All conventional helicopters have the same basic controls to manipulates the helicopter flight controls to achieve and maintain controlled aerodynamic flight:
- Collective stick to enable power changes and vertical motion.
- Cyclic stick to enable turns and forward speed.
- Anti-torque also known as rudder or tail rotor pedals for anti-torque to the main rotor in conventional helicopters.
- Throttle controls the power of the engine.
Depending on the complexity of the helicopter the cyclic and collective may be linked together by a mixing unit. A mechanical or hydraulic device that combines the inputs from both and then sends along the “mixed” input to the control surfaces to achieve the desired result.
Automatic Flight Control Systems (AFCS)
More advanced aircraft may offer Automatic Flight Control System AFCS, as opposed to mechanical MFCS. Modern AFCS are digital computers, electrical actuators, and sensors that augment the mechanical system to accomplish trim, autopilot, and/or stability enhancement. The system is fully electronic, from the control sticks to the inputs to the servos below the swashplate. The system also relies on inputs from an air data computer, which measures pressure, air speed, and air temperature, and also uses rate and acceleration damping as required to fully tailor the controls to the situation at hand. The computer can readily handle the sine and cosine functions required for determining correct servo motion.
- Yaw damper.
- Stability Augmentation System SAS.
- Flight Director FD.
- Autopilot AP.
The yaw damper damps or reduces the rolling and yawing oscillations due to the aircraft’s tendency to rocking from side to side called Dutch roll. The yaw damper computes servo commands based on sensor input data only. It supplies yaw rate damping and makes no input or control to the flight director. It also helps turn coordination through the autopilot. In some systems, the yaw damper can be engaged without the autopilot, but this is unusual. The servo position reference is synchronized to zero at engagement, and is constantly washed out to ensure that tail rotor forces are zero.
Stability Augmentation System SAS
SAS stabilizes the helicopter against outside disturbances, and augments or helps pilot cyclic control input. The SAS mode is designed, so that pilot controlled pitch and roll are enhanced. While helicopter motions caused by outside disturbances are counteracted. This mode of operation improves basic helicopter handling qualities. When a wind is detected, a stabilizing control signal proportional to the amplitude and rate of the motion is generated in the AFCS computer and routed to the appropriate actuators. SAS is generally used during low and slow maneuvering where the pilot might be making constant attitude changes in preparation for landing.
Flight Director FD
The flight director FD provides the pilot and/or autopilot with computed lateral and vertical steering commands to fly the helicopter along a desired lateral and vertical flight path.
AP is a system used to control the trajectory of an aircraft without constant ‘hands-on’ control by a human operator being required. Autopilots do not replace human operators, but instead they assist them in controlling the aircraft. This allows them to focus on broader aspects of operations such as monitoring the trajectory, weather and systems.
Helicopter Actuation Systems
Due to the solution used, and purpose of the unit we have hydro-mechanical and electro-mechanical actuator systems. Hydro-mechanical type of actuator is used in large helicopters. This solution is able to produce the large forces required to manipulate the orientation of a rotating main rotor disc. Smaller helicopters such as Unmanned Aerial Vehicles UAV. And Remote Controlled RC models utilise electric servo-actuators due to smaller force requirements. Hydro-mechanical actuators are controlled directly by the pilots control inputs. Which are amplified through the hydraulic system and transmitted to the control surfaces of the aircraft to achieve the desired attitude changes. Electric servo-actuators receive control signals from the pilot through an RF receiver in the form of a position reference signal.
The key difference between the two systems is that the hydro-mechanical actuator receives a physical input through the aircraft control linkages. Whilst the electric servo-actuator requires a controller to decode the position reference signal and drive the servo-actuator motor to achieve and maintain the desired position. The ability of the electric servo-actuator to accurately acquire and maintain the desired angle under load is a key performance factor for smaller helicopter control input response.
The electromechanical actuators EMAs are gaining a growing interest owing to their force and power density capability and the high dynamical performance by electronic control. Hence, very compact and high-efficiency drives can be designed, with satisfactory characteristics from the reliability point of view. Optimized electromechanical actuators EMAs are remarkably compact and lightweight, making them a uniquely ideal solution for helicopter motion control applications such as rotor blade trailing edge flaps, onboard beam control, gear and access doors. Automatic Flight Control Systems AFCS would be impossible to create without actuation system.
So far for upcoming upgrade v.04 in OMH project, I have prepared the Rotax engine model 912 with exchangeable components, for fine-tune. Allowing us to create five types of Rotax engine: starting with base model 912 F with 80 HP, and 55.4 kg, which is upgradable to 912 S, 912 iS, 914 F, and the 915 iS version with 141 HP and 84.6 kg. Two types of Semi-Rigid hub with swashplate. Also, we have 3 Airfoils types for specific flight characteristics, based on NACA0012, NACA6409, NACA10.
Our aspiration is to create a “flying racing machine” not just another flyer.DAS.
One of the most important conditions for all flying units is the mass-to-power ratio. Safety is another important aspect, but it is not the most important thing in this moment for us. The weight! We have to save as much we can, therefore I want to use electrical actuators instead of traditional mechanical connection MFCS . The transmitted information from instruments like cyclic stick, collective stick with throttle and pedals will be converted into coordinates for actuators to control swashplate, fuel injection level and rear rotor blades position. Moreover in the future this innovation will allow us to build “software” with AP, FD, and SAS functions. What you think?
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