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Windknife Aluminum Extrusions
125 cm lengths (48 inches)

Foil Nose - $48.28 
qty
Full Foil 13 - $80.13 
qty
Full Foil 27 - $128.32 
qty

Briefly:

Windknife offers the D.I.Y builder a simple, inexpensive and fast way to create accurate and durable aluminium foils of varying sizes without the need for expensive tooling.We now offer three products the "Full Foil 27", "Full Foil 13" and the "Foil Nose".


click to enlarge

Foil Nose [FN]
Nose section only 6082-T6 (mill finish)
60mm wide
Standard Length
125cm 1.2kg

Full Foil 13 [FF13]
Complete 6063-T5 Anodised section
135mm chord
Standard Length
125cm 1.9kg

Full Foil 27 [FF27]
Complete 6063-T5 Anodised section
270mm chord
Standard Length
125cm 5.6kg

More details below:
Foilnose
Full Foil

Foilnose  
Extruded Hydrofoils for the DIY builder created from an aluminium extrusion.

Using the foilnose the DIY builder can create inexpensive rudders, daggerboards and centreboards for any dinghy or catamaran.

Concept

The concept of the windknife, is to give the DIY builder the ability to produce, accurate, durable foils of varying sizes, quickly without the need for expensive tooling each time a new size is required. 

Extruded Aluminium foils have been used successfully on Dinghies such as the Laser Pico, 29er, 59er and Mega Byte for over 10 years.

The most important part of an aerofoil is the nose section, this is where most of the work is done and hence where most of the accuracy is required.

The other noticable thing about the front section is that the nose of a long thin foil is similar to that of a short fat foil. Below is a NACA0009 section and a NACA0012 section both of similar thickness super imposed, it can be seen that it is really only the rear sections that differ. Therefore it is valid to use the same nose section for the construction of different sized foils.

The windknife uses a common nose section which can be compressed or expanded, the rear section on the windknife is simply 2mm thick aluminium or plastic sheet bonded to the front section.

The nose of the windknife foil is a 22.5mm thick NACA0012 section, this is a good middle of the road section. Equally good for centreboards and rudders.

The principle application for these foils is for dinghy and beach catamaran rudders and boards. For rudders these tend to be designed to fit standard rudder stocks which are either 20mm or 25mm thick, the windknife falls between these two at 22.5mm, the principle is that the foilnose section is compressed slightly to be 20mm thick or expanded slightly to be 25mm thick. Centreboards are often thicker, up to 35mm, and the smallest boats such as the optimist might go down to 15mm thick.  Therefore the windknife has been designed to make foils between 13mm-35mm thick.

Some standard sections

 Boat  Type  Length  Width  Depth  Spacer  Rear Plate
 Pico
 Rudder  230  25  880 17  185
 Pico  Board  275  30  900  22  230
 Laser  Rudder  203  20  750  12  158
 Laser   Board  341  33  1250  25  296
 Optimist  Rudder  260  15  725  7  215
 Optimist   Board  285  15  1067  7  240
 Standard  NACA 0012  187.5  22.5  833  14.5  142.5

In the images below we see three sections, each is a NACA 0012 of three different thickness 15, 22.5 and 30mm thick.

The foil nose extrusion has been compressed or expanded to fit the profile, demonstrating the versatility of the extrusion for creating different sized profiles.


Finally we see examples of a finished hydrofoil.


Construction

The extrusion is made from 6082_T6 grade aluminium. 6082-T6 is a high quality strong corrosion resistant alloy, more info can be found HERE.

Provision in the extrusion allows spacers to be added to alter the width and provide additional reinforcement or stiffness when necessary.

By altering the width of the extrusion and using different length tail pieces aerofoils and hydrofoils of different sizes can be constructed.

Also the addition a 1/2"x10Swg tube, as shown above, would provide a good hole for an M8 thread to be tapped into.

Even asymmetric aerofoils can be constructed

All this from this single clever extrusion


click to enlarge

DXF files of Windknife extrusions available here.

More information on the Windknife website.

Full Foils

Our latest extrusion is a complete foil which can be altered to create foils of different profiles without the need to purchase additional parts. It requires less operations to complete and has less joints.

Just like the original Foil Nose this extrusion can be used to create foils of different shapes and sizes

Analysis showing a Full Foil being deformed to create a shorter thinner section.

The full foil can be cut and compressed or expanded to create foils of different sizes.In the picture below we see three sizes 270mm, 210mm and 160mm chord lengths. The rear section which was cut off can be used to improve the glue joint by enlarging the surface area to be glued.

In this sequence of images a standard 25mm section is expanded to 30mm wide by using a 1" ball bearing and pushed through with a 1" Diameter Alumunium bar. The resulting section is a 30mm thick section identical to a Laser Pico Centreboard.

In addition to the full foil 27 (above) we have a new model called the Full Foil 13 [FF13] which is a half size full foil that is 13cm long. this has been in response to a request from people building foiling boats and kite foils.

 
 
See a build guide on instructables