Having found the radius, the diameter of the circle can be found: As we don't know the half chord of a blade, but it's total chord, l can be rewritten:Īs the recommended airfoil has 4% camber, and ideally would have no thickness, we can use this percentage to find find the depth of the arc, in terms of blade chord: By increasing the maximum thickness from 4% to 8%, the camber line could be restored.įor the purpose of a blade, these parameters can be substituted. To regain the 4% camber line, I needed to change the thickness of the airfoil. It affects the mean camber line halving the maximum camber from 4% to 2%. This makes it substantially thicker, while making construction no more complicated. One change is to add flat bottom to the section. I was likely to build this airfoil, thus I wanted to make the modifications very simple. I had to make sure my modifications did not change this parameter, as to produce the least alterations in performance. It is the mean distance between the top and bottom surface of a section. The mean camber line is a critical factor for airfoil design. I decided to use both sources to make a set of blades, then compare which produced the best results.Ģ) How can the recommended ( 4% camber, circular arc ) airfoil be modified to allow greater thickness, without substantially affecting performance?

As I didn't have carbon cloth and resin, the only sources of sizeable CF I had were a 0.5mm thick sheet, and a set of broken T-rex 450 blades. This directly points to a composite material, carbon fiber seeming like the first choice. Two questions arise from this though:ġ) What material is rigid enough, yet light enough to be used sizeably, to make a thin cambered strip stiff in torsion?

There are two solutions for this: The blades are constructed out of a very rigid material, or they are somehow made thicker. As this power extraction directly affects how much lift a rotor can produce, the blades should be as rigid as possible to avoid this effect. This reduction in angle can be very detrimental to the power a rotor can extract. Low torsional rigidity of a blade and camber pitching moment

Pvc wind turbine blade template