Transcript Pitch Divergence Suppression of a Subscale Wing in Ground

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
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
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
History of WIG Aircraft
Designs are extremely
varied
Early Designs
– U. S. “Spruce Goose”
– Russian “Erkanoplans”
The KM, Lun and Orlyronk
in the (1960’s)
PAR motors, strait wing
– Amphistar
The Lippisch Design,
single motor
– Airfisch 3
– L-325 Flarecraft
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
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
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
The Aircraft Model
Based off of Graham Taylor’s 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
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
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
Results
4
3.5
Divergence Time (s)
3
2.5
Without Stabilization
With Stabilization
2
1.5
1
0.5
0
15
17
19
21
23
25
27
29
31
Flight Speed, Vflt (ft/s)
Effect of Rate Stabilization on Divergence Times for Full
Elevator Deflection
Results
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
Results
20
18
Elevator Time Held, t (sec.)
16
Without
Feedback,
Divergence
Time
14
12
With
Feedback,
Divergence
Time
10
8
No
Divergence
(with
feedback)
6
Poly.
(Without
Feedback,
Divergence
Time)
4
2
0
0
10
20
30
40
50
Flight Speed, Vflt (ft/s)
Overall View of the Effectiveness of the Pitch Divergence
Suppression at Half Elevator with Pitch Rate Feedback System
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
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
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.
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
References
1. Online. “Divergence”. 2005. April 1, 2005. http://www.hypercraftassociates/divergence/divergence.htm.
2. Online. The Wig Page. “Wing in Ground Effect Aerodynamics.”
2005. February 14, 2005. http://www.setechnology.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.
Questions?