1、MIL-A-8870C(AS)25 March 1993SUPERSEDINGMIL-A-8870B(AS)20 May 1987MILITARY SPECIFICATIONAIRPLANE STRENGTH AND RIGIDITYVIBRATION, FLUTTER, AND DIVERGENCEThis specification is approved for use by the NavalAir Systems Command, Department of the Navy, and isavailable for use by all Departments and Agenci
2、es ofthe Department of Defense.1. SCOPE1.1 Scope. This specification contains the general and detail designrequirements and criteria in the design and construction of airplanes to:a. Prevent flutter, divergence, and other dynamic and staticaeroelastic instabilities.b. Control structural vibrations.c
3、. Prevent fatigue failure of the airframe structure or structuralcomponents induced by vibrations, aeroacoustic and other oscillatoryloads for the service life of the airplane.d. Prescribe structural dynamic analyses, laboratory and ground tests,and structural dynamic flight tests required to demons
4、tratecompliance with design requirements.e. Apply to airplanes acquired by the Navy for all conditions of flightand surface operations for which the airplanes are required to operate.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)2. A
5、PPLICABLE DOCUMENTS2.1 Government documents.2.1.1 Specifications. The following specifications form a part of thisspecification to the extent specified herein. Unless otherwise specified, theissues of these documents shall be those listed in the issue of the Department ofDefense Index of Specificati
6、ons and Standards (DODISS) and supplement thereto,cited in the solicitation.SPECIFICATIONSMILITARYMIL-A-8860 Airplane Strength and Rigidity,General Specification for.MIL-A-8861 Airplane Strength and RigidityFlight Loads.MIL-A-8863 Airplane Strength and RigidityGround Loads for Navy Acquired Airplane
7、sMIL-A-8866 Airplane Strength and RigidityReliability Requirements, Repeated Loads,Fatigue and Damage Tolerance.(Unless otherwise indicated, copies of federal and military specificationsstandards, and handbooks are available from the Standardization Document OrderDesk, Building #4, Section D, 700 Ro
8、bbins Avenue, Philadelphia, PA 19111-5094.)2.1.2 Other Government documents and publications. The following Governmentpublications form a part of this specification to the extent specified herein.Unless otherwise specified, the issues shall be those in effect on the date ofthe solicitation.PUBLICATI
9、ONSAIR FORCE FLIGHT DYNAMICS LABORATORY (AFFDL)TR-67-140 Design Criteria for the Predictionand Prevention of Panel Flutter;Volume I Criteria Presentation.Volume II Background Studies and Review of State of the Art.TR-74-112 Sonic Fatigue Design Guide for Military Aircraft.(Copies of other Government
10、 documents/publications required by contractors inconnection with specific acquisition functions should be obtained from thecontracting activity or as directed by the contracting activity.)2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(
11、AS)2.2 Orcer of precedence. In the event of a conflict between the text of thisspecification and the references cited herein (except for associated detailspecifications, specification sheets or MS standards), the text of thisspecification shall take precedence. Nothing in this specification, however
12、,shall supersede applicable laws and regulations unless a specific exemption hasbeen obtained.3. REQUIREMENTS3.1 General requirements. Construction, materials and design of the airplaneshall be such that:a. Flutter, buzz, divergence, aeroservoelastic instability,aerothermoelastic Instability, or oth
13、er related static or dynamicaeroelastic instabilities, including sustained limit amplitudeinstabilities, shall not occur consistent with the requirementsof 3.1.1.b. Airframe fatigue failures resulting from structural dynamicresponses induced by aeroacoustic, mechanical, structural or otheroscillator
14、y loadings shall not occur consistent with therequirements of 3.1.2.These requirements shall apply throughout the design range of altitudes, speeds,maneuvers, weights, fuel content, thermal conditions, maneuvers where losses inrigidity may occur, external and internal store configurations, and other
15、 loadingconditions and configuration variables for the service life of the airplane.3.1.1 Aeroelastic stabillty. All configurations of the airplane shall befree from any aeroelastic instability for all combinations of altitude and speedencompassed by the limit speed (VL/ML) versus altitude envelope
16、enlarged at allpoints by the airspeed margin of safety. The airplane shall meet the followingstability design requirements for both-normal and failure conditions:a. Airspeed margin: The equivalent airspeed, We, margin of safetyshall be not less than 15 percent at all points on the VL/MLenvelope of t
