1. A Brief Introduction to Helicopters
Robert L. Roedts II
The Pennsylvania State University
Rotorcraft Center of Excellence

2. Helicopter Flight for Beginners Video

3. What is a Helicopter? Unique Features
Rotating-wing vehicles
Ability to hover
Land and take-off vertically
Fly forward, backward and sideways
Helicopters are closely related to autogyros and tiltrotors.

4. Motivation
The overall unique aspect of a helicopter is it’s ability to hover for extended periods of time.
The ability to hover is a very useful attribute.
A good example is that of a hummingbird.

5. Helicopters at Work
With this ability to hover, helicopters can perform a wide range of missions.

6. Comparison of Fixed-Wing Aircraft and Helicopters

7. Comparison of Fixed-Wing Aircraft and Helicopters

9. Configurations of Rotorcraft
Many different ways to counter 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?

10. Configurations of Rotorcraft Main Rotor - Tail Rotor Config.

11. Configurations of Rotorcraft Tandem Rotors (Chinook)

12. Configurations of Rotorcraft Coaxial Rotors (Kamov KA-52)

13. Configurations of Rotorcraft NOTAR Helicopter

14. Configurations of Rotorcraft Tilt Rotor (BA 609)

15. Unequal Lift Distribution
Lift ~ V2

16. High-Speed Forward Flight Limitations
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.

17. Interactional Aerodynamics
There are many ways to deal with these problems. One
example would be the airfoil selection.

18. Rotor Descent States

19. Ground Interactions
At low forward speeds, less power is required.

20. Airfoil Design
Rotorcraft present an interesting problem for airfoil design.
Fixed Wing Aircraft can be designed for certain conditions.
The Rotorcraft environment changes rapidly as the blade travels around the rotor disk.
Separate slides for pictures.

21. Airfoil Design
Reynolds Number and Mach Number

22. Airfoil Design Four Rules of Rotorcraft Airfoil Design
High CLmax
High MDD
Good L/D over a wide range of Mach Numbers
Low Cm
Design constraints are much narrower for rotorcraft. (I.e.: Cm  0.02)
Change straightforward

23. Early Helicopter Airfoil Design
Initially, symmetric airfoils were used
Low Pitching Moment, Cm
Cyclic Pitch
Juan de la Cierva
Autogyros
First to use a cambered airfoil
Resulted in a crash in 1939
Crash and low torsional stiffness resulted in universal use of symmetric airfoil until the 1960s.

24. The 60’s & 70’s Revolution
Vast Improvements in Modern Computers allowed engineers to utilized them.
Panel Methods
Inviscid Solutions but still insightful
Conformal Mapping introduced into computer codes
Reintroduction of Cambered Airfoils
Computer design
Improved Structures
More concentration on transonic effects

25. The 60’s & 70’s Revolution Example: YAH-64 Apache, 1976
Heavy use of computer during design process.
Reduced amount of wind tunnel testing necessary
Design costs and time decrease
Started with a NACA 63A-410 and ended with the HH-02

26. 1980’s Airfoil Development
Trailing Edge Tabs
Offset the pitching moment of a cambered airfoil
By simple application of thin-airfoil theory, one may see the effect.
Research showed that these tabs led to a small increase in drag and little effect on lift.

27. 1990’s Development Change blade geometries
British Experimental Rotor Program (BERP)
Developed to deal with tip effects on blade.
Transonic Effects (Advancing Side)
High Alpha Stall (Retreating Side)

28. 2000 and Beyond Morphing Technologies Unsteady Aerodynamics
Gurney Flaps
Keeps flow attached in high alpha conditions.
Unsteady Aerodynamics
Current design methods assume static CLmax & Cm as in a steady flow condition.
With blade wake interactions, this is not the case.
Current research is concentrated in this area where a N-S solver will be used along side the Eppler code to design airfoils.

29. References
Gessow, A. and Myers, G.C., Aerodynamics of the Heilcopter, 3rd Edition, College Park Press, College Park, MD, 1999.
J. Seddon, Basic Helicopter Aerodynamics, 2nd Edition, AIAA, Washington, DC, 2001.
Leishman, J. G., Principles of Helicopter Aerodynamics, 2nd Edition, Cambridge University Press, New York, NY, 2005.
McCormick, B. W., Aerodynamics of V/STOL Flight, Academic Press, Inc., New York, NY, 1967.
Johnson, W. Helicopter Theory, Princeton University Press, Princeton, NJ, 1980.

30. Final Thought
“Helicopters don’t fly. They beat the air into submission.”
~ Dr. Ed Smith