XX OSTIV CONGRESS
'THE SPIN MANOEUVRE'
BY
C.A.MARTIN AND D.J.PILKINGTON
SYNOPSIS OF THE PAPER
Aircraft spinning is an important area of design for recreation aircraft, general aviation aircraft and military aircraft. Since the early days of flying, both stalling and spinning have been major causes of aircraft handling accidents. The fact that the stall/spin manoeuvre still causes aircraft accidents shows that in spite of extensive research over many years, in leading aeronautical laboratories an economic design solution to the problem of spinning has not yet been found.
Although the basic mechanics of the spin manoeuvree are the same for all classes of aircraft, the wide range of aircraft shapes results in a marked variation in both their aerodynamic and inertia forces and consequently in the characteristics of the spin manoeuvre.
A distinguishing feature of the glider is the large wing aspect ratio. This results in significantly different aerodynamic and inertia distribution characteristics compared with general aviaton and military aircraft. Although a number of flight investigations of glider spinning have been carried out, few research or design papers have been published on the aerodynamic characteristics of the glider spin. Therfore, it is likely that the spin design information and prediction methods are less reliable than those for general aviation and military aircraft which, in turn, in the absence of extensive model testing, are themselves only adequate for predicting gross trends in aircraft spin behaviour. Therefore, there is still a need to provide designers with more accurate methods for the prediction of aircraft and glider spinning characteristics.
In this paper, the more general aspects of aircraft spinning will be discussed. Where possible, relevance to the problems of the glider will be made. Firstly the nature of the spin will be descrived. The major phases of the spin will be defined and the particular characteristics of the steady spin will be emphasized. Next, the considerations and compromises that need to be addressed in reaching a design solution will be discussed. Of particular importance is the layout of the empennage and the information will be presented on the relative merits of different arrangements. Thirdly, the various methods for spin model testing will be described. The choice and extent of a spin model test programme is intimately linked with the costs and risks involved in the subsequent flight test programme. Typically, many recreation and general aviation aircraft proceed to flight testing without any model test programme while for combat aircraft a variety of different spin model techniques are commonly used.
Finally, it is acknowledged that a
considerable amount of pilot experience of the aircraft spin
manoeuvre exists, particularly concerning spin entry and recovery
techniques. The need to interpret this information in terms of
aircraft inertia, aerodynamic and control surface characteristics
is discussed.
NOTATION
b wing span cbar wing mean aerodynamic chord Cm pitching moment coefficient Cl rolling moment coefficient Cn yawing moment coefficient Ix, Iy, Iz moments of inertia about X, Y, Z body axes m aircraft mass Sw wing area V free stream velocity a angle-of attack ß sideslip angle p air density ø inclination of flight path to vertical Ø rate of rotation about the vertical axis
LIST of FIGURES
Figure 1 The Spin Manoeuvre
Figure 2 Longitudinal Trim Conditions
Figure 3 Balance of Forces
Figure 4 Balance of Pitching Moments
Figure 5 Balance of Rolling Moments
Figure 6 Balance of Yawing Moments
Figure 7 Tail Damping Characteristics for Various Designs
Figure 8 Rotary Balance Data
Figure 9 Angle-of-Attack and Spin Rate for Pitching Moment Balance
Figure 10 Sideslip Angle for Rolling Moment Balance
Figure 11 Aerodynamic and Inertia Yawing Moments in a Steady Spin
1. INTRODUCTION
Aircraft spinning is an important area of design for general aviation and military aircraft, and has been so, since the early days of aviation. In many of the major aeronautical laboratories in the world, aircraft spinning has been the subject of intensive periods of research. However, the resulting design criteria are still only adequate for predicting gross trends in aircraft spin behaviour. This information has to be augmented by extensive scale model testing, usually of a qualitative nature, to enable flight testing and development to proceed with confidence. In this paper, these features of the subject will be emphasized.
Following a discussion of the nature of the spin, the methods currently available to the aircraft designer for spin prediction are discussed. The need to interpret pilot experience of aircraft spin behaviour in terms of aircraft characteristics is presented.
