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219 3.3.14 Aerodynamic Balancing The fioating characteristics of a control surface depend on the hinge-moment characteristics and, as we will see later, the stick force also depends on the hinge- moment characteristics. Too low values of the hinge-moment would make the control highly sensitive to small disturbances, whereas too high values would make the controls sluggish to operate. Therefore, a careful design of the hinge-moment parameters Cha and ChtS.e iS necessanjt to achieve a proper balance between these two conflicting requirements. The control of hinge-moment parameters is called aerodynamic balancing. When the hingeline is at the control surface leading edge. both Cha and C,,b.e are negative. If the hingeline is moved further aft, both Chct and Cn8.e become more positive because the control surface forward of the hingeline produces an opposing moment to that produced by the surface aft of the hingeline. The net hinge moment, which is the algebraic sum of these two moments,is greatly reduced. This type of aerodynamic balance is called set-back hinge balance (Fig. 3.45a). However, one has to be careful because too much area forward of the hingeline may lead to an overbalance of the control at some flight conditions that may affect the pilot's feel of the aircraft. Horn balance (Fig. 3.45b) is similar to the set-back hinge, except that all the area ahead of the hingeline is concentrated on one part of the surface. The horn Section A-A Hing tlini a) Set-back hingeLine b) Horn balance Bevtl c) Internal balance d) Beveled trailing edge e) Tab Fig.3.45 Aerodynamic balancing concepts. 220 PERFORMANCE, STABILfTY, DYNAMICS, AND CONTROL Estimation of Ct" atsubsonic speeds. We havel Cha- -A' A )Chab,,+AChcr (3.121) Ar +2cos Ac/4 STATIC STABILITY AND CONTROL 221 where Ar is the aspect ratio of the main control surface and, in this case, it is the aspect ratio of the horizontal tail. The estimation of the parameter Chabd is done as follows:l Chabal = [CC:. ] C;lct c/a=cc,C. ](C,,).eory (3.122) (3.123) HINGE LINE o NACAO . NAC~OO:; } o NACA 66009 j o NACA0009 I ~. NACA 0015 J 4 NACA0009 (chor) balance HINGE LINE ELLIPI'IC NOSE SHARP NOSE HINGE LINE tc F --7r-- {- 2 ┏━━━━━┳━━━━┓ ┃L~ ┃-cf4- ┃ ┣━━━━━╋━━━━┫ ┃ ┃ ┃ ┗━━━━━┻━━━━┛ SUBSONIC SPEEDS fflNGE LINE ~ ~ ┏━┳━┳━┳━┳━┳━┳━━━┳━━┳━━┳━┓ ┃ ┃ ┃ ┃ ┃\ ┃\ ┃.l ┃ ┃ ┃ ┃ ┣━╋━╋━╋━╋━╋━╋━━━╋━━╋━━╋━┫ ┃ ┃ ┃ ┃ ┃~ ┃X ┃\1. ┃~ ┃~b ┃ ┃ ┣━╋━╋━╋━╋━╋━╋━━━┻━━┻━━┻━┫ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┣━╋━╋━╋━╋━╋━╋━━━┳━━┳━━━━┫ ┃ ┃ ┃ ┃ ┃ ┃ ┃~~E. ┃Q~ ┃S ~ ┃ ┃ ┃ ┃ ┃ ┃ ┃\ ┃ ┃ ┃ ┃ ┣━╋━╋━╋━╋━╋━╋━━━╋━━╋━━┳━┫ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL2
