Pitch Divergence Suppression Pitch Divergence Suppression of a Subscale Wing in Ground of a Subscale Wing in Ground

Effect (WIG) AircraftEffect (WIG) Aircraft

5656thth Annual AIAA Southeastern Regional Student Conference Annual AIAA Southeastern Regional Student ConferenceApril 4-5, 2005April 4-5, 2005

Robert LoveRobert LoveAuburn UniversityAuburn University

What is a WIG Aircraft?What is a WIG Aircraft?

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

Advantages of WIG AircraftAdvantages of WIG Aircraft

Chord DominatedChord Dominated– ““RAM” effect increases RAM” effect increases

LiftLift

Span DominatedSpan Dominated– Reduction of wing tip Reduction of wing tip

vortices dramatically vortices dramatically lowers induced draglowers induced drag

Therefore high L/D Therefore high L/D ratiosratios

History of WIG AircraftHistory of WIG Aircraft

Designs are extremely Designs are extremely variedvariedEarly DesignsEarly Designs– U. S. “Spruce Goose”U. S. “Spruce Goose”– Russian “Erkanoplans”Russian “Erkanoplans”

The KM, Lun and Orlyronk The KM, Lun and Orlyronk in the (1960’s)in the (1960’s)

PAR motors, strait wingPAR motors, strait wing– AmphistarAmphistar

The Lippisch Design, The Lippisch Design, single motorsingle motor– Airfisch 3Airfisch 3– L-325 FlarecraftL-325 Flarecraft

What is being done now?What is being done now?

AustraliaAustralia– FS-8 (with Singapore)FS-8 (with Singapore)– Incat Wing (trimaran with Incat Wing (trimaran with

WIG support)WIG support)

ChinaChina– TY-1TY-1– XTW-4XTW-4

United StatesUnited States– Boeing PelicanBoeing Pelican– Aerocon Atlantis 1Aerocon Atlantis 1

GermanyGermany– HoverwingHoverwing– X-114X-114

IntroductionIntroduction

Divergence due to ground Divergence due to ground effect is well known in effect is well known in other fieldsother fieldsLongitudinal Stability a Longitudinal Stability a historic problem for WIG historic problem for WIG aircraftaircraft– Sudden pitch and height Sudden pitch and height

changes cause divergencechanges cause divergence– ContributorsContributors

High thrust line, throttle High thrust line, throttle cut too quickly, lack of cut too quickly, lack of inherent stability, wrong inherent stability, wrong CG, slowness/inability to CG, slowness/inability to respond to pitching respond to pitching motionsmotions

– Caused loss of many Caused loss of many aircraft, reputation as aircraft, reputation as unreliableunreliable

Previous ApproachesPrevious Approaches

Structural FixesStructural Fixes– Large Tail Wing, Canards, slats, elevators, the Large Tail Wing, Canards, slats, elevators, the

Lippisch design of the wing, S-shaped airfoilsLippisch design of the wing, S-shaped airfoils– Disadvantages include large amounts of drag and Disadvantages include large amounts of drag and

little effectiveness little effectiveness

Tweaking Dynamic CharacteristicsTweaking Dynamic Characteristics– Movement of the center of pitch, center of gravity, and Movement of the center of pitch, center of gravity, and

aerodynamic centeraerodynamic center– Some success, but dependent on careful balancingSome success, but dependent on careful balancing

The Aircraft ModelThe Aircraft Model

Based off of Graham Taylor’s MK5 WizzyWIG XGE plansBased off of Graham Taylor’s MK5 WizzyWIG XGE plansMaterials UsedMaterials Used– Balsa woodBalsa wood– Carbon fiber motor mountsCarbon fiber motor mounts– Bonding with Cyano-Acrylate Resin and Hysol 9433Bonding with Cyano-Acrylate Resin and Hysol 9433– Covered with model skinning material and flashing tapeCovered with model skinning material and flashing tape

HardwareHardware– 3 Astro 020 Direct Drive Brushless motors3 Astro 020 Direct Drive Brushless motors– 3 Lithium Polymer Batteries3 Lithium Polymer Batteries– 2 servos, 1 JR DS368 and 1 Futaba FP-S-14B2 servos, 1 JR DS368 and 1 Futaba FP-S-14B– 1 Cirrius micropiezo MPG-10 gyroscope1 Cirrius micropiezo MPG-10 gyroscope

Overall SizeOverall Size– 2.5 lbs, 3.5 ft long, 11.5 in high, CG at 1/32.5 lbs, 3.5 ft long, 11.5 in high, CG at 1/3rdrd of chord of chord– Main wing 17.5 in span by 17 in chordMain wing 17.5 in span by 17 in chord

