Reciprocating Wing Motor or Generator (RWMG)
Conceptual Development – December 2025
AquaFlyer WPPS Catamaran
The Wind-Sun-Waves driven Sailing Machine is currently at the conceptual stage.
The ongoing project is the "AquaFlyer WPPS Catamaran".
Used Acronyms:
- RWMG – Reciprocating Wing Motor or Generator (unique to the AquaFlyer solution)
- AWS – Apparent Wind Speed
- AWA – Apparent Wind Angle
- WPPS – Wind to Propeller Propulsion System (for water-borne vehicles)
- WWPS – Wind to Wheels Propulsion System (for land or ice vehicles)
- TW – Transformer Wing (a wing capable of rapid camber transformation)
- RMC – Reciprocating Motion Converter (unique solution for WPPS and WWPS)
- KER – Kinetic Energy Recovery (proposed pneumatic or magnetic system at the mast foot)
- MRP – Mast Rotating Platform (one or two masts mounted on the MRP for AWA adjustment)
- UCU – Universal Control Unit (25 g unit including 2.4 GHz RC with 126 channels)
Central to the AquaFlyer concept is the RWMG — Reciprocating Wing Motor or Generator. Unlike traditional sails, it transforms vertical wing oscillation into usable energy: mechanical drive for ice/land variants (WWPS), electrical generation for marine propulsion and onboard systems (WPPS), or direct mechanical backup to the CRP in case of electrical failure. Versatile by design.
The following description presents the RWMG in simplified form and includes the proposed components, subsystems, and functionality. Some basic conceptual outlines have been sketched in earlier documents not included here; further detailed discussion is still required.
1. Mast
The mast consists of two vertically oriented NACA0021-profile sections placed one behind the other and connected by truss elements to increase structural stiffness. These are designated Mast_1 and Mast_2.
Each mast comprises a Deck Section and a Top Section, with the central portion featuring cut-outs to allow the Wing Axis to pass into the mast interior. Internally, vertical tracks are integrated along the leading and trailing edges to guide the Wing Wagon during its up-and-down movement. The two mast halves are connected at deck level and at the top, and are dynamically linked via the Wing Wagon. Additionally, the trailing edge of Mast_1 is connected to the leading edge of Mast_2 by truss elements (one or two trusses depending on mast height).
During standard operation, the masts are aligned with the incoming airflow at an angle of attack (AoA) of 0°. The cut-outs required for the Wing Axis passage will increase aerodynamic drag; this effect must be carefully addressed during detailed foil design to minimise unwanted drag. Structural design of the masts will depend on their final height and may incorporate advanced materials and sandwich construction techniques.
2. Wing Wagon
The Wing Wagon is the structural element that holds the Wing Axis perpendicular to the mast span. It is equipped with wheels to minimise friction as it travels up and down the mast.
The Wing Wagon experiences the highest loads in the vertical direction from the wing forces, while torsional loads in all directions are also present. The wheels may be designed to function as micro-generators by incorporating small permanent magnets reacting with miniature windings mounted on the wagon.
Because the Wing Wagon travels long distances (10–20 m), supplying electrical power to the Transformer Wings is challenging. A wireless power supply station is planned, active when the wagon approaches the lowest position near the deck. The Wing Wagon will also carry a small onboard battery pack.
Mechanically, the Wing Wagon is connected to the RMC (Reciprocating Motion Converter) via Dyneema wires driving the Wire Drums. There are two driving wires and two rewinding wires. The rewinding wires are attached to the Wing Wagon through a tensioning device (spring or active tensioner). These rewinding wires carry no significant load; they only maintain wire tension and rewind the driving wires after each power stroke.
The Wing Wagon must be designed to be as lightweight and strong as possible.
3. Wing Axis
The Wing Axis is a carbon-fibre (CF) elliptical-section tube chosen to provide high vertical bending stiffness while allowing a narrower cut-out in the mast. It is a single-piece component that supports both the starboard (SB) and port (PS) Transformer Wings.
Forces are transmitted as follows: Wing → Axis → Wagon → Wire → Drum → Gear.
