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Enabling Technologies to Support Individual Blade Control for Rotorcraft


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Computing and Software; Advanced Materials The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: To enable Individual Blade Control (IBC) on future fielded rotorcraft through development and demonstration of novel/robust supporting technologies that address practical implementation issues for safety critical rotor control. DESCRIPTION: There is a sizeable body of research establishing the benefits of IBC on rotorcraft including increased performance, improved handling qualities, extended component life, improved ride quality, reduced noise, and more. Reference 1 outlines a series of full-scale wind-tunnel tests of IBC technology on a modern, hingeless rotor design. The authors showed a reduction in power required in forward flight conditions of up to 7% (benefits increase further with speed). They also found up to 80% simultaneous suppression of the in-plane hub forces and moments, and up to 99% suppression of the vertical shear forces at the primary, per-blade frequency. This directly translates to longer component life and a smoother ride. Further, they observed up to a 12 dB (85%) reduction in noise generated by blade-vortex interaction (a major source of rotorcraft noise). References 2-6 provide additional examples of IBC's benefits. Successful implementation of IBC in a safety critical application represents the next big leap in rotorcraft capabilities. To realize this leap, flight control systems must be able to move each blade on a rotor-system independently of one another at frequencies up to an order of magnitude higher than the primary (1P) rotor frequency. At this time, IBC technology has flown only in limited fashion on demonstration aircraft [Refs 7-9]. IBC technology has not progressed past limited flight tests; primarily because it is very challenging for a flight control system to provide the kind of actuation needed in the rotating rotor frame while addressing all of the practical concerns of production rotorcraft. All of the flight tests referenced relied on classical swashplate controls in addition to the IBC system to ensure airworthiness with respect to failure immunity and adequate system performance. In order to make IBC realistic for production rotorcraft, the challenges of practical implementation must be addressed. Practical implementation issues include, but are not limited to, reliability, redundancy, failure modes, system performance, packaging, production, cost, and maintainability. This SBIR topic seeks technologies that would enable application of IBC technology in future production rotorcraft by addressing the aforementioned implementation issues. The primary technical challenge is that the blades to be controlled reside in the rotational environment (rotor head) while the rest of the aircraft is in the stationary frame. Proposed technological solutions will be expected to address this challenge through allocation and design of control components in the stationary and rotating frames, as well as the transmission of power, mechanical motion, information, and so forth, across the frames. The proposed technology is not required to represent a complete, tip-to-tail solution to IBC, but complete solutions are of interest. This SBIR topic is also interested in foundationally enabling technology that could be employed in a number of full IBC solutions (e.g., redundant, high-bandwidth, high-throw actuators that are robust to the rotational environment; improvements/alternatives to hydraulic or electronic sliprings; fail-op/fail-safe redundancy management strategies). Whether the proposed technology is an enabling solution or a full IBC concept, it is expected to be able to support a complete, IBC rotor-control system without the need for traditional rotorcraft control systems as a back-up in order to realize benefits in total aircraft cost, complexity, and weight. Proposed full IBC solutions should include, but not be limited to: Performance: 1. Have the ability to completely replace existing rotor-control systems by demonstrating +/- 15° (Threshold)/ +/- 20° (Objective) of blade pitch authority at 1P. 2. 2. Have the ability to support Higher Harmonic Control (HHC) modalities by demonstrating +/- 2° (Threshold) / +/- 5° (Objective) of blade pitch authority at 2P and +/- 1° (Threshold) / +/- 2° (Objective) of blade pitch authority at 7P. Safety/Reliability: 1) In support of demonstrating the ability to completely replace existing rotor-control systems, show architecture and analyses to demonstrate a Probability—Loss of Control (PLOC) of the rotor head of 1 E-8 or less per flight hour. 2) Plan/approach for meeting environmental requirements of MIL-STD-810. If the technology is not a full IBC solution, then its ability to support technical measures above should be demonstrated through a combination of test, simulation, and analysis. Although not required, it is highly recommended that the proposer work in coordination with the original equipment manufacturer (OEM) to ensure proper design and to facilitate transition of the final technology. PHASE I: Determine the technical feasibility of the proposed, IBC-enabling technologies. If a full IBC solution is proposed, the ability of the technology to completely replace existing rotor-control systems and support all published IBC/HHC modalities will be assessed. If the proposed technology is a supporting technology, the technical description of the types of IBC mechanizations that it would support, and the details of the specific implementation, should be established. In both cases, the proposed technology should be assessed for impact on practical implementation issues such as reliability, redundancy, failure modes, system performance, packaging, production, cost, and maintainability. