EPOD Rotorcraft Loss of Lubrication
Enable Extended Operation during Loss of Lubrication (LoL) Events in Rotorcraft
The Problem
Current US Army Rotorcraft have a requirement to provide 30 minutes of operational capability following a loss of lubrication (LOL) event in the drivetrain per ADS-50-PRF (Rotorcraft Propulsion Performance and Qualification Requirements and Guidelines). This 30 minute period is critical; providing a window where operators can maneuver to a safe landing zone or crew can egress the damaged vehicle.
Many platforms are grandfathered in to this requirement and remain untested. Additionally, newer platforms have yet to undergo qualification.
Weight is one of the largest design challenges for rotorcraft. In the event of a loss of lubrication event, a redundant, full backup system is currently the only technology available to enable meeting this requirement.
US Military Loss of Lubrication Requirement Evolution
Hover over the image below to interact with the timeline
The U.S. Army and NASA began investigating strategies
to extend operational capabilities after LoL due to the high
vulnerability of the lubrication system to ballistic damage
during combat operations. These vulnerability concerns
led directly to the formalized oil-out operational requirements.
LOL capability was formalized as a key design requirement
under the Utility Tactical Transport Aircraft System (UTTAS) program
- Program led to the development and fielding of the
UH-60 Black Hawk.
The US Army Aeronautical Design Standard ADS-50
detailed the original Loss of Lubrication qualification test
successfully conducted in 1981.
The Federal Aviation Regulation (FAR) 29.927(c)
(at Amendment 26) was amended to require
gearboxes utilizing pressurized lubrication systems
to demonstrate a capability to continue operation
for a minimum of 30 minutes after loss of lubrication
via a bench test.
Requirement was codified as an institutional
standard by the U.S. Army Aviation Troop Command
(AVCOM/AMCOM) under Aeronautical Design
Standard (ADS) ADS-50-PRF, Rotorcraft Propulsion
Performance and Qualification Requirements and Guidelines.
- Standard dictates that, following the detection of lubricant
loss, the drive system must continue to operate at
operational power settings for a minimum of 30 minutes,
ensuring a critical window for crew egress or tactical
maneuvering to a safe landing zone. - ADS-11 Qualification Test (ADS-50-PRF, 5-4.3.5):
Compliance must be demonstrated by conducting two
30-minute duration, oil-out bench tests on each
transmission and gearbox configuration following the
200-hour Qualification Endurance Test. Alternatively,
the requirement can be satisfied by a single, 60-minute
run performed at the required flight and landing loads.
The 30-minute interval (or 60-minute run time) begins
upon the activation of the low-level warning system
Department of Defense issues the Joint Services
Specification Guide for Air Vehicle Subsystems
which “establish a common framework to be
used by Government-Industry Program Teams
in the Aviation Sector for developing program
unique requirements documents for Air Systems,
Air Vehicles, and major Subsystem."
Due to recent LOL failures, the Canadian
Transportation Safety Board (TSB) recommended
that the FAA, Transport Canada, and EASA remove
the "extremely remote" provision from the rule
requiring 30 minutes of safe operation for
Category A transport helicopters. This led to the
formation of a Joint Cooperation Team (JCT) to
review and update LoL certification specifications
EASA releases an initial Certification
Memorandum, “Large Helicopter Main Gearbox
Certification Requirements.”
- A Certification Memorandum (CM) is non-
binding guidance, in this case, related to
loss of lubrication testing requirements. - However, a CM is taken very seriously and
normally is a precursor to an updating of a
Certification Specification. - A Certification Specification (CS) is law
within the European Union. - The CM recommended extending bench
testing beyond 30 minutes to demonstrate
such a capability.
The Army's FY 2015 plans for Engine and Drive
Train Technology included evaluating drivetrain
technologies to achieve a 50% increase in time-to-
scuffing-failure after lubricant termination,
supporting Next Generation Rotorcraft
Transmission objectives
A US DoD loss of lubrication study on an AH-64
Engine Nose Gearbox (ENGB) with advanced
Isotropic Superfinished (ISF) gears successfully
demonstrated continued torque transmission for
60 minutes after lubricant loss, satisfying the ADS-
50-PRF requirement
EASA released “Certification Specifications and
Acceptable Means of Compliance for Large
Rotorcraft, CS-29 Amendment 7”
- Gearboxes must satisfactory operational
inflight testing capability of 50 to 60 minutes
Rotorcraft gearboxes capable of internal pitch line
velocities exceeding 20,000 feet per minute and
operating 30 minutes with loss of lubrication
without an emergency or auxiliary lubrication
system are still specifically identified as
controlled military items (Demilitarization Code
D). This highlights the sustained nature of the
30-minute minimum requirement as a
critical design threshold.
The Zulu Pod solution: The EmergencyPOD (EPOD)
Application Benefits
- Extended Operational Capabilities During an Emergency LoL Event
- Metered Technology for Precise Lubrication
- Decentralized and Modular Design
Safeguard human life and critical assets during a loss of lubrication event with the EmergencyPOD, or EPOD. The EPOD is a fully self-contained, decentralized unit, designed to be strategically placed in and around critical mechanical systems. The EPOD will sense when a loss of lubrication event has occurred and trigger, providing an emergency burst of oil to critical hardware, allowing extended operation.
Functionality
Self-Pressurized
Unitized
Sensors & Electronic Controls
Embedded Software
Fluid Agnostic
10 Year Shelf-Life
Proprietary Deployment Technology
The EPOD builds off of Zulu Pods’ patented, flagship product the ZPOD. It evolves the technology into a Smart product by integrating a suite of sensors, electronic controls, and embedded software to form a robust solution that will detect when a loss of lubrication event has occurred and deploy.
Watch the video to learn more about this technology.
Rotorcraft Failure Mechanisms Under LoL
When LoL occurs, system faces immediate and severe stress, leading to a complex cascade of mechanical failure modes.
Loss of lubricant results in two immediate problems:
- The removal of the heat dissipation medium
- The cessation of hydrodynamic lubrication
The resulting absence of lubrication under heavy loading contacts generates immense heat due to friction.
- This heat generation rapidly destabilizes the components.
- High temperatures degrade the surface hardness of the gears and bearings, which in turn reduces their ability to carry intended loads.
- As the damage progresses, the increased friction accelerates heat production, creating unstable thermal effects that eventually lead to catastrophic failure.
- Furthermore, thermal expansion within the system can cause rotating parts to seize.
Due to the inherent unpredictability of the heat management under these conditions, the behavior of the transmission is highly difficult to forecast when the lubricant is no longer available.
How the EPOD Works
Supplying 50 mL per hour has the potential to support a typical aerospace grade bearing for up to 5 hours in a LoL event.
Zulu Pods specializes in fluid delivery and minimal lubrication theory. The engineering team has amassed hundreds of hours of test data on providing minimum amounts of oil to critical hardware. The EPOD will supply a minimal amount of lubrication to each of the critical components, ensuring a film of oil remains.
This film of oil will prevent thermal runaway and subsequently catastrophic damage.
Minimal Lubrication testing to date has shown a 50 mL Pod has the potential to support a typical aerospace grade bearing for up to an hour in a LoL event.
Depending on system parameters, a 120 mL EPOD may support a typical aerospace grade bearing for up to five hours in a Loss of Lubrication event.
Validated in partnership with the
Army DEVCOM Aviation and Missile Center (AvMC)
Phase 1 & 2 RDT&E Contract
COMPLETED
