The cyclogyro, or cyclocopter, is an aircraft design that uses cycloidal
rotors which consist of airfoils rotating around a horizontal axis for
both lift and thrust. They are capable of vertical take off and landing and
hovering performance like a helicopter, without the same disadvantages such as
limited forward speed, very high noise and vibration levels, limited flight
altitude etc. The biggest hope of Cyclocopter developers which remains
unrealised in any flying prototypes is to achieve higher efficiency in terms of
lift per engine horsepower which would translate into higher lifting capability
and longer flight range. Although a number of cyclogyros were built in the
1930s, none were known to have successfully flown until 2011. The
cyclogyro should not be mistaken for flettner airplanes, the unsuccessful and
aerodynamically different aircraft designs using cylindrical wings which
attempted to harness the Magnus effect. Function
The cyclogyro wing resembles a paddle wheel, with airfoils replacing the
paddles. The airfoils' pitch is adjusted either collectively or the blades are
individually adjustable in pitch and are adjusted continually by the control
system as they move around the rotor's axis. In normal forward flight the
airfoils are given a slight positive pitch at the upper and forward portions
of their arc, producing lift and forward thrust. They are given flat or negative
pitch at the bottom, and are "flat" through the rest of the circle to
produce little or no lift in other directions. The pitch can be adjusted to
change the thrust profile, allowing the cyclogyro to travel in any direction.
Differential thrust between the two wings can be used to turn the aircraft
around its vertical axis, although conventional tail surfaces are generally
used as well. History
= Early designs= Jonathan Edward Caldwell appears to have
been the first to patent the concept, and invent the term. He filed a patent
on the concept that was granted in 1927, but immediately moved on to an
ornithopter design and then an autogyro. Several attempts to build a working
cyclogyro were made by other designers. The earliest full-sized example appears
to be the Schroeder S1 from 1930, which used the cyclogyro "wheels" for forward
thrust only. Adolf Rohrbach of Germany designed a full VTOL version in 1933,
which was later developed in the US and featured a tall fish-like fuselage to
keep the wings well clear of the ground. Another early example was by Rahn
Aircraft in 1935, which used two much larger chord wings instead of a
multi-blade wheel driven by a 240 hp supercharged Wright Whirlwind In 1935
NACA carried out a series of wind tunnel experiments on the cyclogyro concept,
and found that the power required to turn the wheels was much higher than
expected. Theoretical tools of the era simply weren't useful for prediction on
the highly asymmetrical lift profiles and the greatly simplified models they
used varied dramatically from real-world results. Early experiments then ended.
= Recent advances= The concept has recently been applied to
smaller Unmanned aerial vehicle designs, where the hovering capability would be
particularly useful. Several of these designs have produced flying prototype
models: In 2007 a team at the University of
Singapore built a working model of cyclogyro, although it has only flown in
tethered flight. Their cycloidal model was a modified helicopter, with the
rotor replaced with two sideways cycloidal rotors, each with three blades
sticking out of them in the perpendicular.
A team at Northwestern Polytechnical University in China built a free flying
Cyclogyro. This design used two cycloidal rotors for the efficient
generation of lift and small and noisy conventional head and tail rotors to
stabilize the craft and provide control of its horizontal position and direction
of flight. Video of the team's test flights can be found here. In September
2013 another Cyclocopter model was flight tested in China
In December 2011 a team at the University of Maryland successfully
built and tested a micro Cyclocopter, as seen here. Their design does not require
a head rotor in addition to the usual tail rotor.
The Austrian company Innovative Aerodynamic Technologies premiered a 4
rotor cyclogyro at the Paris Air Show in June 2011. IAT has christened their
creation Project D-DALUS. A video can be found here.
A team at the Seoul National University has built and in December 2012
successfully demonstrated a stable, mostly hovering flight of a 4 rotor
Cyclocopter The Korean team design solution provides
for stable and controllable flight by having two pairs of the counter-rotating
rotors which are parallel to each other and rotate at the same rpm. However this
approach will not work for the higher forward speeds. Not one of the teams so
far has achieved the Power Loading which is any better than that achieved by the
helicopters. The University of Maryland team and the team in China use
individual motors for each rotor for stability by varying their rpm. Using a
number of individual motors makes that design heavier, more complicated and
costlier. The Korean team has announced the building of a two main rotor 90 kg
UAV back in 2012. A European Seventh Framework Programme
consortium, the CROP, also studied cycloidal rotors with the optic of
optimizing their performances. Within this project, various possible aircraft
configurations were considered. One of those is the Heligyro, for which a
conceptual aeroelastic study rendering is shown. A 3-meter demonstrator is
expected to fly in 2016 along with the 20kg D-DALUS.
= Future developments= Future developments, such as a variable
cycloidal rotor, may improve the cyclogyro design. This technology allows
the blades to travel about the horizontal axis along the most
aerodynamically desirable orbit as continuously determined by the control
system. This orbit will generally be non-circular and elongated, with that
orbit shape dynamically modified by the control system as the flight regime and
conditions change to keep the relative airflow about the blades optimized. The
dynamic counterbalancing of the blades radial movements is used to keep the
rotor balanced. This design would also allow their operation and the blade
orbit shape to be optimized not only for the highest efficiency, but
alternatively also for the highest flight speed or for the highest possible
lifting capability or for the most silent operation. In addition to the
horizontally elongated blade orbits being conducive to greater stability,
the ability of this technology to precisely control in real time the
localization and distribution of the lift/thrust generation may also largely
eliminate the stability issues which is the most serious problem faced by
current cyclogyro designs.; the second biggest problem faced by the current
designs, namely that of blade bending due to the centrifugal forces, can also
be addressed via the trajectory shape as on flat or nearly flat portions of the
trajectory the centrifugal force acting on the blades will respectively be
either zero or small. See also
FanWing Flettner airplane
Fixed-wing aircraft Rotary-wing aircraft
Ornithopter Gyroplane
VTOLVSTOL/STOVL Voith Schneider Propeller
References Further reading
"The Cyclogyro", Vertiflight, The American Helicopter Society, 2005, Vol.
51; No. 2, pages 16–19 External links
Another Look at 1930's Cyclogyro Plane Design
A small cyclogyro in tethered flight A series of Cyclocopters was developted
in Seoul National University, Korea YouTube: Test flight of a Cyclocopter in
Korea The CROP Project: an European research
consortium working on the cyclogyro concept and its optimization