Flapping propulsion

##Dual Flapping Propulsion System##

Dear Visitor

I do not have any traditional blog Blog, however, on Home page, you can find kind of technical blog about Lateral Ballast Variable Wing boat.

On this page, I will let you follow my work about Dual Flapping Propulsion System and Flapping to Propeller.
This is also kind of technical blog.
The idea is to skip any detailed calculus and simulations I have done in that metter just in order to provide simple and probably inspiring information.

Note also that these pages are about walking in the “Babel Library” or digging around the BOX and things I find there are not always practical or might be nonsense as well.
Still, I like do this job as it is fascinating and more fun and giving than watching TV.  

Today is 2016-09-29 My sailboat "Sea Hawk" is already on land and I will start to fill some more info here soon.... 



The Lateral Ballast Variable Wing project proposed for sailing boats on HOME page gets suddenly transformed into flapping propulsion boat. Particularly propulsion of a catamaran will be tested at first.
The proposed acronym for this propulsion solution will be DFPS which stands for Dual Flapping Propulsion System.

The main goal of this project is to prove that another way to provide propulsion for wind driven boat might be valid.
It is almost certain that this kind of boat will be called wingboat instead of sailboat, however, sailing still will be possible….;-)

One of the surprising ability of proposed solution is that the boat will be able sailing fast directly heading into the wind’s eye.

A very short explanation of the functionality of this new boat depicted below:
The above deck wing is driven by lift force and move up and down. The lift direction is changed via the angle of attack or angle and camber when using variable shape wing proposed for LBVW boat. 

The above deck wing is mechanically connected to the underwater flapping fin thus a propulsive force is provided to the boat.

One very important feature of proposed propulsion system is that the above deck wing and the connector are floating on the buoyancy of the underwater flapping parts which are designed to balance the gravity force of the whole propulsion system. The boat hull has its own buoyancy.
Note also that eventually mounted stern rudders are not depicted as it is not certain if they are necessary.


Above:  Conceptual sketch of an experimental catamaran with proposed Dual Flapping Propulsion System.
Note that the propulsion provided by the water fin can be directed forward, astern or any other direction.
The deck hub (blue) can rotate together with the wing-fin connector (yellow) which is free to slide up and down at the same time.
Note also that any direction of the true wind will provide propulsion including when heading directly into the true wind.
The above deck wing will be utilised at 3-6 degrees of attack angle when at high speed, therefore, the drag of the boat propulsion system is very low promising good efficiency.
The above deck wing and the underwater flapping fin will have the ability to set the attack angle +/- 90 degrees for different purposes.   

The way of thinking is as follow:  when a traditional sailing boat is sailing close to the wind then only approx 15-30% of the force produced by sail is directed in direction of travel. The remaining force is heeling the boat and therefore a keel as ballast or other righting methods are necessary.
In order to utilise the full power of sail, it is necessary to sail Beam Reach, however, if the boat is fast then it will end Close Hauled anyway.
No sailing boat equipped with soft sails is able to sail directly into the wind eye yet but that is about to change….;-)
So the question is how to fix Beam Reach sailing all the time?

This is leading us to the conclusion that a wing can be mounted horizontally, like on an aeroplane.
It means that the lift can be directed effectively, straight up or down, just by setting right camber and right attack angle.
It also means that the by wing produced force - straight up or down directed lift force is at its possible maximum all the time.


Lately acquired knowledge about flapping propulsion like the fishes it telling us that it can be expected high efficiency
when such air “flapping” wing drives directly a flapping fin in the water – no gears, no losing efficiency.
It is to be noted that the ground-effect is probably important part of proposed solution as the wing is exactly placed where the ground-effect take place.

The beauty of proposed solution is that the wing systems weight is balanced by the flapping fin-rudder buoyancy in the water so it is to understand that the wings propulsion system is floating on the water – well… the weight is almost zero.
The idea results that there is no need to hold the weight of the wing system. However, it needs to accelerate the mass of the system by every stroke and overcome the resistance on the stroke of the underwater parts of the system. It might be an easy way to recover the kinetic energy at each reversing by means of the magnetic spring device. Such a magnetic spring damper has almost no losses.

