The Swashplate of a Helicopter: Engineering Marvel in Rotary Wing Flight
Helicopters are marvels of modern engineering, capable of taking off, landing vertically, and hovering in place. At the heart of this functionality lies a critical component known as the swashplate. Understanding the swashplate’s role in helicopter flight reveals much about the intricate mechanics of rotary-wing aircraft.
A Swashplate is a key component in controlling a Helicopter. It is a mechanical device that translates input via the helicopter flight controls into the motion of the main rotor blades. The swashplate consists of two main parts: a stationary swashplate and a rotating swashplate. The stationary swashplate is mounted on the main rotor mast and is connected to the cyclic and collective controls by a series of pushrods. The rotating swashplate is mounted to the stationary swashplate using a bearing and is allowed to rotate with the main rotor mast.
How a Blade Creates Thrust:
To know about how swashplate works, let's first get an idea of how thrust is generated using propellers. Propeller blades or rotor blades are like wings: They move through the air, and when they have the right angle of attack, they bend the air backward (in the case of a propeller) or downwards (in the case of a helicopter). On a wing, this causes downwash; on a propeller, this causes a prop blast. Both are essentially the same. Air gets a kick in a direction orthogonal to the movement of the airfoil, whether it is on a wing, a propeller, or a rotor. To ensure the angle of attack is correct, a helicopter rotor uses a mechanism called collective pitch control to vary the angle of attack on all blades simultaneously. Additionally, the rotor airfoil is carefully trimmed to have no chordwise shift in the center of pressure over an angle of attack.
Figure 1.1: The basic principle of generating thrust by the propeller. How do Helicopter Swashplates Work:
There are two parts to the swashplate. The upper part contains a spherical bearing that allows the whole assembly to rock on the main shaft, which goes through the middle. The four balls are connected to the blades by push rods, allowing the blades to rock on their shafts. The upper part fits into a large bearing in the lower part. This part stays stationary while the upper part rotates with the rotor head. The balls on the lower part are connected to the control pushrods, preventing the bottom part from rotating. Moving the cyclic control tilts the lower part in the same direction as the cyclic control and consequently tilts the upper part in the same direction. One of the upper links is coupled to a special link that makes the upper part rotate on the main shaft. The whole assembly can slide up and down the main shaft on the spherical bearing. This is done by moving the collective control up and down, depending on whether the pilot wants to climb or descend the helicopter. The process of mixing the two controls to manage both direction and climb can be mechanical, hydraulic, or, in the case of model helicopters, controlled by a computer mixer.
The swashplate, located in the rotor hub, is a key component in controlling a helicopter. Pilot control inputs tilt and raise or lower the swashplate, effectively feathering the rotor blades. Pulling the collective control up raises the swashplate (pushing it down lowers it). Pushing the longitudinal cyclic forward typically tilts the swashplate down in the front and up in the back. Pushing the lateral cyclic right tilts the right side of the swashplate down and the left side up. Pitch links connect the upper (rotating) swashplate to the pitch horns on the rotor blades, outboard of the feathering hinge. Raising the pitch horns feathers the blade, leading edge up. Lowering them decreases feathering. There is typically a 90-degree azimuth offset between the pitch link attachment point on the swashplate and the blade it’s connected to.
Figure 2.1 demonstrates how the pitch link slides up and down due to the angle of the plates. Here, the pitch link is shown in dark blue color while the rotating plates are shown in light and dark green respectively. (Note: The mechanism is demonstrated for one blade only)
Figure 2.2 demonstrates how the up-and-down movement of the pitch link tilts the blade at a certain angle which changes the pitch angle for the helicopter. Here, the pitch link is shown in a dark blue color. (Note: The mechanism is demonstrated for one blade only)
Advantages of Using a Swashplate in Modern Helicopters:
When we think of helicopters, the image of rotor blades slicing through the air often comes to mind. However, behind this mesmerizing dance of aerodynamics lies a crucial component that makes it all possible: the swashplate.
Mastering Flight Control: Cyclic and Collective Pitch
At the core of helicopter maneuverability is the swashplate mechanism. This ingenious device allows pilots to control both the cyclic and collective pitch of the rotor blades. What does this mean? Essentially, it enables the helicopter to roll, pitch, and change its lift. By adjusting the angle of the rotor blades, the pilot can direct the helicopter to move in any desired direction. This level of control is crucial for the precision and versatility that helicopters are known for, from hovering in place to performing complex aerial maneuvers.
Boosting Efficiency and Reducing Power Consumption
In the quest for efficiency, the swashplate plays a key role. Interestingly, while a conventional swashplate-controlled rotor system is highly effective, a swashplate-less configuration can offer some advantages, particularly in high-speed forward flight. By reducing parasite drag, a swashplate-less design can moderately lower power consumption during these conditions. However, it’s worth noting that in hover and low-speed flight, the power consumption remains similar to that of a swashplate system. This balance ensures that helicopters can perform efficiently across a range of flight conditions.
Simplifying Actuation Requirements
One of the notable benefits of the swashplate system is its reduced actuation requirements. The trailing-edge flap deflections needed to trim the rotor are moderate, leading to smaller actuation demands. This simplification not only makes the swashplate system more efficient but also reduces the overall complexity of the design. For engineers and maintenance crews, this translates to a more streamlined and manageable system, enhancing reliability and ease of operation.
Versatile Adaptability Across Rotor Configurations
The versatility of the swashplate is another aspect that cannot be overlooked. It can be adapted to accommodate various rotor configurations, whether in single-rotor or dual-rotor helicopters. This adaptability ensures that the swashplate mechanism remains relevant across a wide range of helicopter models, catering to diverse needs and applications in the aviation sector.
Cutting Weight and Maintenance Costs
The swashplate system, while critical, does add to the weight, drag, and maintenance burden of a helicopter. However, advancements in design have led to significant improvements. A swashplate-less design, for instance, can mitigate some of these drawbacks by reducing weight and maintenance needs. This reduction not only improves the helicopter’s overall mission performance and range but also lowers operating costs. In an industry where efficiency and cost-effectiveness are paramount, these savings are substantial.
In summary, the swashplate is much more than a mere component; it is the heart of modern helicopter flight control. It provides precise maneuverability, improves efficiency, and reduces complexity, making it a cornerstone of helicopter design. While it does introduce some weight and maintenance considerations, the benefits it offers generally far outweigh these drawbacks. For most helicopter applications, the swashplate remains an indispensable mechanism, enabling the remarkable capabilities that helicopters are celebrated for. So, the next time you see a helicopter gracefully hovering or swiftly cruising through the sky, remember the swashplate—an engineering marvel that makes it all possible.
