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Tham khảo tài liệu 'thiết kế kỹ thuật máy bay chiến đấu episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LONGITUDINAL STABILITY 395 Table 11-1 Stabiliser volume coefficient Stabiliser volume coefficient Vs Power flap Sport competition and agricultural aeroplanes Transport All-moving stabilator Propeller-driven simple flaps Propeller-driven 0.3-0.65 0.5-0.8 0.35-0.55 high lift flaps rare 0.85-1.2 0.5-0.65 Jet simple flaps Jet 0.2-0.55 0.4-0.65 0.2-0.4 high lift flaps 0.3-0.4 0.5-0.68 about 0.4 Sailplane Manpowered 0.57-0.6 0.64 based on total area of a vee tail 0.53-0.59 about 0.2-0.25 Note Canard designs are not commonplace enough for there to be much evidence but the tail volume coefficient with an economically-sized foreplane appears to be about 0.8 to 0.85 times Vs with a tailplane. Too much stability makes agricultural aeroplanes exhausting to handle and pilots want stick forces to be light. If the centre of gravity lies ahead of the neutral point the aeroplane will be statically stable. If it moves aft of the NP the aeroplane will be statically unstable. CG static and manoeuvre margins When an aeroplane is rigid strictly an unreal condition stability can be measured in terms of fixed geometrical factors like configuration and location of the centre of gravity. Aerodynamic properties like wing and tail lift slopes are theoretically constant and do not change with speed or Mach number or with loads applied to the skin and structure. Then we are able to assume that the neutral points are fixed and distances measured between the CG and NP called CG margins stick-fixed and free Hn H n respectively are absolute measures of stability. In the real world they are not. Real aeroplanes bend and twist. Their skins deform and there is a constant aeroelastic interaction between what the pilot and other disturbances do to the apparent constants. For example fuel is consumed and the CG moves. Aerodynamic pressures suck the skin out here and push it in there altering profiles. CG margins cease to have strict relevance. Instead we measure stability in terms of static margins .
