Blade Element Theory

Blade element theory (BET) is a mathematical process originally designed by William Froude (1878), David W. Taylor (1893) and Stefan Drzewiecki to determine the behavior of propellers. It involves breaking a blade down into several small parts then determining the forces on each of these small blade elements. These forces are then integrated along the entire blade and over one rotor revolution in order to obtain the forces and moments produced by the entire propeller or rotor. One of the key difficulties lies in modelling the induced velocity on the rotor disk. Because of this the blade element theory is often combined with the momentum theory to provide additional relationships necessary to describe the induced velocity on the rotor disk. At the most basic level of approximation a uniform induced velocity on the disk is assumed:

Alternatively the variation of the induced velocity along the radius can modeled by breaking the blade down into small annuli and applying the conservation of mass, momentum and energy to every annulus. This approach is sometimes called the Froude-Finsterwalder equation.

If the blade element method is applied to helicopter rotors in forward flight it is necessary to consider the flapping motion of the blades as well as the longitudinal and lateral distribution of the induced velocity on the rotor disk. The most simple forward flight inflow models are first harmonic models.

Famous quotes containing the words blade, element and/or theory:

    Each blade of grass has its spot on earth whence it draws its life, its strength; and so is man rooted to the land from which he draws his faith together with his life.
    Joseph Conrad (1857–1924)

    There is only one element that can break the Afrikaner, and that is the Afrikaner himself. It is when the Afrikaner, like a baboon shot in the stomach, pulls out his own intestines. We must guard against that.
    —P.W. (Pieter Willem)

    The things that will destroy America are prosperity-at-any- price, peace-at-any-price, safety-first instead of duty-first, the love of soft living, and the get-rich-quick theory of life.
    Theodore Roosevelt (1858–1919)