Stabilization of Externally Slung Helicopter Loads

Abstract

The analytical techniques developed under this helicopter external load stabilization program represent a significant contribution to assist in future investigations of this type. The investigation was somewhat narrowed by the lack of dynamic data pertaining to typical external loads; however, dynamic data on the MILVAN container was obtained experimentally by the contractor and formed the basis for this investigation. The load stabilization concepts investigated herein were verified by piloted flight simulation on Northrop's Large Amplitude Moving Base Simulator.This report has been reviewed by this Directorate and is considered to be technically sound. The technical monitor for this contract was Mr. Richard E. Lane, Military Operations Technology Division. DISCLAIMERSThe finding* in thit report are not to be construed at an official Department of the Army position unless so designated by other authorized documents.When Government drawings, specifications, or other data are used for any purpose other than in connection with a definitely related Government procurement operation, the United States Government thereby incurs no responsibility nor any obligation whatsoever; and the fact that the Government may have formulated, furnished. or in any way supplied the said drawings, specifications, or other data is not to be regarded by implication or otherwise as in any manner licensing the holder or any other person or corporation, or conveying any rights or permission, to manufacture, use, or sell any patented invention that may in any way be related thereto.Trade names cited in this report do not constitute an official endorsement or approval of the use of such commercial hardware or software. DISPOSITION INSTRUCTIONSDestroy this report when no longer needed. Do not return it to the originator. The stability of external loads carried by helicopters is examined and analyzed. Use is made of experimental data and theoretical analyses to understand why load carrying speed is limited, and an attempt is made to identify promising stabilization concepts and to determine their capability to extend carrying speed. This effort is concentrated on the 8-by-8-by-20-foot cargo container; however, implications relating to other loads are given. An attempt is made to select the appropriate combination of analysis techniques that will yield a practical solution to the problem. Wind tunnel tests were performed on the cargo container during the followon effort, but their use did not Improve the accuracy of the analysis. Unsteady aerodynamic effects were present which required additional dynamic wind tunnel tests in order to understand them. These tests were performed for only the 8-by-8-by-20-foot container. So while the analysis of this container is now accurate, a more comprehensive study of other loads is not warranted until confidence can be gained that their behavior is not also dominated by unsteady aerodynamic effects, A case in point is the unsuccessful attempt during this study to predict the dynamics of an 8-by-8-by-40-foot ...

Aerodynamic modelling of fin stabilised underslung loads

“…In the case of box-like loads, the instabilities consist of a periodic yaw response that couples with the sling's longitudinal and lateral pendulum motions. These modes that were observed during isolated slung load dynamic wind-tunnel tests (3)(4)(5)(6) , are mainly the result of the unsteady aerodynamic attributes of boxes. Once attached to a helicopter, the coupling between helicopter and load modes creates complex response patterns, which affect the combined system's stability, handling qualities and ride quality.…”

Testing-Based Approach to Determining the Divergence Speed of Slung Loads

“…Nagabhushan [63] conducted a thorough mathematical analysis of the dynamics of slung loads. Other and more recent work has come from [10,[64][65][66][67][68][69][70][71][72][73][74][75]. Stuckey [8,76] revisited the problem with a comprehensive mathematical formulation.…”

Modelling of static aerodynamics of helicopter underslung loads

“…Looking specifically at the MILVAN container, Fig. 14 compares published data for wind-axis drag, sideforce and yawing moment variation with sideslip angle (9,26,27,28) , for models with representative geometry (i.e. surface corrugations, base skids etc).…”

“…Unpublished data from City University shows a 13% reduction in drag (and a smaller reduction in yawing moment) at higher incidences. The Sikorsky data is typical of excessive interference The majority of published data relates to the 8ft × 8ft × 20ft MILVAN container (11,15,26,27,28,29) , with a review in Ref. 9), although some more work has been done recently on the 6ft × 6ft × 8ft CONEX container (30,31) .…”

“…Figure 14. Comparison of MILVAN (8ft × 8ft × 20ft) aero datasets for planar yawing motion at zero angle of attack (9,26,27,28) .…”