Use of variable-pitch rotors was compared against variable-RPM rotors on a 2-kg (20 N) quadcopter in simulation. To generate 5 N of thrust in hover while maintaining a 2:1 maximum thrust-to-weight ratio, the variable-pitch rotor required 29% more power. At low climb rates the variable-RPM
rotor requires less power, but near its maximum rate it required more power than the variable-pitch rotor. The maximum climb rate for the variable-pitch rotor was up to 70% greater than that of the variable-RPM rotor. A quadcopter equipped with variable-pitch rotors required more power to
operate compared to the aircraft with variable-RPM rotors over its operational airspeed range. The variable-pitch quadcopter required 30% more power at best-endurance speed and had 18% less range than the variable-RPM quadcopter (at maximum-range speed). The 1/rev root drag shear was 42% larger
for the variable-RPM rotor, and the 2/rev H- and Y-forces were 37% and 50% larger. The 2/rev thrust vibration was 6.5% smaller for the variable-RPM rotor, and the hub pitching and rolling moments were 11% and 9% smaller, respectively. Unlike the quadcopter equipped with variable-pitch rotors,
the quadcopter equipped with variable-RPM rotors experienced a beating phenomenon in the aircraft-level vibratory loads.
Ever more restrictive regulations have necessitated minimal impact drilling procedures that have led to the development of a variety of methods for the disposal of liquid drilling waste. Current Alaska regulations severely limit the use of reserve pits other than in an emergency situation for the disposal of liquid phase waste. Current efforts are being directed at minimizing liquid discharges while conserving water and maximizing solids control efficiency.
This paper presents a case history of a recent project on Alaska's North Slope where operator requirements and logistics necessitated on site dewatering of drilling fluids. A retrofitted chemically enhanced centrifuge was utilized for this process. The design, fabrication, operations, and economics are summarized. The conclusions should prove beneficial for future planning of restricted discharge drilling operations such as will be necessary should Alaska's Arctic National Wildlife Refuge be opened to drilling.
Hover analysis is performed on a 1200-lb gross weight UAM-scale quadcopter with both variable rotor speed and collective pitch control. With these redundant controls, the hover performance and flight dynamics are considered at three trim points, where power consumption can be increased to improve authority of the pitch inputs for changes in rotor thrust. An explicit model following control laws is optimized using CONDUIT® to meet ADS-33E-PRF handling qualities specifications, with design margin optimization on each axis. The responses of the linearized system are examined with either control type, and pitch control is shown to outperform RPM-control in heave, while the opposite is true for yaw. Trim in axial climb is simulated, where the collective pitch can be scheduled with the climb rate to maintain effective stall margin. Hybrid control mixing is implemented using a complementary filter, allowing the aircraft to use pitch control for short-term responses and RPM control for trim. The benefits of this hybrid control scheme are demonstrated through simulation of hot/high/heavy conditions, where trimming with RPM control allows the pitch actuators to maintain margin for maneuvers. It is concluded that hybrid control allows the aircraft to reap the benefits of pitch control for maneuverability while maintaining stall margin by using RPM control for trim.
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