DTIC ADA434029: Noise Reduction Efforts for Special Operations C-130 Aircraft Using Active Synchrophaser Control

4 Pages·0.17 MB·English

by  Defense Technical Information Center

This paper was cleared by ASC-99-0898 on 27 Apr 1999
NOISE REDUCTION EFFORTS FOR SPECIAL OPERATIONS C-130
AIRCRAFT USING ACTIVE SYNCHROPHASER CONTROL
Dr. Daryl Hammond, P.E.
Mr. Richard McKinley
Mr. Bill Hale
Air Force Research Laboratory
Wright-Patterson AFB, OH 45433
BACKGROUND environments, arrays of loudspeakers are
needed, but are often ineffective due to their
Aircraft noise often inhibits mission size and weight. Since the primary noise on
effectiveness. As a result, flight crews, multi-engine turboprop aircraft, such as the
ground maintenance personnel, and C-130, originates from the engine-propeller
passengers suffer degraded voice system, the noise from one engine-propeller
communication, impaired performance, can be tuned to provide a canceling acoustic
increased fatigue, and hearing loss. The wave to reduce the noise generated from
magnitude of these effects is dependent on another engine-propeller operating on the
both the exposure time and level of the same aircraft.
noise. In an effort to reduce the level of
noise both inside and outside of the aircraft, Because the levels of noise generated from
techniques have been developed that attempt each engine-propeller combination are
to quiet the environment. The simplest similar under normal operating conditions, a
approach uses passive noise reduction means to adjust the propeller phasing to
methods, including installing acoustic create a noise canceling effect is needed.
insulation and exhaust modifications, but For multi-engine propeller-driven aircraft,
these only provide limited success. A more engine-propeller phase control is
complicated approach uses an active noise accomplished using an electromechanical
cancellation system, which offers improved device called a synchrophaser. Most
performance that can augment passive turboprop aircraft in the Department of
methods to significantly reduce both internal Defense (DoD) inventory incorporate
and external aircraft noise. synchrophasers that have fixed engine-
propeller phase angle relationships that are
ACTIVE NOISE CANCELLATION factory set. Unfortunately, these pre-
determined phase angles are not acoustically
Active noise cancellation (ANC) achieves optimized for maximum noise reduction
noise reduction by creating an anti-noise, during all flight conditions.
which is an equal and opposite acoustic
wave that cancels the unwanted noise. This ACTIVE SYNCHROPHASER SYSTEM
type of cancellation works well in smaller
volumes, like headset ear cups, where the Thus, to optimally control the phase angle
calculated acoustic canceling wave can relationships among the four engine
easily drive tiny speakers located in the head propellers, a controllable or active
set ear cup. For larger volumes or synchrophaser system is needed. One such
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1. REPORT DATE 3. DATES COVERED
1998 2. REPORT TYPE -
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
NOISE REDUCTION EFFORTS FOR SPECIAL OPERATIONS C-130
5b. GRANT NUMBER
AIRCRAFT USING ACTIVE SYNCHROPHASER CONTROL
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
Air Force Rsearch Lab,Wright Patterson AFB,OH,45433 REPORT NUMBER
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
NUMBER(S)
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14. ABSTRACT
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Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
system was demonstrated on a NASA Lewis to show the amount of exterior noise
Research Center OV-10A aircraft in 1992. reduction accomplished by the new system.
This system was a manually tuned analog The primary objective of the LMCS contract
system and resulted in 10-15 dB of interior was to reduce the exterior noise signature of
noise reduction, but provided no external the aircraft and interior noise levels by using
noise reduction because propeller phase acoustic measurements to optimally adjust
angles were not dynamically controlled by the four propeller phase angles to cancel
the system. The Air Force Research noise generated by the engine-propeller
Laboratory (AFRL) funded a second- system.
generation phase-locked-loop digital
synchrophaser in 1994. That system was CURRENT PROJECT STATUS
flight-tested on a NASA Lewis Research
Center OV-10A in 1995. The system The prototype active synchrophaser control
demonstrated 3-5 dB reduction in exterior has passed the preliminary and critical
noise levels and a 10-15 dB reduction in design reviews and was initially ground
cockpit noise levels. In 1995 and 1996, tested in March 1999. Due to the
Lockheed Martin Control Systems (LMCS) unavailability of an AFSOC C-130 aircraft,
designed and flight-tested a digital active the 40 FTS at Duke Field, Florida provided
synchrophaser in a commercial Beech their C-130, ground, and maintenance crews.
1900C aircraft. Photo 1 shows the 46 OG Test Director,
Captain Todd Efaw, and other personnel
MEETING AFSOC NEEDS installing the test equipment rack in the
crowded cargo bay of the C-130.
Realizing the noise canceling potential of an
active synchrophaser system, Air Force
Special Operations Command (AFSOC)
prepared a technology roadmap in 1997 that
identified several aircraft noise interference
deficiencies related to operation of their C-
130 aircraft. In fact, one concern stated that
the aircraft commander might lose control of
the crew during high stress conditions or
emergencies due to the aircraft noise. Thus,
United States Special Operations Command
(USSOCOM) successfully obtained funding
from the Office of Special Technology
(OST) to partner with AFRL in
demonstrating a new active synchrophaser
technology for noise cancellation in Special
Operations C-130 aircraft. AFSOC(cid:213)s
responsibility was to provide the C-130
aircraft, flight and ground crew, test range,
Photo 1. 46 OG Test Director Capt. Todd
and other flight-test support. AFRL(cid:213)s
Efaw Installs an Equipment Rack Needed
responsibility was to initiate and manage a
for the New Active Synchrophaser
contract with LMCS who was to design,
Checkout.
fabricate, integrate, install, and demonstrate
Photo 2 shows the rack of flight test
the new active synchrophaser system. In
instrumentation for the initial data
addition, AFRL was to collect acoustic data
collection. If the system goes into full capabilities will be measured during flight
production, installation of the new active demonstrations.
synchrophaser will be as simple as removing
the old synchrophaser box and installing the
new unit. As LMCS was performing ground
testing, the AFRL Noise Measurement Team
was collecting baseline acoustical data
needed prior to flight-testing.
Photo 3. Mr. Mike Patterson of AFRL(cid:213)s
Noise Measurement Team Prepares to
Record Engine-Propeller System Noise from
the C-130.
IN CONCLUSION
Higher priority AFSOC mission
requirements have temporarily delayed the
final installation and flight-testing of the
new active synchrophaser system.
However, AFRL remains optimistic that
flight-testing will resume later this year
when reduced mission requirements will
allow a C-130 aircraft to become available
for this program. The benefits in relieving
crew and passenger stress and fatigue,
improvement in speech intelligibility,
enhancement of mission effectiveness, and
reduction in hearing loss of DoD personnel
Photo 2. Prototype Active Synchrophaser make demonstration of the new active
and Other Test Equipment for System synchrophaser system for noise cancellation
Checkout. imperative. It also remains a high priority
with AFRL, who stands ready to meet the
Photo 3 shows a member of the AFRL Noise operational and safety needs of the Air
Measurement Team performing system Force.
checkout of the acoustical data collection
array installed around the aircraft. Recent Additional information on this project may
analysis of the collected baseline acoustical be obtained by contacting Dr. Daryl
data from the Duke Field test by AFRL Hammond at DSN 785-3671 Ext. 411 or via
research scientist Dr. Douglas Brungart email at [email protected].
indicates a potential for significant reduction
in propeller noise from the new
synchrophaser system. Final noise reduction