JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD 
III Year B.Tech. AE - I Sem      L  T/P/D  C 
                                               4   - / - /-  4 
(A52111) FLIGHT MECHANICS - II

Objective:

To familiarize the student with the statitics, synamics, trim and control of aircraft.

UNIT - I:

Aircraft in Equilibrium Flight - Elevator Anglr to Trim - Longitudinal Static and Maneuver Stability: Need for controlled flight, Equilibrium, stability, trim, control- definitions- examples. Longitudinal forces and moments on aircraft in unaccelerated flight- contribution of principlal components. Equations of equilibrium- thrust, angle of attack, elevator angle required to trim. Control gradient, total airplane lift curve slope and pitch stiffness. Tailless aircraft and aircraft with foreplanes. Longitudinal static stability- definition, relation to control gradient, pitch stiffness. Stick fixed neutral point- static margin. Effect of flaps and flight speed on force and moment coefficients, aerodynamic derivatives, stability, trim.

Steady, symmetric pull-up maneuvers-equations of motion- pitch rate, pitch damping. Control to trim, trim curves- elevator per g- maneuver point, maneuver margin- relation to static margin, Statutory limits on postion of centre of gravity. Deermination of neutral and maneuver points by flight testing.

UNIT - II:

Estimation of Aerodynamic Force and Moment Derivatives of Aircraft: Significance of aerodynamic derivatives. Derivatives of axial, normal force components and pitching moment with respect to the flight speed, angle of attack, angle of attack rate, pitch rate, elevator angle- dependence on vehicle geometry, flight configuration- effects of flaps, power, compressiblity and aeroelasticity.

Lateral directional motion- coupling- derivatives of side force, rolling and yawing moments with respect to the sideslip, rate of sideslip, roll rate, yaw rate, aileron, rudder deflections- dependence on vehicle geometry, flight configuration. Estimation- the strip theory method. Relation between dimension-less and dimensional aerodynamic derivatives.

UNIT - III:

Stick Free Longitudinal Stability- Control Forces to Trim, Lateral- Directional Static Stability and Trim: Elevator hinge moments- relation to control stick forces. Hinge moment derivatives, Stick force to trim in symmetric unaccelerated flight, maneuvering flight. Stick force gradients- effect of trim speed- role of trim tab. Effect of freeing elevator on tail effectiveness, static and maneuver stability, Elevator- free factor. Stick- free neutral and maneuver points, stability margins- relation with stick force gradients. Aerodynamic and mass balancing of control surfaces. Control tabs- types, function construction.

Lateral- directional static stability, definition, requirements. Equilibrium of forces and moments. Aileron, rudder, elevator and thrust required to trim aircraft in steady sideslip, roll, coordinated turn, engine out condition. Cross wind landings.

UNIT - IV:

Aircraft Equations of motion- Perturbed Motion- Linearised, Decoupled Equations: Description of motion of flight vehicles- systems of reference frames- Euler angles, angles of attack and sideslip- definitions- earth to body axis transformation, Rotation axis system- expressions for linear and angular momenta of rigid body, time derivatives- inertia tensor, components of linear and angular velocities, accelerations. Resolution of aerodynamic, gravity forces, moments acting on flight vehicle. Relation between angular velocity components and lateral-directional. Relation between angular velocity components and Euler angle rates, Determination of velocities of airplane in earth axis system, Determination of vehicle trajectory- outline of method.

Description of motion as pertubation over prescribed reference flight condition. Equation of motion in pertubation variables. Assumption of small pertubations, forst order approximations- linearised equations of motion. Decoupling into longitudinal and lateral-directional motions- conditions for validity- role of symmetry. Linearised longitudinal and leteral-directional equations of pertubed motion.

UNIT - V:

Longitudinal and Lateral- Directional Dynamic Stability: Linearised longitudinal equations of motion of aircraft- three degree of freedom analysis- characteristic equations- solutions- principal modes of motion- characteristics- time constant, undamped natural frequency and damping ratio- mode shapes- significance. One degree of freedom, two degree of freedom approximations- constant speed (short period), constant angle of attack (long period) approximations- solutions- comparison with three degree of freedom solutions- justification of approximations. Lateral directional equations- three degree of freedom analysis. Principal modes- characteristics- mode shapes- significance, lower order analysis- approximate solutions.

Determination of longitdinal and lateral stability from coefficients of characteristic equation- stability and lateral stability from coefficients of characteristics equation- stability criteria, approximate roots, Special problems in aircraft dynamics- roll coupling, high angle of attack operation. Aircraft spin- entry, balance of forces in steady spin, recovery, pilot techniques.

TEXT BOOKS:

1. Yechout, T. R. et al., Introduction to Aircraft Flight Mechanics, AIAA education Series, 2003, ISBN 1-56347-577-4.
2. Nelson, R. C., Flight Stability and Automatic Control, 2nd Edition., Tata Mc Graw Hill, 2007, ISBN 0-07-066110-3.

REFERENCE BOOKS:

1. Etkin, B. and Reid, L. D., Dynamics of Flight, 3rd Edition., John Wiley, 1998, ISBN 0-47103418-5.
2. Schmidt, L. V., Introduction to Aircraft Flight Dynamics, AIAA Education Series, 1998, ISBN A-56347-226-0.
3. McCormick, B. W., Aerodynamics, Aeronautics and Flight Mechanics, 2nd Edition., Wiley India, 1995, ISBN 978-

Outcome: 

The student should be able to estimate the aerodynamic derivatives of a given airplane, determine its stability and compute the control deflections and control forces required to trim the airplane in any given flight configuration.