17、he airplane, both at constant Mach number, M, andseparately, at constant altitude, (see Figure 1).b. Damping: The total (aerodynamic plus structural) dampingcoefficient, g, shall be not less than 3 percent (g=0.03) forany critical flutter mode for all altitudes and flight speedsfrom minimum cruising
18、 speeds up to VL/ML, (see Figure 2).3.1.1.1 Aeroservoelastic stability. Interaction of the flight control systemwith the airplane structural modes shall be controlled to prevent anyaeroservoelastic instability. The stability design requirement of 3.1.1 shall bemet in all operational states of the fl
19、ight control system (such as normal andfailure states, reversionary modes, and augmentation system on and off (if off isa design condition) and for the range of operating temperatures of the flightcontrol system. In addition, for any single flight control system feedback loop,the airplane structural
20、 modes shall have the stability margins listed below atspeeds up to VL/ML.3Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)a. The gain margin shall be not less than 6 dB.b. And separately, the phase margin shall be not less than 60.3.1
21、.2 Vibroacoustic loads and fatigue. The design of the airplane shall befree from fatigue failures resulting from structural dynamic responses induced byvibroacoustic loadings of 3.2.2.1 for the exposure time of 3.1.2.1. The designof the airplane shall satisfy the design factors of safety and fall-sa
22、ferequirements of 3.1,2.2 and 3.2.2.3, respectively, and the fatigue and damagetolerance requirements aS specified in MIL-A-8866.3.1.2.1 Exposure time. Cumulative exposure times to vibroacoustic loadingsshall be consistent with the planned service life and utilization spectra asspecified in MIL-A-88
23、66, and the planned operational scenarios and missionprofiles for all speeds up to VL/ML. In addition, time of exposure for thefollowing specific conditions shall be:a. Thirty seconds at maximum power when in launch position onshipboard catapult.b. Thirty seconds behind raised jet blast deflector (J
24、BD) whenin position for next launch.c. Fifteen minutes per 50 flight hours during ground runs at maximumpower.d. Fifteen minutes per 50 flight hours during hush house operations atmaximum power.3.1.2.2 Design factors of safety. The airplane shall meet the followingdesign requirements:a. Design facto
25、r of safety for aeroacoustic loads: The structure andstructural components shall be designed with a design factor ofsafety of 1.5 on aeroacoustic pressures.b. Scatter factor: A scatter factor of 2 on the vibroacoustic servicelife exposure of 3.1.2.1 shall be used in demonstration of fatiguelife of a
26、irplane structure and structural components.3.2 Detail design requirements.3.2.1 Aeroelastic stability.4Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)FIGURE 1. Graphical representation of minimum required flutter margin.5Provided by
27、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)FIGURE 2. Graphical representation of required damping.6Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)3.2.1.1 Control surfaces and t
28、abs. Control surfaces and tabs shall bedesigned to contain either sufficient static and dynamic mass balance, orsufficient bending, torsional and rotational rigidity, or a combination of thesemeans, to prevent, flutter of all critical modes under all flight conditions fornormal and failure operating
29、 conditions of the actuating systems. The adequacyof mass balance or rigidity of control surfaces and tabs shall be established “during the flutter prevention program. In addition, the following is requiredfor tabs:a. Trim or lagging balance tabs: A lagging balance tab iS a tabinstalled such that it
30、s rotation is in the direction oppositethat of the supporting control surface. Trim tabs or laggingbalance tabs shall be not less than completely statically balancedabout their hinge lines.b. Leading balance or spring-loaded tabs: A leading balance tab is atab installed so that its rotation is in th
31、e same direction as thatof the supporting control surface. Leading balance tabs and spring-loaded tabs shall be dynamically balanced with respect to the hingeline of the supporting control surface and the tab hinge line.3.2.1.1.1 Mass balance of control surfaces and tabs. If static mass balanceor dy
32、namic mass balance or both are used on control surfaces, tabs, and theassociated components to their control systems to prevent any aeroelasticinstability, the requirements as specified in 3.2.1.1.1.1 through 3.2.1.1.1.5shall be met.3.2.1.1.1.1 Location of balance weights. Balance weights in control
33、 surfacesand tabs shall be located so that flutter safety of both tab and control surfaceand main surface are assured. In addition, the following shall apply:a. Balance weights shall be located in regions where deflections ofcritical mode shapes are a maximum.b. Whenever possible, balance weights sh
