Vertiflite Sep-Oct 2013 sample article - page 2

On July 11, AHS International and
Sikorsky Aircraft presented the $250,000
AHS Sikorsky Prize to Toronto, Ontario-
based AeroVelo for flying the first human-
powered helicopter to meet technical
requirements set by AHS more than a third
of a century earlier, in 1980. – Ed.
Beginnings
I
n May 2011, we heard about the
University of Maryland’s Team
Gamera conducting their first flight
tests of a human-powered helicopter.
The two of us had led the Snowbird
Human-Powered Ornithopter Project,
which in 2010 resulted in the world’s
first piloted, flapping-wing aircraft to
sustain flight.
Passionate about lightweight
engineering and design for human
power, we realized that the AHS Sikorsky
Prize might be an opportunity to pursue
our true interest and passion again.
Meeting the prize’s requirements of a
single flight that achieved a height of
9.84 ft (3 m), remained aloft for 60 sec
and stayed within 32.8 ft (10 m) of its
liftoff point also could set the stage for a
career of doing what we loved to do.
Todd had just finished his Ph.D. at the
University of Toronto Institute for
Aerospace Studies. Cameron left his
position in the unmanned air vehicle
industry, and we began the Atlas
Human Powered Helicopter (HPH)
Project.
At the outset, it looked as if Team
Gamera had several years’ head start.
However, we had worked on the
Snowbird for four years and were
experts in human-powered aircraft
(HPA) technology and construction.We
had zero helicopter background, but
surmised that this was more similar to a
typical HPA than a helicopter.
Starting our initial configuration
study in January 2012, we looked at the
size of previous HPHs and eliminated
the most obvious constraint: we would
not design Atlas to fit inside a gym. Our
objective was a minimum-power
helicopter focused on achieving the
prize flight. The flight test venue was a
logistics concern for later.
Based on the simplified power
estimates, we eliminated hinged main
and tail rotors and further evaluated
quad-rotor and coaxial, counter-
rotating, and tip-propeller-driven,
single-rotor configurations.We applied a
basic aerostructural optimization
scheme to the quad-rotor and prop-
driven configurations. This showed that
the optimal sizes were larger than
expected (with a quad-rotor radius of
about 42.6 ft or 13 m), and the powers
very similar.
We selected the quad rotor for
several reasons. It is inherently stable.
The maximum sizes of its primary
structural elements were reasonable
and would minimize joints. There were
economies of scale for manufacturing,
with four- or eight-instance repetition of
the main components. And it had
heritage.We fixed the rotor radius at
32.8 ft (10 m), given that the optimum
was very shallow and we had greater
confidence that an aircraft of this size
was feasible.
We programmed a more advanced
aerostructural optimizer for design of
the rotor blade. It includes a vortex-ring
model that is similar to a vortex lattice
but with vortex filaments from each
revolution collated in a ring; this was
inspired by analysis methods for bat
flight. It also included a one-
dimensional frame finite element
analysis (FEA) with detailed composite
laminate and macrostructural failure
models. The vortex-ring model captured
Todd Reichert pilots the Atlas on its prize-winning flight on June 13, with ground crew Trefor Evans
and Cameron Robertson below. (AeroVelo video image)
The Atlas Human Powered Helicopter:
HowWe Won The AHS Sikorsky Prize
The winners of the AHS Igor I. Sikorsky Human Powered Helicopter Competition recount
their quest to achieve what many considered an impossible goal in vertical flight design
By Dr. Todd Reichert and Cameron Robertson
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VERTIFLITE September/October 2013
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