The Aircraft ModelThe Aircraft Model

Notable FeaturesNotable Features– PAR motor mount to serve PAR motor mount to serve

as an elevator (-5° to 40°)as an elevator (-5° to 40°)– Canard wingCanard wing– Large tail wingLarge tail wing– Upward slope of body in Upward slope of body in

front and backfront and back– Flat main wing with Flat main wing with

sponsonssponsons– Center of Gravity Location Center of Gravity Location

and connection to rig at this and connection to rig at this locationlocation

Experimental ProcedureExperimental Procedure

First Flight-free flight on First Flight-free flight on January 27, 2005 experienced January 27, 2005 experienced divergence at low speeddivergence at low speedWhirl test rig made to test the Whirl test rig made to test the longitudinal stability of the longitudinal stability of the aircraft in a stable environmentaircraft in a stable environmentTest settingsTest settings– With and without maximized With and without maximized

gain pitch rate feedback gain pitch rate feedback stabilizationstabilization

– Full and Half Elevator Full and Half Elevator DeflectionDeflection

– Throttle setting at 2.5, 3, and 4 Throttle setting at 2.5, 3, and 4 of 6of 6

Digital Video analyzed with Digital Video analyzed with ImagePro Analysis software ImagePro Analysis software – velocity, divergence times, velocity, divergence times,

and body pitch attitudes and body pitch attitudes

ResultsResults

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

0

0.5

1

1.5

2

2.5

3

3.5

4

15 17 19 21 23 25 27 29 31

Flight Speed, Vflt (ft/s)

Div

erg

en

ce

Tim

e (

s)

Without Stabilization

With Stabilization

ResultsResults

ResultsResults

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

ResultsResults

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

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50

Flight Speed, Vflt (ft/s)

Ele

va

tor

Tim

e H

eld

, t (

se

c.)

WithoutFeedback,DivergenceTime

WithFeedback,DivergenceTime

NoDivergence(withfeedback)

Poly.(WithoutFeedback,DivergenceTime)

Summary of ResultsSummary of Results

Longitudinal instability for full elevatorLongitudinal instability for full elevator– Divergence was not preventable through pitch Divergence was not preventable through pitch

rate stabilization with a gyroscoperate stabilization with a gyroscope

Longitudinal instability for half elevatorLongitudinal instability for half elevator– Suppressed at speeds lower than 26 ft/s Suppressed at speeds lower than 26 ft/s

indicated by divergence taking three times indicated by divergence taking three times longer than without stabilizationlonger than without stabilization

– Prevented completely at speeds higher than Prevented completely at speeds higher than 30 ft/s through pitch rate stabilization30 ft/s through pitch rate stabilization

SignificanceSignificanceIncreased thrust available to overcome “hump drag” due Increased thrust available to overcome “hump drag” due to higher allowable elevator settingsto higher allowable elevator settingsIncreased stability for transitioning between modesIncreased stability for transitioning between modesIncreased maneuverability to avoid obstaclesIncreased maneuverability to avoid obstaclesIncreased reaction time for pilot or control system to Increased reaction time for pilot or control system to prevent divergence as it starts to occurprevent divergence as it starts to occurIncreased “pitch stiffness” of aircraft without substantial Increased “pitch stiffness” of aircraft without substantial drag penalties from large tail or canard wingsdrag penalties from large tail or canard wingsIncreased safety marginIncreased safety marginSimplified design while providing a solution to problemSimplified design while providing a solution to problem

ConclusionConclusion

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

ThanksThanks

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

ReferencesReferences

1. Online. “Divergence”. 2005. April 1, 2005. http://www.hypercraft-1. Online. “Divergence”. 2005. April 1, 2005. http://www.hypercraft-associates/divergence/divergence.htm.associates/divergence/divergence.htm.2. Online. The Wig Page. “Wing in Ground Effect Aerodynamics.” 2. Online. The Wig Page. “Wing in Ground Effect Aerodynamics.” 2005. February 14, 2005. 2005. February 14, 2005. http://www.se-technology.com/wig/index.php. http://www.se-technology.com/wig/index.php. 3. Online. “Wing in Ground Effect Aerodynamics.” 2005. March 18, 3. Online. “Wing in Ground Effect Aerodynamics.” 2005. March 18, 2005. 2005. http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml.http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml.4. Online. 2005. March 18, 2005. 4. Online. 2005. March 18, 2005. http://foxxaero.homestead.com/indrad_044.html.http://foxxaero.homestead.com/indrad_044.html. 5. Taylor, G. K., “Are you missing the boat? The Ekranoplan in the 5. Taylor, G. K., “Are you missing the boat? The Ekranoplan in the 2121stst Century Its Possibilities and Limitations”. February 2002, 18 Century Its Possibilities and Limitations”. February 2002, 18 thth Fast Ferry Conference, 2002.Fast Ferry Conference, 2002.

Questions?Questions?