David Rozovski

An experiment was conducted to compare a conventional helicopter Thrust Control Lever (TCL) to the Rotational Throttle Interface (RTI) for tiltrotor aircraft. The RTI is designed to adjust its orientation to match the angle of the tiltrotor‟s nacelles. The underlying principle behind the design is to increase pilot awareness of the vehicle‟s configuration state (i.e. nacelle angle). Four test pilots flew multiple runs on seven different experimental courses. Three predominant effects were discovered in the testing of the RTI: 1. Unintentional binding along the control axis resulted in difficulties with precision power setting, 2. Confusion in which way to move the throttle grip was present during RTI transition modes, and 3. Pilots were not able to distinguish small angle differences during RTI transition. In this experiment the pilots were able to successfully perform all of the required tasks with both inceptors although the handling qualities ratings were slightly worse for the RTI partly due to unforeseen deficiencies in the design. Pilots did however report improved understanding of nacelle movement during transitions with the RTI.

Since 1942, all rotary and fixed wing aircraft have been designed with controls that map congruently to their primary thrust vector. For example, the throttle in a fixed wing aircraft moves forward in order to accelerate forward while the collective in helicopters moves upward in order to increase lift. This design criterion eliminates the need for the pilot to conduct a mental transformation to map the control movement to the vehicle control strategy. Although the pilot’s ability to perform such a mental transformation can be dramatically improved through training, control reversal errors have been seen with non-congruent control mappings even for highly skilled pilots.  Such events are more common under high workload, high stress conditions.

Thrust-vectored aircraft, such as the tiltrotor, pose a problem in attempting to apply this design principle, since a fixed-axis controller will only be congruent when the thrust is aligned with the controller’s axis.  For example, an airplane style throttle inceptor only maps properly when a tiltrotor is in “airplane mode,” while a helicopter style collective only maps properly when a tiltrotor is in “helicopter mode.”  Currently, the V-22 Osprey utilizes an airplane style inceptor, resulting in non-congruent mapping when the V-22 is operating as a rotary-winged aircraft. The Bell-Agust 609 utilizes a helicopter-style inceptor, resulting in non-congruent mapping when the BA-609 is operating as a fixed-wing aircraft.

A variable-axis thrust inceptor has been designed for tiltrotor aircraft that maps congruently to the magnitude and direction of the thrust vector. This device, known as the Rotational Throttle Interface, maintains a congruent mapping from control axis to thrust vector throughout the entire flight regime by rotating its control axis to match the thrust vector of the engine nacelles.  A non-functional prototype has been constructed, and completion of the first fully functioning prototype is slated for Q4 of CY2009.  Experiments are being planned using flight  simulators to test whether the Rotational Throttle Interface improves tiltrotor pilot situation awareness, workload, and performance over the current inceptors.

New terrain following algorithms specific to rotorcraft navigation were developed and tested on a fixed base simulator. Guidance and cueing were accomplished through a Synthetic Vision System (SVS) and the Altitude and ground Track Predicting Flight Path Marker (ATP-FPM) from prior work. Pilots flew two separate courses that were designed to replicate real world environments as well as test key components of the algorithms. Experiment data showed significant improvement in the Max Descent and Climb (MD+C) algorithm in comparison to our base line Single Point (SP) and Max Descent (MD) algorithms with no additional perceived workload.