2001 Assessment of the Office of Naval Research's Aircraft Technology Program (2001)

The special aviation projects thrust is essentially a management umbrella for coordination, administration, and technical review of system-level efforts involving substantial funding. Currently this thrust consists of two projects, the impetus for which came from outside the normal ONR program development process: (1) vectoring extremely short takeoff and landing control, tailless operational research (VECTOR) and (2) vectored thrust ducted propeller (VTDP) compound helicopter. Table 8.1 gives the ONR budget projection for the ATP special aviation projects area.

Funding required for special aviation projects is estimated to total $79 million from U.S. sources over 5 years and, as of June 2001, $57 million is needed to complete the planned work. Table 8.1 does not contain any provision for this shortfall in FY02. Importantly, funding for special aviation projects (see Tables 1.1 and 8.1) constitutes a large portion of the Aircraft Technology Program budget—39 percent in FY01, for example. The funds come principally from within the Navy, with ONR being the main contributor. Like all government programs, the VECTOR and the VTDP compound helicopter projects are subject to the vagaries of the annual budget process. And further, it is not clear whether all the objectives of the two projects can be fully achieved within the current funding plan.

VECTOR is a technology development and demonstration program that will employ the X-31 flight test vehicle to achieve three loosely related goals:

• Demonstrate extremely short takeoff and landing (ESTOL),

• Flight test the German-designed advanced air data system (AADS), and

• Analyze, design, install, and flight test a reduced-tail or tailless X-31 configuration.

The project’s X-31 aircraft was originally fabricated and used for the enhanced fighter maneuverability (EFM) program, a NASA/DOD cooperative effort with Germany that was completed in 1995. The earlier program focused on slow speed, high angle of attack, and maneuvering at altitude and demonstrated the tactical advantage of a fighter equipped with a vectoring nozzle for post-stall flight control.

Recognizing that naval aviation operates in a STOL environment characterized by catapults and arresting gear, VSTOL aircraft like the AV-8B, and extensive use of rotorcraft, the idea of employing the X-31 for an ESTOL evaluation was advanced. The hope was that data from such a demonstration would contribute significantly to the body of knowledge supporting development of STOL concepts. Candidate platforms for improved STOL performance include F/A-18E/F and JSF derivatives, any new manned aircraft design, and unmanned air vehicles such as UCAV-N and the MRE UAV.

Planning for VECTOR began in 1997, a cooperative agreement with Germany was signed, and project operations commenced in 1999. The test vehicle was brought out of storage, restored to operational condition, and underwent a non-ESTOL safety-of-flight test in February 2001.

The ESTOL phase of the project has as its goal demonstrating one technique for reducing aircraft landing speed. Lower landing speeds would facilitate tactical air operations from smaller carriers and smaller airfields or, alternatively, permit takeoffs and landings from existing bases with increased gross weights. The ESTOL task involves employing the X-31, a test vehicle originally designed for slow-speed maneuvering flight at altitude, to evaluate a slow-speed, short landing and roll-out technique. The proposed landing procedure calls for transitioning from normal flight to a near-stall, very nose-high attitude and then executing a slow-speed, controlled rate of descent on a 3- to 5-degree glide slope. To permit the plane to land on its main landing gear and prevent the tail from striking the deck, the approach ends with a pitch down (de-rotation) at a precise moment just prior to touchdown. The desired result is reduction of the X-31’s landing speed from its normal 170 knots to as low as 100 knots.

The goal of the AADS portion of VECTOR is to design, develop, install, and flight test, in a modified X-31 nose cone, an advanced air data system that replaces the current probe employed on most aircraft. By positioning the sensor away from the influence of the vehicle’s local flow field, the system will provide accurate air data during all types of aircraft maneuvers, including those in stalled, high-angle-of-attack flight, without degrading normal fighter operational capability.

This project goal calls for installation and flight test of a reduced tail or tailless design equipped with a multiaxis thrust vectoring nozzle in lieu of the paddles used for the original EFM program. As presently structured and funded, however, it appears this effort will be limited to analysis and wind tunnel testing of reduced-tail configurations working in concert with thrust vectoring to provide control and stabilization. Although the payoffs of a reduced tail or tailless design are well known (they include lower aircraft weight, drag, and radar cross section), to date there have been no flight tests of tailless manned tactical aircraft.

As presented to the committee, funding required for VECTOR by the United States and Germany totals $78.6 million, with the U.S. share being $47 million. This figure does not cover development, installation, and flight test of a reduced-tail design. A quarter of the U.S. funds will come from NATO R&D accounts (Nunn-Warner); the remainder will come from internal Navy dollars garnered from acquisition programs and the ONR S&T budget. To date some $17 million of U.S. funds have been spent, with an estimated $30 million required to complete the project by FY03. Table 8.1 does not contain any provision for the shortfall.

