A program of flight testing of an instrumented subscale model of the X-33 aerospace vehicle is underway. The objectives of this program are the following:
- Successful flight of a model of the X-33;
- Development of a small, lightweight, instrumentation system suitable for model research;
- Determination of limited X-33 aerodynamic characteristics from flight data; and
- Quantification of how well parameter-estimation techniques perform when applied to data acquired by use of the lightweight instrumentation system on a model of this type.
The program is justified by the fact that model flight-testing often highlights unforeseen characteristics, and by the potential for applying the flight-test techniques and instrumentation developed in this program to flight testing of other subscale, lightly loaded models of aerospace vehicles.
The X-33 model (see figure) is 4 ft (1.2 m) long and was fabricated in the landing-gear-down configuration. The model has been flown 29 times to date, and 16 channels of instrumentation were in use during the last 20 flights. The model weighs 8 lb (3.6 kg) empty and 11 lb (5 kg) with instrumentation. The 3-lb (1.4-kg) instrumentation system, developed specifically for the X-33 model, includes a power supply, sensors, and related wiring. The model is visually controlled from the ground and has no stability augmentation. Because of its limited performance, stability, and control, the X-33 configuration is a challenging one to fly and land.
A typical flight operation starts with the launching of the X-33 model from a larger, powered model at an altitude of 1,000 ft (305 m). There is time to perform one flight-data maneuver prior to setup for landing. The model is back on the ground about 25 seconds after launch. The flight data are then downloaded into a laptop computer. The flights thus far have been used to mature the hardware, establish the best combination of vehicle trim and center of gravity, and gather limited flight data.
Some of the flight data gathered thus far have been analyzed. Several maneuvers have been successfully analyzed by use of parameter-estimation techniques. Moments of inertia were recently experimentally determined. A detailed calibration of air-data parameters will soon follow, and further analyses of flight data will be performed once the calibration is complete. There are plans to evaluate additional lightweight sensors.
This work was done by Alex G. Sim and Jim Murray of Dryden Flight Research Center and Tony Frackowiak of Analytical Services and Materials, Inc. DRC-99-22