Effect of limited amplitude and rate of flap motion on vane-controlled gust-alleviation system
L. Keith Barker, Daniel J. Crawford, Gene W. Sparrow, United States. National Aeronautics and Space Administration, Langley Research Center
National Aeronautics and Space Administration, 1972 - Crafts & Hobbies - 43 pages
An airplane (light transport type) is assumed to be in level flight (no pitching) through atmospheric turbulence which has a mean-square vertical gust intensity of 9.3 (m/sec)sq. The power spectral density of the vertical acceleration due to gusts is examined with and without a gust-alleviation system in operation. The gust-alleviation system consisted of wing flaps that were used in conjunction with a vane mounted ahead of the airplane to sense the vertical gust velocity. The primary purpose of this study was to examine the change in the effectiveness of the gust-alleviation system when the flap motion is limited in amplitude and rate. The alleviation system was very effective if no restrictions were placed on flap motion (rate and amplitude). Restricting the flap amplitude to 0.5 radian did not appreciably change the effectiveness. However, restricting the flap rate did reduce the gust alleviation, and restricting the flap rate to 0.25 rad/sec actually caused the alleviation system to increase the vertical acceleration above that for the no-alleviation situation. Based upon this analysis, rate limiting appears to be rather significant in gust-alleviation systems designed for passenger comfort.
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0.25 rad/sec actually 1.0 Gust frequency aircraft response airplane light transport airplane to sense alleviation system amplitude and rate amplitude to 0.5 analog computer analysis angle of attack APPENDIX associated with equation atmospheric turbulence attack on wing autocorrelation function autocovariance function closed-form expression designed for passenger due to gusts Effectiveness of Flap equation A2 Flap rate limit flap servo forward-flight speeds Gust sensor located gust velocity Wg(t gust-alleviation system consisted Keith Barker Langley Research Center limit on flap limit-cycle oscillation limited in amplitude NASA TN no-alleviation situation nonlinear passenger comfort potentiometer power spectral density rad/sec actually caused radian rate limiting appears reduce the gust restricting the flap root mean square sense the vertical servomechanism shown in figure simulation Spanwise Variations spectral density curves spectral shaping filter theorem tral density vane mounted ahead VANE-CONTROLLED GUST-ALLEVIATION SYSTEM vertical gust intensity vertical gust velocity wing aerodynamic center wn/V