AERSP 407 and AERSP 504 Aerodynamics of V/STOL Aircraft

PENNSTATE

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Kenneth S. Brentner Department of Aerospace Engineering The Pennsylvania State University

Kenneth S. Brentner, Dept. of Aerospace Engineering 1

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AERSP 407 and 504 1 8 5 5

Goals: To introduce and study key concepts related to aerodynamic loads, vehicle performance, basic rotor dynamics, and control of helicopters and tilt-rotor aircraft. Time: Monday, Wednesday, Friday: 1:25-2:15pm Place: 151 Willard Building Instructor: Dr. Kenneth S. Brentner 233 D Hammond Building Tel: (814) 865-6433 Email: [email protected] Office Hours: Monday and Wednesday 10:30-11:30am; by appointment; I also have an open door policy.

Kenneth S. Brentner, Dept. of Aerospace Engineering 2

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Reference Materials 1 8 5 5

Textbook: Principles of Helicopter Aerodynamics, J. Gordon Leishman

I will be basing lecture note primarily on this book.

Other Good References: Aerodynamics of V/STOL Flight, B. W. McCormick, Jr. Helicopter Theory, W. Johnson Rotary-Wing Aerodynamics, W. Z. Stepniewski and C. N. Keys Aerodynamics of the Helicopter, A. Gessow and G. C. Meyers

Kenneth S. Brentner, Dept. of Aerospace Engineering 3

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Outline 1 8 5 5

1. Introduction (also read Chapter 1) 2. Fundamentals of Rotor Aerodynamics (Chapter 2) 3. Blade Element Analysis (Chapter 3) 4. Blade Motion and Rotor Control (Chapter 4) 5. Basic Helicopter Performance (Chapter 5) 6. Conceptual Design of Helicopters (first part of Chapter 6) 7. Introduction to Unsteady Aerodynamics, Dynamic Stall, and Rotor Wakes – time permitting (portions of Chapters 7-10)

This is my first time teaching this course, so I don’t have dates for when we will cover each of the sections.

Kenneth S. Brentner, Dept. of Aerospace Engineering 4

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Grading – AERSP 407 1 8 5 5

Homework and computer assignments – 35% Approximately 7-8 assignments Mid-term exam 20% in class 10% take-home tentatively Oct 21, 2005 Final exam - 35% Term paper - extra credit

Kenneth S. Brentner, Dept. of Aerospace Engineering 5

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Grading – AERSP 504 1 8 5 5

Homework and computer assignments – 20% Mid-term exam 20% in class 10% take-home tentatively Oct 21, 2005 Final exam – 35% Term paper and presentation – 15% Topic due Sept. 30 Outline due Oct. 28 Paper due Nov 23 Presentations – sometime during last two weeks of class.

Kenneth S. Brentner, Dept. of Aerospace Engineering 6

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Academic Integrity 1 8 5 5

Faculty Senate Rule 49-20 states, in part, "Academic integrity is the pursuit of scholarly activity free from fraud and deception and is an educational objective of this institution." Faculty are required to clarify the application of this rule to each course: You are encouraged to study together and to discuss the homework assignments, but the work that you submit for grading must be your own. Acts of academic dishonesty will result in either a grade of zero for an assignment, or an F for the course.

If you have any questions about this, please feel free to talk to me first – this will avoid any problems.

Kenneth S. Brentner, Dept. of Aerospace Engineering 7

PENNSTATE About Your Instructor: Kenneth S. Brentner 1 8 5 5

Education BS Aeronautics and Astronautics, Purdue University – 1983 MS Aerodynamics, The George Washington University – 1987 Ph.D. Acoustics, University of Cambridge (UK) – 1991 (J.E. Ffowcs Williams, advisor)

Experience (1983 – 2000) Senior Research Engineer at NASA Langley Research Center Rotorcraft Acoustics Computational Aeroacoustics Author of WOPWOP rotorcraft noise prediction program (2000 – present) Associate Professor at The Pennsylvania State University, Department of Aerospace Engineering Personal

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Today’s Lecture 1 8 5 5

Introduction to Course Administration Motivation Introduction to Helicopter Lay ground work for Helicopter Aerodynamics

Kenneth S. Brentner, Dept. of Aerospace Engineering 9

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What is a Helicopter? 1 8 5 5

Leishman “Helicopters are highly capable and useful rotating-wing vehicles that have a variety of civilian and military applications. Their usefulness lies in their unique ability to take off and land vertically, to hover stationary to the ground, and to fly forward, backwards, or sideways. These unique flying qualities, however, come at a price, including complex aerodynamic problems, significant vibrations, high levels of noise, and relatively large power requirements compared to fixed-wing aircraft.” Unique features: Rotating-wing vehicles Ability to hover Land and take off vertically Fly forward, backward, and sideways Helicopters are closely related to autogiros and tiltrotors

Kenneth S. Brentner, Dept. of Aerospace Engineering 10

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Introduction and Motivation 1 8 5 5

A unique aspect of a helicopter is its ability to hover. The ability to hover is a very useful attribute Example: A hummingbird is able to feed on the nectar in flowers by hovering for several seconds at a time.

