N093-165 TITLE: Optimal Autorotative Profiles Using Active Inceptor Cueing

TECHNOLOGY AREAS: Air Platform, Human Systems

ACQUISITION PROGRAM: PMA-261 H-53 Heavy Lift Helicopter Program, ACAT I; PMA-276 H-1

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop innovative methods for improving handling qualities and/or safety by reducing flight path variability in autorotative descent and landing using the additional cues provided by active controller inceptors.

DESCRIPTION: If a rotorcraft loses engine power, the pilot must enter an autorotation. A rotor is in an autorotative state when it is being driven only by the upwards airstream. This condition is reached in relatively high rates of descent that are proportional to the square-root of a rotorcraft�s disk loading, which is defined as the weight of the rotorcraft divided by the area of the main rotor. The amount of kinetic energy that can be stored within the rotor system and the rate it is dissipated in a flare are important factors that must be considered. A common measure of these characteristics is called the "autorotative index," which is the ratio of the kinetic energy stored in the main rotor system to the rotorcraft�s gross weight. Disk loading and autorotative index may be extremely difficult to optimize for autorotative performance due to conflicting requirements, such as mission requirements driving overall weight, shipboard compatibility driving main rotor size, and structural constraints driving rotor inertial characteristics.

Modern rotorcraft designs have tended toward high disk loading and lower autorotative indices increasing the difficulty of performing a safe, repeatable autorotation to landing. Training, in a simulator or in-flight, provides the pilot with much needed practice for this high workload, dynamic, difficult maneuver. The pilot has to master the various phases of the autorotation. The autorotation entry is important since too long a delay can decay rotor speed. During the descent, the pilot will have to turn toward a suitable landing area while maintaining rotor speed within limits. The final phase is critical, requiring a cyclic flare to bleed off airspeed and increase rotorspeed coupled with a timed collective pull to slow the descent rate before touchdown. However training alone has not been able to completely remove flight control misapplication and/or improve the handling qualities in an autorotation to a sufficient level needed to guarantee a safe landing where physically possible. This means Height-Velocity avoid regions are drawn larger than what physics alone dictates. As rotor inertias decrease in future rotorcraft designs, the pilot will have to perform this maneuver with less reaction time and in a more precise manner in order to survive engine failure or tail rotor loss.

Previous research work, such as that done by STI on autorotation training displays, has been done to increase the visual cues in the cockpit provided to the pilot in an autorotative descent. These cues ensure the rotorcraft has the maximum amount of stored kinetic energy available just prior to the flare and landing. While helpful, these artificial display cues require the pilot to continuously look inside the cockpit to ensure the autorotation profile is adhered to. A method to provide guidance to the pilot, while keeping the pilot scan external to the cockpit, is needed. Tactile cues via the control inceptors are immediate, unambiguous, and require no interpretation as to what control response is required to remedy the situation. Active control inceptors (pilot cyclic, collective and pedals) have been recognized as being more effective and accepted than other systems such as the Tactile Situational Awareness System (TSAS.) The upcoming CH-53K program specifies active control inceptors due to the potential tactile cueing that would allow "Carefree Maneuvering." Carefree Maneuvering is the concept that the aircraft won''t allow the pilot to exceed limits by using advanced control laws and tactile cues, thus reducing workload resulting in increased safety and mission effectiveness. The employment of tactile inceptors toward this is not fully understood and much research needs to be done.

There has also been research in the area of tactile cueing systems, via the pilot�s active control inceptors. While the focus of this research has been to reduce pilot workload in maneuvering flight by making the monitoring of certain structural, engine and flight limits more intuitive, the benefits of a tactile cueing system in autorotative flight have never been explored. Preliminary research recently done by ONERA and DLR presented the use of tactile cueing to prevent pilots from reaching high sink rates and Vortex Ring State (VRS). The VRS research was done to give the pilot cueing to stay within a certain envelope, whereas this autorotation research would provide pilotage commands in order to make a safe autorotative landing. This preliminary research into using tactile cues for VRS avoidance is a good start, but the autorotation problem is much more complex and dynamic.

The advent of the active stick/cyclic and active throttle/collective coupled with digital flight control laws provides an opportunity to provide very specific tactile cueing to the pilot through the cyclic and collective on optimum speed and descent rate to maintain the correct balance of kinetic energy and potential energy throughout the autorotation profile. Bidders should explore possible mechanizations and programming of cyclic and collective gradients, soft or hard stops to assist the pilot more effectively in managing energy during the autorotation profile. Existing research on methods for determining optimum autorotation profiles based on available aircraft state information should be utilized to the maximum extent possible.

PHASE I: Determine via simulation and/or analysis the optimal tactical cue(s), via the control inceptors, that can be provided to the pilot during an autorotative descent through to a landing that will increase the probability of a safe landing. Examine various control inceptor configurations to ensure proposed cue(s) are beneficial regardless of cockpit layout. Evaluate the feasibility of such an approach. Develop a conceptual design for a heavy lift helicopter (H-53K) configuration.

PHASE II: Demonstrate the proposed cues through a piloted rotorcraft simulation evaluation where various autorotative descent and landing profiles must be followed. Demonstrate that these cues, via piloted simulation, effectively improve handling qualities and reduces the possibility of misapplication of pilot controls in an autorotative descent, to include the landing. Demonstrate that the cueing solution is robust to misapplication of controls and is flexible to environmental or mission changes post engine(s) failure.

PHASE III: Develop a production ready solution. Perform verification and validation of the developed technology and demonstrate that the cueing system can be easily installed in a wide range of rotorcraft, regardless of inceptor configuration and rotor/airframe characteristics.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The solution developed here can be applied to helicopter platforms. Incorporation in other platforms can result in a potential reduction in development and operation costs.

REFERENCES:
1. Leishman, J. G., Principles of Helicopter Aerodynamics, Cambridge University Press, New York, 2006.

2. Bachelder, E., Lee D., Aponso, B., Pollack, M., Germanowski, P., "Improved Method for Evaluating OEI Height Velocity Boundaries," presented at the American Helicopter Society Forum, 2006

3. Sahasrabudhe, V. et al., "Simulation Investigation of a Comprehensive Collective-Axis Tactile Cueing System," presented at the American Helicopter Society 58th Annual Forum, Montreal, Canada, 11-13 June 2002.

4. Abildgaard, M., Binet, L., von Grünhagen, W., Taghizad, A., "VRS Avoidance as Active Function on Side-Sticks," presented at the American Helicopter Society 65th Annual Forum, Grapevine, Texas 27-29 May 2009.

5. Aponso, B., Lee, D., Bachelder, E., "Evaluation of a Rotorcraft Autorotation Training Display on a Commercial Flight Training Device," Presented at AHS Forum 61Grapevine, Texas 3 June 2005.

6. Howitt, Jeremy, "Carefree Maneuvering In Helicopter Flight Control", American Helicopter Society 51 st Annual Forum, Fort Worth, TX, USA, May 9-11, 1995.

7. Whalley, M. S., "A Piloted Simulation Investigation of Helicopter Limit Cueing", USAATCOM TR 94-A-020, NASA TM-108851, October 1994.

8. Einthoven, P. E., Miller, D. G., and Thiers, G., "Tactile Cueing Experiments with a 3-Axis Active Sidestick Controller", American Helicopter Society 57 th Annual Forum, Washington, D.C., USA, May 8-11, 2001.

KEYWORDS: Autorotation; Active; Inceptor; Cueing; Tactile; Safe

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