CS-VLA 629  Flutter

ED Decision 2003/18/RM

(a)                            It must be shown by one of the methods specified in sub-paragraph (b), (c), or (d) of this paragraph, or a combination of these methods, that the aeroplane is free from flutter, control reversal, and divergence for any condition of operation within the limit V-n envelope, and at all speeds up to the speed specified for the selected method. In addition -

(1)                            Adequate tolerances must be established for quantities which affect flutter, including speed, damping, mass balance, and control system stiffness; and

(2)                            The natural frequencies of main structural components must be determined by vibration tests or other approved methods. This determination is not required if (c) and (d) are both applied, and V_D is lower than 259 km/h (140 kt).

(b)                            A rational analysis may be used to show that the aeroplane is free from flutter, control reversal, and divergence if the analysis shows freedom from flutter for all speeds up to 1.2 V_D.

(c)                            Flight flutter tests may be used to show that the aeroplane is free from flutter, control reversal, and divergence if it is shown by these tests that -

(1)                            Proper and adequate attempts to induce flutter have been made within the speed range up to V_D;

(2)                            The vibratory response of the structure during the test indicates freedom from flutter;

(3)                            A proper margin of damping exists at V_D; and

(4)                            There is no large and rapid reduction in damping as V_D is approached.

(d)                            Compliance with the rigidity .and mass balance criteria (pages 4-12), in Airframe and Equipment Engineering Report No. 45 (as corrected) ‘Simplified Flutter Prevention Criteria’ (published by the Federal Aviation Administration) may be accomplished to show that the aeroplane is free from flutter, control reversal, or divergence if -

(1)                            The wing and aileron flutter prevention criteria, as represented by the wing torsional stiffness and aileron balance criteria, are limited in use to aeroplanes without’ large mass concentrations (such as engines, floats or fuel tanks in outer wing panels) along the wing span; and

(2)                            The aeroplane is conventional in design, and -

(i)                             Does not have a T-tail, boom-tail, or V-tail,

(ii)                            Does not have unusual mass distributions or other unconventional design features that affect the applicability of the criteria, and does not have a significant amount of sweep,

(iii)                           Has fixed-fin and fixed-stabiliser surfaces.

(e)                            For longitudinal, lateral and directional controls, freedom from flutter, control reversal, and divergence up to V_D must be shown after the failure, malfunction, or disconnection of any single element in any tab control system.