blade twist

blade twist

blade twistclick for a larger image
Propeller blades are designed with a twist with higher angle at the hub than at the tip. This is to equalize the lift distribution along the blade to the extent possible. During the rotation the tips of the blades move at a faster pace than those areas near the hub. If the blade did not have twist all along from hub to the tip, there would be dissymmetrical rotation speed and consequently lift. Hence, the necessity for blade twist.
i. The undesirable variation in pitch from root to tip caused by aerodynamic loading.
ii. The twist built into a propeller or rotor blade. In the case of a propeller, it is to ensure that the pitch angle at the root is greater than the tip. In the case of rotors, it is to compensate for unequal lift between inside and outside the rotor as well as to maintain RPM during autorotation.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
In that study, the main rotor blade radius, blade chord length, blade twist, blade linear mass density, blade flapping spring stiffness, and angular speed were the passive morphing parameters.
In that study, some additional parameters, that is, the blade twist and coefficients of the airfoil distribution function, were also investigated.
In this study, the blade twist angle, chord length, and relative layer thickness are, respectively, defined as optimization design variables, and these variables determine the blade aerodynamic performance.
Figure 3 shows the curve of the blade twist angle before and after coupling optimization under aerodynamic and structural conditions.
from which it is possible to determine geometric relations and constructional parameters of a propeller--the angle of a blade twist [phi], the blade depth b and the blade thickness t.
Wind flow analysis is done over each configuration of the rotor with the blade twist angles ranging from 5[degrees] to 60[degrees] in steps of 5[degrees].
The cooling capacity, cross sectional profile, blade arrangement, blade length, blade twist, tip width and tip clearances, are all configured for optimum performance.
Further, considering thin airfoil theory [14] and airfoil data to be origin centered, the product, [C.sub.d][beta], is assumed to be very small and the lift curve slope can be approximated as [C.sub.l[alpha]] [approximately equal to] 2[pi], where [alpha] = ([theta] - [beta]) and [theta] is the blade twist. With these assumptions, (A.9) can be simplified to
5, each element of the blade undergoes a slightly different flow because they have a different rotational speed, a different chord length C and a different twist angle for a blade twisted [beta] is schematic of blade elements; dr is radial length of element; r is rotor radius; [OMEGA] is angular velocity of rotor [13].