Benchtop and rotating tests of a fluidic flexible matrix composite lag damper for stiff-inplane hingeless rotor blades
Open Access
- Author:
- Lanari, Valentin
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 15, 2020
- Committee Members:
- Edward Smith, Thesis Advisor/Co-Advisor
Christopher D. Rahn, Thesis Advisor/Co-Advisor
Jose Palacios, Committee Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Fluidic flexible matrix composite
lag damper
hingeless
stiff-inplane
soft-inplane
rotor blade
lead-lag
damped absorber
benchtop
rotor stand
experimental testing
Adverse environment rotor test stand - Abstract:
- High speed coaxial rotor configurations often integrate stiff-inplane hingeless blades to address safety issues of the design. Due to the small lead-lag deflections at the blade root in these rotor configurations, traditional damping solutions are not effective. Fluidic Flexible Matrix Composite (F2MC) dampers have been investigated for their light weight and high pumping authority at small strain levels. A coupled F2MC damped absorber was modeled and early benchtop testings were conducted showing 10% damping performance of the technology. In this research, the damping treatment simulation has been extended to a full scale soft-inplane blade showing a damping improvement of the first lag mode to = 14.8%. Additionally, tests of the F2MC damped absorber prototype are further explored on a small-scale stiff-inplane rotor blade (1.4/rev). For the first time, the technology efficacy is tested in a rotating environment. A remote motor-controlled excitation method is designed to excite the blade lead-lag motion. A high torque stepper motor pulls a Kevlar chord rigidly attached to the blade and quickly releases the chord to produce a transient response at the first chordwise natural frequency. Bending strain at the root and fluid internal pressure are measured via a slip ring to identify the damping improvement of the F2MC damped absorber in a rotating environment. Benchtop testing measured a dramatic increase in first lag mode damping with F2MC treatment, from = 0.5% baseline damping ratio to = 9.5%, consistent with the frequency response measurements using a shaker and laser vibrometer that are not possible on the rotating test stand. Rotating blade tests also demonstrate higher damping with the F2MC treatment when compared to the untreated blade. Under the tuned condition at 140 RPM, the F2MC damped absorber demonstrate a damping ratio of the first lead-lag mode up to = 10.5% when compared to the blade without active lag damper where the measured damping is only = 3.5%. Pressure measurements also demonstrate the higher damping of the F2MC treated blade. The system performance outside its tuned condition is studied varying the rotor RPM from 130 RPM to 210 RPM. Results showed only a 2.5% drop in the damping ratio of the F2MC treated blade when operating far from the tuned condition.