Photo: Luiz Claudio Marigo

Kenneth S. Brentner, Dept. of Aerospace Engineering 11

PENNSTATE Introduction: Helicopters at Work 1 8 5 5

Helicopters perform a wide range of missions that benefit from this unique capability (hover or vertical lift)

Executive Transport

Scheduled Passenger Service

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6 PENNSTATE Introduction: Helicopters at Work 1 8 5 5

Medical evacuation

source: www.hmc.psu.edu/lifelion

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PENNSTATE Introduction: Helicopters at Work 1 8 5 5 Aerial Logging Aerial fire fighting

source: helispot.com

Kenneth S. Brentner, Dept. of Aerospace Engineering Pacific Rotors Magazine 14

7 PENNSTATE Introduction: Helicopters at Work 1 8 5 5

Heavy Lift (tiltrotor in helicopter mode)

Agricultural: crop spraying

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PENNSTATE Introduction: Helicopters at Work 1 8 5 5

Military Helicopters

Boeing AH-64

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8 PENNSTATE Comparison of Fixed-Wing Aircraft and Helicopters 1 8 5 5

Fixed Wing Aircraft Helicopter Wings produce lift and roll Rotor control Produces lift Engines produce thrust Produces thrust Tail – primarily for directional Produces directional and pitch control control AND – unbalanced torque! Primary functions and controls Lift, Thrust, and Control are all are decoupled coupled in a helicopter

Kenneth S. Brentner, Dept. of Aerospace Engineering 17

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Unique Helicopter Problems 1 8 5 5

1. Rotor Torque 2. Unequal Lift 3. Higher Power Requirements More power required than a F/W aircraft at any forward velocity Turbine engines; composites; improved rotor airfoils all helped 4. Control Tilting of thrust vector (mechanically difficult) Swashplate and cyclic pitch Cross coupling of motions (pitch, roll, yaw, etc.) 5. Structural Weight 6. Vibration and Dynamics Issues 7. Interactional Aerodynamics 8. Costs and Complexity Direct Operating Costs (DOC) of helicopter is significantly higher than fixed-wing aircraft Maintenance hours / flight hour also higher

Kenneth S. Brentner, Dept. of Aerospace Engineering 18

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Rotor Torque Control 1 8 5 5

Ways of countering the Reactive Torque

Other possibilities: Tip jets, tip mounted engines

Question: Why do each of these methods work? What are the likely advantages and disadvantages of each?

Kenneth S. Brentner, Dept. of Aerospace Engineering 19

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Main Rotor - Tail Rotor Configuration 1 8 5 5

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Tandem Rotors (Chinook) 1 8 5 5

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Coaxial Rotors (Kamov KA-52) 1 8 5 5

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NOTAR Helicopter 1 8 5 5

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NOTAR Concept 1 8 5 5

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Tilt Rotor (BA 609) 1 8 5 5

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Unequal Lift Distribution 1 8 5 5

VRVtip =Ω + ∞

VRVtip = Ω−∞

VRtip = Ω

Lift ~ V2

Kenneth S. Brentner, Dept. of Aerospace Engineering Ref: Principles of Helicopter Aerodynamics, J. Gordon Leishman 26

13 PENNSTATE High-Speed Forward Flight Limitations 1 8 5 5

As the forward speed increases, advancing side experiences shock effects, retreating side stalls. This limits thrust available. Vibrations go up, because of the increased dynamic pressure, and increased harmonic content. Shock noise goes up. Fuselage drag increases, and parasite power consumption goes up as V3. We need to understand and accurately predict the air loads in high speed forward flight.

Kenneth S. Brentner, Dept. of Aerospace Engineering 27

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Interactional Aerodynamics 1 8 5 5

The aerodynamic environment for a helicopter rotor is complex – rotor aerodynamics important for: Performance Structural Analysis Dynamics Flight Dynamics Acoustics …

This is my area of research

Kenneth S. Brentner, Dept. of Aerospace Engineering 28

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Next Time 1 8 5 5

Read Chapter 1 We will start on Momentum Theory for a hovering rotor

Kenneth S. Brentner, Dept. of Aerospace Engineering 29