S&C questions1 (1)

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Oct 30, 2023

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Study Questions EANG 420 Exam I Stability and Control What are a) trim, b) stability, and c) control? What is static stability? What is longitudinal/lateral/directional stability? What is dynamic stability? Can you have dynamic stability without static stability? What is stable/neutrally stable/unstable? What is the aerodynamic center? What is the neutral point? What the center of pressure? What is the center of gravity? Longitudinal Stability What are the requirements for longitudinal static stability? Sketch the moment- versus lift-coefficient curve of an aircraft that can be trimmed and has a) static stability, b) neutral stability, c) is statically unstable. Sketch typical moment- versus lift coefficient curves of the fuselage, wing, and horizontal tail of an aircraft that has static stability. Also sketch the total moment curve. o Where is trim? o Indicate C mo of the aircraft o How do moment curve and trim change as either  the center of gravity is moved aft/forward?  the elevator is deflected? What is the disadvantage of trimming through weight shifting? What is the horizontal tail volume? What main parameters of an aircraft influence the longitudinal stability of an aircraft? Neutral Point Explain the following expressions: aerodynamic center, neutral point, center of pressure Going from sub- to supersonic, what is most likely to happen to the neutral point? How does the influence of the fuselage affect the aerodynamic center of in comparison to the aerodynamic center of the wing alone? What does the effective angle of attack of the horizontal tail depend on? How does the distance between center of gravity and neutral point influence static stability. What is static margin? What is control-fixed versus control-free stability? How does control-free versus fixed that influence the neutral point location? How is the neutral point determined in flight tests?

Longitudinal Control What main parameters of an aircraft influence the longitudinal controllability of an aircraft? What does the deflection of elevators/flaps result in? Explain the working of such control devices. How are they manipulated by the pilot? What is an acceptable control-force variation with airspeed? Sketch. For a free floating control surface, what is the hinge moment? What is a trim tab? Explain the working of a trim tab. What kind of control-force gradient (dP/dV) is desired for proper handling qualities? Why? How does CG location influence the control force gradient at trim? When does the control-force gradient become zero? How does the change in load factor influence static margin and the location of the neutral point? How does an elevated load factor due to a constant g-pull up influence the control force? What is a desirable control forces per g (Q) versus airspeed. Sketch Q vs V, indicate the control-free maneuver point and control-free neutral point. Furthermore, indicate where the control-fixed NP would be with respect to the control-free neutral point. Lateral-Directional Stability What is directional stability? What is sideslip? What is yaw? What is the criterion for directional stability? How do wing/fuselage/tail/power contribute to the directional stability of an aircraft? What is directional control? What are the stability/control requirements for the rudder? What is adverse yaw? What is weathercock stability? What rudder- force behavior is desirable? What is “rudder lock” and how can it be fixed? What is yaw-roll coupling? How does dihedral/anhedral influence lateral-directional stability? What is the dihedral effect? How does a high/mid/low wing effect roll stability? Why do some aircraft have dihedral, some anhedral? Explain lateral control. What is the purpose of the rudder? What controls are required during a cross wind takeoff and landing. What controls are required with asymmetrical thrust? What is roll-yaw coupling? What is roll damping? What is yaw-roll coupling? What is aileron reversal? How is turning flight initiated and terminated? What control inputs are needed?

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