Pitch Divergence Suppression of a Subscale Wing in Ground Effect (WIG) Aircraft

1
Pitch Divergence Suppression of a Subscale Wing
in Ground Effect (WIG) Aircraft

• 56th Annual AIAA Southeastern Regional Student
  Conference
• April 4-5, 2005
• Robert Love
• Auburn University

2
What is a WIG Aircraft?

• An aircraft which flies over a mostly level
  surface at a height lower than half of the span
  to use advantageous ground effect conditions

3
Advantages of WIG Aircraft

• Chord Dominated
• RAM effect increases Lift
• Span Dominated
• Reduction of wing tip vortices dramatically
  lowers induced drag
• Therefore high L/D ratios

4
History of WIG Aircraft

• Designs are extremely varied
• Early Designs
• U. S. Spruce Goose
• Russian Erkanoplans
• The KM, Lun and Orlyronk in the (1960s)
• PAR motors, strait wing
• Amphistar
• The Lippisch Design, single motor
• Airfisch 3
• L-325 Flarecraft

5
What is being done now?

• Australia
• FS-8 (with Singapore)
• Incat Wing (trimaran with WIG support)
• China
• TY-1
• XTW-4
• United States
• Boeing Pelican
• Aerocon Atlantis 1
• Germany
• Hoverwing
• X-114

6
Introduction

• Divergence due to ground effect is well known in
  other fields
• Longitudinal Stability a historic problem for WIG
  aircraft
• Sudden pitch and height changes cause divergence
• Contributors
• High thrust line, throttle cut too quickly, lack
  of inherent stability, wrong CG,
  slowness/inability to respond to pitching motions
• Caused loss of many aircraft, reputation as
  unreliable

7
Previous Approaches

• Structural Fixes
• Large Tail Wing, Canards, slats, elevators, the
  Lippisch design of the wing, S-shaped airfoils
• Disadvantages include large amounts of drag and
  little effectiveness
• Tweaking Dynamic Characteristics
• Movement of the center of pitch, center of
  gravity, and aerodynamic center
• Some success, but dependent on careful balancing

8
The Aircraft Model

• Based off of Graham Taylors MK5 WizzyWIG XGE
  plans
• Materials Used
• Balsa wood
• Carbon fiber motor mounts
• Bonding with Cyano-Acrylate Resin and Hysol 9433
• Covered with model skinning material and flashing
  tape
• Hardware
• 3 Astro 020 Direct Drive Brushless motors
• 3 Lithium Polymer Batteries
• 2 servos, 1 JR DS368 and 1 Futaba FP-S-14B
• 1 Cirrius micropiezo MPG-10 gyroscope
• Overall Size
• 2.5 lbs, 3.5 ft long, 11.5 in high, CG at 1/3rd
  of chord
• Main wing 17.5 in span by 17 in chord

9
The Aircraft Model

• Notable Features
• PAR motor mount to serve as an elevator (-5 to
  40)
• Canard wing
• Large tail wing
• Upward slope of body in front and back
• Flat main wing with sponsons
• Center of Gravity Location and connection to rig
  at this location

10
Experimental Procedure

• First Flight-free flight on January 27, 2005
  experienced divergence at low speed
• Whirl test rig made to test the longitudinal
  stability of the aircraft in a stable environment
• Test settings
• With and without maximized gain pitch rate
  feedback stabilization
• Full and Half Elevator Deflection
• Throttle setting at 2.5, 3, and 4 of 6
• Digital Video analyzed with ImagePro Analysis
  software
• velocity, divergence times, and body pitch
  attitudes

11
Results

• Effect of Rate Stabilization on Divergence Times
  for Full Elevator Deflection

12
Results
13
Results

• Divergence prevention by pitch rate feedback
  system for speed of 29.7 ft/s without gyroscope
  and 33.0 ft/s with gyroscope, at throttle 3
  settings

14
Results

• Overall View of the Effectiveness of the Pitch
  Divergence Suppression at Half Elevator with
  Pitch Rate Feedback System

15
Summary of Results

• Longitudinal instability for full elevator
• Divergence was not preventable through pitch rate
  stabilization with a gyroscope
• Longitudinal instability for half elevator
• Suppressed at speeds lower than 26 ft/s indicated
  by divergence taking three times longer than
  without stabilization
• Prevented completely at speeds higher than 30
  ft/s through pitch rate stabilization

16
Significance

• Increased thrust available to overcome hump
  drag due to higher allowable elevator settings
• Increased stability for transitioning between
  modes
• Increased maneuverability to avoid obstacles
• Increased reaction time for pilot or control
  system to prevent divergence as it starts to
  occur
• Increased pitch stiffness of aircraft without
  substantial drag penalties from large tail or
  canard wings
• Increased safety margin
• Simplified design while providing a solution to
  problem

17
Conclusion

• Divergence of a subscale wing in ground effect
  aircraft was able to be suppressed or prevented
  using a pitch rate feedback system at speeds from
  20 ft/s to 45 ft/s for an elevator disturbance
  which normally would cause divergence.

18
Thanks

• To Auburn University and Dr. Ron Barrett for
  support and technical advice
• To Christoph Burger and Adam Chesler for lab help
  and construction advice
• To Graham Taylor for the WIZZYWIG plans and
  technical advice
• To all the other employees of the Adaptive
  Aerostructures Lab for their occasional helping
  hands and encouragement

19
References

• 1. Online. Divergence. 2005. April 1, 2005.
  http//www.hypercraft-associates/divergence/diverg
  ence.htm.
• 2. Online. The Wig Page. Wing in Ground Effect
  Aerodynamics. 2005. February 14, 2005.
  http//www.se-technology.com/wig/index.php.
• 3. Online. Wing in Ground Effect Aerodynamics.
  2005. March 18, 2005. http//www.aerospaceweb.org/
  question/aerodynamics/q0130.shtml.
• 4. Online. 2005. March 18, 2005.
  http//foxxaero.homestead.com/indrad_044.html.
• 5. Taylor, G. K., Are you missing the boat? The
  Ekranoplan in the 21st Century Its Possibilities
  and Limitations. February 2002, 18th Fast Ferry
  Conference, 2002.

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Questions?