Phase II Final Report - NASA's Institute for Advanced Concepts

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
.
Figure 3-115: LEV Formation (View 1) Figure 3-116: LEV Formation (View 2)
The wake deformations also play a major role in thrust characteristics of the vehicle at these low
Reynolds numbers. Many researchers have tried to visualize the flow patterns of these wakes
and have suggested that these tend to augment the thrust tremendously. These unsteady wakes
also cannot be modeled using the conventional fixed wing aerodynamics.
Another approach is to model flapping wing as a propeller as suggested by Theodore Theoderson
[255]. Azuma [12] has also used this approach to predict flapping wing performance. Rotorcraft
aerodynamics has different approaches for computation of forces, which are as follows:
3.3.3.2.4 Momentum Theory
This is a very basic back-of-the-envelope type calculation approach which considers the propeller
or rotor as a rotating disc and then computes forces based on mass and momentum conservation.
This cannot be used as for case of flapping because the wing is not covering the entire 360 o
or 2π radians, and also direction of rotation is changing twice within each cycle during the
upbeat and downbeat.
3.3.3.2.5 Blade Element Theory
This approach divides each propeller blade into different equal-length small strips/segments and
then each strip/segment is analyzed separately taking into account the incoming flow velocity as
well as angular velocity. The forces on the entire blade are then computed by summation of
forces on all the segments. This approach considers the effective angle of attack at different segments,
but still assumes a uniform inflow. This model has been modified to account for the non
uniform flow by blade element momentum theory. Still these models do not consider the leading
122
Phase II Final Report