Second prototype was first painted Navy gray with a red line.
Type: tilt-rotor VTUAV 7/8th scale demonstrator
Powerplant: 1 x Allison 250-C20B gas turbine
First flight: 1992
The Bell TR911X Eagle Eye Tiltrotor UAV demonstrators were developed to validate and refine basic flying qualities and performance characteristics of a small scale tiltrotor with the potential for future applications to VTOL UAV missions. Scaled Composites was selected to design and fabricate the composite structure for the two demonstrator airframes, including the landing gear, and to integrate Bell-supplied propulsion and flight control systems.The Eagle Eye demonstrator used 70% off-the-shelf manned-rated helicopter and common hardware parts, notably the same tiltrotor system as a number of other Bell-Boeing VTOL designs such as the V-22 Osprey and the V-44 Quad Tiltrotor.
Because of its dual requirements to both hover and to fly as a conventional aircraft, the Eagle Eye required a very complex structural arrangement. Its gas turbine engine (an Allison C20) was mounted in the center fuselage and was attached to a combining transmission. Drive shafts from the combining transmission passed through the center of the wing and connected to transmissions at each wingtip. The wingtips housed the transmission as well as the actuator used to tilt the wingtip transmission and rotor assemblies.
The composite sandwich fuselage featured three removable sections: the nose, center section and tail. This was done to allow for a reduction in overall length during transport and storage. The nose section was mounted on hinges to allow easy access to the avionics and other mission equipment. The center section incorporated the wingbox, fuel tanks engine and landing gear. Access to the center section is through the removal of the entire top section of the fuselage.
The removable tail was attached with a simple lightweight screw row. The tail contains numerous antenna and actuators for the pitch control surfaces. All of the hard points and mounts were installed by Scaled and all the system components including engine, transmissions, oil coolers, avionics, flight control systems, flaps, and control surfaces were mounted and checked for clearance, interference and fit in the fuselage structure before the vehicles were delivered to Bell. Scaled Composites also manufactured and integrated all the landing gear components for both vehicles.
The TR911X first hovered in early 1992 and conducted extensive tests for the US Navy at Yuma Proving Grounds, Arizona, in late 1993. Bell continued development of the Eagle Eye, promoted the Eagle Eye for a few years without finding a buyer. The demonstrator was selected to participate in VTOL UAV Demonstration at Yuma PG in December 97, where it finally aroused the interest of the military. On November 1, 1999, with teammates Raytheon and Lockheed Martin, Bell submitted the Eagle Eye concept as an entrant in the joint US Navy and Marine Corps Vertical Take Off and Landing Tactical Unmanned Aerial Vehicle (VTUAV) initiative, to demonstrate the performance and maturity of the prototype and its control system. According to the US Navy, the VTUAV system is intended to be a replacement for the Pioneer UAV system "to collect and pass information utilizing an airborne sensor platform that will provide the battlefield commander an extended and enhanced battlespace situational awareness."
The Eagle Eye design was first selected by the U.S. Coast Guard in the summer of 2002, as part of the service's broad "DeepWater" re-equipment effort, which must have been a great relief to Bell officials and engineers. The existing TR911X design was upgraded to satisfy all the VTUAV performance specification requirements and half of the objective requirements, as well as to enable future growth. Some issues had to be addressed, such as the tendancy of the cantilever wing box to experience very diverse structural loads during hover and conventional forward flight. An additional challenge was to make the wingbox a fuel tank (wet wing), while preserving the dry integrity of the transmission drive shaft conduits. The structure was static load tested with the customer's participation (and to their satisfaction). Also included was training to educate Bell's customer (the U.S. Navy) on the composite structures used by Scaled.
Although the first vehicle was damaged in an accident, the second Eagle Eye demonstrator has been extremely successful, demonstrating all flight phases from hover through the transition, and out to over 165 KCAS in forward flight. The TR911X demonstrated that it was capable of cruising at speeds of 340km/h and climbing to altitudes of up to 6000 m. Bell Textron even claimed that Eagle Eye is the “unofficial VTOL UAV World Speed Record Holder”. The low-cost fast-paced TR911X demonstrator program was yet another highly visible demonstration of Scaled's unique capabilities, flying over 90 hours, and achieving 200 knots in level cruise while carrying 210 pounds of payload at 7/8 the scale of the planned production version.
The Coast Guard/Marines version is known as the TR916 Eagle Eye, and a new version called the TR918 Eagle Eye is especially aimed at foreign markets.
Joint Service Missions:
This picture gives a good idea of the TR911X Eagle Eye's size.
A twist of fate
There were three finalists in the VTUAV competition: Bell, Sikorsky, and a collaboration of Ryan and Schweizer Helicopters submitted designs. The Ryan-Schweizer UAV was selected as the winner in the spring of 2000. The RQ-8A Fire Scout was a derivative of the Schweizer three-passenger, turbine powered 330SP helicopter, itself a derivative of the Hughes 300 series helicopters. The Fire Scout featured a new fuselage, new fuel system, and UAV electronics and sensors.