An Overview of the NASA Flying Test Platform Research

A methodology for improving attitude stability and control for low-speed and hovering air vehicle is under development. In addition to aerodynamically induced control forces such as vector thrusting, the new approach exploits the use of bias momenta and torque actuators, similar to a class of spacecraft system, for its guidance and control needs. This approach will be validated on a free-flying research platform under development at NASA Langley Research Center. More broadly, this platform also serves as an in-house testbed for research in new technologies aimed at improving guidance and control of a Vertical Take-Off and Landing (VTOL) vehicle. 1 Research Motivation This paper gives an overview of the ongoing research in precision guidance and robust control based on the NASA Flying Test Platform (NFTP) research vehicle currently under development at NASA Langley Research Center. The research is motivated by core GN&C objectives that include optimal guidance and navigation, and robust attitude and position stabilization under uncertain exogenous disturbances and model variations. A key goal of this research is to investigate novel technologies to improve attitude stability particularly during hovering or at low airspeed flight wherein conventional control effectors become ineffective. This particular need arises from current limitations in attitude stabilization performance for ∗Senior Research Engineer, Guidance and Controls Branch, k.b.lim@larc.nasa.gov †Staff Scientist, NIA, j.y.shin@larc.nasa.gov ‡Senior Research Engineer, Systems Integration Branch, e.g.cooper@larc.nasa.gov §Senior Research Engineer, Guidance and Controls Branch, d.d.moerder@larc.nasa.gov ¶Research Engineer, Guidance and Controls Branch, t.h.khong@larc.nasa.gov ‖Technician, Guidance and Controls Branch, m.f.smith@larc.nasa.gov vector-thrusted air vehicles such as Osprey, Harrier VTOL, and for helicopters with sling loads. The basic and common limitation in the above control problem appears to be a lack of an accurate dynamical model suited for response prediction and controller design to attain precision and reliable performance under unsteady aerodynamics. In retrospect, this apparent performance limitation in the use of a vector-thrusting approach for dynamical stabilization of the vehicle is not surprising since stability is fundamentally an unsteady aerodynamics phenomenon. This phenomenon is the current limiting factor in predicting loads and responses on the vehicle (see for example, [1], [2]), which are necessary ingredients for robust and precise stabilizing feedback control. 2 Test Platform Description 2.1 System Configuration Figure 1 shows the NFTP system, which consists of a square rigid platform levitated and propelled by a set of four battery-powered ducted fans each with a pair of control vanes. The vehicle employs a sensing system that fuses Inertial Measurement Unit (IMU) sensors and an optically based 6-DOF target tracking inertial position/attitude sensing system. The rigid platform is about 1.2 meters wide and weighs about 12 kg. The NFTP is a free flying vehicle designed to fly within a flight envelope box which is approximately 5 meters wide, indoors. Figure 2 is a schematic of the hardware architecture and major components for the basic NFTP system. The PC104 is used as the onboard flight control computer, which will implement an inner-loop controller for stability augmentation and has the capability of a wireless datalink to a ground control computer. A dSPACE system is used as the ground computer whose primary function is guidance from an operator, data logging, and communication with a vision system which tracks the flying vehicle. The flight control system will be capable of using all sensor measurements which include inertial measure-