Appendix G to Part 25 - Continuous Gust Design Criteria
The continuous gust design criteria in this appendix must be used in establishing the dynamic response of the airplane to vertical and lateral continuous turbulence unless a more rational criteria is used. The following gust load requirements apply to mission analysis and design envelope analysis: (a) The limit gust loads utilizing the continuous turbulence concept must be determined in accordance with the provisions of either paragraph (b) or paragraphs (c) and (d) of this appendix. (b) (1) All critical altitudes, weights, and weight distributions, as specified in §25.321(b), and all critical speeds within the ranges indicated in paragraph (b)(3) of this appendix must be considered. (2) Values of A
where: &phis;=power-spectral density (ft./sec.)
σ=root-mean-square gust velocity, ft./sec. Ω=reduced frequency, radians per foot. L=2,500 ft. (3) The limit loads must be obtained by
multiplying the A
(i) At speed V (1) The transfer function of the new design should exhibit no unusual characteristics as compared to the similar design which will significantly affect response to turbulence; e.g., coalescence of modal response in the frequency regime which can result in a significant increase of loads. (2) The typical mission of the new airplane is substantially equivalent to that of the similar design. (3) The similar design should
demonstrate the adequacy of the U (ii) At speed V (iii) At speed V (iv) At speeds between V (4) When a stability augmentation system is included in the analysis, the effect of system nonlinearities on loads at the limit load level must be realistically or conservatively accounted for. (c) (1) The expected utilization of the airplane must be represented by one or more flight profiles in which the load distribution and the variation with time of speed, altitude, gross weight, and center of gravity position are defined. These profiles must be divided into mission segments or blocks, for analysis, and average or effective values of the pertinent parameters defined for each segment. (2) For each of the mission segments
defined under paragraph (c)(1) of this appendix, values of A
(3) For each of the load and stress quantities selected, the frequency of exceedance must be determined as a function of load level by means of the equation -- $$
where -- t=selected time interval. y=net value of the load or stress. Y N(y)=average number of exceedances of the indicated value of the load or stress in unit time.
N P The limit gust loads must be read from the frequency of exceedance curves at a frequency of exceedance of 2×10−5 exceedances per hour. Both positive and negative load directions must be considered in determining the limit loads. (4) If a stability augmentation system is utilized to reduce the gust loads, consideration must be given to the fraction of flight time that the system may be inoperative. The flight profiles of paragraph (c)(1) of this appendix must include flight with the system inoperative for this fraction of the flight time. When a stability augmentation system is included in the analysis, the effect of system nonlinearities on loads at the limit load level must be conservatively accounted for. (d) (1) In paragraph (b)(3)(i) of this
appendix, the value of U (2) In paragraph (b) of this appendix,
the reference to paragraphs (b)(3)(i) through (b)(3)(iii) of this appendix
is to be understood as referring to the paragraph as modified by paragraph
(d)(1).
[Amdt. 25-54, 45 FR 60173, Sept. 11, 1980] |