The committee believes VECTOR is an appropriate ATP endeavor and the kind of S&T project ONR should pursue. This view affirms a prior conclusion of the Naval Studies Board that identified STOL as a key enabling technology meriting increased attention by the Navy. In its 1997 report, the NSB observed that an affordable STOL capability will require substantially improved flight stability and control at slow speeds and urged a follow-on to the X-31 EFM effort to explore multiaxis thrust vectoring and integrated flight and propulsion controls.¹ Although the X-31 is not representative of an operational aircraft, a properly structured and executed VECTOR project could yield data that would benefit current aircraft and influence the design of future manned and unmanned systems.

It is clear to the committee that ESTOL is the key, pacing element of VECTOR. While the AADS and Tailless research tasks may be interesting and worthy subjects of inquiry, with the exception of multiaxis thrust vectoring they appear to be ancillary and secondary in importance to ESTOL and would not in themselves justify starting or continuing a VECTOR project as presently defined. AADS data could be collected using other platforms if necessary. And as for benefits of the Tailless task, considerable flight and simulation data from Navy and Air Force programs are already available, and more will be forthcoming in the future.

The ESTOL landing maneuver involves high technical and operational risk. The slow-speed, nose-high approach demands good flight control authority, particularly for directional stability under certain wind conditions and in turbulence near the ground, as well as a reliable, very precise aircraft-to-surface ranging device to facilitate the critical, final derotation at touchdown. This risk could be mitigated

somewhat by employing a multiaxis thrust vectoring nozzle, which the committee understands was originally planned, in lieu of the current EFM paddles. Further, the reward aspect of the risk/reward equation, which governs most R&D decision making, would be strengthened because ESTOL flight data garnered from an X-31 with a true multiaxis nozzle would be more akin to data from an operational aircraft design. The committee is mindful that such a change in project direction would induce delay and increase cost. However, there appears to be no urgent need for ESTOL data, and the data’s utility would be significantly enhanced if generated by a test vehicle equipped with a proper thrust-vectoring nozzle. In sum, incorporating a multiaxis thrust-vectoring nozzle in the X-31 ESTOL configuration would reduce risk while increasing the project’s reward potential.

The VECTOR project undergoes periodic internal reviews by teams made up of representatives from ONR and the Naval Air Systems Command but does not undergo reviews by external panels of highly qualified experts with no connection to the project team, NAVAIR, or ONR.

The committee recommends that ONR convoke a comprehensive review of VECTOR by an independent panel of outside experts for the purpose of evaluating project goals and technology transition potential, assessing technical, operational and financial risk and determining the need for restructuring where appropriate. Further, the committee believes serious consideration should be given to incorporating a multiaxis thrust vectoring nozzle in the ESTOL X-31 in order to reduce technical and operational risk and generate flight data more representative of an operational aircraft design.

The stated objectives of the VTDP compound helicopter ATD are to assess the potential for a VTDP-equipped compound helicopter to improve the speed, range, and survivability of naval aviation rotorcraft while reducing ownership cost. And since the demonstration aircraft will be substantially modified, a key aspect of the ATD is to determine the impact of the wing and increased weight on hover performance.

The concept, to be demonstrated by the Piasecki Aircraft Corporation, is a refinement of an earlier one—the Pathfinder of 1962 to 1965—with the principal difference being the VTDP tail thruster, which is said to be a more efficient design. The ATD calls for substantial modifications to the YSH-60F test vehicle, including (1) installation of a wing for added lift in cruise flight and to reduce rotor loading, (2) the VTDP for directional control as well as added thrust in cruise flight, and (3) a third engine to compensate for additional aircraft weight (empty) induced by the required alterations and to generate more thrust for faster, higher-gross-weight flight.

Regarding ownership or life-cycle costs, Piasecki believes its VTDP compound design would result in cost reductions across all H-60 mission areas, attributing the lower cost to decreased vibration in all flight modes and better specific range in cruise flight. The reduction in vibration is said, in turn, to increase airframe and rotor life, while a partially unloaded rotor in cruise flight induces less wear on bearings and rotating mechanisms. Considerable disagreement exists between the government and the contractor over these claims of potential improvement. Hence, an important goal of the project is to determine the impact on life-cycle cost of the VTDP compound helicopter design. And here, costs are very much determined by the type of mission flown—a typical short-range “lifting” mission characteristic of Navy helicopter operations or long-range cruise flight typical of commercial operations and Marine Corps ship-to-objective inland penetration.

The DOD and U.S. helicopter manufacturers extensively studied compound helicopter technology from the late 1940s to the mid-1980s, and several flight demonstrations were funded, principally by the Army. The results of such tests indicate that, if increased speed is a priority requirement, then compounding does offer an advantage over the conventional helicopter. This increase in speed does not come without penalty, however. If a compound helicopter must be used for short-range lifting missions, its efficiency is diminished and operating costs increase.

In the early 1990s the Army looked in detail at a Piasecki compound concept similar to that proposed for the current ONR project, committing $10.7 million to doing so. Engineering and mission studies, wind tunnel tests, and piloted simulations were conducted, with the AH-64 as a potential candidate platform. While concluding that the Piasecki design had some positive attributes, the negatives were said to outweigh the positives, and the Army was unable to envision a unique requirement that the concept might satisfy.

