1

STABILIZATION OF HELICOPTER SLING LOADS

Vefa Narli

2

Introduction

• High Rise Rescue• Fire Fighting• Offshore• Construction

• Hover• Vertical Take-off

and Land

3

Transportation Modes of Helicopters

23000 lbs

5000 lbs

40000 lbs

4

Helicopter Sling Loading Capacities

Reference HelicopterHelicopter

WeightExternal Load

WeightLoad Mass

Ratio Cable Length

3 ( Handling Qualities

Requirements for MilitaryRotorcraft, Aeronautical Design

Standard)

NA NA NA 0.33 NA

4 (Requirements for the

Certification of Sling Loaded Military

Equipment for External Transportation by

Department of Defense Helicopters )

NA NA 39800 lbs (max) NA 12-16 ft

7 UH-60A 14600 lbs 1130-6384 lbs 0.07-0.3023 ft (single)

15.83 ft -(4-legged)

7 NA NA 40000 lbs NA 3-140 ft

11 UH-60 16000 lbs 1102-4409 lbs 0.06-0.22 9.84-26.2 ft

Superior Helicopter

Kaman K-1200

12000 lbs 6000 lbs 0.33 NA

5

Helicopter Sling Loading

• Load is suspended beneath the helicopter

• Free to rotate in all 3 axis

• Long cable lines are used

• Requires pilot effort

6

Literature Survey

• Dukes, T. A., “Maneuvering Heavy Sling Loads Near Hover, Part I: Damping the Pendulous Motion,” Journal of the American Helicopter Society, Vol. 18, (2), Apr. 1973.

• Dukes, T. A., “Maneuvering Heavy Sling Loads Near Hover, Part II: Some Elementary Maneuvers,” Journal of the American Helicopter Society, Vol. 18, (3), July 1973.

• Poli, C., and Cromack, D., “Dynamics of Slung Bodies Using a Single-Point Suspension System,” Journal of Aircraft, Vol. 10, (2), Feb. 1973.

• Cliff, E. M., and Bailey, D. B., “Dynamic Stability of a Translating Vehicle with a Simple Sling Load,” Journal of Aircraft, Vol. 12, (10), Oct. 1975.

• Nagabhushan, B. L., “Low-Speed Stability Characteristics of a Helicopter With a Sling Load,” Vertica, Vol. 9, 1985.

• Sheldon, D. F., “An Appreciation of the Dynamic Problems Associated with the External Transportation of Loads from a Helicopter—State of the Art,” Vertica, Vol. 1, 1977.

• Prabhakar, A., “Stability of a Helicopter Carrying an Underslung Load,” Vertica, Vol. 2, 1978.

• Cicolani, L. S., Kanning, G., and Synnestvedt, R., “Simulation of the Dynamics of• Helicopter Slung Load Systems,” Journal of the American Helicopter Society, Vol. 40,

(4), Oct. 1995.• Gabel, R., and Wilson, G. J., “Test Approaches to External Sling Load Instabilities,”

Journal of the American Helicopter Society, Vol. 13, (3), July 1968.

7

HSL Flight Tests

[7]

8

Stability of HSL - I

[7]

9

Stability of HSL - II

[7]

10

Stability of HSL - III

[ 11]

Level 1 – Load maintains directional stability throughout the maneuvers.

Minimal oscillation. Requires minimal concentration by the flight crew

Level 2 – Load may oscillate, rotate. Directional orientation is not stable. Does

not pose a threat to the aircraft. ost maneuvers. Moderate oscillation.

11

Safety - I

Manwaring, J. C., Conway, G. A., Garrett, L. C., “Epidemiology and Prevention of Helicopter External Load Accidents,” Journal of Safety Research, Vol. 29,

No. 2, pp. 107-121, 1998.

12

Safety - II

• …The helicopter departed with a 150-foot long-line attached and no external load on the hook… After lift-off, the long-line tangled in the trees, causing the helicopter to crash…

• …An Aerospatiale 316B was moving equipment in mountainous terrain with a 100-foot long cable… the cargo hook snagged on an equipment trailer adjacent to the take-off area. As the tension on the line increased, the hook broke free of the trailer and the cable recoiled into the main rotor blades, rendering the helicopter uncontrollable…

• …During the flight to reposition the helicopter that was transporting seismic equipment with a 100-foot long line, the load caught on a nearby fence…

13

Literature Survey

• Lucassen, L. R., and Sterk, F. J., “Dynamic Stability Analysis of a Hovering Helicopter With A Sling Load,” Journal of the American Helicopter Society, Vol. 10, (2), Apr. 1965.

• - 2001 (Dynamics and Stability)• Stiles et al, (2004, [22],) mention sling load

active stabilization as a future direction of research in his review of Helicopter AFCS.

14

Statement of the Problem

• Keep the oscillations of the payload under a critical angle, or deviation

• The effect of the load on the helicopter dynamics should not exceed more than 10% of the static weight of the load.

• System should be adjustable to different line length and load weight and should be robust to 10% changes of the nominal values.

15

Approach - I

• Modified AFCS that stabilizes the slung load

• Stand-alone stabilizing system– Cartesian mechanism– Spherical mechanism

16

Approach - II

Cho, S.-K., Lee, H. H., “An Anti-Swing Control of a 3-Dimensional Overhead Crane,” Proceedings of the American Control Conference, Chicago, Illinois, pp. 1037-1041, 2000.

[2]

17

Future Work

• Anti-sway control of shipboard boom cranes• Simulations of a quadrotor suspended mass • Update the statement of the problem• Stabilization of a 3D suspended pendulum with

a cartesian mechanism• Stabilization of a 3D suspended pendulum with

a spherical mechanism• UH-60 helicopter MatLAB model• Simulations of 3D suspended pendulum

attached to UH-60

18

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