The rotation of the propeller generates a speed and an apparent angle, which vary depending on the position of the observed point on the radius of the blade. To keep an optimum angle of incidence, the profiles of the blade of the wind turbine or the propeller, will have a pitch adjusted to apparent velocities along the blade. Pitch profiles varies and causes a twist of the blade.twisting of the blade of the propeller or turbine blade, is the angle measured between the chord of the profile at the blade root, and the profile chord at the blade tip.
The twist of the blade of the wind turbine or the propeller is related to the operating point. If the operating point varies, the blade twist must be changed. The propeller blades and the blades of wind turbines are generally rigid, them twist is fixed.
Varying the rotational speed or velocity of the fluid relative to the operating point of construction, degrades the performance of the propeller or turbine..
The variation of the pitch is to rotate the blade of the wind turbine or the propeller on its axis so as to correct the loss of performance.The pitch variation also helps regulate the speed of the wind turbines.The number of blade of the wind turbine or the propeller varies according to the torque and velocity at operating point .A wind pump will not have same number of blade, than wind turbine of electricity generation. A sailing boat propeller has a blade shape different from a speedboat propeller.
We saw in the article distribution chord profiles, that the lift of wind turbine blades and propellers, should be distributed as far as possible from blade tipl eaks , This leads to an elliptical distribution of lift, but not the same distribution of the chords:. The speed of movement of the blade elements being smaller at the root of the blade, the surface should be increased at the foot of the wind turbine blade (.. or the tidal turbine, propeller) to respect the elliptical distribution of lift.
A compromise between the overhead of matter and the yield earned must be evaluated because the matter used in the blade root is very important. A high aspect ratio of the blades, usually offers better performance, but for boat propeller blade length is reduced by the maximum depth of the propeller shaft, tip velocity of blades quickly generates cavitation when the blade approximates the surface, and limited Draught... These constraints impose very different forms of blades from the shapes of aircraft or wind turbines blade.
Blade manufacturing: Materials and technology
the matter and the structure of the blade, are taken into account in the calculation of resistance of the propeller or the wing by Heliciel software.A quick tour of the horizon on the technical materials and construction of the blades will be useful.
- Blade propeller plane
Of course, we tried to replace the duralumin with a lighter metal : Magnesium alloy. The lightness of the blade is an extremely significant element because the centrifugal forces - tens of tons - are proportional to the density of the material used.The reduction of weight of the blade saves us on all fronts: reducing of: sections, weight, size of the parts of the hub.However forging blades magnesium requires a more powerful tool, as forging blades duralumin. On the other hand, a solution has been provided by the development of matrixing for the manufacture of the blades. Another material used for the propeller blades: the steel. Steel is used for large propellers, which is hollow,then it is made of two half shells pressed, sealed over their periphery and having internal stiffeners;the durability of the welds naturally asked a long development,sheets "rolling" on each other for the first achievements.
Carbon is increasingly used and seems to impose. The performance of lightness and strength make it material of the future. A perfect mastery of the molding is however need, to a good balance and absence of defects.
- Blade propeller boats
the propeller blades of boats are generally molded: a mold bed is constructed, and the smoothed out to pitch propeller using a rotating plate around a sliding and guided by a rail axis giving it propeller pitch:
The bed of the mold is hollowed and formed, with boards, cuts at shape of profiles of the blade.
The top of the mold is made in the same way and the blade is cast.
A new generation of propeller is created with carbon entering and winning in the market for boat propeller::
- wind turbine blade
A construction technique used for small wind turbines is sometimes pultruded fiberglass. The pultruded blades pass through a shape that gives them their profile, but the distribution of chord is necessarily constant.Molded blade thus help create more efficient aerodynamic shape, than the pultruded blade.
another method to construct fiber and resin, is to wrap a wire coating resin around the blade by turning on a lathe::
again the carbon appeared but it is rather reserved for small wind turbines because of the price of the material.