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

Helicopter Flight for Beginners Video

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.

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.

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

Comparison of Fixed-Wing Aircraft and Helicopters

Comparison of Fixed-Wing Aircraft and Helicopters

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?

Configurations of Rotorcraft Main Rotor - Tail Rotor Config.

Configurations of Rotorcraft Tandem Rotors (Chinook)

Configurations of Rotorcraft Coaxial Rotors (Kamov KA-52)

Configurations of Rotorcraft NOTAR Helicopter

Configurations of Rotorcraft Tilt Rotor (BA 609)

Unequal Lift Distribution Lift ~ V2

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.

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

Rotor Descent States

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

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.

Airfoil Design Reynolds Number and Mach Number

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

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.

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

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

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.

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)

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.

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.

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