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Develop a prototype of the technology proposed in Phase I. The prototype will be tested and demonstrated in a relevant environment to validate the feasibility of the concept as well as to uncover and mitigate any unforeseen technological challenges. For full IBC solutions, the prototype may be sub-scale or partial systems where appropriate. A full-scale prototype with a bench-test level of fidelity is acceptable for component solutions though specifics may be tailored for the given technology. For all technologies, practical implementation issues such as weight, power demand, thermal management, reliability, redundancy, failure modes, packaging, production, cost, and maintainability will be assessed in detail through analysis, simulation, test, or a combination of methods. Provide a final report covering design, analysis, simulation, testing, results, and discussion of findings. Potential analysis may include Fault Tree Analyses (FTA’s)/Reliability Block Diagrams (RBD’s), Failure Modes and Effects Analysis (FMEA), summary of fault detection/accommodation for the proposed architecture, and so forth. A copy of any software or simulation models developed for Phase II should be delivered. Any hardware (full prototype or component) developed for Phase II should be delivered. PHASE III DUAL USE APPLICATIONS: Further mature the technology developed in Phase II by addressing any substantive technical issues uncovered and either demonstrating the technology in flight on a sub-scale aircraft, or on full scale on whirl stand/ground test rig. Perform engineering design to incorporate the technology in a potential future rotorcraft. All of the benefits of IBC listed above translate directly to the commercial rotorcraft market. The link to more traditional rotorcraft is clear; however, the recent push towards urban mobility and the electric Vertical Take-Off and Landing (eVTOL) market could see IBC technology being adopted commercially before military applications. Urban mobility implies an emphasis on noise reduction while operating in cities/suburbs, a desire for reduced vibration for passenger comfort, and the need for very low PLOC. While closely related, eVTOL demands increase efficiency to offset current limitations in battery technology. This technology also has potential to apply to other, nonrotorcraft markets that could utilize IBC such as ship/submarine propellers and the wind-turbine industry. REFERENCES: 1. Jacklin, S. A., Swanson, S., Blaas, A., Richter, P., Teves, D., Niesl, G., Kube, R., Gmelin, B., & Key, D. L. (2020, July). NASA/TP-20205003457 Vol 1: Investigation of a helicopter individual blade control (IBC) system in two full-scale wind tunnel tests: volume 1. 2. Friedmann, P. P., & Millott, T. A. (1995). Vibration reduction in rotorcraft using active control-a comparison of various approaches. Journal of Guidance, Control, and Dynamics, 18(4), 664-673. 3. Kessler, C. (2011). Active rotor control for helicopters: motivation and survey on higher harmonic control. CEAS Aeronautical Journal, 1(1-4), 3. 4. Millott, T., & Friedmann, P. (1992, April). Vibration reduction in helicopter rotors using an active control surface located on the blade. In 33rd Structures, Structural Dynamics and Materials Conference (p. 2451). 5. Jacklin, S., Leyland, J., & Blaas, A. (1993, January). Full-scale wind tunnel investigation of a helicopter individual blade control system. In 34th Structures, Structural Dynamics and Materials Conference (p. 1361). 6. Norman, T. R., Theodore, C., Shinoda, P., Fuerst, D., Arnold, U. T., Makinen, S., Lorber, P., & O’Neill, J. (2009, May). Full-scale wind tunnel test of a UH-60 individual blade control system for performance improvement and vibration, loads, and noise control. In American Helicopter Society 65th Annual Forum, Grapevine, TX. 7. Arnold, U. T. P., & Fuerst, D. (2005). Closed loop IBC-system and flight test results on the CH-53G helicopter. Aerospace Science and Technology, 9(5), 421–435. 8. Roth, D., Enenkl, B., & Dieterich, O. (2006, September 12–14). Active rotor control by flaps for vibration reduction-full scale demonstrator and first flight test results [Paper presentation]. 32nd European Rotorcraft Forum, Maastricht, The Netherlands. 9. Teves, D., & Klöppel, V. (1992, September 15–18). Development of active control technology in the rotating system [Paper presentation]. 18th European Rotorcraft Forum, Avignon, France. 10. Bartels, R., Kueffmann, P., & Kessler, C. (2010, September 7–9). Novel concept for realizing individual blade control (IBC) for helicopters [Paper presentation]. 36th European Rotorcraft Forum, Paris, France. 11. Duling, C., Gandhi, F., & Straub, F. (2010, May 11–13). On power and actuation requirement in swashplateless primary control using trailing-edge flaps. In 66th Annual Forum of the AHS, Phoenix, AZ. 12. Woods, B. K., Kothera, C. S., & Wereley, N. M. (2014). Whirl testing of a pneumatic artificial muscle actuation system for a full-scale active rotor. Journal of the American Helicopter Society, 59(2), 1-11. 13. Arnold, U. T., Fuerst, D., Neuheuser, T., & Bartels, R. (2006, September 12–14). Development of an integrated electrical swashplateless primary and individual blade control system. 32nd European Rotorcraft Forum, Maastricht, The Netherlands. 14. Wierach, P. (2006, October 16–19). Low profile piezo actuators based on multilayer technology. Conference Proceedings. 17th International Conference on Adaptive Structures and Technologies, Taipei, Taiwan. 15. Fenny, C.A. (2017, May 9–17). Individual blade control for rotorcraft using mechanically programmable displacement control [Paper presentation]. 73rd Annual Forum & Technology Display, Fort Worth, TX. 16. US Department of Defense (2008, October 31). MIL-STD-810G. Department of Defense Test Method Standard: Environmental Engineering Considerations and Laboratory Tests. KEYWORDS: Individual Blade Control; Higher Harmonic Control; Future Vertical Lift; Swashplate; Fault Tolerant Flight Control; Rotorcraft
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