Flight Test and Simulation of a Cargo Container Slung Load in Forward Flight

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Previously, the authors showed that dynamic wind tunnel tests of a suspended CONEX cargo container model exhibited encouraging levels of success in predicting the stability characteristics and speed envelope of the full-scale load. The present study includes further use of the UH-60/CONEX system to investigate effects that were observed previously, but not fully addressed. These effects include the influence of pilot inputs and helicopter motions on the coupled pilot/helicopter/slungload dynamics, the influence of center of gravity offset of the slung load, and the behavior of a load when a yaw swivel is not used in the suspension. It is shown that all three effects are important and affect the slung-load dynamics. The capability of wind tunnel tests to predict the behavior of slung loads in flight is shown for these effects. NomenclatureA () amplitudes of () cg center of gravity D aerodynamic drag force, N PF principal frequency, rad/s SPF simple pendulum frequency, rad/s W weight, N Y aerodynamic lateral force, N φ c , θ c roll (lateral) and pitch (longitudinal) cable angles, deg. ω ψ yaw oscillation angular frequency, rad/s * Corresponding author;

Section: Introductionmentioning

confidence: 95%

“…Data were recorded at 100 Hz (for more details, see Refs. 2,3,12). Of special importance was the load instrumentation package that measured the load motions using a medium-accuracy military-grade GPS/INU plus load cells inserted in the sling legs at the lift points to measure sling leg tensions.…”

Section: General Description Of the Testsmentioning

confidence: 99%

Using Wind Tunnel Tests for Slung-Load Clearance, Part 1: The CONEX Cargo Container

Raz¹,

Rosen²,

Cicolani³

et al. 2014

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“…This comparison is described in Ref. 1. It showed good agreement including trail angle and yaw rate as functions of airspeed, as well as frequency analyses of load motions at various airspeeds.…”

Section: General Descriptionmentioning

confidence: 67%

“…A recent detailed investigation of the problem appears in Ref. 1. Such instabilities may occur at air speeds well below the power-limited speed of the configuration, thus reducing the speed envelope significantly.…”

Section: Introductionmentioning

confidence: 98%

Wind Tunnel and Flight Evaluation of Passive Stabilization of a Cargo Container Slung Load

Raz¹,

Rosen²,

Carmeli³

et al. 2010

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In forward flight helicopters carrying slung loads frequently encounter load instability problems that reduce their speed envelope to well below the power limit of the helicopter/slung-load system. The paper presents a procedure for the development and flight test verification of passive stabilizers designed to increase the maximum flight speed of the system. Most of the development is carried out during wind tunnel tests. A scale model is suspended from the tunnel ceiling by a gimbaled setup that simulates the hook-sling attachment. The model is free to perform lateral and longitudinal pendulum motions, as well as yaw rotation. All three motions are recorded as functions of time. The model dynamics are studied as a function of the wind tunnel speed. Various techniques for stabilizing the load can be investigated by wind tunnel tests, which are much cheaper, faster, and less risky than equivalent flight tests. The present study investigates the use of passive vertical fins to stabilize the 6 × 6 × 8 ft CONEX cargo container. The optimal geometry and location of the fins are determined in wind tunnel tests. Later on this optimal configuration is built and tested in full-scale flight tests. The dynamic behavior during these flight tests is compared with the wind tunnel results. Good agreement between both can result in a significant reduction in the number and duration of the flight tests that are required to certify the stabilization method. By using the above-described technique, the maximum flight speed of a UH-60/CONEX system is increased from 60 kt (the operational limit for the unstabilized CONEX) to 110 kt (the power limit of the system).

“…Unsteady aerodynamic behavior of specific loads, in particular containers, has been widely investigated with simulation, wind tunnel testing, and flight test (Refs. 15,16). It is known that external load instability can reduce the safe flight envelope well below limits due to power loading.…”

Section: Introductionmentioning

confidence: 98%

Dynamic Stability of a Helicopter with an External Suspended Load

Guglieri¹,

Marguerettaz²

2014

A simplified but comprehensive model for helicopter and external suspended load, based on the linear superposition of effects, is defined. The coherence of the external load modal response and of the helicopter response to control input is verified through available reference data. Finally, the impact of the slung load on the overall system dynamic stability, on the helicopter response to control input, and on flight qualities is assessed. Nomenclatureforces vector, N DOF degrees of freedom F force vector, N f residual g gravity acceleration, m/s 2 i, j, k unit vectors along x, y, z axis J x , J y , J z , J xz moments of inertia, kg · m 2 K suspension line elastic constant, N/m K G gravity forces vector, N L suspension line length, m [L BE ] rotation matrix from body to inertial axes M, N moments w.r.t. y and z axes, Nm m mass, kg p, q, r angular speed w.r.t. x, y, and z axes, rad/s R position vector, m S reference area, m 2 u, v, w velocity components along x, y, and z axes, m/s V velocity vector, m/s X, Y, Z forces along x, y, and z axes, N [X] states vector L elongation vector (cable)