34、all be distributed and eachthird of the span of each control surface shall be staticallybalanced.c. Balance weights shall not be located externally with respect tothe planes of the control surfaces.d. Balance weights and actuating systems for control surfaces andtabs shall be designed to prevent con
35、trol surface or tab rotationsresulting from inertia loads acting on the balance weights andactuating systems clue to catapulting or rocket assist takeoffs.3.2.1.1.1.2 Rigidity of balance weight attachment. The natural frequenciesof the balance weights as installed shall be not less than twice the hi
36、ghestfrequency of the flutter mode for which the balance weight is required to beeffective.7Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)3.2.1 .1.1.3 Design loads for balance weight attachment. Balance weights andthe adjacent suppor
37、ting structure shall be designed to the following conditions:a. A limit inertial load factor of 100 g and repeated inert a loadfactor of 60 g for 500 kilocycles in a direction normal to theplane of the control surface or tab.b. A limit inertial load factor of 50 g and repeated inertial loadfactor of
38、 30 g for 500 kilocycles in the other two mutuallyperpendicular directions of the control surface or tab.3.2.1.1.1.4 Provisions for rebalancing. Provisions shall be made to enableincreasing or decreasing the balance to compensate for the effects of changes,repairs and painting.3.2.1.1.1.5 Static bal
39、ance tolerance. The range of allowable service staticoverbalance or unbalance, including manufacturing tolerances and effects ofpainting and repairs, of each control surface (including attached tab) and tabshall be established and included in all control surface and tab assemblydrawings.3.2.1.1.2 En
40、vironmental effects on mass properties. The design of allcontrol surfaces and tabs shall prevent detrimental changes in mass properties(such as mass, static balance and mass moments of inertia) due to any naturalenvironment throughout the service life of the airplane. Water absorption andwater entra
41、pment shall be prevented.3.2.1 .1.3 Rigidity and frequency of control surfaces and tabs. If bending,torsional and rotational rigidity criteria are used for control surfaces and tabsto prevent any aeroelastic instability, the following requirements shall apply:a. The adequacy of control surface or ta
42、b bending, torsional androtational rigidity about the hinge line and frequency for bothnormal and failure operating conditions of the actuating systemshall be established together with the maximum allowable changesin inertia properties (from nominal) of control surface or tab.b. The maximum allowabl
43、e inertia properties (such as weight, CGlocation, static unbalance about hinge line and mass moments ofinertia during service conditions) shall be established andinclude effects of changes, structural repair and painting.c. The bending, torsional, and rotational rigidity shall include therigidity of
44、 all actuating elements, rigidity of the structure towhich these elements are attached, and the rigidity of controlsurface or tab.d. The actuators shall be located as close as practicable to thecontrol surface or tab and to a hinge to minimize the flexibilitycaused by connecting elements.8Provided b
45、y IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-A-8870C(AS)3.2.1.1.4 Freeplay of control surfaces and tabs. Detail design shall assurethat normal wear of components, of control surfaces and tabs, and actuatingsystems will not result in values of freeplay g
46、reater than those specified belowthroughout the service life of the airplane. Components having an adeuatelyestablished wear life may be replaced at scheduled intervals as approved by thecontracting activity. However, all replacements shall be included in the wearoutreplacement budget established fo
47、r the overall airplane.a.b.c.d.e.f.g.h.i.For a trailing edge control surface which extends outboard of the75 percent span station of main surface, the total freeplay shallbe not greater than 0.13.For a trailing edge control surface which extends outboard of the50 percent but inboard of the 75 percen
48、t span station of mainsurface, the total freeplay shall be not greater than 0.57.For a trailing edge control surface which is inboard of the 50percent span station of main surface, the total freeplay shallbe not greater than 1.15.For an all-movable control surface, the total freeplay shall benot gre
49、ater than 0.034.For a tab span that is less than 35 percent of the span ofsupporting control surface, the total freeplay shall be notgreater than 1.15.For a tab span that is equal to or greater than 35 percent of thespan of supporting control surface, the total freeplay shall benot greater than 0.57.For leading edge flaps, the total freeplay shall be not greaterthan 0.25.For wing fold, the total freeplay shall b
