Browse Topic: Mountings
Helicopter aircrew are exposed to high levels of whole-body vibration (WBV) in fight operations, which may degrade their ride comfort and performance in the short-term, and contribute to some health issues in the long-term. This paper presents the latest development and flight test demonstration results of an active seat mount system that is designed to reduce helicopter aircrew WBV levels through active cancellation of the N/rev vibration peaks related to the helicopter main rotor speed. A prototype airworthy hardware of the active seat mount system has been developed based on previous bench-top-test designs to meet airframe integrity requirements for installation and flight testing on the Bell-412 helicopter. Extensive experimental results on human occupants using a shaker table facility and flight demonstrations on the NRC Bell-412 helicopter in representative flight conditions are presented and discussed. The active seat mount system has achieved significant reduction to the occupant WBV levels at the bottom seat cushion interface per ISO2631/MIL-STD-1472G metrics, and also showed effective mitigation to the occupant head vibrations. These investigations demonstrate that the active seat mount technology is a feasible solution for helicopter aircrew WBV mitigation.
This paper investigates the role of the aerodynamic torque on propeller whirl flutter stability. The generalized force due to the torque is first computed and subsequently included in the equations of motion of a rigid propeller-pylon system. Preliminary evaluations indicate that the torque modifies the real part of the backward and forward modes, providing a stabilizing effect on powered propellers. Analyses are conducted on a 3-bladed propeller driven by an electric motor. Stability predictions are obtained with a simple analytical model and validated by multibody simulations coupled with a mid-fidelity aerodynamic solver, based on a vortex particle method. Furthermore, a simple control law acting on the propeller's collective pitch and rotational speed is presented. The control variables are modified to increase the whirl flutter stability margins, without altering the trim conditions of the aircraft. Results demonstrate the effectiveness of the proposed control strategy, although propeller efficiency is reduced. In a failure scenario, the control law can be exploited to compensate for a weak mounting stiffness, allowing the aircraft to land safely.
The purpose of this aerospace information report is to provide a listing of national and international metric standards for use in aerospace fluid systems with their equivalent SAE inch, International ISO, and European AECMA standards.
This SAE Recommended Practice sets forth a method for evaluating the flow properties of automotive sealers that have been dispensed via a high pressure automatic system.
A multi-domain Eulerian/Lagrangian approach for modeling transient behavior of countermeasures released from tactical rotorcraft is being developed, that tracks chaff/flares/pyrophorics properties from initial dispensing and bloom, through entrainment within the rotorcraft flowfield, to final settling to the ground. Development of the software leverages extensive prior simulation and experimental work conducted at CDI on droplet and particle modeling, fuel jettisoning, agricultural airborne spraying applications, icing accretion, brownout cloud simulation, and store separation clearance determination. The software is designed for supporting applications that include chaff dispenser mounting design, piloted simulation training and tactics development, and radar cross-section (RCS) determination and engagement simulations. The code couples in CDI's real-time free wake analysis to support the development of accurate time-varying signature calculations and expands the potential for analysis of tactics and doctrine for countermeasure dispensing in both steady and maneuvering rotorcraft flight conditions.
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