The method used to analyze maneuvering flight will be to determine a stick-fixed maneuver point (Hm) and stick-free maneuver point (H'm). These are analogous to their counterparts in static stability, the stick-fixed and stick-free neutral points. The maneuver points will also be derived in terms of the neutral points, and their relationship to cg location will be shown.
Static stability is the reaction of a body to a disturbance from equilibrium. To determine the static stability of a body, the body must be initially disturbed from its equilibrium state. If, when disturbed from equilibrium, the initial tendency of the body is to return to its original equilibrium position, the body displays positive static stability or is stable. If the initial tendency of the body is to remain in the disturbed position, the body is said to be neutral stable. However, should the body, when disturbed, initially tend to continue to displace from equilibrium, the body has negative static stability or is unstable. Longitudinal static stability or gust stability of an aircraft is determined in a similar manner. If an aircraft in equilibrium is momentarily disturbed by a vertical gust, the resulting change in angle of attack causes changes in lift coefficients on the aircraft (velocity is constant for this time period). The changes in lift coefficients produce additional aerodynamic forces and moments in this disturbed position. If the aerodynamic forces and moments created tend to return the aircraft to its original undisturbed condition, the aircraft possesses positive static stability or is stable. Should the aircraft tend to remain in the disturbed position, it possesses neutral stability. If the forces and moments tend to cause the aircraft to diverge further from equilibrium, the aircraft possesses negative longitudinal static stability or is unstable.
Dynamics is concerned with the time history of the motion of physical systems. An aircraft is such a system, and its dynamic stability behavior can be predicted through mathematical analysis of the aircraft's equations of motion and verified through flight test. During this study of aircraft dynamics, the solutions to both first order and second order systems will be of interest, and several important descriptive parameters will be used to define the dynamic response of either a first or a second order system.
Pilots might be inclined to associate the phrase control system with only aircraft flight control systems. Although the control system theory of this course has a large application to flight control sysems, this material applies to any process or system in which control is exercised over some output variable. Examples of these controlled variables are: the speed of an automotile, the temperature of a room, the attitude of a spacecraft, ad infinitum.
A set of aircraft maneuvers has been developed to augment evaluation maneuvers used currently by the flying qualities and flight test communities. These maneuvers extend evaluation to full aircraft dynamics throughout the aircraft flight envelope. As a result, a tie has been established between operational use and design parameters without losing control of the aircraft evaluation process. Twenty maneuvers are described as an initial set to examine primarily high-angle-of attack conditions. Perhaps as important as the maneuvers themselves is the method used to select them. These maneuvers will allow direct measurement of flying qualities throughout the flight envelope instead of merely comparing parameters to specification values. Aircraft maneuvers, Flight test, Flying qualities, Agility.
Divergence experienced during rolling maneuvers has frequently been referred to as inertial coupling. This leads to a misconception of the problems involved. The divergence experienced during rolling maneuvers is complex because it involves not only inertial properties, but aerodynamic ones as well. The material in this chapter is intended to offer a physical explanation of the more important causes of roll coupling.
The second edition of Flight Stability and Automatic Control presents an organized introduction to the useful and relevant topics necessary for a flight stability and controls course. Not only is this text presented at the appropriate mathematical level, it also features standard terminology and nomenclature, along with expanded coverage of classical control theory, autopilot designs, and modern control theory. Through the use of extensive examples, problems, and historical notes, author Robert Nelson develops a concise and vital text for aircraft flight stability and control or flight dynamics courses.
As spinning is still involved in around 60% of all aircraft accidents (BFU, 1985 and Belcastro, 2009), this aerodynamic phenomenon is still not fully understood. As U.S. and European Certification Specifications do not require recoveries from fully developed spins of Normal Category aeroplanes, certification test flights will not discover aeroplane mass and centre of gravity combinations which may result in unrecoverable spins. This book aims to contribute to a better understanding of the spin phenomenon through investigating the spin regime for normal, utility and aerobatic aircraft, and to explain what happens to the aircraft in terms of the aerodynamics, flight mechanics and the aircraft stability. The approach used is to vary the main geometric parameters such as the centre of gravity position and the aeroplane’s mass across the flight envelope, and to investigate the subsequent effect on the main spin characteristic parameters such as the angle of attack, pitch angle, sideslip angle, rotational rates, and recovery time. First of all, a literature review sums up the range of technical aspects that affect the problem of spinning. It reviews the experimental measurement techniques used, theoretical methods developed and flight test results obtained by previous researchers. The published results have been studied to extract the effect on spinning of aircraft geometry, control surface effectiveness, flight operational parameters and atmospheric effects. Consideration is also made of the influence on human performance of spinning, the current spin regulations and the available training material for pilots. A conventional-geometry, single-engine low-wing aeroplane, the basic trainer Fuji FA-200-160, has been instrumented with a proven digital flight measurement system and 27 spins have been systematically conducted inside and outside the certified flight envelope. The accuracy of the flight measurements is ensured through effective calibration, and the choice of sensors has varied through the study, with earlier sensors suffering from more drift than the current sensors (Belcastro, 2009 and Schrader, 2013). In-flight parameter data collected includes left and right wing α and β-angles, roll-pitch-yaw angles and corresponding rates, all control surface deflections, vertical speeds, altitude losses and the aeroplane’s accelerations in all three directions. Such data have been statistically analysed. The pitch behaviour has been mathematically modelled on the basis of the gathered flight test data. Nine observations have been proposed. These mainly cover the effects of centre of gravity and aircraft mass variations on spin characteristic behaviour. They have all been proven as true through the results of this thesis. The final observation concerns the generalisation of the Fuji results, to the spin behaviour of other aircraft in the same category. These observations can be used to improve flight test programmes, aircraft design processes, flight training materials and hence contribute strongly to better flight safety.
Flying Qualities is that discipline in the aeronautical sciences that is concerned with basic aircraft stability and pilot-in-the-loop controllability. With advent of sophisticated flight control systems, vectored thrust, forward-swept wings, and negative static margins, the concept of flying qualities takes on added dimensions. In aeronautical literature there are three terms bandied about which are generally considered synonymous. These terms are flying qualities, stability and control, and handling qualities. Strictly speaking, they are synonymous. An early publication by Phillips in 1949 defines flying qualities of an aircraft as those stablity and control characteristics that have an important bearing on the safety of flight and on the pilots' impressions of the ease of flying an aircraft in steady flight and in maneuvers. The specification's stated purpose of application is to assure flying qualities that provide adequate mission performance and flight safety regardless of design implementation or flight control system mechanization. Successful execution of the military mission then is the key to flying quality adequacy. A definition of flying qualities which can be agreed upon by both the USAF and the US Navy is: Flying qualities are those stabilty and control characteristics which influence the ease of safely flying an aircraft during steady and manuevering flight in the execution of the total mission.
