Browse Topic: Pitot-static instruments
Air data measurement and calibration are fundamental components in the pursuit of accurate and reliable aerodynamic assessments. The systematic collection of essential data regarding air properties are important for evaluating aircraft performance under various conditions and configurations. The scope is to achieve a comprehensive understanding of airflow characteristics, which is fundamental for design improvements and operational strategies, contributing to safer and more efficient flight operations in a several range of scenarios. This type of data measurement is even more challenging for the AW609 Tiltrotor which combines vertical take-off technology capabilities with the fixed-wing flight efficiency. The activity starts from known pitot-static system calibration methodologies for conventional applications and shows what were the difficulties encountered in a non-conventional Tiltrotor approach. The paper goes through the presentation of the original Pitot-Static and Air Data system and all the problematics that driven to a design change. After the presentation of the new architecture and the new data collection activity, it will be discussed the optimization of the data calibration strategy, also related to some peculiarities of the Tiltrotor, and how it drives to infer the calibration curves for the Air Data Computers (ADCs).
FAA rotorcraft airworthiness regulations require calibration of pitot-static systems in all flight regimes. Of all methods commonly used, none has been applied in a manner showing full compliance, specifically in the takeoff phase and in determining CG (Center of Gravity) effects. A review of accepted Position Error Correction methods identifies the GPS-based true airspeed method, with an adapted execution and analysis technique, as the most practical in terms of equipment and efficiency to provide a complete airspeed system calibration. The level flight limitations of the GPS method are solved by a combination of flight profiles, continuous data recording and reduction technique. The GPS horseshoe method and the ORBIS constant turn radius method are expanded by varying the airspeed, altitude, and heading as required to provide an equation set solved for the wind components and true airspeed. The new variable parameter methods minimize wind variability effects and flight test time.
Bell Helicopter's 525 Relentless will be the world's first commercially certified fly-by-wire helicopter. As a fully computer controlled aircraft, the design aims at higher safety through reduced pilot workload, increased situational awareness, and improved handling qualities. The flight control system that achieves these results operates with numerous redundant sensors that provide flight data and feedback to the flight control logic. This paper describes the development of the Bell 525's redundant Pitot static airspeed system, showing how computational fluid dynamics (CFD) models were used to perform initial calibration of the triplex system far ahead of first flight. Since air data readings interact with the flight control logic, it was important to have a reasonable airspeed calibration available for first flight. The Bell 525 aerodynamics team developed an analytical approach to model the triplex airspeed system to account for position error across the flight envelope. The analysis developed calibration curves for forward flight, descent, and climbs to meet FAA rules for accuracy. The resulting process has allowed the 525 to conduct its first flight and full envelope expansion with an accurate and reliable production airspeed system.
In efforts to increase the accuracy and reliability of altimetry, speed measurement and other aspects of air data, a great deal of attention and money have been expended on new and refined pressure transducing and computing systems and on the standards by which they are calibrated. So much progress has been made in this that the limiting factor is, or may soon be, the sensing and transmitting in the aircraft of the pressures to be transduced. Until the appearance of References 1-13 and 18 there was little guidance available on the maintenance of pitot and static systems. This report presents what information is available, suggests limits, and lists the principal original papers on the subject.
The four engined Upper Surface Blowing (USB) STOL research aircraft ASKA was developed by National Aerospace Laboratory of Japan and has been in the flight test phase to provide various kinds of flight data. The position error in airspeed and angle of attack is discussed, and the low speed performance demonstrated in the flight test is provided by the figures of lift/drag coefficient curves and V-Gamma plot. Several indications of powered lift and dynamic stability derivatives obtained from the V-Gamma plot are discussed. The flight measured pitching moment shows the distinctive features such as pitch up tendency. The wing-body pitching moment and the downwash angle are analyzed from the flight load measurments of the horizontal tail. The ground effect of the ASKA is also presented quantitatively in this paper. THE QUIET SHORT TAKE-OFF AND LANDING (STOL) capability is very beneficial for the Japanese domestic aviation, since airports have short runways in the vicinity of the residential area in Japan. The National Aerospace Laboratory (NAL) developed the experimental aircraft ASKA to make a flight research on the quiet upper surface blowing (USB) STOL technology (1)*. The ASKA is a conversion of the Kawasaki C-1 tactical transport installed with four newly developed FJR710/600S turbofan jet engines. The ASKA made the first flight in October 1985, and the flight verifications on the basic aircraft systems and performance had been made first in a step by step manner from shallower to deeper flap angle. The basic airworthiness flight test including the Stability and Control Augmentation system (SCAS) was finalized by the actual STOL configuration landing, and the intensive evaluation of the STOL landing configuration follows that. Various kinds of the flight test have been made (2), (3) and (4), however, the key issues of the USB STOL technology are low speed capability. In this paper, the position error in airspeed and angle of attack is discussed first and the low speed and powered lift characteristics of the landing configuration of the ASKA were presented. The lift and drag performance was surveyed and the airspeed and flight path angle plot, namely V-Gamma plot, was derived from the lift and drag curves. Several indications for the powered lift and dynamic stability derivatives were obtained from the V-Gamma plot. The distinctive pitching moment performance was analyzed by decomposing the wing-body and horizontal tail components with using the tail load measurement system. The ground effect was also analyzed to give quantitative information to achieve the precision point touchdown of the aircraft. The discussions in this paper are based on the newest flight data until the fall of 1988, and are the current status report of the flight test of the ASKA.
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