(1)
Adequate tolerances must be established for quantities which a.ect .utter, including speed,damping, massbalance, and control system sti.ness; and
(2)
The natural frequencies of main structural components must be determined by vibration tests or other approved methods.
(b)
[Flight .utter tests must be made to show that the airplane is free from .utter, control reversal and divergence and to show that–]
(1)
Proper and adequate attempts to induce .utter have been made within the speed range up to VD ;
(2)
The vibratoryresponse of the structureduring the testindicates freedomfrom .utter;
(3)
A proper margin of damping exists at VD ; and
(4)
There is no large and rapid reduction in damping as VD is approached.
(c)
[Any rational analysis used to predict freedom from .utter, control reversal and divergence must cover all speeds up to 1.2 VD.]
(d)
Compliance withthe rigidity and massbalance criteria(pages4-12),inAirframe and EquipmentEngineeringReportNo.45(ascorrected)”Simpli.edFlutterPrevention Criteria”(publishedby theFederalAviationAdministration) maybe accomplished to show that the airplane is free from .utter, control reversal, or divergence if–
(1)
VD/MD forthe airplaneislessthan260knots(EAS) andlessthanMach0.5,
(2)
The wing and aileron .utter prevention criteria, as represented by the wing torsional sti.ness and aileron balance criteria, are limited in use to airplanes without large mass concentrations (such as engines, .oats, or fuel tanks in outer wing panels) along the wing span, and
(3)
The airplane–
(i)
[Does not have a T-tailor other unconventional tail con.gurations;]
(ii)
Does nothaveunusual massdistributionsorotherunconventionaldesign features that a.ect the applicability of the criteria, and
(iii) Has .xed-.n and .xed-stabilizer surfaces.
(e)
For turbopropeller-powered airplanes, the dynamic evaluation must include–
(1)
Whirl mode degree of freedom which takes into account the stability of the plane of rotation of the propeller and signi.cant elastic, inertial, and aerody-namic forces, and
(2)
Propeller, engine, engine mount, and airplane structure sti.ness and damping variations appropriate to the particular con.guration.
(f)
Freedom from .utter, control reversal and divergence up to VD/MD must be shown as follows :
(1)
Forairplanesthatmeetthe criteriaofparagraphs(d)(1) through(3) ofthis section, after the failure, malfunction, or disconnection of any single element in any tab control system.
(2)
For airplanesotherthanthosedescribedinparagraph(f)(1) ofthis section, after the failure, malfunction, or disconnection of any single element in the primary .ight control system, any tab control system, or any .utter damper.
(g)
[For airplanes showing compliance with the fail-safe criteria of Secs. 23.571 and 23.572,theairplanemustbeshownbyanalysistobefreefrom .utterup to VD/MD after fatigue failure, or obvious partial failure, of a principal structural element.
(h)
For airplanes showing compliance with the damage tolerance criteria of Sec. 23.573, the airplane must be shown by analysis to be free from .utter up to VD/MD with the extent of damage for which residual strength is demonstrated.
(i)
For modi.cations to the type design that could a.ect the .utter characteristics, compliance withparagraph(a) of this section mustbe shown, exceptthat analysis basedonpreviously approveddatamaybeused alonetoshowfreedomfrom .utter, control reversal and divergence, for all speeds up to the speed speci.ed for the selected method.]
Amdt. 23-48, E.. 03/11/96
31.1 Wings
FAR 23.641 : Proof of strength.
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本文链接地址：FAA规章 美国联邦航空规章 Federal Aviation Regulations 2(25)
