Flutter Analysis of the Polen Special II Emphasizing Addition of a Wet Wing and Ailerons to Flutter Model ASE463Q [Fall2002] Final Presentation Structural Engineers Erich Gross, Masayuki Wakamatsu Advisor: Marcus Kruger

Presentation Outline Polen Special II Background and Specs Project Motivation and Objectives Past Polen Group Work Flutter Theory AMAFALA Objectives Completed (Results) Conclusions

Polen Special II Background Outline Polen & Project background Flutter AMAFALA Results Conclusion Polen Special II Background Designed by Dennis Polen Aluminum body, cantilevered low-wing, conventional gear monoplane Designed to achieve high speed (300mph+) Development began in 1967 First flew in 1972 Currently owned by Dick Keyt Ex-Air Force, current American Airlines Pilot

Polen Special II Background Outline Polen & Project background Flutter AMAFALA Results Conclusion Designed as a racing airplane Mr. Keyt participates in various competitions A longer range would be desirable Wings are the only practical place to store additional fuel Addition of wing fuel tanks was one of the primary project objectives

Polen Special II Specifications Outline Polen & Project background Flutter AMAFALA Results Conclusion Polen Special II (Specifications courtesy of the EAA) Model Year: 1967 Engine: Lycoming TSIO-360 Horsepower: 180 hp normally aspirated, 200 hp turbocharged Number of Seats: 1 Length: 19'6“ Height: 4'10“ Wing Span: 21'5“ Gross Weight: 1,500 lbs. Max Speed: 345 mph Cruise Speed: 325 mph Service Ceiling: 28,000 feet

Critical Problem and Project Motivation: Insufficient Flutter Analysis Outline Polen & Project background Flutter AMAFALA Results Conclusion Rudder Damage Courtesy of Spring 2001 463Q group High frequency rudder flutter occurred during a low-pass fly-by Fortunately, Mr. Keyt landed safely Mr. Keyt requested a flutter analysis from the ASE department at UT Austin Project has been developed since Fall 2000

Past Polen Groups’ Works Outline Polen & Project background Flutter AMAFALA Results Conclustion Fall 2000 & Spring 2001 (Not Accessible) GVT, Modal Studies Summer 2001 AMAFALA user manual & initial input files Fall 2001 Revision of input files & wing tip EI and GJ Spring 2002 Completed general Polen Models

Project Objectives Research flutter and analyze past data Outline Polen & Project background Flutter AMAFALA Results Conclusion Research flutter and analyze past data Learn AMAFALA Add components to the Polen model Ailerons (Case 1) Fuel Tanks [Wet Wing] (Case 2, Case 3)

Team Organization Outline Dr. Ronald Stearman Marcus Kruger Polen & Project background Flutter AMAFALA Results Conclusion Team Organization Dr. Ronald Stearman Consultant Department of Aerospace Engineering and Engineering Mechanics The University of Texas at Austin Marcus Kruger Adviser Masayuki Wakamatsu Theoretical Research Past Group Data Analysis AMFAFALA Editing Erich Gross Team Leader Team Organization AMAFALA Editing Javier Fuentealba AMAFALA Consultant

Phenomena of Flutter (Flutter Theory) Outline Polen & Project background Flutter AMAFALA Results Conclusion Definition: a self excited vibration of a flexible body [ASE355 notes] Imagine a ball in these conditions   a) Stable b) Neutral c) Unstable Flutter speed is defined as a minimum (neutral condition) speed at flutter occurs  

Flutter Video! Outline Polen & Project background Flutter AMAFALA Results Conclusion Flutter Video! Courtesy of www.airspacemag.com

Causes of Flutter (Flutter Theory) Outline Polen & Project background Flutter AMAFALA Results Conclusion Inability of an airframe to dissipate energy to the airstreams Airframe—elastic; deflects due to bending and torsion New geometry - new aerodynamic force And so on…

To find the Flutter Speed Outline Polen & Project background Flutter AMAFALA Results Conclusion Eigenvalue problems i.e. seek the flutter speed and frequency Structural Analysis and Aerodynamics V-g Method