The experimental boat needs to be able to provide maximal utilisation of wind and water for propulsion therefore no much simplifications are planned. So, the system needs to be highly controlled by electronics, however, a simple solution will be tested at the beginning as well.

A benefit can be observed that the flapping fin system has own buoyancy and its kind of unique that the propulsion system does not need to be calculated into the boat (hull) weight. So the result is that we drive a very light boat and this promises high speed?

It is very convenient characteristics of the boat that there is no need to provide a ballasting means as the heeling is mostly due to waves and not the result of the aerodynamical forces. This means very light boat – more speed and probably record speed when sailing into the wind eye.
Still, the Lateral Ballast can be used together and be efficient way to collect electrical energy from the system while damp the pitching and roll of the boat. It is no doubt that the solar panels will be used and contributes to energy maintenance on the boat.


Above: Parts mark blue has own buoyancy (separate from catamaran’s hulls) and moves up and down together as a weightless unit.
The point here is that just a little wind can already move the propulsion unit up and down as only inertia is involved.
This is most important part of the invention – little wind speed will do the propulsion as well.



Above: Parts mark blue are connected in a way allowing 360 degrees rotation while moving up and down and adjusting angle of attack




Above: Parts mark blue are connected in a way allowing 360 degrees rotation regardless rotation of the yellow mark part while moving up and down together with the yellow part while adjusting air wing angle of attack.


At first sight, all this looks stupid but think that it is:

- Not necessary to have ballast, or little one, on single hull boat, however, lateral ballast may be beneficial for energy production

- Not necessary to de-power the sails to keep the heeling at optimum (no reefing or sail deformation)

- The rig and “sails” has virtually no weight – the propulsion system float on its own

- Possibly ground effect can be utilised to improve the CD and CL

- The lee-way of the boat is eliminated

- Possibly bi-plane can increase wing area

- The centre of gravity can be lowered at high wind speed by limiting the stroke length (moving just little bit above the deck)

- Ability to produce electric energy by means of linear generator/motor

- Variable Shape Wing can improve the efficiency of proposed system by improving the CD and CL

- Possibly to obtain some propulsion by utilising wave’s energy

- The upper wing surface can be covered by solar cells, and when possible adjusted perpendicular to the sun rays

- Here proposed, new topology for wind, sun and waves propelled vessel has big potential to be developed further  


One can wonder why this should work when all testing with rotating wind turbine shows that it is not working well.
The answer is hiding in the simple fact that rotating land mounted turbine is not very sensitive to where the vector of lift is directed - it still producing power.
Note that the fast rotating blade makes own wind, then the resulting lift vector is not directed perpendicular to the blowing wind but rather to the apparent wind.
Once such rotating turbine is mounted on a boat with the aim to sail direct into wind eye then only a part of the lift vector is directed as propulsion.
Observe that it is not only the aerodynamic drag of the propeller blades hindering the boat but also part of the miss-directed lift vector pointing at an angle to the stern of the boat.


Therefore the possible solution is to increase the wing area and slow down wings perpendicular to wind motion.
There is a big difference between land mounted turbine and ship – the ship is moving. When the ship moves against the wind then the area of the system increases laterally, therefore, more power can be extracted from the wind per time unit. All this makes that that we can operate the wing at small angles of attack and the wing movement perpendicular to the wind can be increased when the apparent wind increases due to the higher speed of the boat.
These facts allow us to utilise all the time the force of the lift vector directed up or down at very low drag when compared to the wind turbine.



Above:  A simple model of "record demolisher" ;-)  – can run only into the wind – no electronic control used but some magnets are helping to change the angle of attack at the end of a stroke and to recover the kinetic energy.




The propulsion system needs to be dimensioned when based on proportionality dictated by air/water density and air/water speed.
In addition, there is an optimum for stroke height, flapping frequency, and attack angles.
Once all this is set correctly we will get some answers about performance och such system
and first, then we can improve it to be better....

