High Alpha Basics Class Presentation

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  • Slide 1 4/20/15

    Some High Alpha andHandling Qualities Aerodynamics

    W.H. Mason Configuration Aerodynamics Class

  • Slide 2 4/20/15

    Issues in Hi- Aero General Aviation

    Prevention/recovery from spins Beware: Tail Damping Power Factor (TDPF)

    Sometimes advocated for use in design Has been shown to be inadequate!

    Fighters Resistance to departure from controlled flight Carefree hi- air combat maneuvering

    Fuselage pointing Velocity vector rolls Supermaneuverability etc.

    Transports Control/prevention of pitchup and deep stall (the DC-9 case study)

  • Slide 3 4/20/15

    High Angle of Attack

    Aerodynamics are nonlinear- complicated component interactions (vortices)- depends heavily on WT data for analysis- This means critical conditions outside linear aero range

    Motion is highly dynamic - often need unsteady aero Keys issues (from a fighter designer s perspective):

    - adequate nose down pitching moment to recover- roll rate at high alpha- departure avoidance- adequate yaw control power- the role of thrust vectoring

  • Slide 4 4/20/15

    The Hi- StoryLongitudinal

    Typical unstable modern fighter the envelope is the key thing to look at

    90

    +

    -

    Cm

    Max nose up moment

    Max nose down moment

    Cm*

    Minimum Cm* allowable is an open questionIssue of including credit for thrust vectoring

    Pinch often around ~ 30-40

    0

    Suggested nose down req t: Pitch accel in 1st sec: -0.25 rad/sec2

  • Slide 5 4/20/15

    Example: F-16

    NASA TP-1538, Dec. 1979

    Found in flight, and also in tests at the NASA Full Scale Tunnel, other tunnels didn t find this, and so the design was made with this issue

    An -limiter was put in the control system to prevent pilots from going above about 28

  • Slide 6 4/20/15

    The Hi- StoryDirectional

    Cn

    +

    -

    900

    Stable

    Unstable

    Vertical Tail

    ForebodyEffect

    Config w/o V-Tail

    V-Tail in wake

    0

    Directional problem alsooften around 30

  • Slide 7 4/20/15

    Example: F-5

    -0.0050

    0.0000

    0.0050

    0.0100

    -10 0 10 20 30 40 50

    Cn

    , deg.

    Full Config.,Tail Off

    Full Config.,Vertical Tail On

    Forebody alone

    F-5 WT data: NASA TN D-7716

    Sketch from NASA TN D-7716, 1974

    Chine forebodies are even more effective!

    Above 30, the directional stability comes entirely from the forebody!

  • Slide 8 4/20/15

    Forebody Vortices

    F-5A forebody, = 40, = 5NASA CR 4465, Aug. 1992

    I m looking for a better, color, figure

    At high angles of attack, vortices form over the forebody, producing additional, possibly restoring, forces and often interacting with the rest of the airplane flowfield

  • Slide 9 4/20/15

    Illustration of Forebody Vortices and a Fix

    Laser Light Sheet Video of the RFC forebody

    X-29 forebodyTaken at the USAF Museum,

    WPAFB, Ohio

    And Flow Asymmetries: - an amazing story- solve with nose strakes

  • Slide 10 4/20/15

    Rudder Lock and the B-17 Vertical Tail Mod

    Darrol Stinton, Flying Qualities and Flight Testing of the Airplane, AIAA, 1996

    Dorsal fin added!

    Originally

  • Slide 11 4/20/15

    Vertical Tail Shaping II: Subtle Tail Changes

    Note that yaw is the negative of sideslip, thus the negative slope

    Also note good use of labels to identify effects

    Lockheed ConstitutionAviation Age MagazineFeb. 1952, pg. 37

  • Slide 12 4/20/15

    Who s on first?

    A true story from the Grumman STAC Airplane program

    The Aerodynamics group plane

    The Stability and Control Group Plane See Hendrickson, et al,AIAA Paper 1978-1452for the story

  • Slide 13 4/20/15

    Some High Alpha andHandling Qualities Aerodynamics

    Again

    W.H. Mason Configuration Aerodynamics Class

  • Slide 14 4/20/15

    The Hi- StoryLateral

    Cl

    +

    -

    900

    Stable

    Unstable

    0

    Dihedral Effect(also due to sweep) Flow Separates

    on wing

    Drooping LE deviceshelps controlseverity

  • Slide 15 4/20/15

    Example: F-4

    NASA TN D-7131, July 1973

  • Slide 16 4/20/15

    Example: F-16 Lateral/ Directional

    Control

    Conventional aero control surfaces lose effectiveness at high angles of attack

    ControlEffectivenessChange with alpha

    Cn

    Cl

    , deg

    r = 30

    r = 30

    a = -20d= -5

    a = -20d= -5

    Subscripts:r ruddera ailerond differential horizontal tail

    NASA TP 1538, Dec. 1979

  • Slide 17 4/20/15

    A way to get yaw: differential canard

    Differential deflection of the canard creates differential pressures on the side of the forebody, and hence yawing moment

    Lapins, Martorella, Klein, Meyer and Sturm, NASA CR 3738, Nov. 1983

    Grumman STAC

    See also, Re and Capone, NASA TN D-8510, July 1977

  • Slide 18 4/20/15

    Example: the Evolution of the SCAMP How and Why the modified F-16 supercruiser

    SCAMP became the F-16XL

    Talty and Caughlin, Journal of AircraftVol. 25, No. 3, March 1988, p. 206-215.

