mecaflux functions,Drag force, Polars,foils ans sails, Lift force,Profiles and airfoils

Example calculation for a dagger board with software Mecaflux :

What are the forces?

The wind in the sails (example calculation sail) Generates a propulsive component and drift component . (it's one that makes the boat slip on the side). We assume for this calculation that the component of drift force is 1000 Newtons.

The role of the dagger board is to create a opposite force-drift 1000N through lift force .

The fluid velocity is the speed of the boat.

incidence angle of the profile or airfoil relative to the direction of the fluid is the drift angle (drift of the boat).

Example calculation for a dagger board with software Mecaflux :

What are the forces?

The wind in the sails (example calculation sail) Generates a propulsive component (which is that makes the ship) and component drift. (it's one that makes the boat slip on the side). We assume for this calculation that the component of drift is 1000 Newtons and apply it on a profile that we call: dagger board.

The role of this dagger board is to create a force-drift 1000N balancing through Lift force its profile or airfoil .

The fluid velocity is the speed of the boat.

The incidence Profile relative to the direction of the fluid is the slip angle or (drift boat). You have the converter in a triangle trig you will quickly angle of impact if you enter the distance as the adjacent side and drift (assumed or sought) as opposite side.

In fact the lift is perpendicular to the displacement of fluid but we simplify our example a little

We seek -a lift force that balances the 1000 Newtons

To do this we can use:

speed boat (an average speed for a boat: 6 knots)

angle dagger board/ boat (is the angle formed by the axis of the vessel with its actual trajectory)

The length of dagger board

The Chord or width of the dagger board

calculating dagger board with the software Mecaflux

   Select a profile with drag and lift your wing, whether it is a dagger board of windsurfing or boat it is better to be symmetrical

Two symmetrical profiles are tested in wind tunnel operation: NACA0009 and J5012 (the polar patterns are already in MECAFLUX ,but you can change the Cd and Cl ( links mécafluide profiles ), Here we chose the NACA0009.

- Enter the fluid parameters (speed: 6 knots, temperature 20 ° C, density: 1000Kg/m3)

- Enter the chord ofthe profile (the width of the dagger board, take 1 meter)

- Enter the length of the dagger board (say 1.5 meters)

- Enter the incidence of the profile ( try to set the angle formed between the chord and flow direction on 10.5 °. The pattern proposed are those studied in wind tunnels (they are limited to interesting angles)

-Click on calculate

The result sheet is useful to print or save your calculations, but rather look at our case diagram, close the page of results :

The diagram shows the profile after calculating the value of the lift but the drag ...

we see that the lift is 5588.638 Newtons (570.041095 Kg.f) is much more that we need so we can say that our dagger board, when the boat drift of 10.5 °, largely catching up skidding . We can therefore assume that at this speed (6 knots) will never reach the drift angle. Then adjust the angle of dagger board until it generates a balancing lift 1000 newtons ...

-With 3 ° incidence: lift = 1748.674 Newtons (178.364768 Kg.f) trail: 5.1786 Newtons

"With 1.5 ° incidence: lift = 911.1074 Newtons (92.932951 Kg.f) trail: 4.4018 Newtons

We can therefore say that our dagger board will give us a great boat that derive only 1.5 ° to 2 °.Unfortunately the drag of our dagger board is a super drag-and super-slowing our boat (it will take about 1 m² sail further by force 5 to balance the drag force...)

Seek a lower drag by reducing the friction surface (this profile:

- With an incidence of 6 °, a chord of 0.5 and a length of 1 (area: approx 0.5m ²) we get:

the lift force for naca0009 is 1044.413 Newtons (106.530135 Kg.f)

the drag force for naca0009 is 4.2237 Newtons

With you to find the best compromise between speed,incidence, drag, lift, size, strength ... for your future boat ...

MECAFLUX gives fine enough results to think and approach a good compromise, but for America's Cup you have to invest in software modeling hydrodynamics costing much more setup time and money, unless your talents of marine are sufficient...

Exemples