99a-Thorax: 5X, Fan-fold wing, 2 DOF

Completed Aug 1999. Status: Buckled links


The 99a thorax consisted of two four-bars folded from 12.5 mm stainless steel (etched by Accutech).
Polystyrene wing spars were attached to the distal links of each 4-bar and a 12.5 mm polyester
fan-fold wing was attached. The steel flexures were reinforced w/ tape. Actuation was achieved
with VCAs driving each 4-bar through push rods. The wing was driven up to 30 Hz but
performance degraded at higher frequencies due to the limitations on the VCA.

The base link was a 26mm long box beam. The side links were 28mm long triangle beams. The top
link was a 4mm long triangle beam. All links were 4mm on a side. The steel flexures were 2mm long.

Still images for wing at various phases of stroke

The thorax could provide up to 120 degrees of flapping or 90 degrees of rotation (the latter is
demonstrated in the movie below). However, these ranges could not be achieved independently
as one could be achieved only at the expense of the other. The still images here demonstrate a
stroke trajectory in which 45 degrees of rotation and 60 degrees of flapping is achieved.
NB: The wing is incorrectly mounted with a vertical stroke plane instead of a horizontal one.


PIV images for wing running at 17 Hz

These particle image velocimetry (PIV) images were taken for the wing being run at 17 Hz in still air.
The velocity flow patterns are those for olive oil particles. Some interesting things to notice: (1) the
fan-fold wing billows out (see the beginning of the downstroke), probably effectively reducing the
amount of lift that otherwise would be generated with a rigid wing; (2) the sudden change in the particle
momenta between the end of the upstroke and the beginning of the downstroke would indicate a large
lift force on the wing; and (3) there is evidence of vortex shedding in the 2nd frame of the downstroke,
which should also increase lift.


Movie demonstrating +/-45 degree motion and motion up to 30 Hz (.asf format)