Aerospace & Defense Technology - October 2021 - 34

Tech Briefs
Transmitter
cube
Receiver cubes
Pressure equalization
cylinder
Pulser
Distribution chamber
for receiver cables
Figure 2b. Assembled MBUD2 prototype system.
windings. The cable connections to the
receiver windings are made through tubing
fittings and the cables are surrounded
with reinforced plastic tubing. To further
prevent any seawater intrusion, the tubing
enclosing the cables and any space
around the receiver wiring are oil filled.
This work was done by Erika Gasperikova
and Frank Morrison of Lawrence Berkeley National
Laboratory, and Ugo Conti of Marine
Advanced Research, Inc. for the Strategic Environmental
Research and Development Program.
For more information, download
the Technical Support Package (free
white paper) at www.aerodefensetech.
com/tsp under the DAQ, Testing &
Sensors category. SERDP-0004
Fabrication and Testing of High-Speed Single-Rotor and
Compound-Rotor Systems
Acquiring the data needed to generate a comprehensive set of measurements of the blade surface
pressures, pitch link loads, hub loads, rotor wakes and performance of high-speed single-rotor and
compound-rotor systems necessary to support the development of next-generation rotorcraft, such
as those envisioned in the Joint Multi- Role (JMR) rotorcraft program.
Army Research Office, Research Triangle Park, North Carolina
S
lowed rotors - traditionally associated
with autogyros and gyroplanes - have
long been recognized as one potential solution
for high-speed helicopters (200-300
knots). During the 1950s-70s, there were
several significant programs that led to
the development of high-speed helicopters
with thrust and lift compounding.
The key technology barriers common to
all were extremely high fuel consumption
due to high advancing side drag and large
reverse flow, complexities associated with
RPM reduction, large blade motions during
RPM reduction, and unexplained but
catastrophic aeroelastic instabilities of
rigid rotors (Cheyenne). None of these
helicopters entered regular production.
Today, the CarterCopter gyroplane is
the only aircraft to have demonstrated a
rotor advance ratio of 1.0 in flight in
2005. With the advancement of materials,
controls, and propulsion/drivetrain technologies
(15-20% direct variation in RPM
possible with same nominal specific fuel
consumption and more dramatic reduction
promised with variable drivetrain),
slowed rotors have once again begun to
emerge as a viable solution to high-speed,
high-efficiency helicopters of the future
(along with tilt-rotors and lift-offset coaxial
compounds). The intent is the fundamental
understanding of such rotors,
using both analysis and experiment at the
very high-advance ratio reverse flow conditions
they are envisioned to operate in
(µ~1.5-2.0 and beyond).
Compared to conventional helicopEndevco
miniature transducer (left) embedded in a test specimen (right).
34
Intro
Cov
www.aerodefensetech.com
ToC
+
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ters, there are only a handful of limited
experimental measurements available,
which are neither sufficient for fundamental
understanding of their aeromechanics
nor adequate for validating highfidelity
analyses that hold promise of
predicting them. The only existing data
set that includes performance, pressures
and loads are the recent full-scale UH60A
tests - but this data is only up to
µ=1.0. Model-scale tests performed recently
achieve higher advance ratios (up
to µ=2.2), but with simple blades (symmetric
NACA0012 airfoil, untwisted) in
autorotation or lower advance ratios (up
to µ=1.0) with realistic blades (asymmetric
SC1095, twisted) and powered condiAerospace
& Defense Technology, October 2021
A
µ
È

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Aerospace & Defense Technology - October 2021

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