Building : Workshop, [pg2] | Pictorial drawing , [assembly], [detail1], [d2], [d3] | airfoil bending | arm vibration |
shaft & pipe fatigue | bolt tension | bearing size | bearing friction | arm aerodynamics drag

Wood airfoils

Blurred airfoil image with supporting arm and washer spring nut

The airfoil model can be fabricated using either solid woods or aluminium sheets with spar and rib. The solid wood airfoils were chosen because it is easier to produce small airfoils from wood and unfamiliarity with the spar and rib fabrication method.

Two types of woods, which are easy to shape (for beginners) and available, are the jelutong and balsa wood. Both come in very limited sizes (i.e. balsa strip with maximum 6.5mm thick, 105mm wide, and 900mm length, while jelutong strip with maximum 6mm thick, 71mm wide, and 700mm length). Jelutong wood was chosen instead of balsa because the wood is much stronger and cheaper (RM30/US$8 per balsa strip and RM5.5/US$1.5 per jelutong strip). However, the disadvantages of jelutong are its heavier weight and smaller size.

The chord of the airfoil is limited by the available jelutong strip size to 7cm. The thickness of airfoil is also limited by the jelutong strip thickness to NACA0015 (or thinner). The airfoil length of 50cm is determined from the limited chord length, which will give solidity around .45 and height to diameter ratio of unity.

The fabrication of the airfoil by filing and sanding the jelutong strip can produce good accuracy profile if long time is invested in the final sanding process. The fabrication of airfoil starts by sawing the jelutong strips to length of 50cm. Next, pairs of jelutong strips are glued together using contact adhesive to form a thicker strip. NACA0015 profile is drawn at both sides of the wood strips. These profiles and the glue line at both sides become the main reference when shaping the wood to airfoil shape. Then, these paired wood strips are clamped on a vise and filed to rough shape using very rough wood files and rasps. The flat sanding machine is then used to sand the wood airfoils to a very near shape. Finally, sandpapers with increasing grades are used to sand the airfoil to final shape. Cardboard template with half of the airfoil profile cut out (like a half die, refer figure below) can be used in these sanding processes to check the airfoil shape especially at position far from the sides.

Template (shaded area) for NACA0015

Flat plate supporting arms

The flat plate supporting arms will support the centre of airfoil at one ends and joint to the hub at the other ends. Flat plates were cut to required length using shear machine. A pair of hexagon bolts with head grinded off were spot welded (SMAG) to one of the plate end, which will support the airfoil. At another plate ends, two holes were drilled for fastening to the hub using a pairs of bolts.

Assembled supporting arm and hub view

Last updated at November 6, 2002
Comments are welcomed