2018/3/11 Origins of Aerodynamic Forces 图上活大学 Factors that influence aerodynamic forces 国上清大学 Shear forces->skin friction drag Geometry Pressure difference.>lift,pressure drag Surface roughness Supersonic flight->wave drag ·Flight speed Altitude(air density,temperature,pressure) 。Reynolds Number(Re) SHEAR MOLECULES Wind tunnel -CFD (numerical wing tunnel) O是ZTw保s.OUTWARDO oorn enin Song 圆上清文大些 Lift 圆上洋文廷大蜂 Lift-Aerodynamic force perpendicular to the flow direction 地m业c.G-(侷) CL-essentially linear before reaching the stall angle For setting the wing incidence angle Section B-1 For calculatingdrag-due-to lift AERODYNAMIC FORCES-LIFT -For longitudinalstability analysis For cruise condition,the lift requirement can be calculated from CL=L/q Srer =W/gSrer nwentin ong Effect of Camber and AR on CLa 圈上洋文通大坐 Subsonic Lift-Curve Slope 园上海发大坐 2元A EFFECT OF CAMBER EFFECT OF ASPECT RATIO CLa=- 2+ B ASPECT RATIO 4+ l+tan2 3 B2 where B2=1-M2 7= C 2π/ airfoil efficiency (o.95) fuselage lift factor F=min(1.071+d/b)2,0.98) Wing effective aspect ratio Aegecme =4(1+1.9h/b)Endplate due to wing tip modifications Aee≈l.2 Winglet A is the geometric aspect ratio of the complete reference wing ry-ur.wwennn song 22018/3/11 2 © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Origins of Aerodynamic Forces • Shear forces -> skin friction drag • Pressure difference -> lift, pressure drag • Supersonic flight -> wave drag © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Factors that influence aerodynamic forces • Geometry • Surface roughness • Flight speed • Altitude (air density, temperature, pressure) • Reynolds Number (Re) – Wind tunnel – CFD (numerical wing tunnel) © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics AERODYNAMIC FORCES - LIFT Section B-I © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Lift • Lift – Aerodynamic force perpendicular to the flow direction CL Main aerodynamic coefficients CL max max       D L • CLα – essentially linear before reaching the stall angle – For setting the wing incidence angle – For calculating drag-due-to lift – For longitudinal stability analysis 𝐶𝐿 = 𝐿 𝑞⁄ 𝑆௥௘௙ = 𝑊 𝑞⁄ 𝑆௥௘௙ • For cruise condition, the lift requirement can be calculated from © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Effect of Camber and AR on CLα © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Subsonic Lift-Curve Slope   F S S A A C ref exposed t L                      2 max 2 2 2 2 tan 2 4 1 2      2 2   1 M     2 Cl where  airfoil efficiency (0.95) fuselage lift factor min(1.07(1 ) ,0.98) 2 F   d b A A(1 1.9h / b) effective   Aeffective 1.2A Endplate Winglet Wing effective aspect ratio due to wing tip modifications A is the geometric aspect ratio of the complete reference wing