The current ATD was preceded by earlier exploration of the concept by the Navy Department, with the Marine Corps AH-1W as the candidate platform. Beginning in FY92 and carrying on from previous work for the Army, Piasecki was given $10.2 million by the Navy to ground test a VTDP for the AH-1W. But after the Marines fixed on the AH-1Z as their future attack helicopter, Congress directed a shift in FY99 from AH-1W to H-60 as the VTDP candidate, and $6.6 million in bridging funds were allocated for risk reduction and fabrication of a flightworthy VTDP. In total, $16.8 million in Navy funds had been invested in the VTDP compound helicopter concept before initiation of the ATD in FY00.

The technical approach is to employ design, analysis, and simulation, leading to fabrication, component ground testing, and installation on the test aircraft of the VTDP assembly, lifting wing, added engine, modified drive train, and a new flight and propulsion control system. The YSH-60F will then be subjected to a series of ground tests to validate the proposed concept and its readiness for flight. Flight testing will be approached in two steps: (1) a VTDP-only test of the aircraft without the lifting wing installed and (2) if step 1 is successful, testing the aircraft equipped with both VTDP and lifting wing to validate contractor claims of enhanced performance and reduced ownership costs. The products or deliverables resulting from the ATD will be a Navy YSH-60F equipped with Piasecki VTDP compound helicopter components, flight testing, and the resultant flight test data.

The ATD commenced formally in FY00 and is scheduled for completion in FY05. Since the change, in FY99, to the H-60 as VTDP platform candidate, the following have been accomplished: (1) ground test of the VTDP, (2) ATD master plan, and (3) initiation of design and fabrication of certain system components. As briefed to the committee, the funds required over the life of the ATD total $31.8 million, with some $4 million expended as of June 2001 and an estimated $28 million needed to complete project work. Table 8.1 does not include funds for this shortfall.

The original rationale behind the Navy’s commitment to the ATD was the hope that a VTDP compound variant of the H-60 Seahawk might be suitable as an airborne mine countermeasures (AMCM) platform in the event the standard H-60 was unable to perform the mission. However, that prospect for employment was dashed when, after flight tests in February 2001, the Navy concluded the standard Seahawk was capable of performing all aspects of the AMCM mission.

A compound design is inherently more complex, heavier, and more costly to acquire than a conventional helicopter with the same lift capability. Hence, the argument for compounding turns on the degree of increased speed sought and the mission range requirement. And because top priority to date has, in the main, been placed on lifting ability rather than speed and specific range, no compound scheme derived from a conventional helicopter design has been introduced into operational service in either the commercial or military world. The tilt-rotor and tilt-wing compound concepts do offer marked advantages over conventional helicopters in speed and in specific range for long-distance missions, to such a degree that the former is about to enter military and commercial service.

Under normal circumstances the committee believes there should be only moderate technical risk associated with the proposed Piasecki concept, because lifting wing concepts are not new to the rotorcraft world, a VTDP-like concept flew successfully in the 1960s, and the current VTDP has undergone wind tunnel testing. However, the YSH-60F test vehicle is to be modified not at Paisecki facilities but at the Naval Air Warfare Center, Patuxent River, Maryland, by non-Piasecki contract engineers and technicians. This raises the prospect of ambiguity in management responsibility, with an attendant increase in technical, financial, and programmatic risk associated with execution of the ATD as now planned. Further, it insinuates an unusually high degree of intervention and supervision by the government during the course of aircraft modification and flight test. Here, the degree of risk is contingent on the competence of the contracted engineers and technicians and on how ATD work is to be managed.

Finally, technology transition potential should be an important consideration for initiation and continuation of any S&T program or ATD. The committee is concerned that, even if the planned VTDP compound helicopter demonstration is successful, no candidate platform exists today or can be foreseen in the future that might benefit from incorporation of the technology. Navy H-60s rarely undertake missions involving long-range cruise, where the Piasecki concept might offer some advantage; rather, their modus operandi is characterized by fairly short runs and frequent takeoffs and landings, where a regular helicopter is more efficient. And for long-range missions, a tilt-rotor aircraft such as the V-22 can fly much faster than any lifting wing compound helicopter and has superior specific range as well. Hence, the committee cannot see the reward aspect of the risk/reward consideration mentioned earlier in this report. It therefore believes naval aviation and the government overall would be better served if the funds planned for this ATD were applied to satisfy other, more pressing needs in support of naval aircraft technology development.

Because of cost-benefit considerations, program risk, and most important, the lack of a foreseeable requirement in the Navy and Marine Corps for a VDTP compound helicopter, the committee believes the sizable funding now allocated for this project (roughly 20 percent of the ATP) could be more beneficially utilized in pursuing higher-priority technology development efforts. Accordingly, the committee recommends that the VTDP compound helicopter ATD be terminated and unexpended project funds applied elsewhere within the ATP.