The weakness of such propulsion system is the fact that the speed of the wing stroke up and down needs to increase as the boat speed increase.
So, there is a limit how fast the air wing will be able to move but it exists solution for that...and it might be a special linear gear making the water fin moving faster (longer stroke) that the air-wing. 


Some digits….about hydro and aero-dynamic forces: 

For air the dynamic pressure is q = 0.0625 * (wind_speed) 2     

For water the dynamic pressure is q = 51.5 * (water_speed) 2

Ftotal = q * wing_area * CL  



Just to get some feeling let say that wing_area is 1m2 and CL is 1.0 therefore the force Ftotal to be expected is:

Ftotal =  0.0625 * (wind_speed) * Area * CL  = 0.0625 * 102 *1 * 1 =  6.25 kG force for air speed 10m/s

Ftotal =  0.0625 * (wind_speed) * Area * CL  = 0.0625 * 202 *1 * 1 = 25 kG force for air speed 20m/s


Ftotal =  51.5 * (water_speed) *1 * 1    = 51.5 * 52 = 1287 kG force for water at 5m/s








The presented above solution where the air wing is driving directly an underwater fin have one beautiful characteristic which is that it mimics the propulsion of fishes thus do not disturb the life in the water as much as propellers do.

Still one like to see if there are any other solutions in the Babel Library...
Here is described work particularly dedicated conversion of "flapping" air wing linear force to rotary propulsion for the boat. 
The result can be used on a sailing vessel to rotate water propeller.
Note that I am using world "flapping" however it is not correct. The air wing is moving up and down and is not flapping yet but who knows...


A new conceptual solution for "Flapping" to Propeller is proposed:

The thinking is as follow:
There is a necessity to have kind of variable gear with a big range of ratio in order to control the up and down speed of the wing while receiving the power.
It is to be noted, that the wings lift force is increasing with wind speed v2.
A mechanical solutions exists in plenty, however, most of them kills this idea in one way or another.

The proposed solution is removing the necessity of the mechanical variable gear.

The provided by wings torque force is used to drive a very high-efficiency Lorenz generator-motor.
This generator can be mounted vertically direct on wings track axis or on the bottom, inside the hull, via 1:1 gear easy to be water cooled.
The motor function of the generator is not meant to drive the boat but to reposition the wings when necessary.

The motor for boat propulsion is also a very high-efficiency Lorenz motor and is mounted on the bottom, inside the hull or inside the centreboard/rudder thus indirectly water cooled as well.

When there is enough wind speed then the wings are moving up and down thus rotating the generator which is supplying the motor which is rotating the variable pitch propeller. (I begin to like it ;-)

It looks that such solution is having bad efficiency but the problem here is not the efficiency alone but also how such a system can be functioning already at low wind and utilize also high wind energy from high speed apparent wind.
It can be mentioned here that work related Lorenz motor/generator is described in separate document. This indirect water cooled motor/generator with specially developed windings just for this project is of very high efficiency.

The proposed system is able to move the wings at very light winds already as the generator is able to load the wing system from 0 to maximum and also help to move the wings up when necessary. Therefore avoiding mechanical gearing, as much as possible, is very important.

The motor/generator can be build also as dual motor/generator. By dual is meant that 2 motor/generator are of the same type and mounted close to each other with the possibility to have a kind of clutch on their axes.
This opens some interchange of functions but most interesting is the ability to produce twice as much trust when both used as motors or energy when both used as generators. The latest case is valid when the real wind is very high and i.e. the boat is on the anchor and the energy is used to drive lateral ballast in order to limit the excessive rolling of the boat. The back draw of such solution is that 1:1 gear is necessary to be added, however, the centre of gravity of the system is lowered.

The standard solutions for conversion of linear movement to rotational are not directly applicable.

