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Unformatted text preview: Lab 8 Notes Basic Aircraft Design Rules 6 Apr 06 Nomenclature x, y longitudinal, spanwise positions S reference area (wing area) b wing span c average wing chord ( = S/b ) AR wing aspect ratio C L lift coecient wing dihedral angle sideslip angle bank angle R turn radius S h horizontal tail area S v vertical tail area h horizontal tail moment arm v vertical tail moment arm AR h horizontal tail aspect ratio V h horizontal tail volume coecient V v vertical tail volume coecient B spiral stability parameter angle of attack V velocity Role of Simple Design Rules Aircraft must have a certain amount of inherent stability and controllability to be yable. It is therefore important to consider these characteristics when designing a new aircraft. Accurate evaluation of the stability characteristics of any given aircraft is a fairly complicated process, and is not well suited for preliminary or intermediate design. Fortunately, we have alternative criteria which give reasonable estimates and are vastly simpler to apply. The criteria involve basic dimensions, shown in Figure 1. Longitudinal x locations are typically S cg x v S h S c b x np l h l v c MAC x y Figure 1: Lengths, areas, and angles used in simple stability criteria. 1 measured relative to the leading edge of the wings Mean Aerodynamic Chord , or MAC, which is the rootmeansquare average chord. For most wings this is very nearly equal to the simpleaverage chord c . The h and v tail moment arms are the distances between the Center of Gravity (CG) and the average quarterchord locations of the horizontal and vertical tail surfaces. The criteria which will use these dimensions are estimates, so its acceptable to estimate the CG position and to eyeball the tail average quarterchord locations when measuring h and v . Center of Gravity Position An aircrafts horizontal tail size and position, and the CG position are the dominant factors con trolling the aircrafts pitch stability , which is the tendency to automatically maintain an angle of attack and airspeed. The basic effects of moving the CG position are: Decrease x cg /c (move CG fwd.): increased stability; more resistance to and V changes. Increase x cg /c (move CG back): decreased stability; less resistance to and V changes. There is one particular CG position which gives neutral stability, which is called the Neutral Point (NP). This is shown as x np in Figure 1. The degree of pitch stability or instability is traditionally specified by the Stability Margin ....
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This note was uploaded on 01/28/2012 for the course AERO 16.01 taught by Professor Markdrela during the Fall '05 term at MIT.
 Fall '05
 MarkDrela

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