Document
X - 57 and Whirl Flutter Discussion
Kia Miller and Roger Truax Aerostructures Branch NASA Armstrong Flight Research Center Edwards, CA Aerospace Flutter & Dynamics Council Spring 2018 Savannah, GA
Whirl Flutter Background
• Whirl flutter is most commonly associated with
Lockheed’s Electra fatal mishap
• Research, testing and new analysis techniques
seemed to solve the issue (1960s)
• Propeller propulsion is still an area of interest today
– Advanced propellers a current area of CFD research
– Electrically enhanced propulsion seems to be an area of
interest in the industry
• Whirl flutter research seemed to cap out in the
1960s, yet our computational capabilities have
greatly increased
Photo Credit: NASA
X - 57 Objectives and Tecnam P2006T/Wing Overlay
Primary Objective Cruise Motor • Goal: 5x Lower Energy Use (Compared to Original P2006T @ 175 mph) X - 57 Wing • Internal Combustion Engine vs Electric Ribs/Spars Propulsion Efficiency changes from 28% to 92% (~3.3x) • Synergistic Integration • Propulsion airframe integration provides higher cruise motor efficiency and cruise optimized wing Hi - lift Motors Pod Structure Derivative Objectives • ~30% Lower Total Operating Cost • Zero In - flight Carbon Emissions P2006T Wing Secondary Objectives • 15 dB Lower community noise P2006T Fuselage • Flight control redundancy and robustness (As Delivered) • Improved ride quality X - 57 Key Partners: • Certification basis for Distributed Electric NASA ARFC, NASA LaRC Propulsion (DEP) technologies Empirical Systems Aerospace ( ESAero ) Xperimental LLC, CA.
X - 57 Project Approach
Mod 1 Mod 3 DEP wing development and Mod 2 fabrication Ground validation of DEP high lift system Mod 4 Ground and flight test validation of electric Flight testing of motors, battery, and Flight test electric motors baseline Tecnam Flight test with integrated DEP instrumentation.
relocated to wingtips on P2006T motors and folding props DEP wing including (cruise motors remain in wing - nacelles (but no DEP Goals: tips).
motors, controllers, or Goals: • Establish Baseline folding props).
• Establish Electric Power Tecnam Performance System Flight Safety • Pilot Familiarity • Establish Electric Tecnam Retrofit Baseline Mod 1 Achieves Secondary Objectives Achieves Primary Objective of • DEP Acoustics Testing High Speed Cruise Efficiency Mod 2 • Low Speed Control Robustness • Certification Basis of DEP Technologies Mod 3 Mod 4
Challenges Involving Whirl Flutter
Challenges Involving Whirl Flutter
• Variable prop effects on whirl
modes and flutter margins
• Electric motors have less
vibrations, but motor mount
dampers tend to stabilize whirl
flutter
• Should blade frequencies
effect flutter results?
Challenges Involving Whirl Flutter
• Standard modal testing
acquires pitch and yaw of prop
system
• Gyroscopic whirl modes not
included in ground testing
• Characterizing the damping of
the engine mount requires
environmental chamber testing
Challenges Involving Whirl Flutter
• Flight test planning with
variable speed motors and
variable blade pitch
• Monitoring flight data with
harmonics
• Monitoring flight data with EMI
Challenges Involving Whirl Flutter
• Are there future needs in the
field?
• Can the aircraft industry benefit
from active suppression or
smart materials?
Discussion: Challenges Involving Whirl Flutter
Thank you.
Kia Miller Roger Truax kia.d.miller@nasa.gov roger.a.truax@nasa.gov 661.276.3712 661.276.2230 Aerostructures Branch NASA Armstrong Flight Research Center Edwards, CA