Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III FLIGHT MECHANICS II Previous Question Paper (May/June - 2019 - R13)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
Explain how tail-less aircraft and aircraft with fore-planes are controlled.
Answer
Tail-less aircraft utilize elevons, which are combined elevator and aileron surfaces located on the trailing edge of the main wing, to manage both pitch and roll. Aircraft with fore-planes (canards) use the forward surface to generate lift and pitch control, often requiring careful balancing to ensure the canard stalls before the main wing to maintain longitudinal stability.
Write on control gradient and pitch stiffness of an aircraft.
Answer
The control gradient is the rate of change of stick force with respect to airspeed or load factor, indicating the pilot's effort required for maneuvering. Pitch stiffness (static longitudinal stability) is represented by the derivative of the pitching moment with respect to the angle of attack (C_m_alpha); a negative value ensures the aircraft naturally returns to its equilibrium pitch attitude.
Explain the derivatives of side force and yaw moment with respect to side slip, roll rate and yaw rate.
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Explain the derivatives of axial and normal force components and pitching moment with respect to angle of attack rate and pitch rate.
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What is the function of a tab of an elevator?
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Define stick force gradient.
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Explain earth-fixed to body axis transformation.
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Write short on inertia tensor.
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Define time to half and time to double of a first order system.
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Explain roll-yaw coupling.
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Part B
Starting from fundamentals, derive an expression for the elevator angle required to trim an aircraft in steady level flight with stick-fixed condition.
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Define load factor. Derive an expression for the pitch rate of an aircraft in a pull-up maneuver in terms of the load factor.
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What are the effects of flaps and flight speed on aerodynamic force and moment coefficients of an aircraft?
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How do the flap, elevator and rudder contribute to the forces and moments on an aircraft in flight? Explain in detail.
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Write on the effects of compressibility and aeroelasticity on the stability of an aircraft.
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Following Multhop’s method, estimate the variation of the pitching moment of an aircraft with angle of attack for the following conditions. The pitch rate is 0.03 radian per second.
| Segment location | 0 to 1.0 | 1.0 to 2.0 | 2.0 to 3.0 | 3.0 to 4.0 | 4.0 to 7.0 | 7.0 to 12.0 | 12.0 to 18.0 | 18.0 to 19.0 | 19.0 to 20.0 | 20.0 to 21.0 | 21.0 to 22.0 | 22.0 to 23.0 |
| Average width | 0.1 | 0.5 | 1.0 | 1.5 | 2.5 | 3.0 | 3.2 | 2.8 | 2.6 | 2.4 | 1.5 | 0.1 |
| Upwash/Downwash | 0.3 | 0.25 | 0.22 | 0.2 | 0.18 | 0.15 | 0.02 | -0.1 | -0.1 | -0.2 | -0.2 | -0.3 |
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Derive an expression for the parameter where is yaw moment coefficient and is rudder deflection.
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Derive an expression for where and is stick force, q is pitch rate and is lift coefficient.
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Derive the linearized longitudinal equations of motion of a rigid body.
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Derive the linearized lateral – directional equations of motion of a rigid body.
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Derive an expression where is yaw angle of attack and is aileron deflection angle.
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Derive an expression for the spiral time constant of an aircraft.
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