JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III HELICOPTER AERODYNAMICS Previous Question Paper (February - 2023 - R18)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
What is the need for Pitch changing?
Answer
Pitch changing is essential in helicopter aerodynamics to control the magnitude and direction of the rotor thrust. By adjusting the blade pitch angle, the pilot can regulate the lift produced by the rotor system to achieve vertical flight (collective pitch change) and control the direction of the thrust vector to maneuver the helicopter in forward, backward, or lateral flight (cyclic pitch change).
Explain the term Flapping.
Answer
Flapping is the vertical oscillation of a helicopter rotor blade about a horizontal hinge or flexure, known as a flapping hinge, which allows the blade to move up and down in response to aerodynamic and inertial forces. This motion is primarily employed to balance the lift distribution across the rotor disk during forward flight.
As a helicopter moves forward, the advancing blade experiences higher relative velocity and produces more lift than the retreating blade. Flapping allows the advancing blade to rise, which increases its angle of incidence relative to the flow, thereby reducing its effective angle of attack and lift. Conversely, the retreating blade flaps down, increasing its angle of attack to compensate for lower dynamic pressure. This mechanism effectively equalizes the lift between the advancing and retreating sides, preventing the helicopter from rolling due to asymmetric lift.
Discuss briefly about constant chord.
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Define the term high performance take-off in helicopter.
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What do you mean by Induced power?
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Outline the difference between Induced power and Profile power.
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How would you identify the helicopter is in trimmed condition?
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Relate the term Speed stability.
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Write a short note on drag forces.
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List the applications of Hovercraft.
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Part B
What do you understand by Blade sailing in equivalence of feathering and flapping?
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What is the purpose of providing hinges in helicopter rotor blades? What degrees of freedom do they facilitate?
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Interpret a conventional single rotor helicopter, explain the mechanism to obtain Collective pitch and Cyclic pitch with neat sketches.
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State the technical differences between a rotary wing aircraft and a fixed wing aircraft with necessary sketches.
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Describe the flow condition through the rotor in different flow states in axial flight.
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Make use of Blade elementary theory, explain the vortex system associated with the rotary blades of a helicopter.
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Differentiate between Actuator Disc theory and Blade Element theory.
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The helicopter has a weight of 29,000 kg has a tip speed of 172 m/sec. Wake velocity for such a rotor is 22 m/sec. Evaluate the Thrust coefficient and Power coefficient based on the power estimated by momentum theory.
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State and explain the parameters which affects the rotor thrust with neat sketches.
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Using blade element theory, derive equations for thrust, torque and power for helicopter in hover.
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Illustrate the process of estimating forward flight performance of a helicopter.
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Enumerate the velocity distribution over a helicopter rotor in forward flight and hover.
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Explain the features of the fully articulated rotor system, semi rigid rotor system and rigid rotor system.
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Contrast the working principle and operation of flight control system of helicopter.
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Discuss the following terms related to VSTOL aircraft: Vertical Flight of helicopter
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Discuss the following terms related to VSTOL aircraft: Flow patterns surrounding the rotors.
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Explain hover Out-of-Ground Effect (OGE) and In-Ground Effect (IGE) with the help of neat sketches.
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Highlight the methods of lift augmentation. Explain any one method with neat sketches.
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Label the components and explain the working principle of ‘ground cushion vehicle’ known as Hovercraft.
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Make use of detailed sketches, explain forward motion of hovercraft over water and solid surface.
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