There are some special requirements just for this conversion:

1. It needs to be kind of continuity in the movement of the wing while the kinetic energy is used for stroke reversion.
2. The converting device needs to be in gravitational balance so not any additional work needs to be necessary to hoist the wing.
3. The force/torque during the stroke must be constant at constant wind speed (not like many crank based mechanisms)
4. The losses for conversion need to be low. This implies that sliding gears like friction-disc transmition or multi-stage gearing needs to be avoided.
5. The wing must not show any vibrations due to the conversion as it will disturb the air flow around the wing.

The requirements call for a solution where the conversion method and the track holding the wing are separated.
It looks that a timing belt is the best solution for the conversion while bearings running on track will hold the wing.
Pulley and belt with flights (kind of connection to the belt) or Synchroflex Double Sided
Roller – sprocket – chain is the other solution but there are some disadvantages like mass, vibrations, many parts.


 Above: Servo City X-Rail connected with 3D own printed reversing path. The idea is that the wing is running most of the time on the straight path and is reversing once in uppermost position and once in lowest position.

Note that some other solution are possible however this are the part possible to buy from servocity.com for the model.


Above: Note that the wings are reversing without loosing much speed – the kinetic energy is helping to reverse
The wings are driving the 1:1 ratio gear wheel axis via timing belts….not depicted above for simplicity...
The angle of attack is changed during wing reversing.


Above: The air wing "flapping" to propeller conceptual sketch. The up and down mechanism is covered by tracks cover
             Note that the tracks cover has wing profile like NACA 0015 and can be used to provide some driving force as well….



Above: If possible the wings can be from the most upper position put along the track cover like in port…or anchor….


Above: The electric part of the propulsion system:
Mark green is the electric motor-propeller system, electrically connected to generator or/and batteries.
Mark blue is the "flapping" wing-generator system 1:1 stage gear.
The wings are driving the axis of pulleys via timing belts….not depicted above.

The whole arrangement of the wings and generator can be rotated by means of the deck hub thus enabling sailing in any direction.
The same is for the horizontal part of the propeller system – when rotated, it will provide trust in any direction relative the hull.

Note that this arrangement is space effective and is suitable for any boat type: single hull, catamaran or trimaran.


In order to give you same feeling, about this proposal, see below some calculus to check the feasibility of proposed propulsion system. This example is adjusted for a boat model but it is easy to see what happens when wing area or apparent wind is increased.

Wing area is 2m2

Wing CL = 1.0

Wing allowed speed up and down is max 1m/s


True wind speed 5m/s

Boat speed 5m/s

Apparent wind speed 10m/s

Pulleys diameter 0.028m which gives 87.96 mm / per revolution at wing speed 1m/s   .

If the Timing Belt is doing 1m/s then the Pulley will rotate 1000mm/87.96mm = 11.36 RPS which is 6.28 * 11.36 = 71 rad/s  ; = 681.6 RPM

The wings lift force  FL = 102 * 0.625 * 1 * 2m2 = 125 N


Pulleys torque = 125N * 0.014 = 1.75 Nm


Power = 1.75 Nm * 71 rad/s = 120W for 2m2 wing at 10m/s apparent wind and 1m/s wing speed up and down.

If we increase the wind speed to 10m/s and boat speed also to 10m/s we can expect:

Power = 7 Nm * 71 rad/s = 497W for 2m2 wing at 20m/s apparent wind and 1m/s wing speed up and down.

Some power will be lost due to timing belts, 1:1 gear and rotation resistance of the Lorenz generator/motor.
Additional losses are in the windings of the Lorenz generator/motor.
Best imaginable efficiency at nominal power expected to be 0.7-0.8 as some of the losses are not depending on power amplitude. Observe that this is efficiency of the wings to the system not the wind to the system.

At higher wind speed it will be possible to increase little the vertical wing speed and the angle of attack.
This will result in higher output power.
Note also that used in the calculus above lift coefficient of the wing can be higher as well when better wings arrangements are used.
Note also that the battery system in not a part of the system efficiency as the generator can be connected to the motor directly.


The fact that electric motor is driving propeller is opening for solar energy utilization as the WSW boat concept requires;-)






To be continued.....