MIL-STD-209K APPENDIX D
D.3.3 Method of Analysis for Determination of Retention Loads.
The load factors defined in section D.3.1 shall be applied to the structure to deter- mine cargo retention loads, and analyzed using two methodologies. The first method uses geometry of the chain from the aircraft tiedown ring and cargo item, stiffness of the chain/strap, and cargo item suspension system rates to determine retention loads. This method also takes into account the location of center of gravity of the cargo item. With this method, the chain/strap limit load and aircraft tie down ring limit load are fixed constraints. The sizing, location and geometry of the tiedown provision on the cargo item are varied along with the tiedown device geometry to ensure the limit loads are not exceeded. Examples of the second method is given in the cargo loading manuals cited in section D.2. Briefly, the second method computes total restraint required uni- directionally without regard to center of gravity location and stiffness of tie down mem- ber, with a geometric reduction or knockdown factor. Details of the second method can be found in the cargo loading manuals cited in section D.2. Both methods are required to be presented in a report to NAVAIR for approval when calculating chain/strap loads
for vehicle restraint. Method one shall be labeled the "Engineering Method", and method two labeled the "Loadmaster Method". When determining retention loads using method one, since several worst case load solutions may result. The worst case conditions define the method one design loads for the provision and vehicle backup structure. However, many more solutions are possible during aircrew restraint opera- tions of the cargo item for transport. To assist the loadmaster in his determination of
where to place cargo, the reaction load at the tiedown provision from method one analy- sis should be rounded up to the nearest 5,000 lb whole number increment. The round- ing up of the results from method one to the nearest 5,000lb determines method one design loads. For example, if method one results in a provision design load of 4,900lb., rounding to the nearest 5,000 lb increment results in a method one design load of
5,000lb. If method one results in a provision design load of 8,250lb, the method one design load is 10,000lb. This philosophy is to accommodate loadmaster techniques used in the Navy/Marine Corps. Final retention design loads are determined from the larger values from the two methodologies.
D.3.4.5 Structural Load Criteria.
Structural load factors for determining load requirements for transport of cargo equipment in Navy/Marine Corps aircraft are shown in paragraph D.3.1. Positive margins of safety for limit and ultimate load conditions are required for all structure, aircraft, vehicle and cargo. Limit load cases shall show no permanent set by analysis or test.
D.3.5 Supporting Structure.
The supporting structure is considered to be vehicle/cargo structure which supports and attaches the tiedown provision on the vehicle/cargo. The design and testing of indi- vidual provisions and vehicle back-up structure must be proven structurally adequate for all applied load conditions. The load conditions for the vehicle are in paragraph D.3.1. The back-up or provisions' structure can be structurally substantiated by hand analysis, finite element analysis or static test. Upon review of the analysis, NAVAIR will determine if the supporting analysis is adequate. Whenever possible, such decisions will seek to reduce
Source: https://assist.dla.mil -- DDow-n2loaded: 2014-09-28T23:10Z Check the source to verify that this is the current version before use.
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