had a large investment in our computational tools and our unique experimental facilities that provide high-quality experimental data and validated computational tools. That's what we give to our community, industry and other government agencies.”