    Dave Miller & Schemensky, Design Study Results of a Supersonic Cruise Fighter Wing AIAA Paper 1979-62, Jan. 1979

    Original Concept The Final Airplane

  • Slide 19 4/20/15

    Low Speed Tests Mandated Planform ModsBaseline low speedconfiguration(note crank)

    The Apex mod

    The TE extension mod

    One more not shown: a Wing fence

    Grafton, NASA TM 85776, May 1984

  • Slide 20 4/20/15

    The F-16XL

    Note Wing Fence called a sensor fairing

    Original

    All mods combined

    WT data: Grafton, NASA TM 85776, May 1984

  • Slide 21 4/20/15

    Hi- Flight Mechanics I Departure

    Aircraft departs from controlled flight May develop into a spin

    Wing drop Uncommanded motion: asymmetric wing stall

    Typical spin entry for straight wing GA airplanes, a wing roll-off Became famous again as the F-18E Abrupt Wing Stall Problem

    Wing rock Damping characteristics generate wing roll oscillations

    Nose slice Yawing moments from airplane (mainly forebody) greater then

    rudder power May develop into a yaw-type entry into a spin

    Swept wing fighter, with totally different inertial characteristics So-called fuselage heavy , as oppose to wing heavy light

    planes

    Tumbling Typically associated with flying wings

  • Slide 22 4/20/15

    Hi- Flight Mechanics II Becomes closely integrated with flight control system Requires extensive ground and flight simulation

    From Johnston & Heffley (STI), Investigation of High-AOA Flying Qualities Criteria and Design Guides, AFWAL-TR-81-3108, Dec. 1981.

    Determinants of High a Flying Qualities Approach Example

    Aerodynamic Dominance

    Aerodynamics must provide an all around solution with respect to performance, stability and controllability FCS may give fine tuning, but is not required for basic stability and control

    F-5

    Balanced Aerodynamics and FCS

    Aerodynamic design favors performance with some regions of undesirable flying qualities. FCS necessary to enhance or provide acceptable stability and control

    F-15

    FCS Dominance Aerodynamic design favors performance FCS to provide good flying qualities up to maximum usable lift coefficient

    F-16

  • Slide 23 4/20/15

    The problem: configurations have changed from WWII

    The fuselage is longer and heavier, the wings relatively smaller

    Figure from Joe Chambers, High-Angle-of-Attack Aerodynamics:Lessons Learned, AIAA Paper 1986-1774

  • Slide 24 4/20/15

    Departure Criteria I Really need dynamic data and piloted simulation

    Needs to be connected to flight mechanics analysis Simulation math model requires massive amount of data from WT(s)

    Issue: can we do anything w/o dynamic data? Some rough approximations to get started (note inertia ratio):

    Open loop: (actually a very rough approximation): Cn dynamic > 0

    Several forms depending on coordinate system, this is essentially body axis (actually principal axis) - see Calico, Journal of Aircraft, Vol. 16, No. 12, Dec. 1979, pp 895-896.

    Comes from the lateral-directional equations of motion linearized about steady, rectilinear flight, and an examination of the resulting stability quartic (ignoring rate derivatives) see Greer, NASA TN D-6993, 1972. Essentially a Dutch Roll Approx

    Cn , dyn = Cn cos Iz Ix( )Cl sin

    Note: the classic F-16 study is Simulator Study of Stall/Post-Stall Characteristics of a Fighter Plane With Relaxed Longitudinal Static Stability, by Luat Nguyen, et al, NASA TP 1538, Dec. 1979 (pdf avail)

  • Slide 25 4/20/15

    Departure Criteria II

    Where GARI is the ratio of rudder to aileron deflection for an airplane with an aileron-rudder interconnect (ARI)

    When yaw due to aileron gets large, commanded roll produces a motion in the opposite direction!

    See AFWAL-TR-81-3108 for examples

    LCDP = Cn ClCna + GARICnrCla + GARIClr

    Closed loop: LCDP, the lateral control departure parameter > 0

    Damping derivatives: Cnr < 0 (yaw damping), but not too negative

    Clp < 0 (roll damping), to prevent wing rock

    Note: the value (and drawback) of and LCDP are that they are based on static aero coefficients

    Cn ,dyn

  • Slide 26 4/20/15

    F-16 Hi- characteristics

    NASA TP-1538, Dec. 1979

  • Slide 27 4/20/15

    F-16 LCDP and augmented LCDP

    NASA TP-1538, Dec. 1979