|File Size||27.28 MB|
|Tags||Rotor Blades U.S. Army Air Mobility Research and Development Laboratory|
|USAAMRDL-TR-76-33 Rotor Blade Flapping Criteria Investigation.pdf||Download|
U.S. Army Air Mobility Research and Development Laboratory - Rotor Blade Flapping Criteria Investigation
Critical operational characteristics were: at center of gravity extremes, under low or negative g conditions, with large abrupt control inputs, and in conditions of significant retreating blade stall . Operation outside recommended f light envelopes can cause excessive flapping. Helicopter characteristics in— fluencing flapping were: flapping restraint, fuselage stability characteristics, and helicopter loading condi t ions. A limit flapping criterion is defined the same as current design specif icaLions and should apply for all operations within the recommended flight envelopes of the helicopter. An ultimate flapping criterion is proposed for operations outside the recommended f light envelopes and for failure conditions. The ul timate flapping criterion requires no failure of primary struc— ture due to flapping stop contact, and no rotor blade contact with the fuselage for Condi t ions where probability of occurrence is not extremely remote.
A fundamental hel i copter design consideration is rotor blade Flapping clearance with the fuselage and tail rotor f lapp int,' . aro dictated by design parameters; such as mast length, fuso— lage layout, and rotor blade flapping stops. ','he many possible in—flight and ground operations require consideration of blade coning and flapping motions under a wide variety of operating conditions. Current design criteria state that a minimum rotor blade to airframe clearance of 9 inches must be present to allow safe operations. However, with these criteria apparently satisf incidents caused by excessive flapping in all rotor types still occur in service. The objectives of this study were to generato a general picture of flapping problems by defining the primary causes of high flap— ping and to formulate design criteria. The scope of the study included examining the effect of both physical and operational characteristics of three mission types of helicopters with four rotor systems and identifying differences in flapping charac— teristics.