AirshipPropeller:

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   Airship propeller model.

   The airship has two counter-rotating propellers mounted to opposite 
   sides of the gondola. They are nominally aligned in the +x direction. 

   Each propeller is assumed to have a maximum thrust capability of 
   "d.thrustMax". 

   The thrust may be directed by simultaneously rotating each propeller
   about the y-axis through the angle "control.mu". 

   The total thrust may be controlled via "control.throttle", which 
   linearly scales the magnitude.
 
   The output is a data structure that contains the forces and torques on 
   the airship due to the propeller thrust.
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   Form:
   g = AirshipPropeller( x, d, control, altitude, machNo )
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   Inputs
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   x                     State
   d                     Engine data
   control               Controls
   altitude       (1,1)  Altitude
   machNo         (1,1)  Mach number

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   Outputs
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   g                     Output data structure
                         .torque      (3,1) Core torques
                         .force       (3,1) Core forces
                         .xDot        (:,1) Engine state derivatives
                         .mDot        (1,1) Fuel consumption
                         .inertiaDot  (3,3) Inertia derivative due to fuel consumption
                         .cGDot       (3,1) CG derivative due to fuel consumption
                         .torqueRotor (:,1) Torques on rotors

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Children:

Math: Linear/Cross