TECHNOLOGY AREAS: Air Platform

OBJECTIVE: Develop and demonstrate modeling techniques tailored towards multi-flight-mode rotors that are suitable for efficient thrust-borne and wing-borne flight of small Unmanned Air Vehicles (UAVs)

DESCRIPTION: Current small Unmanned Air Systems (UASs) have great potential for Department of Defense applications. However, the significant launch and recovery footprint of current systems and the limited range and persistence of today's UASs prevent them from being utilized to their full potential. Technologies are needed that facilitate the development of small Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) that have mission range and endurance far surpassing the current state of the art. For example, the current Scan Eagle UAV, with video payload has a range of approximately 2,500 km and an endurance of approximately 25 hrs. With advanced rotor designs, the objective is to increase these values by at least 50% and gain VTOL capability.

Rotors on aircraft such as the V-22 Osprey must operate over a broad envelope, spanning slow vertical descent to forward flight at high advance ratio. While performance and aero-elastic dynamics of such large-scale rotors have been investigated extensively, the smaller-scale regime (1 - 2 meters rotor diameter) typical of small UAVs has been less well explored. There is currently a significant technology gap in the area of aerodynamic modeling of small-scale air-vehicle rotor systems that are required to operate in-and-between the ranges of helicopter and airplane modes of flight. Additionally, a thorough understanding of static and dynamic loading of the rotor will be required to develop blade construction techniques the result in lightweight, rigid structures.

Innovative approaches to aerodynamic and structural modeling, design optimization, analysis, development of fabrication methods, and testing are required to advance the state of the art for application of multi-flight-mode rotor technology at the small UAV scale (up to ~150 lbs gross weight). An understanding of the aerodynamics of small-scale rotors for thrust-borne to wing-borne flight over the broad range of operating conditions will be required. Performance optimization tools which would allow the designer to tailor the rotor for selected operating modes are required. Structural design tools which would facilitate rotor blade construction should be identified. Model fidelity may be shown through wind tunnel tests and actual flight test in thrust-borne flight, wing-borne flight and selected flight modes in between.

PHASE I: Develop modeling techniques tailored towards multi-flight-mode rotors suitable for efficient thrust-borne and wing-borne flight of small UAVs. Demonstrate proof-of-concept by performing modeling and validation exercises on a representative rotor blade.

PHASE II: Based on Phase I modeling, develop processes and techniques for design optimization and analysis. Design and develop fabrication techniques and construct a demonstration rotor blade for research purposes. Show model fidelity through wing tunnel and flight test.

PHASE III: Develop a fully functional VTOL UAV prototype and demonstrate fixed wing flight performance that exceeds that of currently fielded small UAVs.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Small multi-flight-mode UAVs would offer the benefits of VTOL and efficient forward flight to emerging civil UAV applications such as forest-fire and disaster monitoring, environmental reconnaissance, border patrol, and search and rescue.

REFERENCES:

1. David Piatak, Mark Nixon, and John Kosmatka. "Stiffness characteristics of composite rotor blades with elastic couplings." NASA Technical Paper 3641, 1997.

2. Phillipe Poisson-Quinton and Woodrow Cook. "A summary of wind tunnel research on tilt-rotors from hover to cruise flight." http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730010285_1973010285.pdf . NASA-TM-X-68948, 1972.

3. Harsha Prahlad and Inderjit Chopra. "Characterisation of SMA Torsional Actuators for Active Twist of Tilt Rotor Blades." http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=768. 43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Denver, Colorado, Apr. 22-25, 2002.

KEYWORDS: Rotor; Aerodynamics; Tilt-rotor; Prop-rotor; Unmanned Air Vehicle; Unmanned Air System Questions may also be submitted through DoD SBIR/STTR SITIS website.