Autogyro Trim Control


Bensen Autogyro Trim Control


Bensen Aircraft, manufacturer of autogyro aircraft, in Raleigh, North Carolina.

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Steve Hines' 4th-5th-year-college summer job.


       Two years before graduating from college, Steve Hines' summer job in Research & Development at Bensen Aircraft under the direction of Igor Bensen, pioneer in autogyro aircraft.  


      The assignment for the summer was to explore ways for the pilot to trim the autogyro for straight and level flight.  The need came from the changing weight of the fuel tank which was mounted on the front-left side of the air frame.  As the fuel was used, the autogyro would gradually pitch up and roll to the right. 

      The autogyro controls had to be simple and light weight.  Before the summer was out, Steve had filled a notebook with technical ideas, notes, and photos of prototypes.  The solution chosen was to adjust the amount of tension, and the direction of pull of the cable (shown in red) attached to the rear of the rotor's gimbal.  An existing cable was used to pull down on the rear of the gimbal to make the rotor pitch up.  Changing the angle of that same cable, that pulled on the gimbal, controlled the roll of the craft.  The in-flight trim control was successfully test flown by Igor Bensen, in a B-8 Gyrocopter like that shown above.  

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     The trim control is based on the geometry of an ellipse which can be drawn with a string of fixed length, attached at two points. The ellipse is drawn while holding the string taut with the pencil.






     In the trim control, the upper focus of the ellipse is the red cable's attachment at the gimbal (out of  view picture above).  The lower focus is where the intermediate section of the red cable lifts off the fixed roller.  The movable roller swings in an arc, closely simulating a portion of the ellipse.  

      Regardless of how the roller swings left or right, the red cable maintains a constant path length between the foci of the ellipse.  Further, pulling the red pitch-control cable, around the rollers and through the mechanism, has no effect on the swing position of the lower roller.  Therefore, there is complete independence between the two adjustments, both of which control the same cable, in different ways.  

      When the pilot tightens the yellow cable, the movable roller and red cable swing to the left, causing the autogyro to roll clockwise and bank right.  When the pilot tightens the red cable, the back of the rotor gimbal (out of view in the pictures above) is pulled down, causing the autogyro to pitch up and climb.

      The lower ends of both the pitch-control cable (red) and the roll-control cable (yellow) are routed with pulleys to adjustment knobs at the pilot's seat.  The pitch-control knob is mounted on the side of the seat (so that turning the knob makes the autogyro pitch in the same direction that the knob is turned).  The roll-control knob is mounted on the front of the seat, so that rotation of the knob makes the autogyro roll in the same direction that the knob is turned.


Steve Hines, left, with Igor Bensen


      This is not a product for sale, but is shown as an example of technology, developed by Steve Hines, which clients can now expect from HinesLab on a contract basis.

Please contact Steve Hines at :
HinesLab, Inc.
Glendale, California, USA
ph. 818-507-5812