Ball bearings and part of a worm-gear mechanism are mounted on the Wing Axis. A servo motor inside the Transformer Wing rotates the wing around the stationary Axis to adjust AoA. This allows independent AoA adjustment of the SB and PS wings.
Only two wires are required for electrical supply to the Transformer Wings, as all communication is handled wirelessly via 2.4 GHz radio. A wireless power solution is preferred, as it allows the TW to rotate a full 360° around the Wing Axis.
4. PS and SB Transformer Wings (TW)
Two Transformer Wings are mounted per mast, oriented horizontally (in contrast to conventional vertical sails or wingsails).
Each TW consists of:
A one-piece leading-edge section (symmetric foil, e.g., NACA0015) with 5 or 7 rotating trailing-edge sections.
The target performance is CL = 2.0 at AoA = 12°, with L/D in the range of 10–20 across the operating AoA.
The trailing-edge sections rotate 180° to reverse camber. These sections are made of lightweight, rigid material with convex or concave chord-wise edges to enable smooth rotation during camber switching. The target switching time is 1.5 seconds or less, achievable at any mast height. Advanced labyrinth sealing is proposed to ensure tight closure when the sections are in position.
Because camber reversal may occur at high frequency (e.g., 0.1 Hz), flexible materials cannot be used. Each trailing-edge section is actuated by a small dedicated servo motor. The sections are aerodynamically unloaded during the reversing zone, so the energy required for camber switching is very low.
AoA adjustment is performed by a servo motor driving a worm gear. When the Wing Axis is positioned at the aerodynamic centre of effort, the worm gear minimises the torque (and thus energy) needed to hold the desired AoA.
Each TW contains two UCUs: one for AoA control (also measuring AWS via leading-edge sensors) and one for camber switching and solar-panel control (if fitted).
Electrical supply is provided by a wireless power unit on the Wing Axis, powered from the Wing Wagon’s battery. Solar film on the wings can provide redundant power. The AoA servo allows full 360° rotation with a reliable home position and can automatically correct for boat pitching.
5. RMC – Reciprocating Motion Converter
The RMC is mounted at the mast foot on the MRP (deck level). It converts the 10–20 m linear stroke of the TWs into unidirectional rotation
of the Power Shaft.
Mounted on the Power Shaft are:
A lightweight flywheel integrated with a spiral bevel gear (ratio 1:5).
Two Wire Drums mounted on sprag-type overrunning clutches. The drums feature helical grooves so the Dyneema wires never overlap. The wires use a capstan effect (typically 5 turns) or are fixed with extra turns to unload the attachment point.
Two driving wires and two rewinding wires. The rewinding wires connect to the Wing Wagon via a tensioning device (spring or active). They carry no driving load — they only maintain tension and rewind the driving wires after each power stroke.
The rotational kinetic energy of the Wire Drums during direction changes is managed by the KER device.
Rotation speed, direction, and position of the Wire Drums are monitored by two multi-turn position sensors driven 1:1 from the drums. This enables precise tracking of TW position along the mast and regulation of vertical speed.
A locking solenoid can secure the Power Shaft at any TW position for static operation. It acts on the flywheel body and is activated only when the shaft is stationary.
The rotational speed of the RMC shaft is regulated by an electric generator operating in regenerative mode through the spiral bevel gear. The generator can only load the shaft — it cannot drive it. Only the Transformer Wings can drive the RMC. To position the TWs at a desired mast height, either TW lift force or gravity must be used.
6. KER – Kinetic Energy Recovery
The KER device improves overall system efficiency by shortening the time required for TW direction reversal at the end of each stroke.
An active KER system is currently proposed only for the deck-level reversing zone, where conditions differ from the mast-top zone (gravity assists reversal at the top, while strong down-lift is available). In severe storms, the TWs are expected to operate primarily on the lower half of the mast, so the same gravity and lift conditions apply.
The proposed KER at deck level is pneumatic, magnetic, or a hybrid solution. A pneumatic system does not need to be perfectly sealed; deliberately designed orifices can help achieve the desired damping characteristics.
At the mast top, higher AWS produces stronger lift, and gravity assists reversal, so additional mass at the top is undesirable and may not be required.