Aircraft Longitudinal Static Stability
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Questions and Answers

What is the primary advantage of dividing stability and control analysis into longitudinal and lateral-directional analysis?

  • It simplifies the analysis by eliminating the need to consider moderate changes in angle of attack. (correct)
  • It enables the analysis to focus on the pitching moment about the center of gravity.
  • It reduces the importance of considering the wing's aerodynamic center.
  • It allows for a more detailed analysis of the aircraft's yaw and roll.

    • What is the definition of the aerodynamic center of the wing?

  • The point where the wing's drag is minimum.
  • The point about which the wing's pitching moment is constant with respect to angle of attack. (correct)
  • The point where the wing's pitching moment is zero.
  • The point where the wing's lift is maximum.

    • Where is the aerodynamic center of the wing typically located in subsonic flight?

  • At 25% of the MAC (correct)
  • At 50% of the MAC
  • At the trailing edge of the wing
  • At the leading edge of the wing

    • What is the effect of flap deflection on the wing's pitching moment?

    <p>It increases the pitching moment.</p> Signup and view all the answers

    What can be ignored in the pitching moment equation due to its small value?

    <p>The pitching moment of the tail about its aerodynamic center</p> Signup and view all the answers

    What is the significance of the wing being uncambered and untwisted?

    <p>The pitching moment about the aerodynamic center is zero.</p> Signup and view all the answers

    What influences the pitching moments produced by the fuselage and nacelles?

    <p>Upwash and downwash produced by the wing</p> Signup and view all the answers

    What is the purpose of the wing flap in a tailless aircraft?

    <p>To trim and control the aircraft</p> Signup and view all the answers

    What is the effect of the propwash jet induced flowfield on the aircraft?

    <p>It influences the effective angle of attack of the tail and possibly the wing</p> Signup and view all the answers

    What is the equation used to express the sum of moments about the cg?

    <p>Working equations</p> Signup and view all the answers

    What is the term used to describe the vertical force produced at the propeller disk?

    <p>Fp</p> Signup and view all the answers

    What is the purpose of dividing all terms by (qSwc) in the pitching moment equation?

    <p>To express the moments in coefficient form</p> Signup and view all the answers

    What is the result of increasing the tail force to counteract a change in the trim condition?

    <p>Upward deflection of the elevators</p> Signup and view all the answers

    What is the effect of a positive Cl change on the trim tab?

    <p>Requires a positive trim tab angular deflection</p> Signup and view all the answers

    What is the purpose of deflecting the elevator downward to trim for a speed increase?

    <p>To decrease the angle of attack and lower the nose of the aeroplane</p> Signup and view all the answers

    How does the position of the CG affect the pitch handling characteristics?

    <p>It affects the positive longitudinal static stability and pitch handling characteristics</p> Signup and view all the answers

    What happens to the elevator deflection required to counter a forward CG movement during a manoeuvre with a load factor greater than one?

    <p>It is increased</p> Signup and view all the answers

    What is the effect of an aft CG position on the response to elevator deflection?

    <p>A large response for the same angle of deflection</p> Signup and view all the answers

    What type of stability is focused on the angle-of-attack stability derivatives?

    <p>Velocity stability</p> Signup and view all the answers

    What happens to the thrust of a propeller when the aircraft velocity increases?

    <p>It decreases</p> Signup and view all the answers

    What is the effect of a high-mounted propeller on an aircraft's velocity stability?

    <p>It is stabilizing</p> Signup and view all the answers

    What is the approximate increase in static margin for every 1% MAC that the thrust axis is above the c.g.?

    <p>One-quarter of a percent</p> Signup and view all the answers

    Why is a high-mounted propeller usually used only in seaplanes?

    <p>To provide water clearance</p> Signup and view all the answers

    What is the effect of engine vertical position on velocity stability in jet aircraft?

    <p>It has little to no effect</p> Signup and view all the answers

    What is the orientation of the X-axis in the Stability Axis System?

    <p>Aligned at the aircraft's angle of attack</p> Signup and view all the answers

    Why is the Stability Axis System used in aerodynamics?

    <p>Because lift and drag are conveniently aligned with the axes</p> Signup and view all the answers

    What is included in the calculation of nondimensional coefficients for moments?

    <p>The moment arm, dynamic pressure, and wing area</p> Signup and view all the answers

    What is the positive direction of a moment in stability analysis?

    <p>Nose up or to the right</p> Signup and view all the answers

    What is the significance of the yawing moment derivative with respect to sideslip?

    <p>It is a critical parameter in lateral stability</p> Signup and view all the answers

    What does $N_v$ represent in stability analysis?

    <p>The pitching moment response to an elevator deflection</p> Signup and view all the answers

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