Presentation on theme: "A Brief Introduction to Helicopters"— Presentation transcript:
1A Brief Introduction to Helicopters Robert L. Roedts IIThe Pennsylvania State UniversityRotorcraft Center of Excellence
2What is a Helicopter? Unique Features Rotating-wing vehiclesAbility to hoverLand and take-off verticallyFly forward, backward and sidewaysHelicopters are closely related to autogyros and tiltrotors.
3MotivationThe overall unique aspect of a helicopter is it’s ability to hover for extended periods of time.The ability to hover it a very useful attribute.An good example is that of a hummingbird.
4Helicopters at WorkWith this ability to hover, helicopters can perform a wide range of missions.
5Comparison of Fixed-Wing Aircraft and Helicopters
6Comparison of Fixed-Wing Aircraft and Helicopters
7Configurations of Rotorcraft Many different ways to counter Reactive TorqueOther possibilities: Tip jets, tip mounted enginesQuestion: Why do each of these methods work?What are the likely advantages and disadvantages of each?
8Configurations of Rotorcraft Main Rotor - Tail Rotor Config.
9Configurations of Rotorcraft Tandem Rotors (Chinook)
10Configurations of Rotorcraft Coaxial Rotors (Kamov KA-52)
14High-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.
15Interactional Aerodynamics There are many ways to deal with these problems. Oneexample would be the airfoil selection.
17Ground InteractionsAt low forward speeds, less power is required.
18Airfoil DesignRotorcraft 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.
20Airfoil Design Four Rules of Rotorcraft Airfoil Design High CLmaxHigh MDDGood L/D over a wide range of Mach NumbersLow CmDesign constraints are much narrower for rotorcraft. (I.e.: Cm 0.02)Change straightforward
21Early Helicopter Airfoil Design Initially, symmetric airfoils were usedLow Pitching Moment, CmCyclic PitchJuan de la CiervaAutogyrosFirst to use a cambered airfoilResulted in a crash in 1939Crash and low torsional stiffness resulted in universal use of symmetric airfoil until the 1960s.
22The 60’s & 70’s RevolutionVast Improvements in Modern Computers allowed engineers to utilized them.Panel MethodsInviscid Solutions but still insightfulConformal Mapping introduced into computer codesReintroduction of Cambered AirfoilsComputer designImproved StructuresMore concentration on transonic effects
23The 60’s & 70’s Revolution Example: YAH-64 Apache, 1976 Heavy use of computer during design process.Reduced amount of wind tunnel testing necessaryDesign costs and time decreaseStarted with a NACA 63A-410 and ended with the HH-02
241980’s Airfoil Development Trailing Edge TabsOffset the pitching moment of a cambered airfoilBy 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.
251990’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)
262000 and Beyond Morphing Technologies Unsteady Aerodynamics Gurney FlapsKeeps flow attached in high alpha conditions.Unsteady AerodynamicsCurrent 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.
27ReferencesGessow, 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.
28Final Thought“Helicopters don’t fly. They beat the air into submission.”~ Dr. Ed Smith