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New Approach:
Multiple Swashplates
The multiple-swashplate system (META)
patented by DLR and tested on a four-
blade rotor on the rotor test rig in
Braunschweig is a novel approach for
an active rotor control. Electrohydrau-
lic actuators induce high-frequency
movements of multiple concentric
swashplates. The swashplates then
generate the desired dynamic chan-
ges of the individual blade pitch ang-
les on the rotor. The actuators are in-
stalled below the swashplates, which
are each connected to two blades.
Using multiple swashplates makes the
system IBC-capable, i.e., it is possible
to modify the pitch angle of each ro-
tor blade individually and with arbi-
trary control functions and frequen-
cies. META thus combines the advan-
tages of existing approaches without
having to suffer from their drawbacks.
Initial Test Setup
During the VAR-META project (VAR-
META = fully active rotor control via
multiple swashplates) within the frame-
work of the Federal Aeronautical
Research Programme, the multiple-
swashplate system was tested for the
first time on the rotor test rig at the
DLR in Braunschweig. In these tests,
a Mach-scaled wind tunnel model of
a hingeless Bo105 rotor with a dia-
meter of approx. 4 m was used. The
model was equipped with the multi-
ple-swashplate system for the first
time. As a result of the Mach-scaling,
the flow conditions largely reflect
those of the actual helicopter rotor.
However, this also increases the rotor
speed. A particular challenge of the
project was to control the electrohy-
draulic actuators that position and
move the two swashplates. On the
one hand, the desired changes to the
pitch angles of all four rotor blades
have to be translated into the corres-
ponding piston movements of the
actuators. On the other hand, these
actuator movements have to be con-
trolled actively.
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14
Aerodynamic phenomena of helicopter rotors in forward flight.
CUSTOMERS
How the multiple-swashplate system works: One swashplate controls two opposing
rotor blades.
The collective and cyclic pitch control of the rotor blades via a swashplate makes
it possible to fly a helicopter vertically and horizontally.
Cyclic
control
Collective
control
a
b
SP1
SP2
a
c
b
Primary
Booster
Primary
Booster
HHC
HHC
a) Control swashplate 1 (SP1)
b)
Control swashplate 2 (SP2)
c)
Pilot commands
HHC: Higher Harmonic Control
Mach number effects
Rotor wake
interferences
High angles of
attack
Reversed flow
Yawed flow
Source: C. Kessler, D. Fürst, and U. T. P. Arnold,
“Open Loop Flight Test Results and Closed Loop
Status of the IBC System on the CH-53G Helicopter,”
Proceedings of the 59th Annual Forum of the
American Helicopter Society, Phoenix, AZ, May 2003.
Dynamic stall due to
blade-vortex interaction (BVI)
Source: © DLR
dSPACE Magazine 1/2016 · © dSPACE GmbH, Paderborn, Germany ·
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