Patent GB-981187-A (GB)
Title: Rotor pitch control mechanism for a helicopter adapted for high speed forward travel
IPC: B64C27/615
Filed: 1961-12-05
Abstract: 981,187. Helicopters. KAMAN AIRCRAFT CORPORATION. Dec. 5, 1961 [Jan. 5, 1961], No. 43555/61. Headings B7G and B7W. A pitch control mechanism for a helicopter normally moving in a forward direction and having a rotatable hub and a plurality of similar radially extending blades comprises, in combination: a first pilot operable mechanism for effecting collective increase or decrease of the rotor blade pitch, a second pilot operable mechanism for effecting cyclic changes of the rotor blade pitch, and a superimposed cyclic pitch change mechanism operably dependent upon movement of the first pilot operable mechanism in the collective pitch increasing direction and automatically serving during at least a portion of such movement to effect forward cyclic pitch changes which are superimposed upon any cyclic pitch pattern effected by the second pilot operable mechanism, said superimposed cyclic pitch change mechanism being reversely operable to eliminate said superimposed forward cyclic pitch changes during movement of the first pilot operable mechanism in the collective pitch decreasing direction. The control mechanism and rotor construction are conventional in that a collective pitch control member 41 actuates through rod and lever mechanism a link 104 which operates through further rod and lever mechanism to adjust collectively pitch controlling flaps 25 on the rotor blades 16. A further lever 66 operates through rod and lever mechanism to adjust links 106, 108 connected to a conventional swashplate mechanism 28 whereby the pitch controlling flaps 25 may be adjusted cyclically. The mechanism 64, Fig. 4, for carrying out the invention comprises a supporting frame 109, Fig. 7, which supports a rockshaft 111 upon which are mounted a lever 135 (part of the sideways cyclic pitch control mechanism and no part of the invention) and a hub 118 which is formed with a rearwardly extending arm 119 and a downwardly extending arm 141, the hub being capable of limited rotation on the rockshaft. A bellcrank 110, 116 is fixed to rockshaft 111 l and it carries an integral flange 152 to which is bolted a cam plate 150 formed with a cam track 154 to co-operate with a roller 156 on one end of a beam 140 pivotally mounted at 142 on arm 141, the other end of the beam being connected at 148 to a link 143 pivotally mounted on a fixed pivot 146. A pivot 121 at the extremity of arm 119 carries a bellcrank 120 which has one arm connected to fore-and-aft cyclic pitch control link 105 and the other arm is connected by a link 126 to rod 100 forming part of the linkwork from cyclic pitch control lever 66, the common pivot being at one end of a lever 122 which is mounted on a fixed pivot 124. The link 62 extending from the collective pitch control lever 41 is connected to arm 110 and link 104 is connected to arm 116. In operation fore and aft movement of cyclic pitch lever 66 with collective pitch lever 41 held fixed causes pitch adjusting rod 106 to be operated through links 100, 126 and bellcrank 120, which rocks about instantaneously fixed pivot 121. Movement of the collective pitch lever 41 operates rod 62 and, through bellcrank 110, 116, the collective pitch link 104. Since the bellcrank 110, 116 supports cam plate 150, movement of the collective pitch mechanism will cause the cam track 154 to move over roller 156 from the minimum collective pitch position shown in Fig. 11, which by the shape of the cam, will impose varying movement on beam 140 and this, by its connection 142 with bellcrank 141, 119 will shift pivot 121 and thereby cause bellcrank 120 to rock about its connection with link 126 to superimpose an increase of forward cyclic pitch on the collective pitch movement.