To find the Flutter Speed (V-g method) Outline Polen & Project background Flutter AMAFALA Results Conclusion g: artificial structural damping (< 0.033) Mach number and altitude are held constant V-g plot shows when flutter may occur AMAFALA outputs a V-g plot

Flutter: Symmetric VS Antisymmetric Outline Polen & Project background Flutter AMAFALA Results Conclusion Two primary flutter conditions of interest: symmetric and antisymmetric (a) symmetric (b) Antisymmetric For aileron flutter, we are concerned with the antisymmetric case because ailerons are designed to deflect antisymmetrically We need to look at both symmetric and antisymmetric cases to assess the changes caused by the new fuel tanks

AMAFALA (Airplane Modal Aerodynamic Flutter And Loads Analysis) A text-based flutter analysis program Past 463Q teams worked with it This is the main tool that we used in our analysis Hard to learn- took two years for past groups to run the program We modified existing input files created by Javier Fuentealba rather than creating new ones Outline Polen & Project background Flutter AMAFALA Results Conclusion

AMAFALA (Airplane Modal Aerodynamic Flutter And Loads Analysis) Outline Polen & Project background Flutter AMAFALA Results Conclusion AMAFALA Inputs Geometric Data (layout of wing) Mass Data (inertial strips) Stiffness Data (inertial strips) Aerodynamic Data AMAFALA Outputs Mode Frequencies Mode Shapes V-g Plots

Wing Input File Overview Outline Polen & Project background Flutter AMAFALA Results Conclusion Input file contains geometric and mass data required to model the flutter characteristics of the wing Original input file was complete except for the addition of ailerons and wing fuel tanks We modified the original wing input file by adding the ailerons and fuel tanks to the wing

Wing Input File Overview Visual Representation of Data Contained in Wing Input File New wing tanks Aileron Aileron CG

Results: Case 1 (Original, Antisymmetric Condition) Outline Polen & Project background Flutter AMAFALA Results Conclusion No flutter occurrence is indicated for this condition

Results: Case 1 (with Ailerons, Antisymmetric Condition) Outline Polen & Project background Flutter AMAFALA Results Conclusion Flutter occurs at roughly 350 knots

Results: Case 2 (New Fuel Tanks, Antisymmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks empty Note: This is identical to Case 1 Flutter occurs at roughly 350 knots

Results: Case 2 (New Fuel Tanks, Antisymmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks half full Flutter occurs at roughly 290 knots 60 knots slower than for no additional tank case

Results: Case 2 (New Fuel Tanks, Antisymmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks full Flutter speed has fallen to 190-200 knots Flutter is being induced!

Results: Case 3 (Fuel, Symmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks empty Flutter occurs at roughly 350 knots

Results: Case 3 (Fuel, Symmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks half full Flutter speed has fallen to 200 knots (conservative) Realistically, flutter speed is probably closer to 275 knots

Results: Case 3 (Fuel, Symmetric) Outline Polen & Project background Flutter AMAFALA Results Conclusion New fuel tanks full Flutter speed is now approximately 250-260 knots Flutter speed is decreasing as fuel is added

Conclusions Case 1 [aileron, antisymmetric] Outline Polen & Project background Flutter AMAFALA Results Conclusion Case 1 [aileron, antisymmetric] Flutter occurs at around 350 knots Case 2 [antisymmetric, new fuel tanks] Case 3 [symmetric, new fuel tanks] Flutter speed decreases with the addition of fuel to the new tanks This is counterintuitive and undesirable Centers of gravity for the new tanks must be moved closer to the wing leading edge This will mean less fuel can be carried in the wing

Conclusion (Recommendations) Outline Polen & Project background Flutter AMAFALA Results Conclusion Learn AMAFALA ASAP Develop more precise wet wing model i.e, get more information about the structure of the wing and edit wing file accordingly Develop an external fuel tank mode

Questions?