Enstrom’s patent and Uptigrove’s modification

 
See the all the drawings and text herehttp://www.google.com/patents/about?id=8npjAAAAEBAJ&dq=enstrom+controlhttp://www.google.com/patents/about?id=8npjAAAAEBAJ&dq=enstrom+controlhttp://www.google.com/patents/about?id=8npjAAAAEBAJ&dq=enstrom+controlshapeimage_1_link_0shapeimage_1_link_1